ORCID Profile
0000-0002-8941-1222
Current Organisation
James Cook University
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Publisher: ASMEDC
Date: 2011
Abstract: The impingement of a fluid jet onto a surface has broad applications across many industries. Within the UK nuclear industry, during the final stages of fuel reprocessing, impinging fluid jets are utilised to mobilise settled sludge material within storage tanks in preparation for transfer and ultimate immobilisation through vitrification. Despite the extensive applications of impinging jets within the nuclear and other industries, the study of two-phase, particle -laden, impinging jets is limited, and generally restricted to computational modelling. Surprisingly, very little fundamental understanding of the turbulence structure within such fluid flows through experimental investigation is found within the literature. The physical modelling of impinging jet systems could successfully serve to aid computer model validation, determine operating requirements, evaluate plant throughput requirements, optimise process operations and support design. Within this work a method is considered, capable of exploring the effects of process and material variables on the flow phenomena of impinging jets. This is achieved on a number of experimental test rigs of varying scale employing both intrusive and non-intrusive measurement techniques Particle image velocimetry (PIV), ultrasonic Doppler velocity profiling (UDVP) and high speed imaging, through to visual observations and direct measurements, are all techniques that can be deployed. The influence of a number of parameters on the erosion characteristics of sediment beds following application of an axisymmetric impinging jet is presented in detail. Bed erosion is found to be enhanced as the jet height above the sediment bed is increased, due to greater turbulence development. Different erosion characteristics, as jet outlet velocity increased, were found for the particulates tested sand, fine Mg(OH)2 (test simulant representative of waste sludge, has similar particle size to sand, 200–1000μm) and coarse Mg(OH)2 (1000–2000μm). The crater diameter increased with increasing velocity as expected. However, the effect of the increase in velocity on the crater depth was very different, particularly for the coarse material which was found to re-deposit in the crater when the velocity increased above 1.3 ms−1, most likely due to enhanced re-circulation at the higher velocities.
Publisher: American Chemical Society (ACS)
Date: 11-2000
DOI: 10.1021/LA000738U
Publisher: Royal Society of Chemistry (RSC)
Date: 1996
DOI: 10.1039/FT9969202783
Publisher: ASMEDC
Date: 2011
Abstract: The UK nuclear industry has in its inventory legacy waste in the form of complex, polydisperse and “polydense” suspensions, slurries and sludges in a variety of storage and transport vessels. This waste has been difficult to characterise because of radioactivity and limited accessibility, and conditioning and disposal of the waste presents a continuing challenge. In addition, the mechanisms by which very dense particles are transported in pipes are not well understood. Our objectives are to investigate the effect of mono- and bidisperse suspensions with a range of particle sizes and densities on the turbulence characteristics, transport and settling behaviour of slurries that are chosen to be analogues of those found on nuclear sites. Two versatile slurry pipe-flow loops of different diameters have been commissioned which can be operated over a large range of Reynolds numbers and are amenable to ultrasonic measurement methods. Details of the flow loops are presented, including optimisation studies. Results are presented for a variety of particle characterisation studies that have been performed on the particle species that form the suspensions, along with mean and RMS (root mean square) velocity profiles over a range of Reynolds number and particle concentration. In particular, the effect of particle concentration on the formation of settled beds, and mean flow velocity and turbulence characteristics has been investigated.
Publisher: American Chemical Society (ACS)
Date: 12-03-2012
DOI: 10.1021/LA2048568
Abstract: In this article, the adsorption of latex core-responsive polymer-shell nanoparticles at the air-water interface is investigated using a Langmuir trough. Phase transition isotherms are used to explore their responsive behavior at the interface as a function of changes in the pH of the subphase. By adjusting the pH of the water prior to particle deposition, we probe the effect of the stabilizing polymer wetting by the water subphase on the stability of these particles at the air-water interface. In addition, by initially compressing a stable film of adsorbed particles and then subsequently changing the pH of the subphase we study desorption of these particles into the water phase.
Publisher: Elsevier BV
Date: 12-2000
Publisher: American Chemical Society (ACS)
Date: 05-2007
DOI: 10.1021/JP072231Z
Abstract: The first in situ proof of the presence of true nanoscale micelle structure within alternating layers of a self-assembled cationic and anionic diblock copolymer micelle-micelle multilayer film is presented using atomic force microscopy. Apparently similar layer morphologies are distinguished by the interaction force curves normal to each layer. The three-dimensional order in these low Tg diblock copolymer films, together with their mechanical resilience and strongly hydrated nature, suggests many new technological applications.
Publisher: Springer Science and Business Media LLC
Date: 06-1992
DOI: 10.1007/BF00658287
Publisher: American Chemical Society (ACS)
Date: 03-12-2000
DOI: 10.1021/LA990448H
Publisher: Elsevier BV
Date: 03-2015
Publisher: Elsevier BV
Date: 04-2008
Publisher: American Chemical Society (ACS)
Date: 10-11-2007
DOI: 10.1021/MA071878E
Publisher: Springer Science and Business Media LLC
Date: 02-2010
DOI: 10.1038/4631018A
Publisher: ASMEDC
Date: 2011
Abstract: The task of implementing safer and more efficient processing and transport techniques in the handling of nuclear wastes made up of liquid-solid mixtures provides a challenging and interesting area of research. The radioactive nature of nuclear waste means that it is difficult to perform experimental studies of its transport. In contrast, the use of modelling and simulation techniques can help to elucidate the physics that underpin such flows and provide valuable insights into common problems associated with their transport, as well as assisting in the focusing of experimental research. Two phase solid-liquid wasteforms are commonplace within the nuclear reprocessing industry. Currently, there is waste, e.g., in the form of a solid-liquid slurry in cooling ponds and liquid flows containing suspensions of solid particles feature heavily in the treatment and disposal of this waste. With nuclear waste in the form of solid-liquid sludges it is important to understand the nature of the flow, with particular interest in the settling characteristics of the particulate waste material. Knowledge of the propensity of pipe flows to form solid beds is important in avoiding unwanted blockages in pipelines and pumping systems. In cases where the formation of a solid bed is unavoidable, it is similarly important to know how the modified cross-sectional area of the pipe, due to the presence of a bed, will affect particle behaviour through the creation of secondary flows effects that are also common to square duct flows. A greater understanding of particle deposition in square ducts and pipes of circular cross-section is also of significant and broad industrial relevance, with flows containing particulates prevalent throughout the nuclear, pharmaceutical, chemical, mining and agricultural industries. A greater understanding of particle behaviour in square ducts and circular pipes with variable bed height is the focus of this current work. The more computationally expensive but accurate technique of large eddy simulation (LES) is compared against the current industrial standard technique of Reynolds-averaged Navier-Stokes (RANS) modelling to ascertain how each can be best utilised to understand and predict the mobilisation and transport of nuclear waste sludges. Both approaches are coupled with a Lagrangian particle tracking (LPT) technique and have been applied to examine particle dispersion and deposition behaviour across a range of Reynolds numbers in square duct flows. Single-phase predictions are found to be in good agreement with the available experimental data. LES and RANS results are in agreement over particle deposition rate, although disagree on the final locations of deposited particles. The RANS based work is further extended to consider particle deposition in circular pipes with variable bed height (Bh). Average particle distance from the nearest wall for spherical particles with sizes ranging from 5–500 μm is monitored in pipes of circular cross-section with bed heights = 0, 0.25 and 0.5 of the pipe diameter. The particle deposition rate is compared over particle sizes and for all values of Bh, with the implications for sludge transport in practical situations commented upon. The presence of an increasing Bh is found to increase particle deposition for smaller particles. The presence of a bed is found to have little, if any, effect on larger, gravity dominated, particles.
Publisher: Elsevier BV
Date: 2008
DOI: 10.1016/J.JCIS.2007.09.072
Abstract: The adsorption of a zwitterionic diblock copolymer, poly(2-(diethylamino)ethyl methacrylate)-block-poly(methacrylic acid) (PDEA59-PMAA50), at the silica/aqueous solution interface has been characterised as a function of pH. In acidic solution, this copolymer forms core-shell micelles with the neutral PMAA chains being located in the hydrophobic cores and the protonated PDEA chains forming the cationic micelle coronas. In alkaline solution, the copolymer forms the analogous inverted micelles with anionic PMAA coronas and hydrophobic PDEA cores. The morphology of the adsorbed layer was observed in situ using soft-contact atomic force microscopy (AFM): this technique suggests the formation of a thin adsorbed layer at pH 4 due to the adsorption of in idual copolymer chains (unimers) rather than micelle aggregates. This is supported by the remarkably low dissipation values and the relatively low degrees of hydration for the adsorbed layers, as estimated using a combination of quartz crystal microbalance with dissipation monitoring (QCM-D) and optical reflectometry (OR). In alkaline solution, analysis of the adsorption data suggests a conformation for the adsorbed copolymers where one block projects normal to the solid/liquid interface this layer consists of a hydrophobic PDEA anchor block adsorbed on the silica surface and an anionic PMAA buoy block extending into the solution phase. Tapping mode AFM studies were also carried out on the silica surfaces after removal from the copolymer solutions and subsequent drying. Interestingly, in these cases micelle-like surface aggregates were observed from both acidic and alkaline solutions. The lateral dimension of the aggregates seen is consistent with the corresponding hydrodynamic diameter of the copolymer micelles in bulk solution. The combination of the in situ and ex situ AFM data provides evidence that, for this copolymer, micelle aggregates are only seen in the ex situ dry state as a result of the substrate withdrawal and drying process. It remains unclear whether these aggregates are caused by micelle deposition at the surface during the substrate withdrawal from the solution or as a result of unimer rearrangements at the drying front as the liquid recedes from the surface.
Publisher: American Chemical Society (ACS)
Date: 12-03-2019
Abstract: A two-step method to encapsulate an oil core with an impermeable shell has been developed. A thin metallic shell is deposited on the surface of emulsion droplets stabilized by metal nanoparticles. This thin shell is shown to prevent diffusion of the oil from within the core of the metal-shell microcapsules when placed in a continuous phase that fully dissolves the oil. The stabilizing nanoparticles are sterically stabilized by poly(vinyl pyrrolidone) chains and are here used as a catalyst/nucleation site at the oil-water interface to grow a secondary metal shell on the emulsion droplets via an electroless deposition process. This method provides the simplest scalable route yet to synthesize impermeable microcapsules with the added benefit that the final structure allows for drastically improving the overall volume of the encapsulated core to, in this case, >99% of the total volume. This method also allows for very good control over the microcapsule properties, and here we demonstrate our ability to tailor the final microcapsule density, capsule diameter, and secondary metal film thickness. Importantly, we also demonstrate that such impermeable microcapsule metal shells can be remotely fractured using ultrasound-based devices that are commensurate with technologies currently used in medical applications, which demonstrate the possibility to adapt these microcapsules for the delivery of cytotoxic drugs.
Publisher: Elsevier BV
Date: 12-2010
DOI: 10.1016/J.JCIS.2010.08.044
Abstract: Dried deposits of spherical Ludox silica and disk-like laponite clay nanoparticles have been examined by dark-field optical microscopy and atomic force microscopy (AFM) to investigate the effects of nanoparticle shape on the deposit structure. Dark-field optical images indicated that a higher concentration of Ludox nanoparticles was required, compared to laponite, for an optically visible deposit to be formed. Compared with the relatively simple ring-like features observed at the edges of Ludox deposits, the laponite deposits were more complex, with dendritic features appearing below 10ppm that disappeared at higher laponite concentrations. AFM images revealed that whilst the Ludox rim deposit structure gradually increased in height and width with increasing nanoparticle concentration, the laponite rim deposits increased steadily in height up to 1ppm, above which the rim height suddenly decreased and the deposit structure became smoother. The widths of the rim deposits were observed to increase in a similar manner for both nanoparticle types. Nanoparticle shape is suggested as the main reason for differences in the structural features of the rim for each nanoparticle type. The disk-like laponite forms tall thin rim profiles at low concentrations, before creating a more uniform rim profile at higher concentrations. We suggest that a critical laponite rim height is reached before partial collapse of the nanoparticle stack at the rim takes place as the particle concentration is further increased. This produces much thinner and smoother films of laponite at high particle concentrations than is found for similar concentrations of Ludox. Our work suggests that both the shape and the concentration of the nanoparticles themselves are crucial in determining the structure of the final dried nanoparticle deposit.
Publisher: Elsevier BV
Date: 11-2004
Publisher: American Society of Mechanical Engineers
Date: 08-09-2013
Abstract: In situ characterisation of radiotoxic sludges and slurries is critical to numerous operations including those involving their transport and retrieval. An inexpensive, flexible acoustic backscatter system has been employed for the first time here to a 4/10th scale active storage tank comprising of a nuclear simulant suspension, to verify its application. Intricate suspension characteristics and tank operation features emerged.
Publisher: American Chemical Society (ACS)
Date: 16-05-2014
DOI: 10.1021/LA9910935
Publisher: Elsevier BV
Date: 10-2003
DOI: 10.1016/S0021-9797(03)00631-3
Abstract: The equilibrium and kinetic aspects of the adsorption of alkyltrimethylammonium surfactants at the silica-aqueous solution interface have been investigated using optical reflectometry. The effect of added electrolyte, the length of the hydrocarbon chain, and of the counter- and co-ions has been elucidated. Increasing the length of the surfactant hydrocarbon chain results in the adsorption isotherm being displaced to lower concentrations. The adsorption kinetics indicate that above the cmc micelles are adsorbing directly to the surface and that as the chain length increases the hydrophobicity of the surfactant has a greater influence on the adsoption kinetics. While the addition of 10 mM KBr increases the CTAB maximal surface excess, there is no corresponding increase for the addition of 10 mM KCl to the CTAC system. This is attributed to the decreased binding efficiency of the chloride ion relative to the bromide ion. Variations in the co-ion species (Li, Na, K) have little effect on the adsorption rate and surface excess of CTAC up to a bulk electrolyte concentration of 10 mM. However, the rate of adsorption is increased in the presence of electrolyte. Slow secondary adsorption is seen over a range of concentrations for CTAC in the absence of electrolyte and importantly in the presence of LiCl the origin of this slow adsorption is attributed to a structural barrier to adsorption.
Publisher: American Chemical Society (ACS)
Date: 02-1992
DOI: 10.1021/J100182A088
Publisher: American Chemical Society (ACS)
Date: 06-08-2010
DOI: 10.1021/MA101113G
Publisher: Informa UK Limited
Date: 12-2000
Publisher: The Royal Society
Date: 28-09-2010
Publisher: American Chemical Society (ACS)
Date: 27-03-2003
DOI: 10.1021/MA025761W
Publisher: Elsevier BV
Date: 04-2013
Publisher: Elsevier BV
Date: 03-2019
Publisher: American Chemical Society (ACS)
Date: 12-11-2010
DOI: 10.1021/LA103071C
Abstract: A quartz crystal microbalance with dissipation (QCM-D) and an optical reflectometer (OR) have been used to investigate the adsorption behavior of Laponite and Ludox silica nanoparticles at the solid-liquid interface. The adsorption of both Laponite and Ludox silica onto poly(diallyldimethylammonium chloride) (PDADMAC)-coated surfaces over the first few seconds were studied by OR. Both types of nanoparticles adsorbed rapidly and obtained a stable adsorbed amount after only a few minutes. The rate of adsorption for both nanoparticle types was concentration dependent. The maximum adsorption rate of Ludox nanoparticles was found to be approximately five times faster than that for Laponite nanoparticles. The QCM data for the Laponite remained stable after the initial adsorption period at each concentration tested. The observed plateau values for the frequency shifts increased with increasing Laponite particle concentration. The QCM data for the Ludox nanoparticles had a more complex long-time behavior. In particular, the dissipation data at 3 ppm and 10 ppm Ludox increased slowly with time, never obtaining a stable value within the duration of the experiment. We postulate here that this is caused by slow structural rearrangements of the particles and the PDADMAC within the surface adsorbed layer. Furthermore, the QCM dissipation values were significantly smaller for Laponite when compared with those for Ludox for all nanoparticle concentrations, suggesting that the Laponite adsorbed layer is more compact and more rigidly bound than the Ludox adsorbed layer.
Publisher: Elsevier BV
Date: 02-2004
Publisher: Royal Society of Chemistry (RSC)
Date: 2005
DOI: 10.1039/B403180F
Abstract: Selectively quaternising the PDMA block of poly(2-(dimethylamino)ethyl methacrylate)-block-poly(2-(diethylamino)ethyl methacrylate) (PDMA-PDEA) copolymers modifies both their solution and adsorption behaviour. These copolymers exist as free unimers in aqueous solution at low pH and form micelles, with PDMA coronas, at high pH. The critical micellisation pH, the hydrodynamic micelle diameter and electrophoretic behaviour are all affected by the degree of quaternisation of the PDMA block. Highly quaternised copolymers form smaller, more highly charged micelles at lower pH than weakly or non-quaternised copolymers. The adsorption of the copolymer micelles onto muscovite mica is studied by in situ atomic force microscopy. The adsorbed micelle monolayer becomes increasingly disordered as the degree of quaternisation increases. No micelle desorption occurs on removal of the bulk copolymer solution. Addition of acid to the overlying solution leads to different responses from the surface-adsorbed micelles. Unquaternised micelles undergo a reversible change in morphology due to the formation of localised polymer brushes, whereas lightly quaternised micelles are characterised by irreversible changes. Highly quaternised micelle monolayers are disrupted by the addition of acid. Such differences can be rationalised by simple electrostatic arguments. This behaviour has been confirmed by quartz crystal microbalance studies, which show that the adsorbed mass decreases with increasing degrees of quaternisation.
Publisher: American Chemical Society (ACS)
Date: 11-1997
DOI: 10.1021/LA970303F
Publisher: Elsevier BV
Date: 12-2016
DOI: 10.1016/J.JCIS.2016.08.058
Abstract: The solvent evaporation method for producing microcapsules relies upon the correct wetting conditions between the three phases involved in the synthesis to allow core-shell morphologies to form. By measuring the interfacial tensions between the oil, polymer and aqueous phases, spreading coefficients can be calculated, allowing the capsule morphology to be predicted. In this work we explore the effect of surfactant chain length on capsule morphology using poly(methyl methacrylate) as the polymer and hexadecane as the core. We compared the predicted morphologies obtained using the polymer as a solid, and the polymer dissolved in dichloromethane to represent the point at which capsule formation begins. We found that using the polymer in its final, solid form gave predictions which were more consistent with our observations. The method was applied to successfully predict the capsule morphologies obtained when commercial fragrance oils were encapsulated.
Publisher: Royal Society of Chemistry (RSC)
Date: 1993
DOI: 10.1039/C39930000378
Publisher: American Chemical Society (ACS)
Date: 28-10-2010
DOI: 10.1021/LA1033564
Abstract: Responsive core-shell latex particles are used to prepare colloidosome microcapsules using thermal annealing and internal cross linking of the shell, allowing the production of the microcapsules at high concentrations. The core-shell particles are composed of a polystyrene core and a shell of poly[2-(dimethylamino)ethyl methacrylate]-b-poly[methyl methacrylate] (PDMA-b-PMMA) chains adsorbed onto the core surface, providing steric stabilization. The PDMA component of the adsorbed polymer shell confers thermally responsive and pH-responsive characteristics to the latex particle, and it also provides glass transitions at temperatures lower than those of the core and reactive amine groups. These features facilitate the formation of stable Pickering emulsion droplets and the immobilization of the latex particle monolayer on these droplets to form colloidosome microcapsules. The immobilization is achieved through thermal annealing or cross linking of the shell under mild conditions feasible for large-scale economic production. We demonstrate here that it is possible to anneal the particle monolayer on the emulsion drop surface at 75-86 °C by using the lower glass-transition temperature of the shell compared to that of the polystyrene cores (∼108 °C). The colloidosome microcapsules that are formed have a rigid membrane basically composed of a densely packed monolayer of particles. Chemical cross linking has also been successfully achieved by confining a cross linker within the disperse droplet. This approach leads to the formation of single-layered stimulus-responsive soft colloidosome membranes and provides the advantage of working at very high emulsion concentrations because interdroplet cross linking is thus avoided. The porosity and mechanical strength of the microcapsules are also discussed here in terms of the observed structure of the latex particle monolayers forming the capsule membrane.
Publisher: Elsevier BV
Date: 04-2013
Publisher: Acoustical Society of America (ASA)
Date: 07-2014
DOI: 10.1121/1.4883376
Abstract: A technique that is an extension of an earlier approach for marine sediments is presented for determining the acoustic attenuation and backscattering coefficients of suspensions of particles of arbitrary materials of general engineering interest. It is necessary to know these coefficients (published values of which exist for quartz sand only) in order to implement an ultrasonic dual-frequency inversion method, in which the backscattered signals received by transducers operating at two frequencies in the megahertz range are used to determine the concentration profile in suspensions of solid particles in a carrier fluid. To demonstrate the application of this dual-frequency method to engineering flows, particle concentration profiles are calculated in turbulent, horizontal pipe flow. The observed trends in the measured attenuation and backscatter coefficients, which are compared to estimates based on the available quartz sand data, and the resulting concentration profiles, demonstrate that this method has potential for measuring the settling and segregation behavior of real suspensions and slurries in a range of applications, such as the nuclear and minerals processing industries, and is able to distinguish between homogeneous, heterogeneous, and bed-forming flow regimes.
Publisher: Elsevier BV
Date: 04-2008
Publisher: Royal Society of Chemistry (RSC)
Date: 2004
DOI: 10.1039/B402580F
Publisher: Royal Society of Chemistry (RSC)
Date: 1994
DOI: 10.1039/FT9949003415
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C1SM06547E
Publisher: American Chemical Society (ACS)
Date: 07-03-2003
DOI: 10.1021/JP026626O
Publisher: Elsevier BV
Date: 10-2013
Publisher: American Chemical Society (ACS)
Date: 13-12-2006
DOI: 10.1021/LA052274B
Publisher: American Chemical Society (ACS)
Date: 07-09-2001
DOI: 10.1021/LA001396V
Publisher: Elsevier BV
Date: 04-2011
Publisher: Elsevier BV
Date: 06-2013
Publisher: American Chemical Society (ACS)
Date: 24-12-2006
DOI: 10.1021/MA062648N
Publisher: Elsevier BV
Date: 11-2002
Abstract: Dilute aqueous dispersions of colloidal polystyrene latex spheres were flocculated by adding a nonadsorbing polymer s le, poly(acrylic acid). The structural compactness of the flocs thus formed was characterized in terms of their mass fractal dimension using the small-angle static light scattering technique. It was found that with low poly(acrylic acid) concentrations and thus weak depletion attraction forces, the dispersion medium viscosity had a marked effect on the floc structure. An increase in the viscosity led to formation of denser flocs. This was revealed in three sets of depletion flocculation experiments: (a) adjusting the background electrolyte concentration at a fixed level of poly(acrylic acid), (b) using water and 30% (w/w) glycerol as the respective solvents, and (c) inducing latex flocculation with two poly(acrylic acids) of different molecular weights at the respective critical polyacid concentrations. Direct force measurements were made with atomic force microscopy to isolate the influence of viscosity on floc structure from that of interparticle interaction energies. We conclude that the formation of denser flocs with increasing medium viscosity can be attributed to the reduced diffusivity of particles in the solution. The latter resulted in an enhanced rate of floc restructuring (through relaxation of attached particles) relative to floc growth.
Publisher: American Chemical Society (ACS)
Date: 26-06-2015
Abstract: Encapsulation and full retention of small molecular weight active ingredients is a challenging task that remains unsolved by current technologies used in industry and academia. In particular, certain everyday product formulations provide difficult environments in which preventing active leakage through capsule walls is not feasible. For ex le, a continuous phase that can fully dissolve an encapsulated active will typically force full release over a fraction of the intended lifetime of a product. This is due to the inherent porosity of polymeric membranes typically used as capsule wall material in current technologies. In this study, we demonstrate a method for preventing undesired loss of encapsulated actives under these extreme conditions using a simple threestep process. Our developed methodology, which forms an impermeable metal film around polymer microcapsules, prevents loss of small, volatile oils within an ethanol continuous phase for at least 21 days while polymeric capsules lose their entire content in less than 30 min under the same conditions. Polymer shell-oil core microcapsules are produced using a well-known cosolvent extraction method to precipitate a polymeric shell around the oil core. Subsequently, metallic catalytic nanoparticles are physically adsorbed onto the microcapsule polymeric shells. Finally, this nanoparticle coating is used to catalyze the growth of a secondary metallic film. Specifically, this work shows that it is possible to coat polymeric microcapsules containing a model oil system or a typical fragrance oil with a continuous metal shell. It also shows that the coverage of nanoparticles on the capsule surface can be controlled, which is paramount for obtaining a continuous impermeable metal film. In addition, control over the metal shell thickness is demonstrated without altering the capability of the metal film to retain the encapsulated oils.
Publisher: ASMEDC
Date: 2009
Abstract: Preliminary work has been completed to investigate the effect of particle-particle interaction forces on the flow properties of silica slurries. Classically Hydrotransport studies have focused on the flow of coarse granular material in Newtonian fluids. However, with current economical and environmental pressures, the need to increase solid loadings in pipe flow has lead to studies that examine non-Newtonian fluid dynamics. The flow characteristics of non-Newtonian slurries can be greatly influenced through controlling the solution chemistry. Here we present data on an “ideal” slurry where the particle size and shape is controlled together with the solution chemistry. We have investigated the effect of adsorbed cations on the stability of a suspension, the packing nature of a sediment and the frictional forces to be overcome during reslurrying. A significant change in the criteria assessed was observed as the electrolyte concentration was increased from 0.1mM to 1M. In relation to industrial processes, such delicate control of the slurry chemistry can greatly influence the optimum operating conditions of non-Newtonian pipe flows.
Publisher: American Physical Society (APS)
Date: 12-2000
Abstract: Experiments were conducted to investigate the link between particle-particle interaction forces and the bulk properties of granular shear using an idealized system of near-spherical, monosized glass beads. The atomic force microscopy colloidal probe technique was employed to investigate the adhesion and friction between a single bead and a second glass surface, while the annular shear cell was used to measure the shear properties of the bulk granular material. A covalently bound monomolecular film of aliphatic chains was introduced to alter the tribological interactions between the particles. The atomic force microscope was used to measure the reduction in the particle-particle surface forces resulting from the addition of the boundary lubricant, while the shear cell showed that the effect of the lubricant film was to reduce the coefficient of internal friction and the dilation during shear. This is an experimental study to provide quantitative data linking particle-particle interaction forces and the shear properties of a granular body.
Publisher: Elsevier BV
Date: 06-2020
Publisher: Royal Society of Chemistry
Date: 2004
Publisher: Elsevier BV
Date: 03-2005
Publisher: Elsevier BV
Date: 07-2000
Publisher: Elsevier BV
Date: 12-2010
Publisher: AIP Publishing
Date: 28-01-2008
DOI: 10.1063/1.2776263
Abstract: An improved model for the collision efficiency factor of clusters of oppositely charged spheres has been developed, which accounts for repulsive and attractive interactions that occur at a finite distance from the colliding species, i.e., the so-called “soft” interactions. Trends in measured optimum dosages for rapid aggregation with increasing Debye length (a decrease at particle size ratios between 0.3 and 1 and an increase at particle size ratios less than 0.3) are explained qualitatively by employing the modified collision efficiency model. Several observations from the literature, specifically the formation of stringlike aggregates at low ionic strength and the uneven optimum dosage requirements of particles of equal size, are also explained in view of the model presented.
Publisher: Elsevier BV
Date: 12-1996
Abstract: The polymerization of oil-in-water (o/w) emulsions of monomeric species has been performed at 30° C (± ° C) under ultrasonic irradiation, in the absence of any added chemical initiators. Emulsions of butyl acrylate and vinyl acetate as well as emulsified mixtures of the two monomers have been reacted in this way. In all cases, the radicals formed as a result of the ultrasonic cavitation were sufficient to cause polymerization. Stable blue-white or white dispersions of polymer latex particles were obtained. The kinetics of the copolymerization process were monitored. The data obtained here show that the polymerization rate depends strongly upon the monomer concentration dissolved in the aqueous phase and on its vapor pressure. The more volatile of the monomers examined, vinyl acetate, was seen to have a markedly lower polymerization rate at equivalent monomer concentrations when compared to the butyl acrylate. This was attributed to monomer evaporation into the cavities formed by the ultrasound, causing a d ening of the cavitation process and hence a lower radical density. Data of particle sizes and polymer molecular weights for the latex s les support this hypothesis.
Publisher: American Chemical Society (ACS)
Date: 05-05-2006
DOI: 10.1021/LA060662N
Abstract: The similarities and differences in the adsorption behavior of diblock poly(2-(dimethylamino)ethyl methacrylate)-b-poly(2-(diethylamino)ethyl methacrylate) (XqPDMA-PDEA, where X refers to a mean degree of quaternization of the PDMA of either 0, 10, 50, or 100 mol%) copolymers at the mica/ and silica/aqueous solution interfaces have been investigated. These diblock copolymers form core-shell micelles with the PDEA chains located in the cores and the more hydrophilic PDMA chains forming the cationic micelle coronas at pH 9. These micelles adsorb strongly onto both mica and silica due to electrostatic interactions. In situ atomic force microscopy (AFM) has demonstrated that the mean spacing and the dimension of the adsorbed micelles depend on both the substrate and the mean degree of quaternization of the PDMA blocks. In particular, the morphology of the adsorbed nonquaternized 0qPDMA-PDEA copolymer micelles is clearly influenced by the substrate type: these micelles form a disordered layer on silica, while much more close-packed, highly ordered layers are obtained on mica. The key reasons for this difference are suggested to be the ease of lateral rearrangement for the copolymer micelles attached to the solid substrates and the relative rates of relaxation of the coronal PDMA chains.
Publisher: American Chemical Society (ACS)
Date: 09-2006
DOI: 10.1021/LA061708F
Abstract: The pH-responsive behavior of cationic diblock poly(2-(dimethylamino)ethyl methacrylate)-block-poly(2-(diethylamino)ethyl methacrylate) copolymer micelles adsorbed at the silica/aqueous solution interface has been characterized. The micellar morphology of this copolymer, initially adsorbed at pH 9, can be dramatically altered by lowering the solution pH. The original micelle-like morphology of the adsorbed copolymer chains at pH 9 completely disappears as the pH is decreased to 4, and a brush-like layer structure is produced. This change results from protonation of the copolymer chains: the subsequent electrostatic repulsions within the film drive the copolymer chains to expand into the aqueous phase. Returning the solution pH from 4 to 9 causes this brush-like layer to collapse, with atomic force microscopy images suggesting degradation of the film. Hence, the pH-responsive behavior of the copolymer film exhibits irreversible morphological changes. Measurements of the adsorbed/desorbed amounts of the copolymer film were conducted using both a quartz crystal microbalance with dissipation monitoring (QCM-D) and optical reflectometry (OR). After an initial rinse at both pH values, the OR adsorbed mass becomes almost constant during subsequent pH cycling, whereas the corresponding QCM-D adsorbed mass changes significantly but reversibly in response to the solution pH. Since the QCM-D measures a bound mass that moves in tandem with the surface, the discrepancy with the OR data is due to changes in the amount of bound water in the copolymer film as a result of the pH-induced changes in surface morphology. The larger effective mass observed at pH 4 suggests that the brush-like layer contains much more entrapped water than the micellar films at pH 9. The pH dependence of the contact angle of the adsorbed film is consistent with the changes observed using the other techniques, regardless of whether the solution pH is altered in situ or the aqueous solution is completely replaced. In fact, comparison of these two approaches provides direct evidence of the exposure of adsorbed micelle core blocks to the solution during pH cycling and the concomitant impact upon all the other measurements.
Publisher: Elsevier BV
Date: 2010
Publisher: Elsevier BV
Date: 2010
Publisher: Elsevier BV
Date: 06-2000
Publisher: Royal Society of Chemistry (RSC)
Date: 2004
DOI: 10.1039/B401376J
Publisher: Elsevier BV
Date: 04-2015
Publisher: Elsevier BV
Date: 10-2012
Publisher: American Chemical Society (ACS)
Date: 03-1992
DOI: 10.1021/LA00039A018
Publisher: Royal Society of Chemistry
Date: 2008
Publisher: American Chemical Society (ACS)
Date: 12-1994
DOI: 10.1021/LA00024A028
Publisher: Elsevier BV
Date: 2000
Publisher: American Physical Society (APS)
Date: 07-1995
Publisher: Royal Society of Chemistry
Date: 2015
Publisher: Elsevier BV
Date: 05-2006
Publisher: Informa UK Limited
Date: 1998
Publisher: Elsevier BV
Date: 11-1996
Abstract: An atomic force microscope was used to measure the forces between a silica sphere (diameter 10 &mu m) and a n-decane droplet (diameter 0.3 mm) in water. Force-distance profiles showed a weak attraction and adhesion due to van der Waals forces. When the anionic surfactant sodium dodecyl sulfate was added, there was electrostatic repulsion at all separations due to the adsorption of the anionic surfactant at the oil-water interface, and no adhesion of the sphere to the oil droplet was observed upon retraction. Fitting the repulsive curves to the nonlinear Poisson-Boltzmann equation for heterogeneous surfaces yielded surface potentials on the oil surface which were consistently lower than those values found from electrokinetic experiments on oil drops under similar conditions. The measured Debye lengths were also found to be significantly different from those calculated from the surfactant and electrolyte conditions employed. Possible reasons for the discrepancies are outlined.
Publisher: American Chemical Society (ACS)
Date: 15-12-2006
DOI: 10.1021/LA063003J
Abstract: A convenient two-step route was developed to prepare new anionic ATRP macroinitiators from near-monodisperse poly(2-hydroxyethyl methacrylate) precursors by partial esterification with 2-bromoisobutyryl bromide, followed by esterification of the remaining hydroxyl groups using excess 2-sulfobenzoic acid cyclic anhydride. These new macroinitiators can be electrostatically adsorbed onto ultrafine cationic Ludox CL silica sols subsequent surface polymerization of various hydrophilic monomers in aqueous solution at room temperature afforded a range of polymer-grafted ultrafine silica sols. The resulting sterically stabilized particles were characterized by dynamic light scattering, transmission electron microscopy, aqueous electrophoresis, FTIR spectroscopy, and elemental microanalyses.
Publisher: Elsevier BV
Date: 09-2019
Publisher: Elsevier BV
Date: 11-2006
DOI: 10.1016/J.JCIS.2006.07.077
Abstract: The pH-responsive behavior of adsorbed diblock copolymer films of PDMA-PDEA (poly(2-(dimethylamino)ethyl methacrylate)-block-poly(2-(diethylamino)ethyl methacrylate)) on silica has been characterized using a quartz crystal microbalance with dissipation monitoring (QCM-D), an optical reflectometer (OR) and an atomic force microscope (AFM). The copolymer was adsorbed at pH 9 from various copolymer concentrations QCM-D measurements indicate that the level of desorption when rinsed at pH 9 depends on the initial copolymer concentration. The adsorbed films produced at pH 9 generally have low charge densities adjusting the solution pH to 4 results in a significant protonation of the constituent copolymers and a related interfacial structural change for the copolymer film. OR studies show no significant change during pH cycling, while QCM-D measurements indicate that the adsorbed mass and dissipation alter dramatically in response to the solution pH. The difference between the QCM-D adsorbed masses and dissipation values at pH 4 and 9 were found to be dependent on the initial copolymer concentration. This is due to differences in the initial conformations within the adsorbed copolymer layers at pH 9. The effect of the PDMA chain length on the pH-responsive behavior has also been studied both the QCM-D adsorbed mass and dissipation of PDMA54-PDEA24 (shorter PDMA block) at pH 4 and 9 were observed to be greater than those of PDMA9X-PDEA2Y (longer PDMA block). This suggests that the normal extension of the adsorbed PDMA54-PDEA24 copolymer films is more significant than that of the PDMA9X-PDEA2Y films on silica.
Publisher: Elsevier BV
Date: 07-1994
Publisher: ASMEDC
Date: 2009
Abstract: In order to gain good control over a particulate dispersion it is necessary to accurately characterise the strength of interparticle forces that may be operating. Such control is not routinely used, as yet, in the nuclear industry despite the possible benefits. We are investigating the impact of mixed electrolyte systems, for ex le NaCl and Na2SO4, on the stability of oxide simulant particle dispersions. The electroacoustic zeta potentials and shear yield stresses for concentrated dispersions have been measured across a range of pH conditions and electrolyte concentrations (0.001 M – 1.0 M). This paper summarizes initial data from these studies showing how the shear yield stress of concentrated aqueous oxide particle dispersions, can be adjusted through regulation of pH and the addition of background electrolytes (salt). The yield stress as a function of pH for these dispersions in mixed electrolytes showed a direct correlation with corresponding measurements of the zeta potential. Changes in the background electrolyte concentration or type were seen to cause a shift in the position of the isoelectric point (iep). Measurements of the shear yield stress showed a maximum at the iep corresponding to the position of maximum instability in the suspension. The consequences of these data for the efficient treatment of solid-liquid systems will be discussed.
Publisher: Royal Society of Chemistry (RSC)
Date: 2011
DOI: 10.1039/C0SM01072C
Publisher: Elsevier BV
Date: 10-1995
Publisher: American Chemical Society (ACS)
Date: 20-06-2007
DOI: 10.1021/LA700708G
Abstract: The adsorption of rodlike polymer-micelle aggregates of cetyltrimethylammonium 4-vinylbenzoate (p-C16TVB) at the silica-water interface has been characterized using a combination of quartz crystal microbalance with dissipation monitoring (QCM-D) and atomic force microscopy (AFM) studies. Adsorption isotherm data, recorded by QCM-D, indicate a two-stage mechanism: an adsorbed film of free CTA+ ions is initially produced at low concentrations until the surface is charge reversed, whereupon the weakly anionic aggregates can adsorb and the adsorbed mass is seen to increase dramatically. The adsorbed rodlike micelle aggregates are seen to form a close-packed monolayer from AFM images with a high degree of order over micrometer length scales. AFM force-distance data indicate that the adsorbed aggregates retain their cylindrical structure and little or no flattening is seen. Rinsing of the film did not result in removal of the adsorbed layer, and the persistence of these nanoscale ordered films at the solid-liquid interface suggests many possible applications.
Publisher: Informa UK Limited
Date: 21-09-2010
Publisher: American Chemical Society (ACS)
Date: 11-2000
DOI: 10.1021/LA0001272
Publisher: Elsevier BV
Date: 07-2019
Publisher: Elsevier BV
Date: 2010
Publisher: American Chemical Society (ACS)
Date: 12-02-2003
DOI: 10.1021/LA0265070
Publisher: Elsevier BV
Date: 07-2005
Publisher: Cambridge University Press (CUP)
Date: 14-12-2009
DOI: 10.1017/S0144686X0999047X
Abstract: This paper critically reflects upon policy and research definitions of elder mistreatment in light of the findings of the United Kingdom Study of Abuse and Neglect of Older People that was commissioned by Comic Relief with co-funding from the Department of Health. The study uniquely comprised a national survey and follow-up qualitative research with survey respondents. This paper focuses on the findings of the qualitative component. One focus is the idea of ‘expectation of trust’, with an argument being made that the concept needs clarification for different types of relationships. It is particularly important to distinguish between trust in affective relationships and ‘positions of trust’ (as of paid carers), and to articulate the concept in terms that engage with older people's experiences and that are meaningful for different relationship categories. The qualitative research also found that ascriptions of neglect and abuse tend to be over-inclusive, in some instances to avoid identifying institutional and service failures. We also question the role and relevance of the use of chronological age in the notion of ‘elder abuse’. Given that ‘abuse’, ‘neglect’ and ‘expectation of trust’ are ill-defined and contested concepts, we recommend that although consistent definitions are important, especially for research into the epidemiology and aetiology of the syndrome and for informed policy discussion, they will unavoidably be provisional and pragmatic.
Publisher: ASMEDC
Date: 2009
Abstract: Stability control of particulate dispersions is critical to a wide range of industrial processes. In the UK nuclear industry, significant volumes of waste materials arising from the corrosion products of Magnox fuel rods currently require treatment and storage. The majority of this waste is present as aqueous dispersions of oxide particulates. Treatment of these dispersions will require a variety of unit operations including mobilisation, transport and solid-liquid separation. Typically these processes must operate across a narrow optimal range of pH and the dispersions are, almost without exception, found in complex electrolyte conditions of high overall concentration. Knowledge of the behaviour of oxides in various electrolyte conditions and over a large pH range is essential for the efficient design and control of any waste processing approach. The transport properties of particle dispersions are characterised by the rheological properties. It is well known that particle dispersion rheology is strongly influenced by particle-particle interaction forces, and that particle-particle interactions are strongly influenced by adsorbed ions on the particle surfaces. Here we correlate measurements of the shear yield stress and the particle zeta potentials to provide insight as to the role of ions in moderating particle interactions. The zeta potential of model TiO2 suspensions were determined (Colloidal Dynamics ZetaProbe) over a range of pH for a series of alkali metal halides and quaternary ammonium halides at a range of solution concentrations (0.001M–1M). The results show some surprising co-ion effects at high electrolyte concentrations ( .5M) and indicate that even ions generally considered to be indifferent induce a shift in iso-electric point (i.e.p.) which is inferred as being due to specific adsorption of ions. The shear yield stress values of concentrated titania dispersions were measured using a Bohlin C-VOR stress controlled rheometer. The shear yield stress of a material is defined as the minimum applied shear stress required to induce flow. The yield stress vs. pH curves obtained reflected the shifts in i.e.p. seen in the zeta potential results. Interestingly, specific ion adsorption results in an unexplained increase in the value of the yield stress over that expected for simple systems with no such interfacial ion adsorption. Possible reasons for this effect such as ion-ion correlation effects are discussed. The importance of this increased attraction for the mobilisation of settled solids in an aqueous environment and especially the likely effects on the treatment of Magnox fuel waste materials is discussed.
Publisher: Elsevier BV
Date: 06-2001
Publisher: Elsevier BV
Date: 08-2017
Publisher: American Chemical Society (ACS)
Date: 02-02-2010
DOI: 10.1021/LA904784A
Abstract: The adsorption of colloidal laponite at the solid/liquid interface on various substrates and over a range of laponite concentrations (10-1000 ppm) has been investigated. Although a wide range of surfaces were studied, only on a positively charged poly(diallyldimethylammonium chloride) (PDADMAC) surface was any adsorption of the laponite observed. This shows that when fully wetted, laponite adsorption depends primarily on the surface charge rather than the degree of hydrophobicity of the surface. The adsorption of spherical Ludox silica nanoparticles on PDADMAC surfaces was also examined for comparison with the disklike laponite. The QCM data for both laponite and Ludox show strong adsorption on PDADMAC surfaces however, larger frequency shifts were seen for Ludox than laponite at all concentrations tested. Within the concentration range examined in this work, the dissipation data from the QCM suggested a simple monolayer formation for Ludox but a monolayer to multilayer transition for laponite as the concentration increases.
Publisher: American Chemical Society (ACS)
Date: 06-05-2005
DOI: 10.1021/LA050041E
Abstract: We have investigated the structural and depletion forces between silica glass surfaces in aqueous, salt-free solutions of sodium poly(styrene sulfonate). The interaction forces were investigated by two techniques: total internal reflectance microscopy (TIRM) and colloid probe atomic force microscopy (AFM). The TIRM technique measures the potential energy of interaction directly, while the AFM is a force balance. Comparison between the data sets was used to independently calibrate the AFM data since the separation distances cannot be unequivocally determined by this technique. Oscillatory structural forces are excellent for this work since they give multiple reference points against which to analyze. Comparison of the data from the two techniques highlighted significant uncertainties in the AFM data. At low polymer concentrations, a significant uncertainty in the apparent zero separation distance was seen as a result of the AFM cantilever reaching an apparent constant compliance region prior to any real contact between the surfaces. Further complications arising from the number and position of the measured minima were also seen in the dilute polymer concentration regime as a result of hydrodynamic drainage between the approaching surfaces in the AFM perturbing the delicate structural components in the fluid.
Publisher: American Physical Society (APS)
Date: 26-06-2001
Publisher: Elsevier BV
Date: 07-2000
DOI: 10.1016/S1350-4177(99)00040-1
Abstract: Polystyrene latex s les have been synthesised from an oil-in-water (o/w) emulsion of the monomer using ultrasonic irradiation as the initiation source. No added chemical initiators were used in any of the reactions. The free radicals formed from the cavitation process under the action of the ultrasound are sufficient to initiate the polymerisation. In the current study, the effects of varying the input intensity of the ultrasound were investigated. A marked increase in the monomer conversion rate as a function of time was seen as the power was increased. Despite this increase in conversion rate, the increasing intensity did not affect the resultant latex particle sizes. In all cases, the particle diameters at the conclusion of a polymerisation were seen to be in the range of 40 to 50 nm. The effects of changing the concentration of surfactant in the polymerisation medium and of changing the temperature were also probed. Increases in both were seen to lead to an increased rate of conversion at a fixed input intensity. Again, the particle diameters were invariant as a function of changing conditions. The small particle sizes and high conversion rates are thought to be due to a continuous nucleation process that is caused by the scavenging of free radicals throughout the polymerisation by freshly formed small oil droplets.
Publisher: American Chemical Society (ACS)
Date: 23-04-2014
DOI: 10.1021/LA5013439
Publisher: Royal Society of Chemistry (RSC)
Date: 2009
DOI: 10.1039/B820842E
Publisher: American Chemical Society (ACS)
Date: 29-09-2007
DOI: 10.1021/LA701461B
Abstract: The temperature-induced structural changes of a thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) layer grafted onto a silica substrate were investigated in aqueous solution using an atomic force microscope (AFM) and a quartz crystal microbalance with dissipation (QCM-D). A PNIPAM layer was grafted onto the silicon wafer surface by free radical polymerization of NIPAM to obtain a high molecular weight polymer layer with low-grafting density overall. By AFM imaging, the transition of the grafted PNIPAM chains from a brush-like to a mushroom-like state was clearly visualized: The surface images of the plate were featureless at temperatures below the LCST commensurate with a brush-like layer, whereas above the LCST, a large number of domain structures with a characteristic size of approximately 100 nm were seen on the surface. Both frequency and dissipation data obtained using QCM-D showed a significant change at the LCST. Analysis of these data confirmed that the observed PNIPAM structural transition was caused by a collapse of the brush-like structure as a result of dehydration of the polymer chains.
Publisher: American Chemical Society (ACS)
Date: 08-09-2001
DOI: 10.1021/JP011503+
Publisher: Elsevier BV
Date: 11-2001
Publisher: Wiley
Date: 21-06-2017
Abstract: Polymer microcapsules have been used commercially for decades, however they have an inherent flaw which renders them impractical as a carrier of small, volatile molecules. The porous nature of the polymer shell allows for diffusion of the encapsulated molecules into the bulk. The use of metal shells is an innovative way to prevent undesired loss of small molecules from the core of microcapsules, however it is important, particularly when using expensive metals to ensure that the resulting shell is as thin as possible. Here we investigate the fundamental mechanisms controlling the gold shell thickness when a fragrance oil is encapsulated in a poly(methyl methacrylate) shell. We consider the distribution of the nanoparticles on the capsule surface, and from quantification of the adsorbed nanoparticle (NP) density and resulting shell thickness, we propose mechanisms to describe the gold shell growth for systems with high and low NP surface coverage. We suggest from our observations that the gold grows to fill in the gaps between NPs. At low NP concentrations, thicker metal shells form. We postulate that this is due to the low NP density on the surface, forcing the gold clusters to grow larger before they meet the adjacent ones. Thus, to grow the thinnest possible shells a densely packed monolayer of platinum nanoparticles is required on the capsule surface.
Publisher: Elsevier BV
Date: 08-2004
Publisher: Elsevier BV
Date: 2015
Publisher: Elsevier BV
Date: 05-2020
Publisher: AIP Publishing
Date: 13-11-2006
DOI: 10.1063/1.2387172
Abstract: A generalized geometric model is presented which describes the collision efficiency factor of aggregation (the probability of a binary particle or aggregate collision resulting in adhesion) for systems comprised of two oppositely charged species. Application of the general model to specific systems requires calculation of the area of each species available for collision with a second species. This is in contrast to previous models developed for polymer-particle flocculation that are based on the fractional surface coverage of adsorbed polymer. The difference between these approaches is suggested as an explanation for previously observed discrepancies between theory and observation. In the current work the specific case of oppositely charged nondeformable spherical particles (heteroaggregation) is quantitatively addressed. The optimum concentration of oppositely charged particles for rapid aggregation (maximum collision efficiency) as a function of relative particle size is calculated and an excellent correlation is found with data taken from literature.
Publisher: Wiley
Date: 02-03-2017
DOI: 10.1002/AIC.15683
Publisher: American Chemical Society (ACS)
Date: 07-01-2010
DOI: 10.1021/LA904064D
Abstract: Using a layer-by-layer (LbL) approach, this work presents the preparation of hollow microcapsules with a membrane constructed entirely from a cationic/zwitterionic pair of pH-responsive block copolymer micelles. Our previous work with such systems highlighted that, in order to retain the responsive nature of the in idual micelles contained within the multilayer membranes, it is important to optimize the conditions required for the selective dissolution of the sacrificial particulate templates. Consequently, here, calcium carbonate particles have been employed as colloidal templates as they can be easily dissolved in aqueous environments with the addition of chelating agents such as ethylenediaminetetraacetic acid (EDTA). Furthermore, the dissolution can be carried out in solutions buffered to a desirable pH so not to adversely affect the pH sensitive micelles forming the capsule membranes. First, we have deposited alternating layers of anionic poly[2-(dimethylamino)ethyl methacrylate-block-poly(2-(diethylamino)ethyl methacrylate)] (PDMA-PDEA) and cationic poly(2-(diethylamino)ethyl)methacrylate-block-poly(methacrylic acid) (PDEA-PMAA) copolymer micelles onto calcium carbonate colloidal templates. After deposition of five micelle bilayers, addition of dilute EDTA solution resulted in dissolution of the calcium carbonate and formation of hollow polymer capsules. The capsules were imaged using atomic force microscopy (AFM) and scanning electron microscopy (SEM), which shows that the micelle/micelle membrane is sufficiently robust to withstand dissolution of the supporting template. Quartz crystal microbalance studies were conducted and provide good evidence that the micelle multilayer structure is retained after EDTA treatment. In addition, a hydrophobic dye was incorporated into the micelle cores prior to adsorption. After dissolution of the particle template, the resulting hollow capsules retained a high concentration of dye, suggesting that the core/shell structure of the micelles remains intact. Finally, thermogravimetric analysis (TGA) of dried capsules confirmed complete removal of the sacrificial inorganic template. As far as we are aware, this is the first demonstration of LbL assembled capsules composed entirely from responsive block copolymer micelles. The results presented here when combined with our previous findings demonstrate that such systems have potential application in the encapsulation and triggered release of actives.
Publisher: American Chemical Society (ACS)
Date: 16-01-2018
DOI: 10.1021/ACS.LANGMUIR.7B02874
Abstract: Efficient encapsulation of small chemical molecules and their controlled targeted delivery provides a very important challenge to be overcome for a wide range of industrial applications. Typically rapid diffusion of these actives across capsule walls has so far prevented the development of a versatile widely applicable solution. In an earlier publication, we have shown that thin metal shells are able to permanently retain small molecules. The critical step in the microcapsule synthesis is the formation of a strongly adsorbed, dense monolayer of catalytic nanoparticles on the surface as this affects the secondary metal film quality. Control over Pt-nanoparticle adsorption density and a clear understanding of Pt-nanoparticle adsorption kinetics is therefore paramount. Maximising the density of heterogeneous catalysts on surfaces is generally of interest to a broad range of applications. In this work, transmission electron microscopy (TEM) and quartz crystal microbalance (QCM) are used to demonstrate that the concentration of nanoparticle polymer stabilizer used during particle synthesis and nanoparticle suspension concentration can be used to control nanoparticle surface adsorption density. We demonstrate that excess polymer, which is often used in nanoparticle synthesis but rarely discussed as an important parameter in the literature, can compete with and thus drastically affect the adsorption of the Pt-nanoparticles.
Publisher: The Royal Society
Date: 28-09-2010
Abstract: Alternating layers of cationic and anionic block copolymer micelles have been deposited onto colloidal silica particles using a layer-by-layer approach. The resulting films have been investigated using a number of characterization techniques including zeta potential measurements, dynamic light scattering, thermo-gravimetric analysis and microscopy. The micelles used here demonstrate pH-responsive behaviour both in solution and when adsorbed at interfaces. It has been shown that block copolymer micelles can selectively encapsulate and release hydrophobic materials therefore, the incorporation of such responsive species within films has the potential to offer increased functionality. The formation of films onto colloidal particles is of great interest as it can provide pathways to direct encapsulation of materials along with surface modification. This study aims to provide new insights into the nature and properties of responsive films. Such studies will allow for the future development of novel delivery systems that have potential application within a number of industrial sectors including personal care products, pharmaceuticals and agro-chemicals.
Publisher: American Chemical Society (ACS)
Date: 04-12-2007
DOI: 10.1021/LA7021006
Abstract: The in situ layer-by-layer (LbL) self-assembly of low Tg diblock copolymer micelles onto a flat silica substrate is reported. The copolymers used here were a cationic poly(2-(dimethylamino)ethyl methacrylate)-block-poly(2-(diethylamino)ethyl methacrylate) (50qPDMA-PDEA 50q refers to a mean degree of quaternization of 50 mol % for the PDMA block) and zwitterionic poly(methacrylic acid)-block-poly(2-(diethylamino)ethyl methacrylate) (PMAA-PDEA), which has anionic character at pH 9. Alternate deposition of micelles formed by these two copolymers onto a silica substrate at pH 9 was examined. The in situ LbL buildup of the copolymer micelle films was monitored using zeta potential measurements, optical reflectometry, and a quartz crystal microbalance with dissipation monitoring (QCM-D). For a six layer deposition, complete charge reversal was observed after the addition of each layer. The OR data indicated clearly an increase in adsorbed mass with each additional micelle layer and suggest that some interdiffusion of copolymer chains between layers and/or an increase in the film roughness, and hence in the effective surface area of the micellar multilayers, must take place as the film is built up. QCM-D data indicated that the self-assembled micellar multilayers on a flat silica substrate undergo structural changes over a prolonged period. This is attributed to longer-term interdiffusion of the copolymer chains between the outer two layers after the initial adsorption of each layer is complete. The QCM-D data further suggest that the outer adsorbed layers adopt a progressively more extended conformation, particularly for the higher numbered layers. The morphology of each successive layer was characterized using in situ soft-contact atomic force microscopy, and micelle-like surface aggregates are clearly observed within each layer of the complex film, suggesting the persistence of aggregate structures throughout the multilayer structure.
Publisher: Cambridge University Press (CUP)
Date: 27-03-2009
DOI: 10.1017/S1368980009005230
Abstract: To investigate the short- and long-term effectiveness and the predictors of weight loss in a mobile phone weight-loss programme among healthy overweight adults. One hundred and twenty-five healthy, overweight (BMI = 26–36 kg/m 2 ), 25–44-year-old, screened volunteers were randomized to an experimental group ( n 62) to use a mobile phone-operated weight-loss programme or to a control group ( n 63) with no intervention. Via text messaging, the programme instructed a staggered reduction of food intake and daily weight reporting with immediate tailored feedback. Assessments were at 0, 3, 6, 9 and 12 months for the experimental group at 0 and 12 months for the control group. Main outcome variables were changes in body weight and waist circumference. By 12 months the experimental group had lost significantly more weight than the control group (4·5 ( sd 5·0) v . 1·1 ( sd 5·8) kg F (1,80) = 8·0, P = 0·006) and had a greater reduction in waist circumference (6·3 ( sd 5·3) v . 2·4 ( sd 5·4) cm F (1,80) = 55·2, P = 0·0001). Early weight loss, self-efficacy, contact frequency, attitudes towards the medium, changes in work and family life and changes made in dietary habits were the strongest predictors of weight loss. This mobile phone weight-loss programme was effective in short- and long-term weight loss. As a minimum-advice, maximal-contact programme, it offers ideas for future weight-loss programmes.
Publisher: Elsevier BV
Date: 11-2015
Publisher: Elsevier BV
Date: 10-2007
DOI: 10.1016/J.JCIS.2007.06.018
Abstract: The desorption and subsequent pH-responsive behavior of selectively quaternized poly(2-(dimethylamino)ethyl methacrylate)-block-poly(2-(diethylamino)ethyl methacrylate) (PDMA-PDEA) films at the silica/aqueous solution interface has been characterized. The copolymer films were prepared at pH 9, where micelle-like surface aggregates are spontaneously formed on silica. The subsequent rinse with a copolymer-free electrolyte solution adjusted to pH 9 causes partial desorption of the weakly or non-quaternized copolymers, but negligible desorption for the highly quaternized copolymers. Further rinsing with a pH 4 electrolyte solution results in additional desorption and extension (swelling) of the remaining adsorbed copolymer film normal to the interface. This pH-responsive behavior is reversible for two pH cycles (9-4-9-4) as monitored by both quartz crystal microbalance with dissipation monitoring (QCM-D) and also zeta potential measurements. The magnitude of the pH-responsive behavior depends on the mean degree of quaternization of the PDMA block. Moreover, a combination of contact angle data, zeta potential measurements and in situ atomic force microscopy (AFM) studies indicates that the pH-responsive behavior is influenced not only by the number of cationic binding sites on the adsorbed copolymer chains but also by the adsorbed layer structure.
Publisher: Elsevier BV
Date: 06-1994
Publisher: Elsevier BV
Date: 02-2012
Publisher: Elsevier BV
Date: 06-1998
Publisher: Wiley
Date: 27-07-2011
DOI: 10.1002/AIC.12388
Publisher: Elsevier BV
Date: 07-2017
Publisher: American Chemical Society (ACS)
Date: 08-07-2006
DOI: 10.1021/JP062830Q
Abstract: The adsorption behavior of two ex les of a weakly basic diblock copolymer, poly(2-(dimethylamino)ethyl methacrylate)-block-poly(2-(diethylamino)ethyl methacrylate) (PDMA-PDEA), at the silica/aqueous solution interface has been investigated using a quartz crystal microbalance with dissipation monitoring and an optical reflectometer. Dynamic and static light scattering measurements have also been carried out to assess aqueous solution properties of such pH-responsive copolymers. In alkaline solution, core-shell micelles are formed above the critical micelle concentration (cmc) by both copolymers, whereas the chains are molecularly dissolved (as unimers) at all concentrations in acidic solution. As a result, the adsorption behavior of PDMA-PDEA diblock copolymers on silica is strongly dependent on both the copolymer concentration and the solution pH. Below the cmc at pH 9, the cationic PDMA-PDEA copolymers adsorb as unimers and the conformation of the adsorbed polymer is essentially flat. At concentrations just above the cmc, the initial adsorption of copolymer onto the silica is dominated by the unimers due to their faster diffusion compared to the much larger micelles. Rearrangement of the adsorbed unimers and/or their subsequent displacement by micelles from solution is then observed during an equilibration period, and the final adsorbed mass is greater than that observed below the cmc. At concentrations well above the cmc, the much higher proportion of micelles in solution facilitates more effective competition for the surface at all stages of the adsorption process and no replacement of initially adsorbed unimers by micelles is evident. However, the adsorbed layer undergoes gradual rearrangement after initial adsorption. This relaxation is believed to result from a combination of further copolymer adsorption and swelling of the adsorbed layer.
Publisher: Elsevier BV
Date: 09-2002
Abstract: The kinetics of drop penetration were studied by filming single drops of several different fluids (water, PEG200, PEG600, and HPC solutions) as they penetrated into loosely packed beds of glass ballotini, lactose, zinc oxide, and titanium dioxide powders. Measured times ranged from 0.45 to 126 s and depended on the powder particle size, viscosity, surface tensions, and contact angle. The experimental drop penetration times were compared to existing theoretical predictions by M. Denesuk et al. (J. Colloid Interface Sci.158, 114, 1993) and S. Middleman ("Modeling Axisymmetric Flows: Dynamics of Films, Jets, and Drops," Academic Press, San Diego, 1995) but did not agree. Loosely packed powder beds tend to have a heterogeneous bed structure containing large macrovoids which do not participate in liquid flow but are included implicitly in the existing approach to estimating powder pore size. A new two-phase model was proposed where the total volume of the macrovoids was assumed to be the difference between the bed porosity and the tap porosity. A new parameter, the effective porosity epsilon(eff), was defined as the tap porosity multiplied by the fraction of pores that terminate at a macrovoid and are effectively blocked pores. The improved drop penetration model was much more successful at estimating the drop penetration time on all powders and the predicted times were generally within an order of magnitude of the experimental results.
Publisher: American Chemical Society (ACS)
Date: 07-01-2004
DOI: 10.1021/LA0358062
Abstract: Solutions of rodlike polymeric micellar aggregates, formed from the polymerization of cetyltrimethyl-ammonium 4-vinylbenzoate (CTVB), adsorb at the solid-liquid interface. The poly-CTVB aggregates are imaged in situ using soft contact atomic force microscopy. The aggregates form self-organized two-dimensional films that show a high degree of order on nanometer to micrometer length scales. Unlike their simple surfactant analogues, the adsorbed layer structures are permanently adsorbed and the structure is resilient to washing with pure solvent. In the case of poly-CTVB, the adsorbed aggregates appear to be rigid cylindrical structures of between 30 and 60 nm in length. At the interface, the center to center spacing of the aligned aggregates is 8+/-1 nm. Images of a second series ofpolymerized aggregates formed by the copolymerization of CTVB with sodium vinyltosylate revealed a change in the aggregate structure to a set of linked spherical aggregates. These polymerized aggregates also spontaneously form a permanent adsorbed layer at the solid-liquid interface.
Publisher: American Chemical Society (ACS)
Date: 10-10-2002
DOI: 10.1021/JP026425K
Publisher: Elsevier BV
Date: 2015
Publisher: Elsevier BV
Date: 06-2011
Publisher: Elsevier BV
Date: 1999
Publisher: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C8TB00348C
Abstract: Novel method of producing metal microcapsules, using nanoparticles as the stabiliser, allows better control of nanoparticle distribution thus optimisation of metal shells.
Publisher: Royal Society of Chemistry (RSC)
Date: 1995
DOI: 10.1039/FT9959100665
Publisher: American Chemical Society (ACS)
Date: 1995
DOI: 10.1021/LA00001A028
Publisher: Elsevier BV
Date: 12-1996
Publisher: American Chemical Society (ACS)
Date: 27-07-2001
DOI: 10.1021/LA010335+
Publisher: Wiley
Date: 18-10-2004
Publisher: Elsevier BV
Date: 08-1998
Publisher: Elsevier BV
Date: 03-2022
DOI: 10.1016/J.JCIS.2021.11.062
Abstract: The efficient encapsulation of small molecule active ingredients has been a challenge for many decades across many commercial applications. Recently, successful attempts to address this issue have included deposition of thin metal shells onto liquid filled polymer microcapsules or emulsion droplets to provide an impermeable barrier to diffusion. In this work we have developed a novel method to protect small molecule active ingredients by deposition of thin mineral shells. Platinum nanoparticles are used to catalyse and direct growth of a calcium phosphate shell onto liquid filled polymer microcapsules under various reaction conditions. Findings indicate that a non-porous protective shell is formed on the majority of the microcapsule population, with small concentrations of the core material being released only from those microcapsules with defects, over a 7 days period, when conducting forced release studies into a solvent for the core oil. The resulting microcapsules show no significant cell toxicity when exposed to HEK 293 cells for 72 h.
Publisher: ASMEDC
Date: 2009
Abstract: A large amount of nuclear waste is stored in tailings ponds as a solid-liquid slurry, and liquid flows containing suspensions of solid particles are encountered in the treatment and disposal of this waste. In processing this waste, it is important to understand the behaviour of particles within the flow in terms of their settling characteristics, their propensity to form solid beds, and the re-suspension characteristics of particles from a bed. A clearer understanding of such behaviour would allow the refinement of current approaches to waste management, potentially leading to reduced uncertainties in radiological impact assessments, smaller waste volumes and lower costs, accelerated clean-up, reduced worker doses, enhanced public confidence and diminished grounds for objection to waste disposal. Mathematical models are of significant value in nuclear waste processing since the extent of characterisation of wastes is in general low. Additionally, waste processing involves a erse range of flows, within vessels, ponds and pipes. To investigate experimentally all waste form characteristics and potential flows of interest would be prohibitively expensive, whereas the use of mathematical models can help to focus experimental studies through the more efficient use of existing data, the identification of data requirements, and a reduction in the need for process optimisation in full-scale experimental trials. Validated models can also be used to predict waste transport behaviour to enable cost effective process design and continued operation, to provide input to process selection, and to allow the prediction of operational boundaries that account for the different types and compositions of particulate wastes. In this paper two mathematical modelling techniques, namely Reynolds-averaged Navier-Stokes (RANS) and large eddy simulation (LES), have been used to investigate particle-laden flows in a straight square duct and a duct with a bend. The flow solutions provided by these methods have been coupled to a three-dimensional Lagrangian particle tracking routine to predict particle trajectories. Simulation results are shown to be good agreement with experimental data, where available. Based on the LES and RANS-Lagrangian methods, the mean value of the particle displacement in a straight square duct is found to generally decrease with time due to gravity effects, with the rate of deposition increasing with particle size. Using the RANS-Lagrangian method to study flows in a duct bend, there is good agreement between predicted profiles and data, with the method able to simulate particle dispersion, the phenomenon of particle roping and the increase of particle collisions with the bend-wall with particle size. With the LES-Lagrangian method, particle re-suspension from a bed is studied in a straight square duct flow and this process shown to be dominated by secondary flows within the duct, with smaller particles tending to re-suspend in preference to larger ones. Overall, the study demonstrates that modelling techniques can be used to provide insight in to processes that are of relevance to the processing of nuclear waste, and are capable of predicting their transport behaviour. In particular, they are able to provide reliable predictions of particle deposition within flows to form solid beds, the re-suspension of particles from a bed, and the influence of complex flow geometries on particle dispersion. In the latter case, they are also of value to studies of erosion due to particle impact. Such models are therefore of value as engineering tools for use in the prediction of waste behaviour and in cost effective process design.
Publisher: Royal Society of Chemistry (RSC)
Date: 2010
DOI: 10.1039/B924680K
Abstract: Direct measurements of a depletion interaction between silica surfaces immersed in binary mixtures of non-adsorbing sodium poly(styrene sulfonate) have been made with an atomic force microscope. Variations in the secondary minimum depletion interaction as a function of binary mixture composition were recorded for a number of polymer molecular weights. The position and depth of the minimum in the force data was seen to depend on both the binary mixture composition and the choice of polymer molecular weights used in the mixture. For binary mixtures containing a low molecular weight polymer at a concentration near to or below the chain overlap concentration (C*) the position and depth of the minimum was seen to depend strongly on the properties of this low molecular weight component. This is consistent with previous theory predictions that depletion interactions in binary polymer mixtures will be controlled by the smaller component which can reside within the depletion layer of the higher molecular weight component.
Publisher: ASMEDC
Date: 2009
Abstract: The type of particulate systems encountered in legacy nuclear waste slurries is highly complicated, with the aggregation and flow behaviour being at times very variable. However, deconstructing the complex overall slurry activity to singular particle-particle interactions can lead to a greater understanding of the mechanisms involved with particle aggregation, and so to predictions of their settling and flow in nuclear systems. Of particular importance to legacy waste is the role of salts in controlling the attraction of particles (and so in dictating the rheological properties of the system) as sludge may contain a variety of specific ions and generally have high ionic conductivity [1]. In this paper, particle-particle interactions are characterised using a number of complimentary methods, and their influence on resulting flow and bed compression is measured. The methods used to characterise the particle-particle interactions under various salt and pH conditions were electroacoustic analysis (zeta potential) and atomic force microscopy (AFM). Following on from the analysis of particle-particle properties, bulk sediment behaviour was investigated using shear and compressive yield stress measurements, vital parameters in dictating flow and dewatering performance, respectively. Together, these techniques enable the characterisation of a range of particulate systems that may be encountered in legacy wastes, and results point to a number of important factors that can help explain the observed variability in industrial slurry behaviour.
Publisher: ASMEDC
Date: 2009
Abstract: The Keeping the Nuclear Option Open (KNOO) research consortium is a four-year research council funded initiative addressing the challenges related to increasing the safety, reliability and sustainability of nuclear power in the UK. Through collaboration between key industrial and governmental stakeholders, and with international partners, KNOO was established to maintain and develop skills relevant to nuclear power generation. Funded by a research grant of £6.1M from the “Towards a Sustainable Energy Economy Programme” of the UK Research Councils, it represents the single largest university-based nuclear research programme in the UK for more than 30 years. The programme is led by Imperial College London, in collaboration with the universities of Manchester, Sheffield, Leeds, Bristol, Cardiff and the Open University. These universities are working with the UK nuclear industry, who contributed a further £0.4M in funding. The industry/government stakeholders include AWE, British Energy, the Department for Environment, Food and Rural Affairs, the Environment Agency, the Health and Safety Executive, Doosan Babcock, the Ministry of Defence, Nirex, AMEC NNC, Rolls-Royce PLC and the UK Atomic Energy Authority. Work Package 3 of this consortium, led by the University of Leeds, concerns “An Integrated Approach to Waste Immobilisation and Management”, and involves Imperial College London, and the Universities of Manchester and Sheffield. The aims of this work package are: to study the re-mobilisation, transport, solid-liquid separation and immobilisation of particulate wastes to develop predictive models for particle behaviour based on atomic scale, thermodynamic and process scale simulations to develop a fundamental understanding of selective adsorption of nuclides onto filter systems and their immobilisation and to consider mechanisms of nuclide leaving and transport. The paper describes highlights from this work in the key areas of multi-scale modeling (using atomic scale, thermodynamic and process scale models), the engineering properties of waste (linking microscopic and macroscopic behaviour, and transport and rheology), and waste reactivity (considering waste hosts and wasteforms, generation IV wastes, and waste interactions).
Publisher: ASMEDC
Date: 2009
Abstract: A great deal of existing nuclear waste is stored as a solid-liquid slurry, and the effective transportation of such systems is an essential element in the successful implementation of almost all waste treatment strategies involving particulate wastes within the nuclear industry. A detailed knowledge of turbulent, particle-laden liquid flow behaviour is therefore obviously important. However, systematic and detailed studies of solid-liquid flows by experimental investigation are still limited for pipe flows, contrary to the significant amount of work available for channel flows. Research is therefore required to understand the effects of physical parameters, such as particle shape, size and size distribution, and solids concentration, on the properties of solid-liquid systems, particularly in horizontal pipe flows where particles may settle out of the flow and form solid beds which can potentially lead to pipe blockages. The presence of particles in a turbulent pipe flow also modifies the characteristics of the flow, thereby changing its ability to maintain particles in suspension. The work described concerns pipe flows over a Reynolds number range of 1,000–10,000, with varying levels of solids concentration within the flow. Measurements of the flow and particle characteristics have been gathered using particle image velocimetry (PIV) and, for high solids concentrations, ultrasound Doppler velocity profiling (UDVP) techniques. This work has demonstrated that the intensity of turbulence within such flows can be significantly affected by the presence of solid particles, with small particles generally attenuating turbulence levels, while large particles often augment turbulence levels from the pipe centre-line to the near-wall region. In addition, the coagulation of particles into larger agglomerates is also of importance, with data demonstrating that whilst turbulence levels are influenced and augmented by such agglomerates at low Reynolds numbers, high turbulence levels at high Reynolds numbers can destroy the agglomerates and reduce their effect on the carrier fluid. Work has also been undertaken to examine the effect of particle size and Reynolds number on particle deposition within the flows, and also to establish the minimum transport velocity required to re-suspend particles from solid beds. All these findings are of importance in enhancing our understanding of flows of particles in pipes which in turn is of value in enabling the design of cost effective and efficient waste treatment processes.
Publisher: American Chemical Society (ACS)
Date: 17-11-1999
DOI: 10.1021/LA990588R
Publisher: Elsevier BV
Date: 1993
Publisher: ASMEDC
Date: 2009
Abstract: Legacy waste treatment, storage and disposal, as well as decommissioning and site remediation, from the UK’s civil nuclear programme are estimated at a cost of £70B. Within the UK, the Nuclear Decommissioning Authority (NDA) directs the strategy for all civil nuclear decommissioning and demanding timescales have been set for remediation of all nuclear sites. Additionally, the Committee on Radioactive Waste Management (CoRWM) recently delivered a recommendation, accepted by Government, that geological disposal in a mined repository presents the “best available approach” for long term management of the waste legacy. There is therefore a requirement to decommission all power generation and experimental reactors, and fuel reprocessing plants, to decontaminate land, and to return nuclear licensed sites to brown or green field status. The engineering and scientific challenges that lie ahead in meeting these targets are significant, and many of the ideas required to deliver the final end state have not yet been researched. In recognition of this the UK Research Council’s Energy Programme released a call for research proposals in the area of nuclear waste management and decommissioning valued at £4M. A grant was subsequently awarded in 2008 to a consortium led by the University of Leeds, with member universities from Manchester, Imperial College, Sheffield, Loughborough and University College London. The DIAMOND (Decommissioning, Immobilisation And Management Of Nuclear Wastes For Disposal) consortium will undertake research aligned with the strategic priorities of the NDA and the CoRWM recommendations. Its primary purpose is to be adventurous and to deliver innovation. However, research is also being performed that will be of more immediate benefit to industrial stakeholders, with near-term impact achieved through the adoption of off-the-shelf technology currently implemented by other industries. Currently more than 20 industrial organisations are linked directly to the consortium. The aims of the consortium are to carry out internationally leading research in the areas of decommissioning and waste management that underpins the development of innovative and relevant technologies for industrial use. It will broaden the research base that focuses on relevant technologies, support new links within and between universities, promote multi-disciplinary collaboration and new applications of existing knowledge, and train the next generation of researchers to address a developing skills gap.
Publisher: Elsevier BV
Date: 05-2003
Publisher: Elsevier BV
Date: 03-2000
Publisher: American Chemical Society (ACS)
Date: 28-10-2008
DOI: 10.1021/LA802396G
Abstract: This work demonstrates the potential application of stimulus responsive block copolymer micelles as triggerable delivery systems for use within multilayer films. Cationic, pH-responsive micelles of poly[2-(dimethylamino)ethyl methacrylate-block-poly(2-(diethylamino)ethyl methacrylate)] (PDMA-PDEA) were deposited on anionic polystyrene latex particles. The charge reversal of the surface and the amount of adsorbed polymer were monitored by zeta potential measurements and colloidal titrations, respectively. Prior to adsorption, the PDMA-PDEA micelles were loaded with a hydrophobic dye, and UV-vis spectroscopy was used to determine the amount of dye encapsulated within a monolayer of micelles. It was found that subtle chemical modification of the PDMA-PDEA diblock copolymer via permanent quaternization of the PDEA block results in micelles with tunable loading capacities. Multilayers of cationic micelles of partially quaternized PDMA-PDEA and anionic polyelectrolyte (poly(sodium 4-styrene sulfonate)) were deposited on the surface of polystyrene latex particles by sequential adsorption. UV-vis analysis of the dye present within the multilayer after the addition of each layer demonstrates that the micelles are sufficiently robust to retain encapsulated dye after multiple adsorption/washing cycles and can thus create a film that can be increasingly loaded with dye as more micelle layers are adsorbed. Multiple washing cycles were performed on micellar monolayers of PDMA-PDEA to demonstrate how such systems can be used to bring about triggerable release of actives. When performing several consecutive washing steps at pH 9.3, the micelle structure of the PDMA-PDEA micelles in the monolayer is retained, resulting in only a small reduction in the amount of encapsulated dye. In contrast, washing at pH 4, the structure of the micelle layers is severely disrupted, resulting in a fast release of the encapsulated dye into the bulk. Finally, if a sufficient number of micelle/homopolyelectrolyte layers are adsorbed, it is possible to selectively dissolve the latex template, resulting in hollow capsules.
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C2SM00002D
Publisher: American Chemical Society (ACS)
Date: 11-1995
DOI: 10.1021/LA00011A045
Publisher: Elsevier BV
Date: 04-2015
Publisher: American Chemical Society (ACS)
Date: 04-03-2009
DOI: 10.1021/LA8033534
Abstract: A quartz crystal microbalance (QCM) and an optical reflectometer have been used to quantify the long-term adsorption behavior of polyelectrolyte-surfactant aggregates of alkyltrimethylammonium and poly(4-vinylbenzoate) or pCnTVB at the silica-water interface. In solution, these polyelectrolyte-surfactant aggregates exist as weakly anionic semiflexible rodlike structures of several nanometers in radius and hundreds of nanometers in length. The optical reflectivity (OR) data confirmed our earlier proposed model of a two-stage adsorption process (Biggs, S. Kline, S. R. Walker, L. M. Langmuir, 2004, 20 (4), 1085-1094) where free CTA+ ions initially adsorb and charge reverse the silica surface, thus allowing the weakly anionic aggregates to adsorb. Combining data from the two techniques allows a distinction to be made between contributions to the measured signal from the bulk and the interface. The isotherm determined by OR showed a clear plateau at higher concentrations, whereas the isotherm obtained by QCM continues to increase across all concentrations tested. This indicates a significant influence of the bulk fluid on the measured signals from the QCM as the concentration is increased. Slow changes in the apparent adsorbed mass observed with the QCM were not reproduced in the OR data, suggesting that these effects were also caused by the bulk and were not a densification of the adsorbed layer. The combination of techniques clarifies the adsorption kinetics and mechanism of adsorption in polyelectrolyte-surfactant aggregate systems.
Publisher: American Chemical Society (ACS)
Date: 02-09-2009
DOI: 10.1021/LA901321H
Abstract: A quartz crystal microbalance (QCM) and an optical reflectometer (OR) have been used to investigate the adsorption behavior of two different variants of the surfactant-hydrotropic counterion system, alkane trimethylammonium vinylbenzoate (CnTVB), onto silica surfaces. The C18TVB variant, with a longer hydrocarbon tail, produced a three-stage adsorption isotherm in the OR, whereas the C16TVB surfactant showed a two-stage adsorption isotherm. This was explained in terms of the greater degree of hydrophobicity of the C18 carbon chain requiring a significantly higher concentration of surfactant to be present on the surface before any further adsorption can occur. A concentration dependent adsorption rate was observed for both surfactants, with the faster adsorption rate being detected for C18TVB. The OR data showed that each surfactant could be completely rinsed off with the flow of water into the OR cell. This was not observed with the QCM data, where only a partial rinse off was seen. The difference between the two techniques was hypothesized to be due to the ability of the QCM to detect both interfacial and bulk behavior thus complicating the interpretation of the adsorption data.
Publisher: American Chemical Society (ACS)
Date: 04-02-2015
DOI: 10.1021/AM5087177
Abstract: Printing of droplets of pure solvents containing suspended solids typically leads to a ring stain due to convective transport of the particles toward the contact line during evaporation of the solvent. In mixtures of volatile solvents, recirculating cells driven by surface tension gradients are established that lead to migration of colloidal particles toward the center of the droplet. In favorable cases, a dense disk of particles forms with a diameter much smaller than that of the droplet. In the latter stages of drying, convective transport of the particles radially toward the contact line still occurs. Two strategies are described to fix the distribution of particles in a compact disk much smaller than the initial diameter of the drying droplet. First, a nanoparticulate clay is added to induce an evaporation-driven sol-gel transition that inhibits convective flow during the latter stages of drying. Second, a nonadsorbing polymer is added to induce depletion flocculation that restricts particle motion after the particles have been concentrated near the center of the droplet. The area of the resulting deposit can be as little as 10% of the footprint of the printed droplet.
Publisher: American Chemical Society (ACS)
Date: 07-10-1998
DOI: 10.1021/MA9714023
Publisher: AIP Publishing
Date: 08-2001
DOI: 10.1063/1.1386631
Abstract: The quantitative use of atomic force microscopes in lateral mode for friction measurements has been limited by uncertainty about reliable calibration techniques. This article describes a comparison of three methods that have been proposed for the calibration of the lateral sensitivity of atomic force microscopes: (a) one based on movement of the photodiode assembly, (b) one based on the slope of the friction-loop while the contacting surfaces are in static contact, and (c) one based on a comparison of the lateral force signal on a surface with changing slopes of known orientation. All three methods gave comparable results thereby confirming their robust nature, and also confirming the validity of atomic force microscope methods for lateral force measurement. However, (b) indicated that for the commercial instrument used here, the lateral signal sensitivity is load dependent. A simple extension to (a) revealed the nature of this dependence: a misalignment of the four-quadrant photodiode detection system with respect to the alignment of the reflected beam path resulting in a coupling of the normal and lateral signals. The result is that the lateral signal does not scale directly with friction, requiring that for friction versus applied load studies, lateral signal calibration be performed across the full range of applied loads of interest. To a greater or lesser extent, this shortcoming will be evident in a wide range of commercial instruments. All three methods studied here have special advantages: (a) provides the most complete information about the detector response, (b) provides a calibration method when friction characteristics of colloid probes of a wide range of possible materials are of interest, and (c) has the advantage of also providing information about the state of the tip geometry.
Publisher: Elsevier BV
Date: 2007
Publisher: American Chemical Society (ACS)
Date: 31-10-2002
DOI: 10.1021/NL025715+
Publisher: Elsevier BV
Date: 03-2002
Abstract: This work explores the structural compactness of depletion-induced particle flocs with respect to the molecular weight of nonadsorbing polymer flocculants. Small-angle static light scattering was used to monitor the structural characteristics of the flocs, which were formed by the addition of nonadsorbing poly(acrylic acids) to a stable colloidal polystyrene latex dispersion. It was found that the floc mass fractal dimension, considered to be a measure of structural compactness, was dependent upon both the molecular weight and the concentration of the polyacid. In particular, reducing the molecular weight of the polymer at a fixed polyacid concentration resulted in higher mass fractal dimensions, despite the highly polydisperse nature of the polymer s les. This structural behavior was attributed to the lower particle sticking efficiencies upon collision. This reduced sticking ability is the result of the shallowing in the secondary potential energy well with decreasing polymer chain length, which was directly supported by atomic force microscopy data. Our results suggest that the formation of a shallower attraction well with a lower molecular weight nonadsorbing polymer is the result of the insufficiency of the increased osmotic pressure to counter-balance the short-ranged nature of the depletion interaction.
Publisher: ASMEDC
Date: 2009
Abstract: In the UK, irradiated fuels from Magnox reactors are often stored in water-filled ponds under alkaline conditions, so as to minimise corrosion of fuel cladding. This is important to prevent or reduce leakage of soluble fission products and actinides to the pond water. A variety of intermediate level wastes derived from Magnox materials are stored at power stations. Under these alkaline conditions, various species of magnesium are formed, of which magnesium hydroxide is the dominant material. The particle-fluid interactions are significant for the design and operation of facilities for hydraulic retrieval, filtration, dewatering and ion exchange treatment of fuel storage pond water and stored wet Magnox wastes. Here we describe a study of particulate properties and filtration characteristics of oxide particle simulants under laboratory conditions. Cake and medium resistance data were correlated across a range of pH conditions with electroacoustic zeta potential and shear yield stress measurements, as a function of particle volume fractions. The influence of zeta potential on filtration properties arises directly from the interaction of particles within the sediment cake.
Publisher: Elsevier BV
Date: 12-2000
Publisher: American Chemical Society (ACS)
Date: 10-1994
DOI: 10.1021/JA00099A033
Publisher: Elsevier BV
Date: 03-1995
Publisher: American Chemical Society (ACS)
Date: 09-04-2003
DOI: 10.1021/LA026852P
Publisher: Elsevier BV
Date: 09-2009
Publisher: AIP Publishing
Date: 22-11-2005
DOI: 10.1063/1.2117027
Abstract: The rate of flocculation of cationic polystyrene latex (PSL) particles by smaller, anionic PSL particles has been measured using a low-angle static light scattering technique. The rate of aggregate growth has been investigated as a function of particle size ratio and relative concentration of each particle species (for a constant dose of cationic particles). Contrary to many previous reports, two peaks in the flocculation rate were observed as a function of dose. It is speculated that the peak observed at the lower particle concentration coincides with the dose yielding maximum constant collision efficiency in the steady-state regime, a condition which is attained only after complete adsorption of the smaller particles onto the larger particle species. The peak at the higher particle concentration is believed to be related to the maximum collision rate constant upon reaching the steady-state regime, the value of which corresponds to maximum degree of aggregation and therefore the maximum mean collision efficiency prior to reaching this condition. From classical collision kinetics, the rate of aggregate growth may be represented as being proportional to the product of the collision rate constant and collision efficiency at any given time. Given then that the maximum value of these two variables coincides with different particle concentrations, the product of the response of each to particle dosage can in some cases yield a net bi-modal aggregation rate response to particle dosage.
Publisher: American Chemical Society (ACS)
Date: 12-1997
DOI: 10.1021/LA970548S
Publisher: Royal Society of Chemistry
Date: 2008
Publisher: American Chemical Society (ACS)
Date: 03-03-2011
DOI: 10.1021/LA200046K
Abstract: The adsorption of a nonionic surfactant at a silica/room-temperature ionic liquid interface has been characterized on the basis of analytical data obtained through a combination of surface force measurements, in situ soft-contact atomic force microscope (AFM) images, and quartz crystal microbalance with dissipation monitoring (QCM-D) data. The surfactant employed in this study is a kind of phytosterol ethoxylate (BPS-20), and the ionic liquid selected here is aprotic 1-ethyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide (EmimTFSI). This ionic liquid spontaneously forms solvation layers on silica, being composed of an Emim(+) cation layer and EmimTFSI ion pair layers. The addition of BPS-20 disrupts these solvation layers and suggests a surfactant layer adsorbed at the interface. This is the first report demonstrating the adsorption of nonionic surfactants at the solid/aprotic ionic liquid interface.
Publisher: The Royal Society
Date: 28-07-2016
Abstract: Accurate control of particle size at relatively narrow polydispersity remains a key challenge in the production of synthetic polymer particles at scale. A cross-flow membrane emulsification (XME) technique was used here in the preparation of poly(methyl methacrylate) microspheres at a 1–10 l h −1 scale, to demonstrate its application for such a manufacturing challenge. XME technology has previously been shown to provide good control over emulsion droplet sizes with careful choice of the operating conditions. We demonstrate here that, for an appropriate formulation, equivalent control can be gained for a precursor emulsion in a batch suspension polymerization process. We report here the influence of key parameters on the emulsification process we also demonstrate the close correlation in size between the precursor emulsion and the final polymer particles. Two types of polymer particle were produced in this work: a solid microsphere and an oil-filled matrix microcapsule. This article is part of the themed issue ‘Soft interfacial materials: from fundamentals to formulation’.
Publisher: Elsevier BV
Date: 10-2019
DOI: 10.1016/J.JCIS.2019.07.020
Abstract: Metal shell microcapsules have been shown to completely retain their core until its release is triggered, making them a promising candidate for use as a controllable drug delivery vehicle due to their superior retention properties as compared to polymer shell microcapsules. Focused ultrasound (FUS) has been successfully utilised to trigger release of lipophilic drugs from polymer microcapsules, and in this work the response of gold shell microcapsules with and without an inner polymeric shell, to FUS and standard ultrasound is explored. The results show that gold shell microcapsules with an inner polymer shell rupture when exposed to standard ultrasound and that there is a linear correlation between the gold shell thickness and the extent of shell rupture. When FUS is applied to these microcapsules, powers as low as 0.16 W delivered in bursts of 10 ms/s over a period of 120 s are sufficient to cause rupture of 53 nm gold shell microcapsules. Additional findings suggest that gold shell microcapsules without the polymer layer dispersed in a hydrogel matrix, as opposed to aqueous media, rupture more efficiently when exposed to FUS, and that thicker gold shells are more responsive to ultrasound-triggered rupture regardless of the external environment. Release of dye from all successfully ruptured capsules was sustained over a period of between 7 and 35 days. These findings suggest that emulsion-templated gold shell microcapsules embedded in a hydrogel matrix would be suitable for use as an implantable drug delivery vehicle with FUS used to externally trigger release.
Publisher: Springer Science and Business Media LLC
Date: 05-1992
DOI: 10.1007/BF00665996
Publisher: Elsevier BV
Date: 09-1999
Publisher: Elsevier BV
Date: 10-1993
Publisher: American Chemical Society (ACS)
Date: 24-10-2002
DOI: 10.1021/NL025781B
Publisher: Informa UK Limited
Date: 2002
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3SM51534F
Publisher: American Chemical Society (ACS)
Date: 12-09-2016
Publisher: Springer Science and Business Media LLC
Date: 05-1992
DOI: 10.1007/BF00665997
Publisher: Royal Society of Chemistry (RSC)
Date: 2010
DOI: 10.1039/B921372D
Publisher: Elsevier BV
Date: 02-2004
Publisher: Elsevier BV
Date: 10-2013
DOI: 10.1016/J.JCIS.2013.06.046
Abstract: The free adsorption of an end-functionalised weak polybase, poly dimethylaminoethyl methacrylate (pDMAEMA), on the surface of colloidal gold nanoparticles (AuNPs) as a route to produce a responsive core-shell nanoparticle is explored here. Optimal conditions for the physisorption of the polymeric chains onto the colloidal nanoparticles are explored. A dense coverage is facilitated by rapidly mixing the well solvated pH responsive homopolymer, at low pH, into a relatively poor solvent environment, at higher pH, containing a stable dispersion of charge-stabilised gold nanoparticles. The rapid pH change causes the polymer chains to concurrently collapse and adsorb onto the gold nanoparticles. In order to achieve sterically stable, monodisperse and responsive core shell nanoparticles, a crucial factor is the pH difference of the systems prior to their mixing. Once adsorbed, end-functional thiol groups on the adsorbed polymer chains can form more permanent covalent attachments with the core particles. Dynamic light scattering coupled with mobility data of pH titration experiments show that the core-shell particles exhibit a responsive character consistent with the observed potentiometric titration data of the polymer. The same particles demonstrate reversible aggregation when cycled between pH extremes. This is confirmed by shifts in the SPR peak of the corresponding UV-Vis absorption profile. The ease and flexibility of this strategy for core-shell particle production, coupled with the stability and responsiveness of the product, make this a promising colloidal coating mechanism.
Publisher: Elsevier BV
Date: 12-2000
Publisher: ASMEDC
Date: 2011
Abstract: Research being undertaken at the University of Leeds, as part of the DIAMOND university consortium, is exploring the effectiveness of various ultrasonic technologies as in situ probes to characterize and monitor nuclear waste slurries, such as the ‘Legacy’ Magnesium hydroxide sludges found in Sellafield, U.K. Through use of a commercial Acoustic Backscatter Sensor (ABS) with 1–5 MHz transducers, various properties of free-settling oxide simulant sludges were determined. Work was focused upon characterizing essentially ‘static’ sludges (to give prospective use as tools for the wastes in current deposits) although, the sensors also have potential as dispersion monitors during any future processing and storage of the Legacy wastes, as well as many other storage, clarifier or thickener systems across a wide range of industrial processing operations. ABS data of mixed glass powder dispersions was analysed and compared to scattering theory, to understand the correlations between acoustic attenuation and particulate concentration. The ABS was also calibrated to measure changes in average particulate concentration within a settling suspension over time, and showed the depth-wise segregation of the dispersion through the settling column at different particular time intervals. It was found that observed hindered settling also led to an increase in particulate concentration over the sludge zone and significant segregation occurred at moderate time intervals, due to the broad size distribution of the aggregates measured. It is hoped in future that these sensors may be able to be fitted to robotic handlers that have been installed onsite (and previously used for s ling), allowing fully automatic in situ sludge analysis.
Publisher: Elsevier BV
Date: 12-2000
Publisher: Springer Science and Business Media LLC
Date: 14-11-2006
Publisher: Royal Society of Chemistry (RSC)
Date: 1995
DOI: 10.1039/FT9959102921
Publisher: American Chemical Society (ACS)
Date: 31-01-2014
DOI: 10.1021/LA4039304
Abstract: Particles used in electrophoretic display applications (EPD) must possess a number of specific properties ranging from stability in a nonaqueous solvent, high reflectivity, low polydispersity, and high charge density to name but a few. The manufacture of such particles is best carried out in the solvent of choice for the EPD. This opens up new interests in the study of nonaqueous dispersion polymerization methods, which deliver polymer particles suspended in low dielectric constant solvents. We explore in this article the use of a poly(dimethylsiloxane) macromonomer for the stabilization of poly(methyl methacrylate) polymer particles in dodecane, a typical solvent of choice for EPDs. The use of this stabilizer is significant for this method as it is directly soluble in the reaction medium as opposed to traditionally used poly(12-hydroxystearic acid)-based stabilizers. Additionally, the present study serves as a baseline for subsequent work, where nonaqueous dispersion polymerization will be used to create polymer particles encapsulating liquid droplets and solid pigment particles. In this article, the influence of the macromonomer molecular weight and concentration on the properties of the synthesized particles is studied. In addition, we investigate the possibility of synthesizing polymer particles from other monomers both as a comonomer for methyl methacrylate and as the only monomer in the process. The influence of macromonomer concentration is also studied throughout all experiments.
Publisher: Frontiers Media SA
Date: 20-07-2018
Publisher: AIP Publishing
Date: 06-1994
DOI: 10.1063/1.466748
Abstract: The forces between a flat gold surface and a gold-coated silica sphere have been measured in water using an atomic force microscope. A long-range attractive interaction is observed which is ascribed to the van der Waals interaction between the two surfaces. The force data agree extremely well with recent, calculated values of the Hamaker function (including retardation) for gold/water/gold. The best fit to the experimental data yields a value of 2.5±0.5×10−19 J for the unretarded Hamaker constant. In the presence of cetyltrimethyl ammonium bromide (CTAB) monolayers, electrostatic repulsion is observed at all distances for gold sphere (radius 3.3 μm) interactions with a flat gold surface. However, an attractive force is observed at very small separations for gold-coated silicon nitride tips (effective radius 0.1 μm), which is attributed to penetration of the CTAB monolayers by the sharper tip.
Publisher: AIP Publishing
Date: 20-08-2003
DOI: 10.1063/1.1597950
Abstract: A method is described to determine the spring constant of colloid probe cantilevers used in force measurements with the atomic force microscope. An oscillatory drive applied to the substrate is coupled by viscous interactions to the colloid probe. The dynamic response of the probe, which is unaffected by static interactions, is then used to determine the spring constant of the cantilever. Thus an accurate calibration of the spring constant may be performed simultaneously with a normal colloidal probe force measurement in situ.
Publisher: Wiley
Date: 20-01-2007
Publisher: Elsevier BV
Date: 08-2020
Publisher: Elsevier BV
Date: 10-2018
DOI: 10.1016/J.JCIS.2018.05.035
Abstract: Particle-stabilized emulsions and foams are widely encountered, as such there remains a concerted effort to better understand the relationship between the particle network structure surrounding droplets and bubbles, and the rheology of the particle-stabilized interface. Poly(vinylpyrrolidone)-coated silica nanoparticles were used to stabilize foams. The shear rheology of planar particle-laden interfaces were measured using an interfacial shear rheometer and the rheological properties measured as a function of the sub-phase electrolyte concentration and surface pressure. All particle-laden interfaces exhibited a liquid-like to solid-like transition with increasing surface pressure. The surface pressure-dependent interfacial rheology was then correlated to the formed micron-scale structures of the particle-laden interfaces which were imaged using a Brewster angle microscope. With the baseline knowledge established, foams were prepared using the same composite particles and the particle network structure imaged using cryo-SEM. An attempt has been made to correlate the two structures observed at a planar interface and that surrounding a bubble to elucidate the likely rheology of the bubble stabilizing particle network. Independent of the sub-phase electrolyte concentration, the resulting rheology of the bubble stabilizing particle network was strongly elastic and appeared to be in a compression state at the region of the L-S phase transition.
Publisher: Elsevier BV
Date: 03-2003
Publisher: Wiley
Date: 02-05-2017
DOI: 10.1002/AIC.15731
Publisher: Hosokawa Powder Technology Foundation
Date: 2006
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Simon Biggs.