ORCID Profile
0000-0001-8303-6081
Current Organisation
The University of Newcastle
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In Research Link Australia (RLA), "Research Topics" refer to ANZSRC FOR and SEO codes. These topics are either sourced from ANZSRC FOR and SEO codes listed in researchers' related grants or generated by a large language model (LLM) based on their publications.
Colloid and Surface Chemistry | Physical Chemistry (Incl. Structural) | Powder and Particle Technology | Mineral Processing/Beneficiation | Soft Condensed Matter | Colloid and surface chemistry | Physical Chemistry of Materials | Condensed Matter Physics | Quantum Chemistry | Process Control and Simulation | Nanochemistry and Supramolecular Chemistry | Membrane and Separation Technologies | Structural Biology (incl. Macromolecular Modelling) | Physical chemistry | Functional Materials | Hydrometallurgy | Resources Engineering and Extractive Metallurgy | Petroleum and Reservoir Engineering | Computational chemistry | Catalysis and Mechanisms of Reactions | Macromolecular and Materials Chemistry | Chemical Thermodynamics and Energetics | Transport Properties and Non-Equilibrium Processes | Structural Chemistry and Spectroscopy | Nanoscale Characterisation | Surfaces and Structural Properties of Condensed Matter | Electronic and Magnetic Properties of Condensed Matter; Superconductivity | Condensed Matter Imaging | Condensed Matter Characterisation Technique Development
Expanding Knowledge in the Chemical Sciences | Expanding Knowledge in the Physical Sciences | Expanding Knowledge in Engineering | First Stage Treatment of Ores and Minerals not elsewhere classified | Concentrating processes of other base metal ores | Oil and Gas Extraction | Transformation of Coal into Gaseous Fuels | Energy Storage (excl. Hydrogen) | Coal Mining and Extraction | Integrated Circuits and Devices | Treatments (e.g. chemicals, antibiotics) | Mining and Extraction of Aluminium Ores | Clay Products | Soaps and cosmetics | Polymeric Materials (e.g. Paints) | Transformation of Gas into Liquid Fuels | Transformation of Coal into Liquid Fuels | Processed food products and beverages not elsewhere classified | Oil and Gas Refining | Industrial Chemicals and Related Products not elsewhere classified | Human Pharmaceutical Products not elsewhere classified | Precious (Noble) Metal Ore Exploration | Beneficiation or Dressing of Iron Ores | Expanding Knowledge in the Biological Sciences | Concentrating Processes of Base Metal Ores (excl. Aluminium and Iron Ores) | Diamond Exploration |
Publisher: American Chemical Society (ACS)
Date: 03-07-2023
Publisher: American Chemical Society (ACS)
Date: 16-02-2016
DOI: 10.1021/ACS.LANGMUIR.5B04503
Abstract: The adsorbed layer conformation and lubricity of 35, 100, and 300 kDa PEO adsorbed to ionic liquid (IL)-silica interfaces from 0.01 wt % solutions have been investigated using colloid probe atomic force microscopy. The ILs used were propylammonium nitrate (PAN) and 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), which are protic and aprotic ILs, respectively. Normal force curves reveal steric interactions consistent with adsorbed polymer layers which are best fit using the mushroom model. Friction measurements show that the adsorbed polymer layer markedly reduces friction compared to surfaces sliding in the pure ILs and that lubricity increases with polymer length. When polymer is adsorbed to the sliding surfaces, friction is controlled by the creation and disruption of intermolecular interactions between entangled chains and the dragging of polymer chains through the interpenetration region. These experiments show that added polymer can reduce friction while maintaining the useful properties of ILs as lubricants.
Publisher: American Physical Society (APS)
Date: 10-10-2012
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: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C5CP04787K
Abstract: Colloid probe friction force microscopy (FFM) has been used to study the lubricity of propylammonium nitrate (PAN) mixed with n -alkanols confined between sliding silica and mica surfaces.
Publisher: The Chemical Society of Japan
Date: 05-06-2019
DOI: 10.1246/CL.190105
Publisher: American Chemical Society (ACS)
Date: 24-10-2013
DOI: 10.1021/JP407715E
Abstract: The rheological properties of five pure protic ionic liquids (ILs), ethylammonium nitrate (EAN), propylammonium nitrate (PAN), ethanolammonium nitrate (EtAN), ethylammonium formate (EAF), and dimethylethylammonium formate (DMEAF), are characterized and interpreted by considering the effects of both the H-bond network and the solvophobic nanostructure of the liquids. The results demonstrate that these effects are not, however, independent or simply additive. At 20 °C, EtAN has the highest zero shear viscosity of 156.1 mPa·s, followed by PAN (89.3 mPa·s), EAN (35.9 mPa·s), EAF (23.1 mPa·s), and DMEAF (9.8 mPa·s). The primary ammonium ILs behave as Newtonian fluids at low shear rates but shear thin at high shear. Fits to the Vogel-Fulcher-Tammann model reveal that nanostructure is not affected appreciably by temperature and that all the ILs studied are of intermediate fragility. The rheology of binary mixtures of these ILs was analyzed and used to demonstrate fundamental differences in the way IL cations and anions interact. IL mixtures containing both nitrate and formate anions resist flow more strongly than the pure liquids, which is a consequence of the difference in hydrogen bonding capacity of the anions. Mixing cations can give rise to complex behavior due to the offsetting effects of hydrogen bonding and solvophobic nanostructure formation.
Publisher: Frontiers Media SA
Date: 14-06-2018
Publisher: Elsevier BV
Date: 02-2021
Publisher: American Chemical Society (ACS)
Date: 07-10-2014
DOI: 10.1021/JP507408R
Abstract: The thermal conductivities of nine protic ionic liquids (ILs) have been investigated between 293 and 340 K. Within this range, the thermal conductivities are between 0.18 and 0.30 W · m(-1) · K(-1). These values are higher than those typically associated with oils and aprotic ILs, but lower than those of strongly hydrogen bonding solvents like water. Weak linear decreases in thermal conductivity with temperature are noted, with the exception of ethanolammonium nitrate (EtAN) where the thermal conductivity increases with temperature. The dependence of thermal conductivity on IL type is analyzed with use of the Bahe-Varela pseudolattice theory. This theory treats the bulk IL as an array of ordered domains with intervening domains of uncorrelated structure which enable and provide barriers to heat propagation (respectively) via allowed vibrational modes. For the protic ILs investigated, thermal conductivity depends strongly on the IL cation alkyl chain length. This is because the cation alkyl chain controls the dimensions of the IL bulk nanostructure, which consists of charged (ordered domains) and uncharged regions (disordered domains). As the cation alkyl chain controls the dimensions of the disordered domains, it thus limits the thermal conductivity. To test the generality of this interpretation, the thermal conductivities of propylammonium nitrate (PAN) and PAN-octanol mixtures were examined water selectively swells the PAN charged domain, while octanol swells the uncharged regions. Up to a certain concentration, adding water increases thermal conduction and octanol decreases it, as expected. However, at high solute concentrations the IL nanostructure is broken. When additional solvent is added above this concentration the rate of change in thermal conductivity is greatly reduced. This is because, in the absence of nanostructure, the added solvent only serves to dilute the salt solution.
Publisher: American Chemical Society (ACS)
Date: 14-10-2020
Publisher: American Chemical Society (ACS)
Date: 07-05-2013
DOI: 10.1021/LA4004092
Abstract: Coatings consisting of polymer brushes are an effective way to modify solid interfaces. Polymer brush-modified hybrid particles have been prepared by surface-initiated activators regenerated by electron transfer atom transfer radical polymerization (SI-ARGET ATRP) of 2-(diethylamino)ethyl methacrylate (DEA) on silica particles. We have optimized the synthesis with respect to changing the reducing agent, temperature, and reaction solvent from an aqueous ethanol mixture to an aqueous methanol mixture. Our flexible electrostatically adsorbed macroinitiator approach allows for the modification of a variety of surfaces. Polybasic brushes have been grown on silica particles of different sizes, from 120 to 840 nm in diameter, as well as on wafers, and a comparison of the products has allowed the effect of surface curvature to be elucidated. An examination of the thickness of the dry brush and the aqueous hydrodynamic brush at both pH 7 and at 4 demonstrated that growth increased substantially with substrate curvature for particles with a diameter below 450 nm. This is attributed to the increasing separation between active chain ends, reducing the rate of termination. This is believed to be the first time that this effect has been demonstrated experimentally. Furthermore, we have seen that polymer brush growth on planar wafers was significantly reduced when the reaction mixture was stirred.
Publisher: Elsevier BV
Date: 2014
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C8SM01824C
Abstract: The internal structure of PNIPAM brush modified silica particles has been probed as a function of temperature and molecular weight.
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C4SM00801D
Abstract: Coalescence of latex particle covered oil droplets is controlled by the presence of oil-soluble cross-linker in one or both droplets.
Publisher: Elsevier BV
Date: 03-2017
DOI: 10.1016/J.JCIS.2016.11.044
Abstract: The thermoresponse of poly(di(ethyleneglycol) methyl ether methacrylate) (PMEO
Publisher: American Chemical Society (ACS)
Date: 29-04-2020
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: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/D0MA00670J
Abstract: A conductive coating is added to PET plates using a novel synthetic method and liquid marble manufactured using electrostatics forces.
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: American Chemical Society (ACS)
Date: 04-05-2020
Publisher: American Chemical Society (ACS)
Date: 29-08-2023
Publisher: American Chemical Society (ACS)
Date: 07-08-2019
DOI: 10.1021/JACS.9B03484
Abstract: Despite boron nitride nanotubes (BNNTs) first being synthesized in the 1990s, their nucleation mechanism remains unknown. Here we report nonequilibrium molecular dynamics simulations showing how BNNT cap structures form during Ni-catalyzed chemical vapor deposition (CVD) of ammonia borane. BN hexagonal ring networks are produced following the catalytic evolution of H
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C4CP05292G
Abstract: Monomer hydrophobicity dominates the kinetics of the pH-response of tertiary amine methacrylate brushes as determined by in situ ellipsometry and QCM-D kinetic and equilibrium measurements.
Publisher: Elsevier BV
Date: 11-2018
DOI: 10.1016/J.JCIS.2018.04.044
Abstract: Particle cohesion and conductivity affects the electrostatically driven transport of particles to a suspended water droplet. The conditions at which liquid marbles and particle stabilised liquid droplets form are a function of these parameters. Particle beds placed below an earthed pendent water drop had a negative potential applied, thus inducing an opposing positive charge on the liquid, which results in particle transfer and eventual coating of the liquid drop. Experiments where both the particle bed was constantly moved slowly toward the droplet, and the particle bed remained at a fixed, small separation distance were completed. These enabled the investigation of a number of variables that influence successful aggregate formation, including separation distance between the droplet and particle bed, coating mechanism and kinetics of the transfer process. Monodisperse polystyrene core particles with polypyrrole shells of various cohesiveness and conductivity were observed to behave differently in the presence of the applied potential, where the least cohesive and conductive s le (polystyrene) required the smallest separation distance, i.e. the greatest field strength for particle transfer. Increasing conductivity of the particle shell decreases the field strength required for particle transfer, and thus an increase was observed in separation distance at which particles were observed to move to the air-water interface. The transfer kinetics followed the same trend where the least conductive and cohesive s le was the slowest to coat the air-water interface, and vice-versa. Since an increase in cohesion hinders particle transfer, it is concluded that particle conductivity is of greater importance in the electrostatic aggregation process.
Publisher: Elsevier BV
Date: 09-2014
DOI: 10.1016/J.JCIS.2014.05.006
Abstract: Steady shear viscosity measurements have been performed on 100 kDa poly(ethylene oxide) (PEO) dissolved in the protic ionic liquids ethylammonium nitrate (EAN) and propylammonium nitrate (PAN) and in water. The zero shear viscosity in all three solvents increases with polymer concentration, falling into three concentration regimes corresponding to dilute, semi-dilute and network solutions. Huggins plots reveal three distinct solvent conditions: good (water), good-theta (EAN) and theta (PAN). However, differences in the transition concentrations, power law behaviour of the viscosities, and relaxation times arising from shear thinning in the two ILs can be directly related to the effects of solvent nanostructure.
Publisher: American Chemical Society (ACS)
Date: 18-09-2012
DOI: 10.1021/MZ3003566
Abstract: Brush-modified silica hybrids have been synthesized by growing poly(2-(diethylamino)ethyl methacrylate) (poly(DEA)) brushes on 120 nm diameter silica particles by surface-initiated activators regenerated by electron transfer atom transfer radical polymerization (SI-ARGET ATRP). This is the first report of using SI-ARGET ATRP to synthesize poly(DEA) brushes. The kinetics of poly(DEA) brush growth in 4:1 v/v ethanol/water was monitored. The hydrodynamic diameter of the resulting brush-modified particles was dependent on the solution pH due to the weak polybasic nature of the brushes. Below the p
Publisher: American Chemical Society (ACS)
Date: 15-12-2007
DOI: 10.1021/JP076215D
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: AIP Publishing
Date: 29-07-2013
DOI: 10.1063/1.4817586
Abstract: We report observations of a sudden, explosive release of electrostatically charged 100 μm glass beads from a particle bed. These cross an air gap of several millimeters, are engulfed by an approaching pendant water drop, and form a metastable spherical agglomerate on the bed surface. The stability transition of the particle bed is explained by promotion of internal friction by in-plane electrostatic stresses. The novel agglomerates formed this way resemble the “liquid marbles” formed by coating a drop with hydrophobic particles. Complex multi-layered agglomerates may also be produced by this method, with potential industrial, pharmaceutical, environmental, and biological applications.
Publisher: American Chemical Society (ACS)
Date: 21-01-2016
Publisher: Frontiers Media SA
Date: 07-02-2019
Publisher: Elsevier BV
Date: 04-2019
Publisher: American Chemical Society (ACS)
Date: 18-09-2018
Publisher: MDPI AG
Date: 19-05-2022
DOI: 10.3390/MOLECULES27103250
Abstract: The number of food frauds in coconut-based products is increasing due to higher consumer demands for these products. Rising health consciousness, public awareness and increased concerns about food safety and quality have made authorities and various other certifying agencies focus more on the authentication of coconut products. As the conventional techniques for determining the quality attributes of coconut are destructive and time-consuming, non-destructive testing methods which are accurate, rapid, and easy to perform with no detrimental s ling methods are currently gaining importance. Spectroscopic methods such as nuclear magnetic resonance (NMR), infrared (IR)spectroscopy, mid-infrared (MIR)spectroscopy, near-infrared (NIR) spectroscopy, ultraviolet-visible (UV-VIS) spectroscopy, fluorescence spectroscopy, Fourier-transform infrared spectroscopy (FTIR), and Raman spectroscopy (RS) are gaining in importance for determining the oxidative stability of coconut oil, the adulteration of oils, and the detection of harmful additives, pathogens, and toxins in coconut products and are also employed in deducing the interactions in food constituents, and microbial contaminations. The objective of this review is to provide a comprehensive analysis on the various spectroscopic techniques along with different chemometric approaches for the successful authentication and quality determination of coconut products. The manuscript was prepared by analyzing and compiling the articles that were collected from various databases such as PubMed, Google Scholar, Scopus and ScienceDirect. The spectroscopic techniques in combination with chemometrics were shown to be successful in the authentication of coconut products. RS and NMR spectroscopy techniques proved their utility and accuracy in assessing the changes in coconut oil’s chemical and viscosity profile. FTIR spectroscopy was successfully utilized to analyze the oxidation levels and determine the authenticity of coconut oils. An FT-NIR-based analysis of various coconut s les confirmed the acceptable levels of accuracy in prediction. These non-destructive methods of spectroscopy offer a broad spectrum of applications in food processing industries to detect adulterants. Moreover, the combined chemometrics and spectroscopy detection method is a versatile and accurate measurement for adulterant identification.
Publisher: Elsevier BV
Date: 07-2014
Publisher: American Chemical Society (ACS)
Date: 24-07-2019
DOI: 10.1021/ACS.LANGMUIR.9B00695
Abstract: The stability of poly(
Publisher: American Chemical Society (ACS)
Date: 30-12-2021
DOI: 10.1021/ACS.LANGMUIR.1C02507
Abstract: We report an unusually large spacing observed between microparticles after delivery to the surface of a pendent water droplet using a DC nonuniform electrostatic field, primarily via dielectrophoresis. The influence of particle properties was investigated using core particles, which were either coated or surface-modified to alter their wettability and conductivity. Particles that exhibited this spacing were both hydrophobic and possessed some dielectric material exposed to the external field, such as a coating or exposed dielectric core. The origin of this behavior is proposed to be the induced dipole-dipole repulsion between particles, which increases with particle size and decreases when the magnitude of the electric field is reduced. When the particles were no longer subjected to an external field, this large interparticle repulsion ceased and the particles settled to the bottom of the droplet under the force of gravity. We derive a simple model to predict this spacing, with the dipole-dipole repulsion balanced against particle weight. The external electric field was calculated using the existing electric field models. The spacing was found to be dependent on particle density and the induced dipole moment as well as the number of particles present on the droplet interface. As the number of particles increased, a decrease in interparticle spacing was observed.
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: Royal Society of Chemistry (RSC)
Date: 2023
DOI: 10.1039/D2PY01487D
Abstract: Structural characterisation of thermoresponsive polymer brushes in binary DMSO–water mixtures reveals both LCST and UCST behaviour.
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D2CP00847E
Abstract: This perspective reviews the historical explanations for specific ion effects, and explores the frontiers of the field before summarising its challenges and opportunities.
Publisher: American Chemical Society (ACS)
Date: 20-11-2012
DOI: 10.1021/LA3025765
Abstract: The interactions of two 2-mm pendant oil droplets grown in the presence of an aqueous solution of poly(glycerol monomethacrylate)-stabilized polystyrene latex particles was observed using a high-speed video camera. The coalescence behavior was monitored as a function of oil type (n-dodecane versus sunflower oil) and particle size (135 versus 902 nm), as well as in the presence and absence of an oil-soluble cross-linker [tolylene 2,4-diisocyanate-terminated poly(propylene glycol)]. The d ing coefficient of the coalescing n-dodecane droplets was found to increase in the presence of the latex, demonstrating particle adsorption. Coalescence times increased when the oil phase was changed from n-dodecane to sunflower oil, because of the much higher viscosity of the latter oil. In addition, increasing the adsorbed particle size from 135 to 902 nm led to longer coalescence times because of the greater distance separating the oil droplets. Coalescence times observed in the presence of the larger 902-nm particles indicated that two different modes of contact can occur prior to a coalescence event (bilayer or bridging monolayer of particles in the film). Addition of an oil-soluble surface-active cross-linker to the sunflower oil phase to react with the hydroxy groups of the particle stabilizer reduced the interfacial elasticity and ultimately prevented coalescence after cross-linking for 20 min at 25 °C. Such giant colloidosomes can remain in contact for several hours without undergoing coalescence, which demonstrates their high stability. Furthermore, coalescence is prevented even if the cross-linker is present in only one of the pendant droplets. Finally, evidence for cross-linker diffusion from one pendant droplet to another was indicated by a visible filament connecting the two droplets upon retraction.
Publisher: Elsevier BV
Date: 2019
DOI: 10.1016/J.JCIS.2018.09.057
Abstract: The solvation characteristics of poly(ethylene oxide) (PEO) in nanostructured protic ionic liquids (PILs) are driven by polymer-solvent interactions in the polar domains of the PIL. This work hypothesises that the nanostructure of a PIL can be altered via halide addition, directly affecting the solvation of PEO. Small angle neutron scattering (SANS) is used to explore the conformation of 38 kDa PEO dissolved in the PIL propylammonium nitrate (PAN), a mol fraction of 10% propylammonium chloride (PACl) in PAN, and a mole fraction of 10% propylammonium bromide (PABr) in PAN. Each of these solutions are shown to behave as a good solvent for PEO, as determined by their Flory exponents and Zimm plot analysis. The quality of solvation is reduced by the addition of the halide salt, with the order of solvation as follows: PAN > Br
Publisher: American Chemical Society (ACS)
Date: 20-01-2019
Publisher: International Union of Crystallography (IUCr)
Date: 16-04-2021
DOI: 10.1107/S160057672100251X
Abstract: Neutron reflectometry is the foremost technique for in situ determination of the volume fraction profiles of polymer brushes at planar interfaces. However, the subtle features in the reflectometry data produced by these diffuse interfaces challenge data interpretation. Historically, data analyses have used least-squares approaches that do not adequately quantify the uncertainty of the modeled profile and ignore the possibility of other structures that also match the collected data (multimodality). Here, a Bayesian statistical approach is used that permits the structural uncertainty and multimodality to be quantified for polymer brush systems. A free-form model is used to describe the volume fraction profile, minimizing assumptions regarding brush structure, while only allowing physically reasonable profiles to be produced. The model allows the total volume of polymer and the profile monotonicity to be constrained. The rigor of the approach is demonstrated via a round-trip analysis of a simulated system, before it is applied to real data examining the well characterized collapse of a thermoresponsive brush. It is shown that, while failure to constrain the interfacial volume and consider multimodality may result in erroneous structures being derived, carefully constraining the model allows for robust determination of polymer brush compositional profiles. This work highlights that an appropriate combination of flexibility and constraint must be used with polymer brush systems to ensure the veracity of the analysis. The code used in this analysis is provided, enabling the reproduction of the results and the application of the method to similar problems.
Publisher: Royal Society of Chemistry (RSC)
Date: 2015
DOI: 10.1039/C4CP04522J
Abstract: Atomic force microscopy (AFM) force measurements have been used to study the solvate ionic liquid (IL) double layer nanostructure at highly ordered pyrolytic graphite (HOPG) and Au(111) electrode surfaces as a function of potential.
Publisher: American Chemical Society (ACS)
Date: 27-07-2001
DOI: 10.1021/LA010335+
Publisher: American Chemical Society (ACS)
Date: 26-09-2018
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C6CP04405K
Abstract: Atomic force microscopy (AFM) reveals that tribotronic control of friction using an external potential applied to a gold surface is possible for ionic liquid (IL) concentrations as low as 5 mol% in hexadecane.
Publisher: Wiley
Date: 18-10-2004
Publisher: American Chemical Society (ACS)
Date: 21-06-2019
Abstract: An analysis of specific-ion effects in aqueous and nonaqueous solvents using energy decomposition analysis is presented. Specific-ion effects induce or influence physicochemical phenomena in a way that is determined by the identity of the ions present, and not merely by their charge or concentration. Such effects have been known since the seminal work of Hofmeister and are often categorized according to the well-known Hofmeister series. Ex les of specific-ion effects are ubiquitous throughout chemistry and biology and are traditionally explained in terms of the influence ions have on the structure of water. However, this explanation is unsatisfactory because it is unable to adequately explain and predict frequently observed series reversals and anomalies. Further, recent experiments have shown that specific-ion effects are observed in nonaqueous solvents. By modeling solvated ion-
Publisher: Elsevier BV
Date: 02-2018
Publisher: American Chemical Society (ACS)
Date: 15-06-2015
DOI: 10.1021/ACS.LANGMUIR.5B01500
Abstract: Atomic force microscope (AFM) force curves and images are used to characterize the adsorbed layer structure formed by a series of diblock copolymers with solvophilic poly(ethylene oxide) (PEO) and solvophobic poly(ethyl glycidyl ether) (PEGE) blocks at silica-water and silica-ethylammoniun nitrate (EAN, a room temperature ionic liquid (IL)) interfaces. The diblock polyethers examined are EGE109EO54, EGE113EO115, and EGE104EO178. These experiments reveal how adsorbed layer structure varies as the length of the EO block varies while the EGE block length is kept approximately constant water is a better solvent for PEO than EAN, so higher curvature structures are found at the interface of silica with water than with EAN. At silica-water interfaces, EGE109EO54 forms a bilayer and EGE113EO115 forms elongated aggregates, while a well-ordered array of spheres is present for EGE104EO178. EGE109EO54 does not adsorb at the silica-EAN interface because the EO chain is too short to compete with the ethylammonium cation for surface adsorption sites. However, EGE113EO115 and EGE104EO178 do adsorb and form a bilayer and elongated aggregates, respectively.
Publisher: American Chemical Society (ACS)
Date: 28-06-2010
DOI: 10.1021/LA1012473
Abstract: Dynamic force measurements have been made between an oil drop and a silica particle in surfactant and sucrose solutions with viscosities that range up to 50 times that of water. These conditions provide variations in the shear rate and the relative time scales of droplet deformation and hydrodynamic drainage in a soft matter system. The results obtained indicate that soft deformable boundaries have a natural response that limits the maximum shear rate that can be sustained in thin films compared to shear rates that can be attained in films bounded by rigid boundaries. In addition, to extend boundary slip studies on rigid surfaces, we use a smooth deformable droplet surface to probe the dependence of the boundary slip on fluid viscosity without the added complications of surface roughness or heterogeneity. Imposing a Navier slip model to characterize possible slip at the deformable oil-sucrose solution interface gives results that are consistent with a slip length of no larger than 10 nm over the range of solution viscosity studied, although an immobile (zero slip length) condition at the oil-sucrose solution interface is perfectly adequate. In high viscosity solutions, cantilever motion at high scan rates induces a significant cantilever deflection. A method has been developed to account for this effect in order to extract the correct dynamic force between the deformable drop and the particle.
Publisher: Elsevier BV
Date: 07-2012
Publisher: Elsevier BV
Date: 03-2021
Publisher: IOP Publishing
Date: 10-2019
DOI: 10.1088/1742-6596/1322/1/012006
Abstract: A statistical treatment is developed for the electrostatic transfer of particles from a powder bed to a pendent droplet during liquid marble and aggregate formation. The model uses Weibull statistics to calculate the probability of particle transfer events of a given size occurring, for the given electric field strength and geometry. This is used in Monte Carlo simulations of the transfer process. In this preliminary study, some of the most distinctive features of the experiments – transfer event size and spacing, scaling with driving potential – are well-captured using physically plausible parameter values. Other features, such as denuding of the particle bed, are less well reproduced, and require refinement.
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D1SC03568A
Abstract: Analysis of ions’ radial charge densities reveals they correlate with many specific ion effects, and provides a new basis to explain and quantify the 130-year-old Hofmeister series for anions.
Publisher: Elsevier BV
Date: 2017
Publisher: American Chemical Society (ACS)
Date: 19-11-2020
Publisher: Royal Society of Chemistry (RSC)
Date: 04-07-2014
DOI: 10.1039/C4CP02320J
Abstract: The effect of ionic liquid (IL) molecular structure on nanoscale friction has been investigated using colloidal probe Friction Force Microscopy (FFM). The ILs studied were ethylammonium formate (EAF), ethylammonium nitrate (EAN), propylammonium formate (PAF), propylammonium nitrate (PAN), dimethylethylammonium formate (DMEAF), and ethanolammonium nitrate (EtAN). ILs were confined between a silica colloid probe and a mica surface, and the friction force was measured as a function of normal load for sliding velocities between 10 and 40 μm s(-1). At low normal forces, multiple IL layers are found between the probe and the surface, but at higher force, in the boundary layer regime, a single ion layer separates the probe and the surface. In the boundary layer regime energy is dissipated by two main pathways. Firstly, the ionic liquid near the surface, with the exception of the boundary layer, is expelled from the advancing contact made by the probe on the surface. This disruption in the interactions between the boundary layer and the near surface multilayers, leads to energy dissipation and depends on the strength of the attraction between the boundary and near surface layers. The second pathway is via rotations and twists of ions in the boundary layer, primarily associated with the cation terminal methyl group. The friction coefficient did not vary over the limited range of sliding speeds investigated.
Publisher: Elsevier BV
Date: 04-2022
DOI: 10.1016/J.JCIS.2021.12.117
Abstract: Electrostatic extraction of particles from a bed to a pendent droplet to form liquid marbles has previously been investigated with respect to particle conductivity, size and shape, however, interparticle forces have not been specifically interrogated. If cohesion is the dominant force within the particle bed, then particles will be more readily extracted with reduced surface free energy. Glass particles were surface-modified using various alkyltrichlorosilanes. The surface free energy was measured for each s le using colloid probe atomic force microscopy (AFM) and sessile drop measurements on similarly modified glass slides. The ease of electrostatic particle extraction of each particle s le to a pendent droplet was compared by quantifying the electric field force required for successful extraction as a function of the measured surface free energy. Surface free energy calculated from sessile droplet measurements and AFM were not in agreement, as work of adhesion of a liquid droplet on a planar substrate is not representative of the contact between particles. Ease of electrostatic extraction of particles was observed to generally decrease as a function of AFM-derived surface free energy, confirming this is a critical factor in electrostatic delivery of particles to a pendent droplet. Roughness was also shown to inhibit particle extraction.
Publisher: American Chemical Society (ACS)
Date: 09-04-2018
DOI: 10.1021/ACS.LANGMUIR.7B04204
Abstract: Aqueous dispersions of micrometer-sized, monodisperse polystyrene (PS) particles carrying pH-responsive poly[2-(diethylamino)ethyl methacrylate] (PDEA) colloidal stabilizer on their surfaces were dried under ambient conditions at pH 3.0 and 10.0. The resulting dried cake-like particulate materials were ground into powders and used as a stabilizer to fabricate liquid marbles (LMs) by rolling and electrostatic methods. The powder obtained from pH 3.0 aqueous dispersion consisted of polydisperse irregular-shaped colloidal crystal grains of densely packed colloids which had hydrophilic character. On the other hand, the powder obtained from pH 10.0 aqueous dispersion consisted of amorphous and disordered colloidal aggregate grains with random sizes and shapes, which had hydrophobic character. Reflecting the hydrophilic-hydrophobic balance of the dried PDEA-PS particle powders, stable LMs were fabricated with distilled water droplets by rolling on the powders prepared from pH 10.0, but the water droplets were adsorbed into the powders prepared from pH 3.0. In the electrostatic method, where an electric field assists transport of powders to a droplet surface, the PDEA-PS powders prepared from pH 3.0 jumped to an earthed pendant distilled water droplet to form a droplet of aqueous dispersion. Conversely the larger powder aggregates prepared from pH 10.0 did not jump due to cohesion between the hydrophobic PDEA chains on the PS particles, resulting in no LM formation.
Publisher: American Chemical Society (ACS)
Date: 05-08-2016
Publisher: IOP Publishing
Date: 14-02-2008
DOI: 10.1088/0957-4484/19/10/105709
Abstract: Variations in the mechanical properties of nominally identical V-shaped atomic force microscope (AFM) cantilevers sourced from the same silicon nitride wafer have been quantified by measuring the spring constants, resonant frequencies and quality factors of 101 specimens as received from the manufacturer using the thermal spectrum method of Hutter and Bechhoefer. The addition of thin gold coatings always lowers the resonant frequency but the corresponding spring constant can either increase or decrease as a result. The observed broad spread of spring constant values and the lack of correlations between the resonant frequency and spring constant can be attributed in part to the non-uniformity of composition and material properties in the thinnest dimension of such cantilevers which arise from the manufacturing process. The effects of coatings are dictated by the competing influence of differences in mass density and Young's modulus between the silicon nitride and the gold coating. An implication of this study is that cantilever calibration methods based on the assumption of uniformity of material properties of the cantilever in the thinnest dimension are unlikely to be applicable for such cantilevers.
Publisher: Elsevier BV
Date: 12-2022
Publisher: Elsevier BV
Date: 10-2023
Publisher: IOP Publishing
Date: 03-2023
Abstract: Hofmeister effects, and more generally specific ion effects, are observed broadly in biological systems. However, there are many cases where the Hofmeister series might not be followed in complex biological systems, such as ion channels which can be highly specific to a particular ion. An understanding of how ions from the Hofmeister series interact with the proteinogenic amino acids will assist elucidation of why some binding interactions may be favoured over others. Using symmetry adapted perturbation theory (SAPT2 + 3), the interaction energies between a selection of anions and each amino acid have been investigated. The interaction strengths become more favourable in accordance with the Hofmeister series, and also with increasing polarity of the amino acids (with the exception of the negatively charged amino acid side chains). Furthermore, the interactions are generally most favourable when they simultaneously involve the side chain and both protic moieties of the backbone. The total interaction energy in these anion–amino acid complexes is also primarily determined by its electrostatic component, in a manner proportional to the þ (‘sho’) value of the anion.
Publisher: Royal Society of Chemistry (RSC)
Date: 2012
DOI: 10.1039/C2CC35737B
Abstract: The electrical double layer at ionic liquid (IL)-Au(111) interfaces is composed of alternating ion layers. Interfacial layering is markedly weaker when small amounts of LiCl are dissolved in the IL for all potential between -2.0 V and +2.0 V (vs. Pt). This means that models developed for pure IL electrical double layers may not be valid when solutes are present.
Publisher: American Chemical Society (ACS)
Date: 04-02-2014
DOI: 10.1021/LA403978B
Abstract: Silica particle suspensions of 10 wt % have been investigated in the protic ionic liquids (ILs) ethylammonium nitrate (EAN), ethanolammonium nitrate (EtAN), propylammonium nitrate (PAN), and dimethylethylammonium formate (DMEAF). Static and dynamic light scattering reveal that single particles coexist in dynamic equilibrium with flocculated networks at room temperature. These types of systems are classified as weakly flocculated and are quite rare. As weakly flocculated systems generally exist only within a narrow range of conditions, the effect of temperature was probed. When temperature is increased, the thermal motion of suspended particles increases, favoring dispersion, but in ILs suspensions, heating reduces the stabilizing effect of the interfacial structure of the IL. When subjected to a small increase in temperature, particle suspensions in ILs become unstable, indicated by the absence of a peak corresponding to single particles in the light scattering data. For EAN and DMEAF, further increasing temperatures above 40 °C returns the systems to a weakly flocculated state in which thermal energy is sufficient to break particles away from aggregates. Weakly flocculated suspensions in EAN and EtAN settle more rapidly than predicted by the Stokes equation, as the particles spend a significant portion of time in large, rapidly settling flocs. Surprisingly, suspensions in PAN and DMEAF settle slower than predicted. Oscillatory rheology indicates that these suspensions are viscoelastic, due to a persistent, long-range structure in the suspension that slows settling. In aggregated systems, settling is very rapid.
Publisher: Royal Society of Chemistry (RSC)
Date: 2023
DOI: 10.1039/D3CP02206D
Abstract: Hypersaline environments are ubiquitous in nature and are found in myriad technological processes. Recent empirical studies have revealed a significant discrepancy between the predicted and observed screening lengths at high...
Publisher: American Chemical Society (ACS)
Date: 04-03-2016
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: Elsevier BV
Date: 06-2021
Publisher: Elsevier BV
Date: 12-2016
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3CC42844C
Publisher: Royal Society of Chemistry (RSC)
Date: 2008
DOI: 10.1039/B717303B
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: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C5SM02450A
Abstract: Cross-linked PTBAEMA-stabilised colloidosomes are still present after the acid-induced latex-to-microgel transition unlike the analogous Pickering droplets which coalesce.
Publisher: American Chemical Society (ACS)
Date: 12-10-2019
Publisher: American Chemical Society (ACS)
Date: 06-11-2009
DOI: 10.1021/JZ9000642
Publisher: Elsevier BV
Date: 09-2016
Publisher: American Chemical Society (ACS)
Date: 23-03-2015
DOI: 10.1021/ACS.LANGMUIR.5B00116
Abstract: The anion-specific solvation and conformational behavior of weakly basic poly(2-dimethylamino)ethyl methacrylate (poly(DMA)), poly(2-diethylamino)ethyl methacrylate (poly(DEA)), and poly(2-diisopropylamino)ethyl methacrylate (poly(DPA)) brushes, with correspondingly increasing inherent hydrophobicity, have been investigated using in situ ellipsometric and quartz crystal microbalance with dissipation (QCM-D) measurements. In the osmotic brush regime, as the initial low concentration of salt is increased, the brushes osmotically swell by the uptake of solvent as they become charged and the attractive hydrophobic inter- and intrachain interactions are overcome. With increased ionic strength, the brushes move into the salted brush regime where they desolvate and collapse as their electrostatic charge is screened. Here, as the brushes collapse, they transition to more uniform and rigid conformations, which dissipate less energy, than similarly solvated brushes at lower ionic strength. Significantly, in these distinct regimes brush behavior is not only ionic strength dependent but is also influenced by the nature of the added salt based on its position in the well-known Hofmeister or lyotropic series, with potassium acetate, nitrate, and thiocyanate investigated. The strongly kosmotropic acetate anions display low affinity for the hydrophobic polymers, and largely unscreened electrosteric repulsions allow the brushes to remain highly solvated at higher acetate concentrations. The mildly chaotropic nitrate and strongly chaotropic thiocyanate anions exhibit a polymer hydrophobicity-dependent affinity for the brushes. Increasing thiocyanate concentration causes the brushes to collapse at lower ionic strength than for the other two anions. This study of weak polybasic brushes demonstrates the importance of all ion, solvent, and polymer interactions.
Publisher: American Chemical Society (ACS)
Date: 11-09-2014
DOI: 10.1021/CT500394T
Publisher: American Chemical Society (ACS)
Date: 24-10-2002
DOI: 10.1021/NL025781B
Publisher: Springer Science and Business Media LLC
Date: 21-07-2022
DOI: 10.1038/S41597-022-01527-8
Abstract: The importance of ion-solvent interactions in predicting specific ion effects in contexts ranging from viral activity through to electrolyte viscosity cannot be underestimated. Moreover, investigations of specific ion effects in nonaqueous systems, highly relevant to battery technologies, biochemical systems and colloid science, are severely limited by data deficiency. Here, we report IonSolvR – a collection of more than 3,000 distinct nanosecond-scale ab initio molecular dynamics simulations of ions in aqueous and non-aqueous solvent environments at varying effective concentrations. Density functional tight binding (DFTB) is used to detail the solvation structure of up to 55 solutes in 28 different protic and aprotic solvents. DFTB is a fast quantum chemical method, and as such enables us to bridge the gap between efficient computational scaling and maintaining accuracy, while using an internally-consistent simulation technique. We validate the database against experimental data and provide guidance for accessing in idual IonSolvR records.
Publisher: IOP Publishing
Date: 26-10-2015
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: Springer Science and Business Media LLC
Date: 08-03-2021
DOI: 10.1038/S41598-021-84798-2
Abstract: Improving the heat tolerance of cotton is a major concern for breeding programs. To address this need, a fast and effect way of quantifying thermotolerant phenotypes is required. Triphenyl tetrazolium chloride (TTC) based enzyme viability testing following high-temperature stress can be used as a vegetative heat tolerance phenotype. This is because when live cells encounter a TTC solution, TTC undergoes a chemical reduction producing a visible, insoluble red product called triphenyl formazan, that can be quantified spectrophotometrically. However, existing TTC based cell viability assays cannot easily be deployed at the scale required in a crop improvement program. In this study, a heat stress assay (HSA) based on the use of TTC enzyme viability testing has been refined and improved for efficiency, reliability, and ease of use through four experiments. S ling factors that may influence assay results, such as leaf age, plant water status, and short-term cold storage, were also investigated. Experiments conducted in this study have successfully downscaled the assay and identified an optimal s ling regime, enabling measurement of large segregating populations for application in breeding programs. The improved HSA methodology is important as it is proposed that long-term improvements in cotton thermotolerance can be achieved through the concurrent selection of superior phenotypes based on the HSA and yield performance in hot environments. Additionally, a new way of interpreting both heat tolerance and heat resistance was developed, differentiating genotypes that perform well at the time of a heat stress event and those that maintain a similar performance level to a non-stressed control.
Publisher: CSIRO Publishing
Date: 2012
DOI: 10.1071/CH12374
Abstract: Surface tensiometry of binary mixtures of ethylammonium nitrate (EAN), ethanolammonium nitrate (EtAN), and water reveals distinctive hiphilic character for the ethylammonium cation, but not for ethanolammonium. Results also show that the surface film incorporates nitrate counterions, and that electrostatic and H-bonding interactions, rather than alkyl chain packing, determines the saturated adsorbed film structure and limiting molecular area.
Publisher: American Chemical Society (ACS)
Date: 23-02-2021
Publisher: AIP Publishing
Date: 16-02-2018
DOI: 10.1063/1.5012801
Abstract: Nanoscale structure of protic ionic liquids is critical to their utility as molecular electrochemical solvents since it determines the capacity to dissolve salts and polymers such as poly(ethylene oxide) (PEO). Here we use quantum chemical molecular dynamics simulations to investigate the impact of dissolved halide anions on the nanostructure of an archetypal nanostructured protic ionic liquid, propylammonium nitrate (PAN), and how this impacts the solvation of a model PEO polymer. At the molecular level, PAN is nanostructured, consisting of charged olar and uncharged/nonpolar domains. The charged domain consists of the cation/anion charge groups, and is formed by their electrostatic interaction. This domain solvophobically excludes the propyl chains on the cation, which form a distinct, self-assembled nonpolar domain within the liquid. Our simulations demonstrate that the addition of Cl− and Br− anions to PAN disrupts the structure within the PAN charged domain due to competition between nitrate and halide anions for the ammonium charge centre. This disruption increases with halide concentration (up to 10 mol. %). However, at these concentrations, halide addition has little effect on the structure of the PAN nonpolar domain. Addition of PEO to pure PAN also disrupts the structure within the charged domain of the liquid due to hydrogen bonding between the charge groups and the terminal PEO hydroxyl groups. There is little other association between the PEO structure and the surrounding ionic liquid solvent, with strong PEO self-interaction yielding a compact, coiled polymer morphology. Halide addition results in greater association between the ionic liquid charge centres and the ethylene oxide components of the PEO structure, resulting in reduced conformational flexibility, compared to that observed in pure PAN. Similarly, PEO self-interactions increase in the presence of Cl− and Br− anions, compared to PAN, indicating that the addition of halide salts to PAN decreases its utility as a molecular solvent for polymers such as PEO.
Publisher: Elsevier BV
Date: 09-2018
DOI: 10.1016/J.JCIS.2018.04.086
Abstract: Thermoresponsive polymers have received significant research attention as smart materials with particular interest in biomedical applications. The composition and architecture are known to strongly influence the thermoresponsive properties of the materials. For ex le, the strong overlap of end-grafted polymer chains in polymer brushes leads to a broader collapse transition relative to linear ungrafted chains as well as temperature dependent adhesion. The temperature response of free polymer has been widely reported to depend on the concentration and identity of ions in solution and is further modified by the composition of the solvent and presence of cosolutes. However, the influence of polymer architecture on these specific ion effects is relatively unknown. Herein, we compare the current understanding of specific ion effects on free polymer chains and gels with recent studies of polymer brushes. Further studies on mixed salt systems are found to be the next step to predicting the behaviour of these materials in biological systems.
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C8CP06644B
Abstract: The temperature induced swelling/collapse transition of poly(oligoethylene glycol methacrylate) (POEGMA) brushes has been investigated in electrolyte solutions comprised of multiple anions.
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C5CP07468A
Abstract: Specific anion identity and concentration dictates the direction and magnitude of the shift in LCST for a pNIPAM brush determined by in situ ellipsometry, QCM-D and static contact angle measurements.
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: Frontiers Media SA
Date: 10-07-2018
Publisher: Elsevier BV
Date: 10-2013
Publisher: American Chemical Society (ACS)
Date: 13-12-2016
Publisher: American Chemical Society (ACS)
Date: 14-04-2020
Publisher: Elsevier BV
Date: 06-2014
Publisher: Wiley
Date: 20-01-2007
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3CP52281D
Abstract: Polymer brushes are commonly used to modify the properties of solid surfaces. Here a family of polybasic poly(2-(diethylamino)ethyl methacrylate) brushes have been grown using ARGET ATRP from a cationic macroinitiator adsorbed on two types of silica surfaces: QCM crystals and oxidised silicon wafers. The pH-response of these brushes is investigated as a function of brush thickness in a constant flow environment in order to focus on the intrinsic dynamics of the polymer brushes. Independent QCM-D and in situ ellipsometry kinetic studies demonstrate the swelling process of protonation and solvent uptake is typically eight times faster than the corresponding neutralisation and solvent expulsion from the collapsing brush. However, the maximum rate of these processes is independent of brush thickness. The initial pH response of the brushes is hysteretic due to brush entanglement, which once overcome allows highly reversible pH-induced conformational changes. Multiple pH cycles demonstrate that the viscoelastic nature of the swollen state relative to the collapsed brush is independent of brush thickness.
Publisher: American Chemical Society (ACS)
Date: 10-02-2014
DOI: 10.1021/LA4047275
Abstract: The swelling behavior of poly(2-(diethylamino)ethyl methacrylate) (PDEA) brushes in response to changes in solution pH and ionic strength has been investigated. The brushes were synthesized by ARGET ATRP methodology at the silica-aqueous solution interface via two different surface-bound initiator approaches: electrostatically adsorbed cationic macroinitiator and covalently anchored silane-based ATRP initiator moieties. The pH-response of these brushes is studied as a function of the solvated brush thickness in a constant flow regime that elucidates the intrinsic behavior of polymer brushes. In situ ellipsometry equilibrium measurements show the pH-induced brush swelling and collapse transitions are hysteretic in nature. Furthermore, high temporal resolution kinetic studies demonstrate that protonation and solvent ingress during swelling occur much faster than the brush charge neutralization and solvent expulsion during collapse. This hysteresis is attributed to the formation of a dense outer region or skin during collapse that retards solvent egress. Moreover, at a constant pH below its pKa, the PDEA brush exhibited a critical conformational change in the range 0.5-1 mM electrolyte, a range much narrower than predicted by the theory of the osmotic brush regime. This behavior is attributed to the hydrophobicity of the collapsed brush. The swelling and collapse kinetics for this salt-induced transition are nearly identical. This is in contrast to the asymmetry in the rate of the pH-induced response, suggesting an alternative mechanism for the two processes dependent on the nature of the environmental trigger.
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C6CP07932F
Abstract: Ab initio MD and experiments are combined to reveal how the nanostructures in choline chloride deep eutectic solvents, and hence their properties, are modulated by the hydrogen bond donor structure.
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C9SM01467E
Abstract: Larger particles are more readily extracted from an advancing bed of charged particles owing to decreased interparticle cohesion.
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7CP03835F
Abstract: We present a perspective demonstrating the importance of synergy between experiment and theory for modern nanomaterial synthesis.
Publisher: Elsevier BV
Date: 04-2018
DOI: 10.1016/J.JCIS.2018.01.058
Abstract: The thermoresponse of poly(N-isopropylacrylamide) stabilised particles is influenced by the presence of salt and is dependent on the concentration, and ions present. The conformation and electrophoretic mobility of core/shell PNIPAM brush modified silica particles is expected to vary as a function of these specific ion effects. The thermoresponse of PNIPAM brush modified silica particles was investigated via dynamic light scattering and electrophoretic mobility measurements between 5 and 45 °C in the presence of 11 different salt solutions. Specific ion effects were observed in the presence of salt solutions for concentrations between 50 and 1000 mM. The temperature response could be mapped to a master curve unlike PNIPAM brush behaviour on planar substrates. The magnitude of brush layer lower critical solution temperature reduction was found to follow the order F
Location: United Kingdom of Great Britain and Northern Ireland
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Funder: Australian Research Council
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