ORCID Profile
0000-0002-5764-8380
Current Organisation
Nanyang Technological University
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Publisher: American Chemical Society (ACS)
Date: 12-2001
DOI: 10.1021/LA010917R
Publisher: AIP Publishing
Date: 23-04-2009
DOI: 10.1063/1.3120273
Abstract: This paper investigates the phenomenon of Faradaic charging in ac electrokinetics. Faradaic reactions were suggested as a key effect responsible for the reversal of pumping direction in ac micropumps. However, this hypothesis has yet to be proven convincingly and directly. Here we present an ion detection strategy to determine the production of ions through Faradaic hydrolytic reactions originating from direct application of voltage to electrolytic solutions during ac electrokinetics. Experiments were performed with symmetrical planar electrodes aligned along a microfluidic channel. Fluorescein, a pH-dependent dye, was employed as the pH indicator for the detection of ion production. Images were captured for analysis at various voltage levels. From analyzing the fluorescence intensity and its distribution, it can be concluded that the production of ions from hydrolytic reactions takes place and increases with the ac voltage. The coefficient of deviation indicates a significant enhancement at ac voltage above 11 Vpp. Lastly, we demonstrate a strategy using dc-biased ac electrokinetics to achieve controllability in direction and magnitude of the net fluid flow in pumping application.
Publisher: Elsevier BV
Date: 03-2006
Publisher: Springer Science and Business Media LLC
Date: 27-01-2009
Publisher: Japan Laser Processing Society
Date: 07-2016
Publisher: Elsevier BV
Date: 06-2004
Publisher: IOP Publishing
Date: 04-07-2012
Publisher: MDPI AG
Date: 28-08-2015
DOI: 10.3390/NANO5031442
Publisher: Elsevier BV
Date: 2003
Publisher: Elsevier BV
Date: 05-2005
DOI: 10.1016/J.CIS.2005.01.002
Abstract: The effect of cross-linked density on the rheological behavior of model pH-responsive microgel systems consisting of methacrylic acid-ethyl acrylate (MAA-EA) cross-linked with di-allyl phthalate (DAP) was examined. Neutralization of acid groups increases the osmotic pressure exerted by counter-ions trapped in the polymeric network against the ions in bulk solution, which is responsible for the swelling and increase in viscosity. The viscosity exhibits a maximum at approximately 1 wt.% DAP and it decreases to a steady value at 4 wt.% DAP, which is independent of pH and particle concentrations. Static light scattering results confirmed this optimum density as the critical point where sufficient cross-link points are present to produce permanent junctions that permit optimal swelling of the microgel particles. In addition, the variation of relative swelling with cross-linked densities of our model microgel systems agrees with the theoretical scaling law, Q alpha (yalphaN(x))(3/2) for cross-linked densities beyond this optimum point (Q is the swelling ratio, y is the acidic MAA content, N(x) is the average number of monomer units between two cross-linked points, and alpha is the degree of neutralization). By combining the results from light scattering and rheological measurements, we are able to correlate the microstructural evolution of the colloidal systems with their bulk rheological behavior.
Publisher: Elsevier BV
Date: 06-2011
Publisher: Springer Science and Business Media LLC
Date: 12-01-2005
Publisher: MDPI AG
Date: 24-03-2022
DOI: 10.3390/MI13040506
Abstract: With multi-foci laser cutting technology for sapphire wafer separation, the entire cross-section is generally scanned with single or multiple passes. This investigation proposes a new separation technique through partial thickness scanning. The energy effectivity and efficiency of the picosecond laser were enhanced through a two-zone partial thickness scanning by exploiting the internal reflection at the rough exit surface. Each zone spanned only one-third thickness of the cross-section, and only two out of three zones were scanned consecutively. A laser beam of 0.57 W and 50 kHz pulse repetition rate was split into 9 foci, each with a 2.20 μm calculated focused spot diameter. By only scanning the top two-thirds s le thickness, first its middle section then upper section, a cleavable s le could result. This was achieved with the lowest energy deposition at the fastest scanning speed of 10 mm/s investigated. Although with partial thickness scanning only, counter intuitively, the cleaved s le had a previously unattained uniform roughened sidewall profile over the entire thickness. This is a desirable outcome in LED manufacturing. As such, this proposed scheme could attain a cleavable s le with the desired uniformly roughened sidewall profile with less energy usage and faster scanning speed.
Publisher: Elsevier BV
Date: 1996
Publisher: American Chemical Society (ACS)
Date: 16-06-2004
DOI: 10.1021/LA049907R
Abstract: The effects of a salt mixture consisting of a salt-out salt (NaCl) and a salt-in salt (NaI) on the sol-gel transition of methylcellulose (MC) in aqueous solution have been studied by means of micro differential scanning calorimetry and rheometry. The salt mixture was found to have a combined effect from the salt-out and salt-in salts in the mixture, and the salt effect was dependent on the water hydration abilities of the component ions and ion concentration. At a fixed total salt concentration, the sol-gel transition temperature nicely followed a rule of mixing: Tp = m1Tp1 + m2Tp2 where Tp, Tp1, and Tp2 are the gelation peak temperatures for the MC solutions with a salt mixture, NaCl, and NaI, respectively, and mi is the molar fraction of the salt component i in the salt mixture. The linear rule of mixing proved that the effects of NaCl and NaI on the sol-gel transition of MC are completely independent. In addition, the presence of a single salt or a salt mixture in a MC solution does not change the essential mechanism of MC gelation. Therefore, the sol-gel transition of MC can be simply controlled by a salt mixture consisting of a salt-out salt and a salt-in salt. The rheological results supported the micro thermal results excellently. But the gel strength of MC containing salts was influenced by both salt type and salt concentration.
Publisher: Elsevier BV
Date: 12-2010
Publisher: Elsevier BV
Date: 08-2001
Publisher: Elsevier BV
Date: 10-2004
Publisher: AIP Publishing
Date: 03-2010
DOI: 10.1063/1.3319611
Abstract: A laser soft marking technique is developed for laser markings on a silicon wafer. Due to negligible surface modification, the laser soft wafer markings are invisible by naked eyes under room condition and are undetectable using sophisticated instruments. However, these laser markings are found to be visible to naked eyes through a differential condensation of water droplets on the laser-marked and unmarked silicon surfaces. To understand this phenomenon, a model is established to study the condensation of water droplets on laser-marked and unmarked silicon surfaces. Experimental observations and simulation results indicate that the laser soft marking could have modified the silicon surface with a thin polycrystalline silicon layer which has a much lower conductivity than the crystalline silicon. In addition, this thin layer exhibits a thermal conductivity which is approximately two orders of magnitude lower than that of its equivalent bulk material. As a result, heat transfer on the laser-marked silicon surface is much lower than the crystalline silicon and thus makes these laser soft markings easily visible visually under condensation.
Publisher: Elsevier BV
Date: 2005
Publisher: Wiley
Date: 2007
DOI: 10.1002/PEN.20904
Publisher: Elsevier BV
Date: 1995
Publisher: Wiley
Date: 31-07-2001
DOI: 10.1002/APP.1874
Publisher: Elsevier BV
Date: 11-2005
Publisher: Springer Science and Business Media LLC
Date: 10-11-2010
Publisher: Springer Science and Business Media LLC
Date: 22-08-2013
Publisher: ASME International
Date: 06-2005
DOI: 10.1115/1.1865216
Abstract: This study presents a numerical analysis of electrokinetic mass transport in a microchannel with Joule heating effects. A nonuniform electric field caused by the presence of the Joule heating is considered in the model development. Numerical computations for electrokinetic mass transport under Joule heating effects are carried out using the Crank-Nicolson scheme of second-order accuracy in space and time for two different cases: (i) the translating interface and (ii) the dispersion of a finite s le plug. The simulations reveal that the presence of Joule heating not only causes the s le species to transport faster, but also causes the s le peak to decrease and the s le band to deviate from its flat interface or pluglike shape.
Publisher: Society of Rheology Japan
Date: 2003
Publisher: SPIE
Date: 09-02-2012
DOI: 10.1117/12.912950
Publisher: Elsevier BV
Date: 06-2009
Publisher: IOP Publishing
Date: 04-05-2011
Publisher: American Chemical Society (ACS)
Date: 12-03-2014
DOI: 10.1021/AM4054546
Abstract: Appropriate control of substrate surface properties prior to inkjet printing could be employed to improve the printing quality of fine resolution structures. In this paper, novel methods to fabricate patterned surfaces with a combination of hydrophilic and hydrophobic properties are investigated. The results of inkjet printing of PEDOT/PSS conductive ink on these modified surfaces are presented. Selective wetting was achieved via a two-step hydrophilic-hydrophobic coating of 3-aminopropyl trimethoxysilane (APTMS) and 3M electronic grade chemical respectively on PET surfaces this was followed by a selective hydrophilic treatment (either atmospheric O2/Ar plasma or UV/ozone surface treatment) with the aid of a Nickel stencil. Hydrophobic regions with water contact angle (WCA) of 105° and superhydrophilic regions with WCA <5° can be achieved on a single surface. During inkjet printing of the treated surfaces, PEDOT/PSS ink spread spontaneously along the hydrophilic areas while avoiding the hydrophobic regions. Fine features smaller than the inkjet droplet size (approximately 55 μm in diameter) can be successfully printed on the patterned surface with high wettability contrast.
Publisher: AIP Publishing
Date: 07-2015
DOI: 10.1063/1.4927474
Abstract: Many fluids, including biological fluids such as mucus and blood, are viscoelastic. Through the introduction of chaotic flows in a micro-channel and the construction of maps of characteristic chaos parameters, differences in viscoelastic properties of these fluids can be measured. This is demonstrated by creating viscoelastic chaotic flows induced in an H-shaped micro-channel through the steady infusion of a polymeric fluid of polyethylene oxide (PEO) and another immiscible fluid (silicone oil). A protocol for chaos analysis was established and demonstrated for the analysis of the chaotic flows generated by two polymeric fluids of different molecular weight but with similar relaxation times. The flows were shown to be chaotic through the computation of their correlation dimension (D2) and the largest Lyapunov exponent (λ1), with D2 being fractional and λ1 being positive. Contour maps of D2 and λ1 of the respective fluids in the operating space, which is defined by the combination of polymeric fluids and silicone oil flow rates, were constructed to represent the characteristic of the chaotic flows generated. It was observed that, albeit being similar, the fluids have generally distinct characteristic maps with some similar trends. The differences in the D2 and λ1 maps are indicative of the difference in the molecular weight of the polymers in the fluids because the driving force of the viscoelastic chaotic flows is of molecular origin. This approach in constructing the characteristic maps of chaos parameters can be employed as a diagnostic tool for biological fluids and, more generally, chaotic signals.
Publisher: Springer Science and Business Media LLC
Date: 16-03-2004
Publisher: Elsevier BV
Date: 2002
Publisher: Elsevier BV
Date: 10-2010
Publisher: IOP Publishing
Date: 18-08-2011
Publisher: Royal Society of Chemistry (RSC)
Date: 2009
DOI: 10.1039/B813639D
Abstract: This paper presents a novel approach of mixing two laminar flowing streams in microchannels. The mixer consists of a pair of electrodes disposed along a fluidic channel. By energizing the electrodes with a DC-biased (2.5 V) AC voltage (20 Vpp), an electrokinetic flow is induced with a flow profile perpendicular to that of the incoming laminar streams of liquids to be mixed. As a result, the flow lines of the incoming streams and the induced flow are forced to crossover and very efficient stirring and mixing at short mixing length can be achieved. The mixer can be operated from the AC-electroosmotic (ACEO) (sigma=1 mS/m, f=100 kHz) to the AC-electrothermal (ACET) (sigma=500 mS/m, f=500 kHz) flow regimes. The mixing efficiency in the ACEO regime was 92%, with a mixing length of 600 microm (Q=2 microL/min), an estimated mixing time of 69 ms and an induced ACEO flow velocity of approximately 725 microm/s. The mixing efficiency in the ACET regime was 65% for a mixing length of approximately 1200 microm. The mixer is efficient and suitable for mixing reagents in a fluid media from low to high conductivity as required in erse microfluidic applications.
Publisher: SAGE Publications
Date: 02-2007
Abstract: A finite element analysis of the flatness of thin, rolled steel strip is presented. The occurrence of edge-wave and centre-buckle is predicted numerically by solving the eigenvalue problem. The form of buckles is calculated using a non-linear load-displacement analysis. Buckling changes from the centre to the edge as the maximum difference in temperature between the edge and centre increases correspondingly, the litude increases and the wavelength decreases. Because uniform applied tension then decreases the compressive stress at the edge and increases the stress in the centre, a centre-buckled strip is flattened by applied tension, but edge-buckling becomes more severe and applied tension may change the type of buckling from the centre to the edge. Crowned strip resists buckling whereas a concave profile tends to promote it. The effects of the magnitude of the crown or concavity on centre-buckling of the strip are more significant than on edge-buckling.
Publisher: Elsevier BV
Date: 06-2007
Publisher: Wiley
Date: 27-02-2002
DOI: 10.1002/PI.843
Publisher: Wiley
Date: 24-06-2009
DOI: 10.1002/APP.30444
Publisher: ASME International
Date: 09-2015
DOI: 10.1115/1.4030240
Abstract: Electro-osmotic flow (EOF) is widely used in microfluidic systems. Here, we report an analysis of the thermal effect on EOF under an imposed temperature difference. Our model not only considers the temperature-dependent thermophysical and electrical properties but also includes ion thermodiffusion. The inclusion of ion thermodiffusion affects ionic distribution, local electrical potential, as well as free charge density, and thus has effect on EOF. In particular, we formulate an analytical model for the thermal effect on a steady, fully developed EOF in slit microchannel. Using the regular perturbation method, we solve the model analytically to allow for decoupling several physical mechanisms contributing to the thermal effect on EOF. The parametric studies show that the presence of imposed temperature difference/gradient causes a deviation of the ionic concentration, electrical potential, and electro-osmotic velocity profiles from their isothermal counterparts, thereby giving rise to faster EOF. It is the thermodiffusion induced free charge density that plays a key role in the thermodiffusion induced electro-osmotic velocity.
Publisher: Elsevier BV
Date: 11-2004
Publisher: Informa UK Limited
Date: 04-2004
Publisher: Walter de Gruyter GmbH
Date: 03-2005
DOI: 10.3139/217.1860
Abstract: In injection molding, the injection pressure is often limited by the capacity of injection machines. Therefore, for large-volume part, multiple gates are needed so that the maximum flow path can be shortened, with a corresponding decrease in injection pressure. Many components produced by injection molding today require more than one gate. As multiple gates affect resin flow in a mold interactively, their locations might not be easily determined. For a mold with two gates, a pressure gradient search scheme (PGSS) is proposed to optimize their locations in this investigation. A search direction associated with pressure gradient is developed based on the physical nature of the mold-filling process. An alternative scheme based on genetic algorithm is also employed for comparison. Through minimizing the objective function of injection pressure, the optimum gates can be located to achieve balanced flow. Ex les indicate that the proposed pressure gradient search scheme is more efficient than genetic algorithm for two gate location optimization.
Publisher: Springer Science and Business Media LLC
Date: 28-07-2007
Publisher: Wiley
Date: 22-04-2003
DOI: 10.1002/PI.1123
Publisher: Springer Science and Business Media LLC
Date: 29-04-2002
Publisher: Springer Science and Business Media LLC
Date: 05-08-2011
Publisher: American Chemical Society (ACS)
Date: 28-07-2016
DOI: 10.1021/ACS.ANALCHEM.6B01536
Abstract: Electroosmotic flow (EOF) with two or more fluids is often encountered in various microfluidic applications. However, no investigation has hitherto been conducted to investigate the hysteretic or flow direction-dependent behavior during displacement flow of solutions with dissimilar anion species. In this investigation, EOF of dissimilar anionic solutions was studied experimentally through the current monitoring method and numerically through finite element simulations. As opposed to other conventional displacement flows, EOF involving dissimilar anionic solutions exhibits counterintuitive behavior, whereby the current-time curve does not reach the steady-state value of the displacing electrolyte. Two distinct mechanics have been identified as the causes for this observation: (a) ion concentration adjustment when the displacing anions migrate upstream against EOF due to competition between the gradients of electromigrative and convective fluxes and (b) ion concentration readjustment induced by the static diffusive interfacial region between the dissimilar fluids which can only be propagated throughout the entire microchannel with the presence of EOF. The resultant ion distributions lead to the flow rate to be directional-dependent, indicating that the flow conditions are asymmetric between these two different flow directions. The outcomes of this investigation contribute to the in-depth understanding of flow behavior in microfluidic systems involving inhomogeneous fluids, particularly dissimilar anionic solutions. The understanding of EOF hysteresis is fundamentally important for the accurate prediction of analytes transport in microfluidic devices under EOF.
Publisher: Wiley
Date: 09-2009
Abstract: This study reports improved electrokinetically driven microfluidic T-mixers to enhance their mixing efficiency. Enhancement of electrokinetic microfluidic T-mixers is achieved using (i) an active approach of utilizing a pulsating EOF, and (ii) a passive approach of using the channel geometry effect with patterned blocks. PDMS-based electrokinetic T-mixers of different designs were fabricated. Experimental measurements were carried out using Rhodamine B to examine the mixing performance and the micro-particle image velocimetry technique to characterize the electrokinetic flow velocity field. Scaling analysis provides an effective frequency range of applied AC electric field. Results show that for a T-mixer of 10 mm mixing length, utilizing frequency modulated electric field and channel geometry effects can increase the mixing efficiency from 50 to 90%. In addition, numerical simulations were performed to analyze the mixing process in the electrokinetic T-mixers with various designs. The simulation results were compared with the experimental data, and reasonable agreement was found.
Publisher: IOP Publishing
Date: 12-1993
Publisher: Elsevier BV
Date: 12-2007
Publisher: Trans Tech Publications Ltd.
Date: 15-06-2006
Publisher: Elsevier BV
Date: 02-2009
Publisher: Springer Science and Business Media LLC
Date: 22-03-2006
Publisher: IOP Publishing
Date: 04-08-2011
Publisher: Elsevier BV
Date: 04-2008
Publisher: Wiley
Date: 13-10-190728635
DOI: 10.1002/APP.10627
Publisher: Elsevier BV
Date: 03-2000
Publisher: Elsevier BV
Date: 10-1989
Publisher: World Scientific Pub Co Pte Lt
Date: 06-2005
DOI: 10.1142/S0218625X05007098
Abstract: Porous silicon structures were observed in laser-assisted etching in a TMAH solution. The porous structures significantly increase the active surface areas and therefore are of great interest to the pharmaceutical and fine chemicals industry, in the areas of high throughput drug discovery, reaction optimization and process development. Laser-assisted etching of silicon using a Nd :YAG laser with a TMAH solution is rarely studied but desirable as the solution is nontoxic. To the best of our knowledge, the porous structures directly produced this way have not been reported previously. In this paper, we discuss our experimental results and the possible mechanism of formation of the porous structures. A dummy micro-reactor was fabricated with selective porous surface structures to demonstrate its potential industrial applications.
Publisher: Springer Science and Business Media LLC
Date: 05-11-2013
Publisher: Springer Science and Business Media LLC
Date: 29-02-2016
DOI: 10.1038/SREP22329
Abstract: Electro-osmotic flow, the driving of fluid at nano- or micro- scales with electric field, has found numerous applications, ranging from pumping to chemical and biomedical analyses in micro-devices. Electro-osmotic flow exhibits a puzzling hysteretic behavior when two fluids with different concentrations displace one another. The flow rate is faster when a higher concentration solution displaces a lower concentration one as compared to the flow in the reverse direction. Although electro-osmotic flow is a surface phenomenon, rather counter intuitively we demonstrate that electro-osmotic flow hysteresis originates from the accumulation or depletion of pH-governing minority ions in the bulk of the fluid, due to the imbalance of electric-field-induced ion flux. The pH and flow velocity are changed, depending on the flow direction. The understanding of electro-osmotic flow hysteresis is critical for accurate fluid flow control in microfluidic devices and maintaining of constant pH in chemical and biological systems under an electric field.
Publisher: American Chemical Society (ACS)
Date: 14-08-2002
DOI: 10.1021/LA020029B
Publisher: Wiley
Date: 25-11-2004
DOI: 10.1002/APP.13330
Publisher: Elsevier BV
Date: 09-1990
Publisher: Elsevier BV
Date: 2018
Publisher: IOP Publishing
Date: 23-06-2009
Publisher: IEEE
Date: 12-2008
Publisher: Wiley
Date: 20-08-2003
DOI: 10.1002/POLB.10522
Publisher: Elsevier BV
Date: 08-2004
Publisher: Elsevier BV
Date: 02-2001
Publisher: IOP Publishing
Date: 04-2006
Publisher: Springer Science and Business Media LLC
Date: 13-10-2011
Publisher: Wiley
Date: 10-2004
DOI: 10.1002/APP.21151
Publisher: Springer Science and Business Media LLC
Date: 25-05-2021
DOI: 10.1038/S41467-021-23427-Y
Abstract: Despite its advantages of scalable process and cost-effectiveness, nanoimprinting faces challenges with imprinting hard materials (e.g., crystalline metals) at low/room temperatures, and with fabricating complex nanostructures rapidly (e.g., heterojunctions of metal and oxide). Herein, we report a room temperature ultrasonic nanoimprinting technique (named nanojackhammer) to address these challenges. Nanojackhammer capitalizes on the concentration of ultrasonic energy flow at nanoscale to shape bulk materials into nanostructures. Working at room temperature, nanojackhammer allows rapid fabrication of complex multi-compositional nanostructures made of virtually all solid materials regardless of their ductility, hardness, reactivity and melting points. Atomistic simulations reveal a unique alternating dislocation generation and recovery mechanism that significantly reduces the imprinting force under ultrasonic cyclic loading. As a proof-of-concept, a metal-oxide-metal plasmonic nanostructure with built-in nanogap is rapidly fabricated and employed for biosensing. As a fast, scalable, and cost-effective nanotechnology, nanojackhammer will enable various unique applications of complex nanostructures in optoelectronics, biosensing, catalysis and beyond.
Publisher: Elsevier BV
Date: 12-2016
Publisher: SPIE
Date: 26-12-2008
DOI: 10.1117/12.810732
Publisher: AIP Publishing
Date: 03-2009
DOI: 10.1063/1.3108462
Publisher: Wiley
Date: 20-04-2010
DOI: 10.1002/PC.20861
Publisher: Springer Science and Business Media LLC
Date: 18-10-2012
Publisher: SAGE Publications
Date: 09-1994
DOI: 10.1177/1045389X9400500513
Abstract: This is a review of the work performed at the Defense Science and Technology Or ganisation, Aeronautical Research Laboratory, Melbourne, Australia and the Department of Mechanical Engineering, Monash University to develop "active" sensor technology using piezoelec tric thin films. The initial part of this review outlines a theoretical and experimental investigation on the characterisation of KYNAR piezoelectric thin film sensors. An experimental and theoretical study was then undertaken demonstrating the feasibility of using piezoelectric sensors to detect and monitor crack growth in a cracked aluminium specimen. The work was then extended to include a numerical investigation into the use of piezoelectric sensors to monitor crack growth, in an aluminium structure, beneath a boron/epoxy patch. Finally, the last section describes the use of piezoelectric sensors for detecting impact damage in composite structures.
Publisher: Springer Science and Business Media LLC
Date: 11-12-2007
Publisher: IOP Publishing
Date: 14-05-2010
Publisher: American Chemical Society (ACS)
Date: 25-01-2005
DOI: 10.1021/LA035124E
Abstract: UV embossing is a replication method whereby an UV-curable polymer is pressed against a patterned mold and cured with UV irradiation, resulting in a patterned polymeric substrate. High aspect ratio UV embossing will find erse applications in tissue engineering, micro-optics, display technologies, and sensors. Demolding of an UV-embossed polymer pattern with aspect ratio of 5 from the mold has previously been demonstrated experimentally. In this paper, parameters that affect the demolding process have been identified and investigated. They include cross-linking shrinkage during curing by UV irradiation, modulus of cured polymer, interfacial fracture strength and toughness, and loading method during demolding. Shrinkage is an important parameter, and an optimum level of shrinkage to avoid breakage of the embossing during demolding was found to exist. This optimum level is that at which the maximum stress (sigma(1)max) experienced by the polymer during demolding is minimized. The micromechanics of demolding was found to be different for shrinkage values lower or larger than the optimum value.
Publisher: ASMEDC
Date: 2008
Abstract: To study the effect of geometry on electroosmotic flow in micro channels, we fabricated PDMS-glass microchannels of different designs, which have patterned channels with abrupt contraction of different sizes. Using fluorescent imaging technology, we demonstrated the effect of geometry on the instability of DC driven electroosmotic flow in microfluidic channels. For certain geometry and conductivity of the electrolyte solution (Sodium Bicarbonate), there is a threshold voltage for electroosmotic instability, exhibiting itself as “ripple”. Generally, the factors which affect the threshold voltage include channel width, channel geometry, and electrolyte conductivity. Narrower channel resulted in higher onset voltage. As conductivity of the electrolyte increases, the threshold voltage tends to increase. Early transition to unstable electroosmotic flow in microfluidic channels was observed under relatively low Re.
Publisher: Elsevier BV
Date: 06-2020
Publisher: Elsevier BV
Date: 08-1986
Publisher: Wiley
Date: 29-10-2010
DOI: 10.1002/AIC.12095
Publisher: Elsevier BV
Date: 02-2010
Publisher: Informa UK Limited
Date: 15-05-2004
Publisher: AIP Publishing
Date: 03-2012
DOI: 10.1063/1.3665721
Abstract: Electroosmotic flow that involves one fluid displacing another fluid is commonly encountered in various microfludic applications and experiments, for ex le, current monitoring technique to determine zeta potential of microchannel. There is experimentally observed anomaly in such flow, namely, the displacement time is flow direction dependent, i.e., it depends if it is a high concentration fluid displacing a low concentration fluid, or vice versa. Thus, this investigation focuses on the displacement flow of two fluids with various concentration differences. The displacement time was determined experimentally with current monitoring method. It is concluded that the time required for a high concentration solution to displace a low concentration solution is smaller than the time required for a low concentration solution to displace a high concentration solution. The percentage displacement time difference increases with increasing concentration difference and independent of the length or width of the channel and the voltage applied. Hitherto, no theoretical analysis or numerical simulation has been conducted to explain this phenomenon. A numerical model based on finite element method was developed to explain the experimental observations. Simulations showed that the velocity profile and ion distribution deviate significantly from a single fluid electroosmotic flow. The distortion of ion distribution near the electrical double layer is responsible for the displacement time difference for the two different flow directions. The trends obtained from simulations agree with the experimental findings.
Publisher: Springer Science and Business Media LLC
Date: 22-07-2008
Publisher: Elsevier BV
Date: 12-2003
Publisher: SAGE Publications
Date: 09-2004
Abstract: A three-dimensional (3D) model for the simulation of the thermoplastic pultrusion process is developed. The simulation procedure and algorithms are based on the Finite Element–Nodal Control Volume (FE–NCV) approach. For illustration purposes, APC-2 CF–PEEK is used as a candidate material along with multiheater steel die assemblies. Heat transfer in the die and the composite is modeled using FEs whereas NCVs are used to model crystallization kinetics and heat of reaction for PEEK. The developed simulation procedure is validated using available data. Subsequently, versatility of the model for simulating various types of die assembly and transient heat transfer effects on crystallization is demonstrated.
Publisher: IOP Publishing
Date: 11-05-2010
Publisher: Springer Science and Business Media LLC
Date: 05-2018
DOI: 10.1038/S41467-018-04172-1
Abstract: Microfluidic biochips hold great potential for liquid analysis in biomedical research and clinical diagnosis. However, the lack of integrated on-chip liquid mixing, bioseparation and signal transduction presents a major challenge in achieving rapid, ultrasensitive bioanalysis in simple microfluidic configurations. Here we report magnetic nanochain integrated microfluidic chip built upon the synergistic functions of the nanochains as nanoscale stir bars for rapid liquid mixing and as capturing agents for specific bioseparation. The use of magnetic nanochains enables a simple planar design of the microchip consisting of flat channels free of common built-in components, such as liquid mixers and surface-anchored sensing elements. The microfluidic assay, using surface-enhanced Raman scattering nanoprobes for signal transduction, allows for streamlined parallel analysis of multiple specimens with greatly improved assay kinetics and delivers ultrasensitive identification and quantification of a panel of cancer protein biomarkers and bacterial species in 1 μl of body fluids within 8 min.
Publisher: Elsevier BV
Date: 12-1997
Publisher: ASME International
Date: 21-10-2006
DOI: 10.1115/1.2709654
Abstract: A total concentration fixed-grid method is presented in this paper to model the two-dimensional wet chemical etching. Two limiting cases are discussed, namely—the diffusion-controlled etching and the reaction-controlled etching. A total concentration, which is the sum of the unreacted and the reacted etchant concentrations, is defined. Using this newly defined total concentration, the governing equation also contains the interface condition. A new update procedure for the reacted concentration is formulated. For demonstration, the finite-volume method is used to solve the governing equation with prescribed initial and boundary conditions. The effects of reaction rate at the etchant–substrate interface are examined. The results obtained using the total concentration method, are compared with available results from the literature.
Publisher: IOP Publishing
Date: 22-02-2018
Abstract: A single step direct picosecond laser texturing process was demonstrated to be able to obtain a superhydrophobic surface on a nickel substrate, a key material for mold fabrication in the manufacture of various devices, including polymeric microfluidic devices. A two-scale hierarchical surface structure of regular 2D array micro-bumps with nano-ripples was produced on a nickel surface. The laser textured surface initially showed superhydrophilicity with almost complete wetting of the structured surface just after laser treatment, then quickly changed to nearly superhydrophobic with a water contact angle (WCA) of 140° in less than 1 d, and finally became superhydrophobic with a WCA of more than 150° and a contact angle hysteresis (CAH) of less than 5°. The mechanism involved in the process is discussed in terms of surface morphology and surface chemistry. The ultra-fast laser induced NiO catalytic effect was thought to play a key role in modifying the surface chemistry so as to lower the surface energy. The developed process has the potential to improve the performance of nickel mold in the fabrication of microfluidic devices.
Publisher: AIP Publishing
Date: 08-07-2008
DOI: 10.1063/1.2959099
Abstract: This paper reports the improvement of rectification effects in diffuser/nozzle structures with viscoelastic fluids. Since rectification in a diffuser/nozzle structure with Newtonian fluids is caused by inertial effects, micropumps based on this concept require a relatively high Reynolds numbers and high pumping frequencies. In applications with relatively low Reynolds numbers, anisotropic behavior can be achieved with viscoelastic effects. In our investigations, a solution of dilute polyethylene oxide was used as the viscoelastic fluid. A microfluidic device was fabricated in silicon using deep reactive ion etching. The microfluidic device consists of access ports for pressure measurement, and a series of ten diffuser/nozzle structures. Measurements were carried out for diffuser/nozzle structures with opening angles ranging from 15° to 60°. Flow visualization, pressure drop and diodicity of de-ionized water and the viscoelastic fluid were compared and discussed. The improvement of diodicity promises a simple pumping concept at low Reynolds numbers for lab-on-a-chip applications.
Publisher: American Chemical Society (ACS)
Date: 06-04-2005
DOI: 10.1021/LA047430D
Abstract: A turbidimetric analysis of particle interaction of model pH-responsive microgel systems consisting of methacrylic acid-ethyl acrylate cross-linked with diallyl phthalate in colloidal suspensions is described. The structure factor at zero scattering angle, S(0), can be determined with good precision for wavelengths greater than 500 nm, and it measures the dispersion's resistance to particle compression. The structure factor of microgels at various cross-linked densities and ionic strengths falls onto a master curve when plotted against the effective volume fraction, phi(eff) = kc, which clearly suggests that particle interaction potential and osmotic compressibility is a function of effective volume fraction. In addition, the deviation of the structure factor, S(0), of our microgel systems with the structure factor of hard spheres, S(PY)(0), exhibits a maximum at phi(eff) approximately 0.2. Beyond this point the osmotic de-swelling force exceeds the osmotic pressure inside the soft particles resulting in particle shrinkage. Good agreement was obtained when the structural properties of our microgel systems obtained from turbidimetric analysis and rheology measurements were compared. Therefore, a simple turbidimetric analysis of these model pH-responsive microgel systems permits a quantitative evaluation of factors governing particle osmotic compressibility.
Publisher: American Chemical Society (ACS)
Date: 21-09-2021
Publisher: Informa UK Limited
Date: 02-2005
Publisher: AIP Publishing
Date: 14-09-2009
DOI: 10.1063/1.3232212
Abstract: Controlled modification of surface wettability of polymethyl methacrylate (PMMA) was achieved by irradiation of PMMA surface with femtosecond laser pulses at various laser fluences and focus distances. Fluences from 0.40 to 2.1 J/cm2 produced a hydrophobic surface and 2.1 to 52.7 J/cm2 (maximum investigated) produced a hydrophilic surface. Fluences less than 0.31 J/cm2 had no effect on the wettability of the raw PMMA. This change in wettability was caused dominantly by laser induced chemical structure modification and not by a change in surface roughness.
Publisher: Elsevier BV
Date: 10-2016
Publisher: Informa UK Limited
Date: 10-2002
Publisher: Informa UK Limited
Date: 2008
DOI: 10.1163/156856208786440460
Abstract: In this study, thermal behavior of aqueous solutions of methyl cellulose (MC) at a constant temperature of 50 degrees C was analyzed. Various s les were studied for two consecutive heating-cooling cycles. The experiments with the solutions prepared using cold de-ionized (DI) water showed that the rate of gelation was higher for higher MC concentrations. However, the rate was slower during the first heating-cooling cycle than during the second cycle. The possible reasons behind such observations are discussed. Various MC solutions prepared using hot DI water were studied for understanding the role of the solvent state in the isothermal gelation process. The gelation of these MC solutions started at a lower MC concentration and resulted in a higher gelation rate. The gelation mechanism responsible for such effects is explored and presented. Finally, a gel-indexing method is proposed to provide a quantitative measure of the gelation state of all the MC gels.
Publisher: Author(s)
Date: 2016
DOI: 10.1063/1.4963493
Publisher: Elsevier BV
Date: 09-2008
Publisher: Wiley
Date: 19-05-2011
DOI: 10.1002/APP.34116
Publisher: Elsevier BV
Date: 10-1989
Publisher: Elsevier BV
Date: 10-2009
Publisher: Elsevier BV
Date: 05-2002
Publisher: Elsevier BV
Date: 02-1995
Publisher: Informa UK Limited
Date: 2001
Publisher: Springer Science and Business Media LLC
Date: 11-2003
Publisher: IEEE
Date: 10-2009
Publisher: Elsevier BV
Date: 09-2019
Publisher: IOP Publishing
Date: 04-2006
Publisher: Wiley
Date: 02-1996
Publisher: Wiley
Date: 14-10-2003
DOI: 10.1002/APP.13078
Publisher: Elsevier BV
Date: 06-1984
Publisher: MDPI AG
Date: 24-02-2021
DOI: 10.3390/MI12030227
Abstract: We conducted a laser parameter study on CO2 laser induced electrical conductivity on a polyimide film. The induced electrical conductivity was found to occur dominantly at the center of the scanning line instead of uniformly across the whole line width. MicroRaman examination revealed that the conductivity was mainly a result of the multi-layers (4–5) of graphene structure induced at the laser irradiation line center. The graphene morphology at the line center appeared as thin wall porous structures together with nano level fiber structures. With sufficient energy dose per unit length and laser power, this surface modification for electrical conductivity was independent of laser pulse frequency but was instead determined by the average laser power. High electrical conductivity could be achieved by a single scan of laser beam at a sufficiently high-power level. To achieve high conductivity, it was not efficient nor effective to utilize a laser at low power but compensating it with a slower scanning speed or having multiple scans. The electrical resistance over a 10 mm scanned length decreased significantly from a few hundred Ohms to 30 Ohms when energy dose per unit length increased from 0.16 J/mm to 1.0 J/mm, i.e., the laser power increased from 5.0 W to 24 W with corresponding power density of 3.44 × 10 W/cm2 to 16.54 W/cm2 respectively at a speed of 12.5 mm/s for a single pass scan. In contrast, power below 5 W at speeds exceeding 22.5 mm/s resulted in a non-conductive open loop.
Publisher: American Chemical Society (ACS)
Date: 25-11-2004
DOI: 10.1021/LA0481290
Abstract: The effect of ionic strength on the rheological behavior of model pH-responsive nanocolloidal systems consisting of methacrylic acid-ethyl acrylate (MAA-EA) cross-linked with diallyl phthalate (DAP) was examined. Neutralization of acid groups increases the osmotic pressure exerted by counterions trapped in the polymeric network against ions in bulk solution, which is responsible for the swelling and increase in viscosity. Swelling decreases with increasing salt concentration as a result of reduced osmotic pressure inside the microgels, which is attributed to the charge shielding effect of counterions (salt) on the negatively charged carboxylate groups. Electromotive measurements using ion-selective electrodes confirmed that not all the counterions, that is, K+, remain mobile, but a fraction of these ions can penetrate the porous microgel particles to shield the negatively charged carboxylate groups. A consequence of this is that some of the Na+ counterions inside the particles are expelled, thus regaining their translational entropy, and become mobile sodium ions in the bulk solution. We successfully developed a new scaling law that relates the swelling ratio, Q, of microgels as a function of neutralization degree, alpha, cross-linked density, Nx, molar fraction of acidic units, y, and concentration of mobile counterions, CK+ and CNa+, represented as (Nx/c0)(CK+ + CNa+Q + Q2/3 proportional, variant yNxalpha. The new scaling law no longer assumes that all the counterions are trapped inside the microgels. The proportionality reduces to the form Q proportional, variant (yalphaNx)3/2 in the absence of salt, that is, CK+ + CNa+ approximately 0. By combining the results from light scattering and rheological measurements, we are able to correlate the microstructural evolution of the colloidal systems with their bulk rheological behavior.
Publisher: Springer Science and Business Media LLC
Date: 2000
Publisher: Emerald
Date: 07-2004
Publisher: Springer Science and Business Media LLC
Date: 19-10-2016
DOI: 10.1038/NPJBIOFILMS.2016.23
Abstract: Life of bacteria is governed by the physical dimensions of life in microscales, which is dominated by fast diffusion and flow at low Reynolds numbers. Microbial biofilms are structurally and functionally heterogeneous and their development is suggested to be interactively related to their microenvironments. In this study, we were guided by the challenging requirements of precise tools and engineered procedures to achieve reproducible experiments at high spatial and temporal resolutions. Here, we developed a robust precise engineering approach allowing for the quantification of real-time, high-content imaging of biofilm behaviour under well-controlled flow conditions. Through the merging of engineering and microbial ecology, we present a rigorous methodology to quantify biofilm development at resolutions of single micrometre and single minute, using a newly developed flow cell. We designed and fabricated a high-precision flow cell to create defined and reproducible flow conditions. We applied high-content confocal laser scanning microscopy and developed image quantification using a model biofilm of a defined opportunistic strain, Pseudomonas putida OUS82. We observed complex patterns in the early events of biofilm formation, which were followed by total dispersal. These patterns were closely related to the flow conditions. These biofilm behavioural phenomena were found to be highly reproducible, despite the heterogeneous nature of biofilm.
Publisher: MDPI AG
Date: 29-10-2020
DOI: 10.3390/MI11110971
Abstract: Electroosmotic flow (EOF) is fluid flow induced by an applied electric field, which has been widely employed in various micro-/nanofluidic applications. Past investigations have revealed that the presence of nanostructures in microchannel reduces EOF. Hitherto, the angle-dependent behavior of nanoline structures on EOF has not yet been studied in detail and its understanding is lacking. Numerical analyses of the effect of nanoline orientation angle θ on EOF to reveal the associated mechanisms were conducted in this investigation. When θ increases from 5° to 90° (from parallel to perpendicular to the flow direction), the average EOF velocity decreases exponentially due to the increase in distortion of the applied electric field distribution at the structured surface, as a result of the increased apparent nanolines per unit microchannel length. With increasing nanoline width W, the decrease of average EOF velocity is fairly linear, attributed to the simultaneous narrowing of nanoline ridge (high local fluid velocity region). While increasing nanoline depth D results in a monotonic decrease of the average EOF velocity. This reduction stabilizes for aspect ratio D/W 0.5 as the electric field distribution distortion within the nanoline trench remains nearly constant. This investigation reveals that the effects on EOF of nanolines, and by extrapolation for any nanostructures, may be directly attributed to their effects on the distortion of the applied electric field distribution within a microchannel.
Publisher: Wiley
Date: 19-03-2002
DOI: 10.1002/PI.889
Publisher: IOP Publishing
Date: 23-04-2010
Publisher: IEEE
Date: 04-2013
Publisher: AIP Publishing
Date: 03-2015
DOI: 10.1063/1.4917386
Abstract: Electroosmotic flow (EOF) with two or more fluids is commonly encountered in various microfluidics applications. However, no investigation has hitherto been conducted to investigate the hysteretic or flow direction-dependent behavior during the displacement flow of solutions with dissimilar ionic species. In this investigation, electroosmotic displacement flow involving dissimilar ionic solutions was studied experimentally through a current monitoring method and numerically through finite element simulations. The flow hysteresis can be characterized by the turning and displacement times turning time refers to the abrupt gradient change of current-time curve while displacement time is the time for one solution to completely displace the other solution. Both experimental and simulation results illustrate that the turning and displacement times for a particular solution pair can be directional-dependent, indicating that the flow conditions in the microchannel are not the same in the two different flow directions. The mechanics of EOF hysteresis was elucidated through the theoretical model which includes the ionic mobility of each species, a major governing parameter. Two distinct mechanics have been identified as the causes for the EOF hysteresis involving dissimilar ionic solutions: the widening/sharpening effect of interfacial region between the two solutions and the difference in ion concentration distributions (and thus average zeta potentials) in different flow directions. The outcome of this investigation contributes to the fundamental understanding of flow behavior in microfluidic systems involving solution pair with dissimilar ionic species.
Publisher: Wiley
Date: 09-08-2005
DOI: 10.1002/POLB.20557
Publisher: Wiley
Date: 08-1997
Publisher: American Chemical Society (ACS)
Date: 17-08-2007
DOI: 10.1021/AC070810U
Abstract: This study presents a new cell manipulation method using a moving dielectrophoretic force to transport or fractionate cells along a microfluidic channel. The proposed moving dielectrophoresis (mDEP) is generated by sequentially energizing a single electrode or an array of electrodes to form an electric field that moves cells continuously along the microchannel. Cell fractionation is controlled by the applied electrical frequency, and cell transportation is controlled by the interelectrode activation time. The applicability of this method was demonstrated to simultaneously fractionate and transport Saccharomyces cerevisiae yeast cells, both viable and nonviable, by operating at conditions under which the cells were subjected to positive and negative dielectrophoresis, respectively. Compared to the conventional dielectrophoresis (cDEP and traveling wave dielectrophoresis (twDEP), moving dielectrophoresis allows cells to be separated on the basis of the real part of the Clausius-Mossotti factor, as in cDEP, but yet allows the direct transportation of separated cells without using fluid flow, as in twDEP. This dielectrophoresis technique provides a new way to manipulate cells and can be readily implemented on programmable multielectrode devices.
Publisher: IOP Publishing
Date: 08-02-2016
Publisher: Elsevier BV
Date: 02-2008
Publisher: Elsevier BV
Date: 10-1991
Publisher: Springer Science and Business Media LLC
Date: 25-10-2009
Publisher: Elsevier BV
Date: 04-2010
Publisher: Wiley
Date: 22-05-2003
DOI: 10.1002/APP.12330
Publisher: MDPI AG
Date: 07-02-2019
DOI: 10.3390/MI10020110
Abstract: Viscous liquid flow in micro-channels is typically laminar because of the low Reynolds number constraint. However, by introducing elasticity into the fluids, the flow behavior could change drastically to become turbulent this elasticity can be realized by dissolving small quantities of polymer molecules into an aqueous solvent. Our recent investigation has directly visualized the extension and relaxation of these polymer molecules in an aqueous solution. This elastic-driven phenomenon is known as ‘elastic turbulence’. Hitherto, existing studies on elastic flow instability are mostly limited to single-stream flows, and a comprehensive statistical analysis of a multi-stream elastic turbulent micro-channel flow is needed to provide additional physical understanding. Here, we investigate the flow field characteristics of elastic turbulence in a 3-stream contraction-expansion micro-channel flow. By applying statistical analyses and flow visualization tools, we show that the flow field bares many similarities to that of inertia-driven turbulence. More interestingly, we observed regions with two different types of power-law dependence in the velocity power spectra at high frequencies. This is a typical characteristic of two-dimensional turbulence and has hitherto not been reported for elastic turbulent micro-channel flows.
Publisher: Wiley
Date: 06-11-2002
DOI: 10.1002/APP.11361
Publisher: Springer Science and Business Media LLC
Date: 16-12-2006
Publisher: Wiley
Date: 24-05-2006
DOI: 10.1002/APP.23565
Publisher: Elsevier BV
Date: 03-2012
Publisher: Springer Science and Business Media LLC
Date: 12-09-2015
Publisher: Elsevier BV
Date: 04-2004
Publisher: Springer Science and Business Media LLC
Date: 06-2002
Publisher: Elsevier BV
Date: 04-2004
Publisher: Wiley
Date: 11-01-2008
Publisher: Springer Science and Business Media LLC
Date: 17-05-2006
Publisher: Elsevier BV
Date: 12-1994
Publisher: IOP Publishing
Date: 04-2006
Publisher: Elsevier BV
Date: 12-1989
Publisher: ASME International
Date: 23-07-2003
DOI: 10.1115/1.1580850
Abstract: Powder injection molding is an important processing method for producing precision metallic or ceramic parts. Experience, intuition and trial-and-error have been the practice for the design and process optimization of such molding operations. However, this practice is becoming increasingly inefficient and impractical for the molding of larger, more complicated and more costly parts. In this investigation, a numerical method for simulating the mold-filling phase of powder injection molding was developed. The flow was modelled using the Hele-Shaw approach coupled with particle diffusion transport equation for the calculation of powder concentration distribution. The viscosity of the feedstock was evaluated using a power-law type rheological model to account for the viscosity dependency on shear rate and powder concentration. A numerical ex le is presented and discussed to demonstrate the capabilities and limitations of the simulation algorithm, which has the potential as an analytical tool for the mold designer. The variation of powder density distribution can be predicted, which is ignored by the existing simulation packages. Preliminary simulation indicated that powder concentration variation could be significant. Non-isothermal analysis indicated that most of the key parameters for filling process would change due to a change in powder concentration distribution.
Publisher: Trans Tech Publications, Ltd.
Date: 06-2009
DOI: 10.4028/WWW.SCIENTIFIC.NET/AMR.74.73
Abstract: Two phenomena for flows in microchannels, namely visco-elastic instability and Faradaic charging effects, are discussed. Aqueous solutions, which do not exhibit elastic behaviors, will behave visco-elastically with the addition of a small amount of polymers. Visco-elastic flow instability which promote mixing has been observed in the flow of these visco-elastic solutions through a constriction in microchannels. In addition, we recently show experimentally the existance of Faradaic charging in AC-electrokinetic (ACEK) flow. Lastly, surface roughness effects in micro- plastic injection molding are highlighted. The micro-injection molding process involves the flow of polymer melt in micro-cavities. Our recent investigations demonstrate that the flow model for macro-cavities could be employed satisfactorily to simulate the flow in micro-cavities if roughness effects are considered in an appropriate manner.
Publisher: Springer Science and Business Media LLC
Date: 03-1996
Publisher: Society of Rheology
Date: 24-06-2004
DOI: 10.1122/1.1763942
Abstract: We describe a unified semi-empirical approach for predicting the viscosity of dilute and concentrated hard and soft sphere systems. A variable specific volume, k was introduced to convert the mass concentration to effective volume fraction. With increasing particle concentration, the concentration of free counter-ions in the solution can be large enough to induce an osmotic de-swelling of soft particles, resulting in the particle shrinkage. The viscosity data for four different microgel systems at different neutralization degree showed excellent agreement with the modified Krieger–Dougherty model.
Publisher: Springer Science and Business Media LLC
Date: 13-01-2009
Publisher: Trans Tech Publications, Ltd.
Date: 06-2009
DOI: 10.4028/WWW.SCIENTIFIC.NET/AMR.74.7
Abstract: UV micro-casting is a promising mass production method for replication of polymeric microdevices due to the non-stringent process conditions and fast curing time. This paper describes a potential method to mass produce polymeric microdevices. The first generation mold for UV micro-casting was fabricated by using chemically micro-etched copper clad laminate (CCL) base substrate. Subsequently a two part silicone rubber was cast over the CCL micro-feature mold. Photosensitive resin was dispensed onto the silicone rubber mold and a transparent Mylar thin film was placed on top of the UV curable prepolymer. After the silicone rubber mold-resin-Mylar assembly was UV irradiated for tens of seconds, the crosslinked polymer, together with the Mylar film was peeled off from the mold. The cross-linked polymer was placed on top of a second layer of Mylar film dispensed with the similar UV curable resin. In this way, a complete polymeric micro device could be efficiently produced.
Publisher: AIP Publishing
Date: 29-05-2006
DOI: 10.1063/1.2206682
Abstract: We demonstrated rapid mixing of viscoelastic fluids in microchannels constructed based on polymethyl methacrylate. Viscoelastic mixing without diffusion was achieved with an effective mixing length of less than 5mm and a relatively fast flow rate. With an abrupt contraction microgeometry (8:1 contraction ratio), we mixed two different viscoelastic fluids experimentally at very low Reynolds numbers, but enormous Peclet and elasticity numbers. This special geometrical configuration triggers flow instability, leading to turbulent and efficient mixing. This flow regime has negligible inertia effects but significant elastic effects.
Publisher: Wiley
Date: 15-02-1995
Publisher: Trans Tech Publications, Ltd.
Date: 06-2009
DOI: 10.4028/WWW.SCIENTIFIC.NET/AMR.74.109
Abstract: This paper presents an experimental investigation on the DC-biased AC-electrokinetic (ACEK) flow vortex in a rectangular microchannel. This is a new flow phenomenon in AC-electrokinetics and had been successfully utilized for microfluidic mixing as reported in our previous work. The microchannel is aligned parallel to a pair of energized coplanar microelectrodes such that the generated flow vortex is perpendicular to the pressure-driven flowing s les. With the application of a DC bias AC voltage, incipient Faradaic reactions occur above the electrodes and thus producing ions and creating a net dominant flow vortex. Further investigation to understand the generation of the DC-biased ACEK flow was conducted. This is performed by direct visualization of such flow vortex formation from the cross-section of a rectangular microchannel.
Publisher: Elsevier BV
Date: 10-2003
Publisher: Springer Science and Business Media LLC
Date: 13-11-2015
DOI: 10.1038/SREP16633
Abstract: In micro-channels, the flow of viscous liquids e.g. water, is laminar due to the low Reynolds number in miniaturized dimensions. An aqueous solution becomes viscoelastic with a minute amount of polymer additives its flow behavior can become drastically different and turbulent. However, the molecules are typically invisible. Here we have developed a novel visualization technique to examine the extension and relaxation of polymer molecules at high flow velocities in a viscoelastic turbulent flow. Using high speed videography to observe the fluorescein labeled molecules, we show that viscoelastic turbulence is caused by the sporadic, non-uniform release of energy by the polymer molecules. This developed technique allows the examination of a viscoelastic liquid at the molecular level and demonstrates the inhomogeneity of viscoelastic liquids as a result of molecular aggregation. It paves the way for a deeper understanding of viscoelastic turbulence and could provide some insights on the high Weissenberg number problem. In addition, the technique may serve as a useful tool for the investigations of polymer drag reduction.
Publisher: Laser Institute of America
Date: 05-04-2019
DOI: 10.2351/1.5096074
Abstract: This study investigated the use of ultrashort femtosecond laser pulses to induce either hydrophilic or hydrophobic surfaces on polycarbonate (PC). It has been observed that controlled modification of wettability could be achieved over a wide range of the water contact angle from below 5° to above 150°. It has been shown that the pulse energy fluence and total energy deposition onto PC are the important factors in determining the laser–PC interaction and therefore the different level of wettability on PC surface. X-ray photoelectron spectroscopy-spectra measurement indicates that the modification was caused dominantly by laser induced chemical bond changes. The changes in surface morphology may not noticeably contribute to the surface wettability. The results would be useful in microfluidics chip design and fabrication with controlled surface wetting properties.
Publisher: Elsevier BV
Date: 04-2000
Publisher: American Chemical Society (ACS)
Date: 31-10-2006
DOI: 10.1021/LA061334Q
Abstract: As-fabricated deep reactive ion etched (DRIE) silicon mold with very high aspect ratio (>10) feature patterns is unsuitable for poly(dimethylsiloxane) (PDMS) replication because of the strong interaction between the Si surface and the replica and the corrugated mold sidewalls. The silicon mold can be conveniently passivated via plasma polymerization of octafluorocyclobutane (C4F8), which is also employed in the DRIE process itself, to enable the mold to be used repeatedly. To optimize the passivation conditions, we have undertaken a Box-Behnken experimental design on the basis of three passivation process parameters (plasma power, C4F8 flow rate, and deposition time). The measured responses were fluorinated film thickness, demolding status/success, demolding force, and fluorine/carbon ratio on the fifth replica surface. The optimal passivation process conditions were predicted to be an input power of 195 W, a C4F8 flow rate of 57 sccm, and a deposition time of 364 s these were verified experimentally to have high accuracy. Demolding success requires medium-deposited film thickness (66-91 nm), and the thickness of the deposited films correlated strongly with deposition time. At moderate to high ranges, increased plasma power or gas flow rate promoted polymerization over reactive etching of the film. It was also found that small quantities of the fluorinated surface were transferred from the Si mold to the PDMS at each replication, entailing progressive wear of the fluorinated layer.
Publisher: American Chemical Society (ACS)
Date: 18-06-2008
DOI: 10.1021/AC800947E
Abstract: Moving dielectrophoresis has been recently developed by the authors as an alternative method to achieve simultaneous cell fractionation and transportation. With an array of independently excitable microelectrodes, this method generates a moving electric field to sequentially fractionate and transport cells across a microchannel. Due to the peculiarity of this method, the motion of the cells is unsteady and there are interesting and distinct differences between cells experiencing positive or negative dielectrophoresis. For a proper understanding and design of a microdevice utilizing this methodology, this study presents a model for the equation of motion for a polarized cell and its unsteady motion under moving dielectrophoresis. The model considers the basic module to generate a moving electric field, where there is a finite-width top electrode and an infinite-width bottom electrode, in a parallel-plate configuration. The forces considered include dielectrophoretic force, fluid drag, buoyancy, and gravitational force. These forces are modeled as equivalent point forces acting at the center of mass of the cell. A parallel-plate wall correction factor is employed to account for the effect of the large cell size to microchannel height ratio. Various parameters are examined including the initial position of the cell relative to the electrodes, cell's Clausius-Mossotti factor, cell size, applied voltage, electrode width, interelectrode gap, microchannel height, number of energized electrodes, and types of electrode configurations. Reasonable agreements were obtained between simulated and experimental results. As the solution of the unsteady motion is rather tedious, a MATLAB algorithm, with all the associated files, for the prediction of the cell trajectory, is available on request.
Publisher: Elsevier BV
Date: 05-1999
Publisher: IEEE
Date: 2006
Publisher: IOP Publishing
Date: 06-2017
Abstract: Electroosmotic flow (EOF) is an electric-field-induced fluid flow that has numerous micro-/nanofluidic applications, ranging from pumping to chemical and biomedical analyses. Nanoscale networks/structures are often integrated in microchannels for a broad range of applications, such as electrophoretic separation of biomolecules, high reaction efficiency catalytic microreactors, and enhancement of heat transfer and sensing. Their introduction has been known to reduce EOF. Hitherto, a proper study on the effect of nanostructures orientation on EOF in a microfluidic channel is yet to be carried out. In this investigation, we present a novel fabrication method for nanostructure designs that possess maximum orientation difference, i.e. parallel versus perpendicular indented nanolines, to examine the effect of nanostructures orientation on EOF. It consists of four phases: fabrication of silicon master, creation of mold insert via electroplating, injection molding with cyclic olefin copolymer, and thermal bonding and integration of practical inlet/outlet ports. The effect of nanostructures orientation on EOF was studied experimentally by current monitoring method. The experimental results show that nanolines which are perpendicular to the microchannel reduce the EOF velocity significantly (approximately 20%). This flow velocity reduction is due to the distortion of local electric field by the perpendicular nanolines at the nanostructured surface as demonstrated by finite element simulation. In contrast, nanolines which are parallel to the microchannel have no effect on EOF, as it can be deduced that the parallel nanolines do not distort the local electric field. The outcomes of this investigation contribute to the precise control of EOF in lab-on-chip devices, and fundamental understanding of EOF in devices which utilize nanostructured surfaces for chemical and biological analyses.
Publisher: Elsevier BV
Date: 11-1998
Publisher: Elsevier BV
Date: 12-2019
Publisher: ASMEDC
Date: 2005
DOI: 10.1115/HT2005-72186
Abstract: This article presents a total concentration method for two-dimensional wet chemical etching. The proposed procedure is a fixed-grid approach. It is analogous to the enthalpy method used for modeling melting/solidification problems. The governing equation is formulated using the total concentration of the etchant. It includes the reacted and the unreacted concentrations of the etchant. The proposed governing equation includes the interface condition. The reacted concentration is used to capture the etchant-substrate interface implicitly. Since the grids are fixed, a diffusion problem remains a diffusion problem unlike the moving grid approach where the diffusion problem becomes the convection-diffusion problem due to the mesh velocity. For demonstration purposes, the finite volume method is used to solve for the transient concentration distribution of etchant. In this article, two-dimensional diffusion-controlled wet chemical etching processes are modeled. The results obtained from the proposed total concentration method are compared with available “analytic” solutions and solutions from moving-grid approach.
Publisher: Springer Science and Business Media LLC
Date: 11-12-2008
Publisher: Wiley
Date: 2008
DOI: 10.1002/PEN.20981
Publisher: Elsevier BV
Date: 12-2018
Publisher: ASMEDC
Date: 2004
Abstract: Unidirectional stratified flow of two fluids between two parallel plates is modeled using the Level-Set method. A localized mass correction term is used to ensure mass conservation at every axial cross section. The mass correction term is based on the mass flowrates. Results for various combinations of density, viscosity and mass flowrate ratios are presented. Available fully-developed exact solutions for unidirectional stratified flow are used to validate the numerical simulations. The evolutions of the interface in the developing region are also captured and compared well with “exact” solutions.
Publisher: IEEE
Date: 12-2014
Publisher: American Chemical Society (ACS)
Date: 09-08-2017
DOI: 10.1021/ACS.ANALCHEM.7B02219
Abstract: Electroosmotic flow (EOF) or electro-osmosis has been shown to exhibit a hysteresis effect under displacement flow involving two solutions with different concentrations, i.e. the flow velocity for a high-concentration solution displacing a low-concentration solution is faster than the flow velocity in the reverse direction involving the same solution pair. On the basis of our recent numerical analysis, a pH change initiated at the interface between the two solutions has been hypothesized as the cause for the observed anomalies. We report the first experimental evidence of EOF hysteresis induced by a pH change in the bulk solution. pH-sensitive dye was employed to quantify the pH changes in the microchannel during EOF. The electric-field gradient across the boundary of two solutions generates an accumulation or depletion of a minority of pH-governing ions such as hydronium (H
Publisher: IEEE
Date: 12-2014
Publisher: American Vacuum Society
Date: 05-2009
DOI: 10.1116/1.3056175
Abstract: Micropunching and laser drilling are conventional techniques for patterning microcavities as well as microvias on low temperature cofirable ceramic (LTCC) green tapes. Micro-hot-embossing is, however, an emerging and promising method for fabricating microstructures on prefired ceramic green tapes. This article presents experimental studies of influential process parameters in hot embossing for micropattern formation on LTCC green substrates. By means of dynamic mechanical thermal analysis, the impacts of process temperature and holding time on embossed profiles were studied and their correlation was discussed. When the temperature exceeds a certain range, the organic additives in the LTCC green substrates start to decompose at the isothermal condition, and this loss of organic additives increases the difficulty in embossing. Micropatterns with various dimensional scales, including microchannels, were formed on green ceramic substrates under optimal process parameters, and the patterned ceramic substrates were obtained via sintering.
Publisher: Elsevier BV
Date: 07-2004
Publisher: Elsevier BV
Date: 05-2005
Publisher: Wiley
Date: 25-02-2008
DOI: 10.1002/ADV.20118
Publisher: MDPI AG
Date: 28-08-2021
DOI: 10.3390/MI12091031
Abstract: Electroosmotic flow (EOF) involving displacement of multiple fluids is employed in micro-/nanofluidic applications. There are existing investigations on EOF hysteresis, i.e., flow direction-dependent behavior. However, none so far have studied the solution pair system of dissimilar ionic species with substantial pH difference. They exhibit complicated hysteretic phenomena. In this study, we investigate the EOF of sodium bicarbonate (NaHCO3, alkaline) and sodium chloride (NaCl, slightly acidic) solution pair via current monitoring technique. A developed slip velocity model with a modified wall condition is implemented with finite element simulations. Quantitative agreements between experimental and simulation results are obtained. Concentration evolutions of NaHCO3–NaCl follow the dissimilar anion species system. When NaCl displaces NaHCO3, EOF reduces due to the displacement of NaHCO3 with high pH (high absolute zeta potential). Consequently, NaCl is not fully displaced into the microchannel. When NaHCO3 displaces NaCl, NaHCO3 cannot displace into the microchannel as NaCl with low pH (low absolute zeta potential) produces slow EOF. These behaviors are independent of the applied electric field. However, complete displacement tends to be achieved by lowering the NaCl concentration, i.e., increasing its zeta potential. In contrast, the NaHCO3 concentration has little impact on the displacement process. These findings enhance the understanding of EOF involving solutions with dissimilar pH and ion species.
Publisher: ASME International
Date: 10-1998
DOI: 10.1115/1.2807017
Abstract: Residual stresses introduced during quenching process in aluminium gas cylinders contribute to the development of cracks. This may result in leakage or fracture of the cylinders. Finite element studies were conducted to evaluate the effect of the quenching process on through thickness inelastic strain and residual stress distributions in the neck area of the gas cylinder. The numerical modeling and experimental studies confirmed that high level of tensile residual stresses exists at the internal surface of the neck of the aluminium gas cylinders which is susceptible to cracking.
Publisher: Chinese Journal of Mechanical Engineering
Date: 2006
Publisher: Informa UK Limited
Date: 2002
Publisher: Elsevier BV
Date: 05-2000
Publisher: Elsevier BV
Date: 09-2005
Publisher: Wiley
Date: 11-2008
DOI: 10.1002/APP.27350
Publisher: Elsevier BV
Date: 12-2003
Publisher: Wiley
Date: 04-1993
Publisher: Wiley
Date: 06-2000
DOI: 10.1002/PEN.11255
Publisher: Elsevier BV
Date: 2011
Publisher: Wiley
Date: 1996
Publisher: Wiley
Date: 09-1993
Publisher: Elsevier BV
Date: 08-2007
Publisher: Wiley
Date: 23-07-2010
Abstract: Soft lithography technology allows for the development of numerous PDMS-based microfluidic devices for manipulation of particles and cells. However, integrating metallic electrodes with PDMS-based channel structures is challenging due to weak adhesion between metal and PDMS. To overcome this issue, we develop a new PDMS-based microfluidic device for continuous sorting and separation of microparticles by size using AC dielectrophoresis (DEP) with 3-D conducting PDMS composites as sidewall electrodes. The composites are synthesized by mixing silver powders with PDMS gel and such composite electrodes can easily be integrated with the PDMS microchannels. Furthermore, the sidewall electrodes also allow DEP forces to distribute three dimensionally, thus enhancing DEP effects in the entire region of channels. The capability of such PDMS-based microfluidic device is demonstrated for continuously sorting and separating 10 and 15 mum particles, and also for separating 5 from 10 mum particles. Together with experimental results, analysis of particle's trajectory based on Lagrangian approach provides insights into how microparticles transport under the effects of hydrodynamic and DEP forces in the present PDMS-based microfluidic device.
Publisher: Elsevier BV
Date: 10-2019
Publisher: Springer Science and Business Media LLC
Date: 20-11-2002
Publisher: Springer Science and Business Media LLC
Date: 03-2004
Publisher: Wiley
Date: 03-1994
Publisher: IOP Publishing
Date: 09-06-2003
Publisher: Springer Science and Business Media LLC
Date: 10-2000
Publisher: IOP Publishing
Date: 19-07-2011
Publisher: Springer Science and Business Media LLC
Date: 07-03-2009
Publisher: Elsevier BV
Date: 03-1993
Publisher: Elsevier BV
Date: 1989
Publisher: Elsevier BV
Date: 1998
Publisher: Informa UK Limited
Date: 05-2004
Publisher: Elsevier BV
Date: 10-2000
Publisher: Elsevier BV
Date: 02-2002
Publisher: Elsevier BV
Date: 12-1991
Publisher: Inderscience Publishers
Date: 2010
Publisher: ASME International
Date: 1997
DOI: 10.1115/1.2805970
Abstract: This paper presents a temperature-based method for the determination of the size of elastoplastic zones. A mathematical model describing the one-dimensional thermal problem of the propagation of a plastic zone is developed enabling the use of nonadiabatic temperature measurements in this role. Validation of the model with numerically generated temperature data has shown the proposed method to yield both accurate and robust estimates for the elastoplastic boundary. An experimental application revealed the method to be efficacious and the estimates for the elastoplastic boundary to agree well with those obtained by finite element analysis.
Publisher: Elsevier BV
Date: 04-2006
Publisher: Springer Science and Business Media LLC
Date: 08-2001
Abstract: Two-dimensional simulation of thermal debinding in powder injection molding based on mass and heat transfer in deformable porous media is proposed. The primary mechanisms of mass transport, i.e., liquid flow, gas flow, vapor diffusion, and convection, as well as the pyrolysis of polymers, and their interactions, are included in the model. The simulated results revealed that polymer removal process is primarily affected by liquid flow, which is mainly dominated by pressure-forced flow rather than capillary-driven flow. A significant phenomenon, enrichment with liquid polymer in the outer surface regions of the compact, is explained.
Publisher: Elsevier BV
Date: 07-2004
Publisher: Optica Publishing Group
Date: 02-10-2006
DOI: 10.1364/OE.14.009261
Abstract: We report our study of deposited thermal energy in silicon induced by multiple-pulse femtosecond laser irradiation. Using infrared thermography, we quantified through in situ direct measurement of temperature fields that a significant portion of laser power (two-thirds or more) was deposited into the silicon substrate instead of being reflected or carried away with the ablated material. This is believed to be the first reported study of direct in situ measurement of temperature fields as the result of deposited thermal energy from multiple femtosecond laser pulses. Our simulation results support the measured data.
Publisher: Hindawi Limited
Date: 28-02-2007
DOI: 10.1017/S0263034607070206
Abstract: With the aid of an infrared thermograph technique, we directly observed the temperature variation across a bulk copper specimen as it was being ablated by multiple femtosecond laser pulses. Combining the experimental results with simulations, we quantified the deposited thermal power into the copper specimen during the femtosecond laser ablation process. A substantial amount of thermal power (more than 50%) was deposited in the copper specimen, implying that thermal effect can be significant in femtosecond laser materials processing in spite of its ultrashort pulse duration.
Publisher: IOP Publishing
Date: 16-02-2004
Publisher: IEEE
Date: 04-2008
Publisher: Elsevier BV
Date: 07-2019
Publisher: Elsevier BV
Date: 09-2004
Publisher: American Chemical Society (ACS)
Date: 28-02-2011
DOI: 10.1021/NN103191Q
Abstract: A gecko's superb ability to adhere to surfaces is widely credited to the large attachment area of the hierarchical and fibrillar structure on its feet. The combination of these two features provides the necessary compliance for the gecko toe-pad to effectively engage a high percentage of the spatulae at each step to any kind of surface topography. With the use of multi-tiered porous anodic alumina template and capillary force assisted nanoimprinting, we have successfully fabricated a gecko-inspired hierarchical topography of branched nanopillars on a stiff polymer. We also demonstrated that the hierarchical topography improved the shear adhesion force over a topography of linear structures by 150%. A systematic analysis to understand the phenomenon was performed. It was determined that the effective stiffness of the hierarchical branched structure was lower than that of the linear structure. The reduction in effective stiffness favored a more efficient bending of the branched topography and a better compliance to a test surface, hence resulting in a higher area of residual deformation. As the area of residual deformation increased, the shear adhesion force emulated. The branched pillar topography also showed a marked increase in hydrophobicity, which is an essential property in the practical applications of these structures for good self-cleaning in dry adhesion conditions.
Publisher: IEEE
Date: 12-2007
Publisher: AIP Publishing
Date: 28-11-2012
DOI: 10.1063/1.4768667
Abstract: Viscoelastically induced flow instabilities, via a simple planar microchannel, were previously used to produce rapid mixing of two dissimilar polymeric liquids (i.e. at least a hundredfold different in shear viscosity) even at a small Reynolds number. The unique advantage of this mixing technology is that viscoelastic liquids are readily found in chemical and biological s les like organic and polymeric liquids, blood and crowded proteins s les their viscoelastic properties could be exploited. As such, an understanding of the underlying interactions will be important especially in rapid microfluidic mixing involving multiple-stream flow of complex (viscoelastic) fluids in biological assays. Here, we use the same planar device to experimentally show that the elasticity ratio (i.e. the ratio of stored elastic energy to be relaxed) between two liquids indeed plays a crucial role in the entire flow kinematics and the enhanced mixing. We demonstrate here that the polymer stretching dynamics generated in the upstream converging flow and the polymer relaxation events occurring in the downstream channel are not exclusively responsible for the transverse flow mixing, but the elasticity ratio is also equally important. The role of elasticity ratio for transverse flow instability and the associated enhanced mixing were illustrated based on experimental observations. A new parameter Deratio = Deside / Demain (i.e. the ratio of the Deborah number (De) of the sidestream to the mainstream liquids) is introduced to correlate the magnitude of energy discontinuity between the two liquids. A new Deratio-Demain operating space diagram was constructed to present the observation of the effects of both elasticity and energy discontinuity in a compact manner, and for a general classification of the states of flow development.
Publisher: Elsevier BV
Date: 05-2006
Publisher: IEEE
Date: 12-2007
Publisher: Elsevier BV
Date: 03-1994
Publisher: Elsevier BV
Date: 05-2000
Publisher: Wiley
Date: 02-2006
Abstract: Joule heating is inevitable when an electric field is applied across a conducting medium. It would impose limitations on the performance of electrokinetic microfluidic devices. This article presents a 3-D mathematical model for Joule heating and its effects on the EOF and electrophoretic transport of solutes in microfluidic channels. The governing equations were numerically solved using the finite-volume method. Experiments were carried out to investigate the Joule heating associated phenomena and to verify the numerical models. A rhodamine B-based thermometry technique was employed to measure the solution temperature distributions in microfluidic channels. The microparticle image velocimetry technique was used to measure the velocity profiles of EOF under the influence of Joule heating. The numerical solutions were compared with experimental results, and reasonable agreement was found. It is found that with the presence of Joule heating, the EOF velocity deviates from its normal "plug-like" profile. The numerical simulations show that Joule heating not only accelerates the s le transport but also distorts the shape of the s le band.
Publisher: Springer Science and Business Media LLC
Date: 18-05-2006
Publisher: Elsevier BV
Date: 09-2002
Publisher: Elsevier BV
Date: 08-2004
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 02-2006
Publisher: Wiley
Date: 21-02-2014
DOI: 10.1002/SIA.5420
Publisher: Elsevier BV
Date: 05-2000
Publisher: AIP Publishing
Date: 03-2010
DOI: 10.1063/1.3279790
Publisher: Springer Science and Business Media LLC
Date: 26-01-2019
Publisher: Springer Science and Business Media LLC
Date: 24-01-2014
Publisher: American Chemical Society (ACS)
Date: 27-07-2012
DOI: 10.1021/AC300079Q
Abstract: The study presents a dielectrophoretic cell separation method via three-dimensional (3D) nonuniform electric fields generated by employing a periodic array of discrete but locally asymmetric triangular bottom microelectrodes and a continuous top electrode. Traversing through the microelectrodes, heterogeneous cells are electrically polarized to experience different strengths of positive dielectrophoretic forces, in response to the 3D nonuniform electric fields. The cells that experience stronger positive dielectrophoresis are streamed further in the perpendicular direction to the fluid flow, leaving the cells that experience weak positive dielectrophoresis, which continue to traverse the microelectrode array essentially along the laminar flow streamlines. The proposed method has achieved 87.3% pure live cells harvesting efficiency from a live/dead NIH-3T3 cells mixture, and separation of MG-63 cells from erythrocytes with a separation efficiency of 82.8%. The demonstrated cell separation shows promising applications of the DEP separator for cell separation in a continuous mode.
Publisher: MDPI AG
Date: 28-10-2021
DOI: 10.3390/MI12111328
Abstract: The multi-foci ision of through thickness nonlinear pulse energy absorption on ultrashort pulse laser singulation of single side polished sapphire wafers has been investigated. Firstly, it disclosed the enhancement of energy absorption by the total internal reflection of the laser beam exiting from an unpolished rough surface. Secondly, by optimizing energy distribution between foci and their proximity, favorable multi-foci energy absorption was induced. Lastly, for effective nonlinear energy absorption for wafer separation, it highlighted the importance of high laser pulse energy fluence at low pulse repetition rates with optimized energy distribution, and the inadequacy of increasing energy deposition through reducing scanning speed alone. This study concluded that for effective wafer separation, despite the lower pulse energy per focus, energy should be ided over more foci with closer spatial proximity. Once the power density per pulse per focus reached a threshold in the order of 1012 W/cm2, with approximately 15 μm between two adjacent foci, wafer could be separated with foci evenly distributed over the entire wafer thickness. When the foci spacing reduced to 5 μm, wafer separation could be achieved with pulse energy concentrated only at foci distributed over only the upper or middle one-third wafer thickness.
Publisher: Elsevier BV
Date: 07-2019
Publisher: Springer Science and Business Media LLC
Date: 31-05-2008
Publisher: Elsevier BV
Date: 07-2011
Publisher: Elsevier BV
Date: 06-1993
Publisher: Springer Science and Business Media LLC
Date: 23-06-2007
Publisher: Springer Science and Business Media LLC
Date: 21-10-2016
Publisher: Trans Tech Publications, Ltd.
Date: 04-2006
DOI: 10.4028/WWW.SCIENTIFIC.NET/SSP.111.87
Abstract: The flow of a suspension system with glass microspheres in polymer EVA (Ethylene Vinyl Acetate) melts system was studied in a capillary rheometer. The slip velocity was determined by Mooney technique. A modified slip law describing the slip velocity as a function of the wall shear stress and particle concentration was proposed and employed to describe the flow behavior of the suspension system.
Publisher: Elsevier BV
Date: 09-2006
Publisher: Wiley
Date: 28-03-2008
DOI: 10.1002/APP.28079
Publisher: World Scientific Pub Co Pte Lt
Date: 04-2004
DOI: 10.1142/S0218625X04006074
Abstract: Crystalline silicon kept at atmospheric pressure was irradiated with 775 nm multiple laser pulses of 150 fs duration at repetition rate 250 Hz. The laser pulses were circularly polarized, with a peak laser fluence of 0.03 J/cm 2 . We observed surface damage at a much lower fluence and lower number of pulses compared to that reported in the literature. Surface damage, cracks and pits formation were observed. The evolution of the surface damage as a function of the number of laser pulses was recorded. The observations were in contrast to the findings in the literature that the silicon surface became structured when irradiated by multiple pulses.
Publisher: Elsevier BV
Date: 09-2007
Publisher: MDPI AG
Date: 11-05-2018
DOI: 10.3390/MI9050229
Publisher: Elsevier BV
Date: 02-2000
Publisher: Trans Tech Publications Ltd.
Date: 15-04-2006
Publisher: Springer Science and Business Media LLC
Date: 11-05-2005
Publisher: Royal Society of Chemistry (RSC)
Date: 2011
DOI: 10.1039/C1LC20495E
Abstract: This paper studies the principles of fluid flow manipulation based on DC-biased AC-electrokinetics. This method makes use of planar parallel electrodes in a microfluidic channel in contact with an electrolyte solution, with a DC biased AC electrical signal applied to the electrode pair. Due to the application of DC bias, incipient Faradaic electrolytic reactions take place resulting in an increase of the ionic content of the bulk solution. The ionic content was found to be dissimilar at the cathodic and anodic sides of the channel and a conductivity difference of approximately 10% was measured for 2 V(DC). Fluid flow is generated by the action of the DC biased AC electric signal acting on the transverse conductivity gradient generated across the microchannel. The induced flow in the form of vortex was characterized experimentally and the results substantiated theoretically. The velocity of the induced flow vortex under the employed experimental conditions was ~600 to 700 μm s(-1) which is faster than those obtained in conventional AC-electroosmosis and AC-electrothermal types of flows.
Publisher: Iron and Steel Institute of Japan
Date: 1996
Publisher: IOP Publishing
Date: 28-04-2009
Publisher: Springer Science and Business Media LLC
Date: 03-2003
Publisher: Elsevier BV
Date: 10-1991
Publisher: Elsevier BV
Date: 12-1994
Publisher: Elsevier BV
Date: 2009
Publisher: Elsevier BV
Date: 02-2002
Publisher: Elsevier BV
Date: 08-2010
Publisher: IOP Publishing
Date: 24-09-2014
Publisher: World Scientific Pub Co Pte Lt
Date: 08-2005
DOI: 10.1142/S0219581X05003462
Abstract: UV embossing for polymeric micro-patterning thin film is an emerging replication technique. This paper investigates UV curable multifunctional acrylates pre-polymer resin patterned by a micro-structured mold and subsequently cured by UV irradiation. To further enhance this duplication method for high aspect ratio production, demolding must be reliable and repeatable without damage to the embossing or mold. Previously, it has been reported that UV embossed patterns for aspect ratios as high as 14 have been achieved experimentally. Finite element analyses for patterns with aspect ratios of 5 using parallel demolding between two parallel plates have also been reported. However, the parallel demolding method may not be suitable for large area patterns as forces generated were high. As such, an alternative demolding method, namely peel demolding, for micro-patterns with an aspect ratio of 14 was investigated and key parameters identified. The parameters governing the demolding process were the peel angle, the pre-crack condition, shrinkage, interface fracture toughness, tensile strength and modulus of polymer. A pre-crack between the polymer and mold was introduced before peel demolding. Numerical analyses in terms of Cohesive Zone Modeling (CZM) were used to simulate the demolding process. Shrinkage caused by UV exposure was represented by thermal strain effects and the fully cured polymer was peeled off using displacement control. The ultimate tensile strength (U.T.S) of the cured polymer was used as a failure criterion. The stresses involved were crucial for determining clean demolding. As peeling progressed, stresses experienced in the polymer matrix increased rapidly in the region ahead of the crack with little or no stress at the cracked region. When stresses experienced by the polymer were below the U.T.S, demolding was deemed to be successful.
Publisher: Springer Science and Business Media LLC
Date: 12-2012
Publisher: Elsevier BV
Date: 1993
Publisher: Springer Science and Business Media LLC
Date: 2001
Publisher: Wiley
Date: 04-12-2019
Abstract: Microarrays are widely used in high-throughput analysis of DNA, protein, and small molecules. However, the majority of microarray assays need improved assay speed and sensitivity due to the slow molecular diffusion from bulk solutions to probe surfaces. Here, a new class of magnetic nanomixers in DNA and protein microarray assays is reported to eliminate the diffusion constraint through dynamic mixing. It is demonstrated that the dynamic nanomixers can improve the assay kinetics at least by a factor of 4 and 2 for DNA and protein microarray assays, respectively. By using the dynamic nanomixers, the sensitivities of detecting Escherichia coli O157:H7 DNA and prostate specific antigen increase by more than four-fold. The dynamic mixing also greatly reduces the spot-to-spot variation to below 10% across a broad concentration range, providing more accurate assay results. In comparison with existing methods, this magnetic nanomixer-based approach offers rapid turnaround, improved sensitivity, good accuracy, low cost, simple operation, and excellent compatibility with commercial microarrays.
Publisher: Elsevier BV
Date: 1993
Publisher: Elsevier BV
Date: 10-2011
Publisher: Elsevier BV
Date: 1991
Publisher: Elsevier BV
Date: 10-2010
Publisher: SAGE Publications
Date: 02-2007
Abstract: Although edge-wave and centre-buckles in rolled strip are believed to be largely self-equilibrated, the result of residual stress, formation of herringbone and quarter-buckles in hot- or cold-rolled strip is believed to require application of external stress. It is verified here that stress distributions such as those indicated by Roberts are possible causes of quarter-buckling and herringbone buckling. Quarter-buckling is believed to result from stress in the sheet or strip produced by non-parabolic bending of the work rolls. Herringbone buckling is attributed to local regions of axial tension and compression in the transverse stress distribution, caused by misalignment, which effectively produces a shear in the sheet that may manifest itself in diagonal buckling.
Publisher: Wiley
Date: 10-12-2003
DOI: 10.1002/POLB.10599
Publisher: IOP Publishing
Date: 27-01-2009
Publisher: SPIE
Date: 21-01-2006
DOI: 10.1117/12.645917
Publisher: ASMEDC
Date: 2008
Abstract: In this paper, we report numerical and experimental studies of the Joule heating-induced heat transfer in fabricated T-shape microfluidic channels. We have developed comprehensive 3D mathematical models describing the temperature development due to Joule heating and its effects on electrokinetic flow. The models consist of a set of governing equations including the Poisson-Boltzmann equation for the electric double layer potential profiles, the Laplace equation for the applied electric field, the modified Navier-Stokes equations for the electrokinetic flow field, and the energy equations for the Joule heating induced conjugated temperature distributions in both the liquid and the channel walls. Specifically, the Joule number is introduced to characterize Joule heating, to account for the effects of the electric field strength, electrolyte concentration, channel dimension, and heat transfer coefficient outside channel surface. As the thermophysical and electrical properties including the liquid dielectric constant, viscosity and electric conductivity are temperature-dependent, these governing equations are strongly coupled. We therefore have used the finite volume based CFD method to numerically solve the coupled governing equations. The numerical simulations show that the Joule heating effect is more significant for the microfluidic system with a larger Joule number and/or a lower thermal conductivity of substrates. It is found that the presence of Joule heating makes the electroosmotic flow deviate from its normal “plug-like” profiles, and cause different mixing characteristics. The T-shape microfluidic channels were fabricated using rapid prototyping techniques, including the Photolithography technique for the master fabrication and the Soft Lithography technique for the channel replication. A rhodamine B based thermometry technique, was used for direct “in-channel” measurements of liquid solution temperature distributions in microfluidic channels, fabricated by the PDMS/PDMS and Glass/PDMS substrates. The experimental results were compared with the numerical simulations, and reasonable agreement was found.
Publisher: Elsevier BV
Date: 10-2019
Publisher: Elsevier BV
Date: 2005
Publisher: Wiley
Date: 17-07-2008
Publisher: Informa UK Limited
Date: 23-02-2005
Publisher: Wiley
Date: 06-02-2002
DOI: 10.1002/APP.10308
Publisher: Wiley
Date: 23-12-2002
DOI: 10.1002/APP.11513
Publisher: Springer Science and Business Media LLC
Date: 03-06-2011
Publisher: IOP Publishing
Date: 13-08-2008
Publisher: Society of Rheology
Date: 05-2003
DOI: 10.1122/1.1566035
No related grants have been discovered for Yee Cheong Lam.