Chemical Engineering Faculty Publications Copyright (c) 2013 University of Rhode Island All rights reserved. http://digitalcommons.uri.edu/che_facpubs Recent documents in Chemical Engineering Faculty Publications en-us Wed, 24 Apr 2013 12:02:21 PDT 3600 Two-Element Dielectric Antenna Serially Excited by Optical Wavelength Multiplexing http://digitalcommons.uri.edu/che_facpubs/24 http://digitalcommons.uri.edu/che_facpubs/24 Wed, 20 Feb 2013 13:20:27 PST A single pulsed laser beam containing multiple wavelengths (wavelength multiplexing) is employed to activate two semiconductor antennas in series. The dielectric nature of the semiconductors permits serial cascading of the antenna elements. Recently observed nonlinear characteristics of the radiated f ield as a function of the free carrier accelerating (bias) voltage are used to minimize the small interactions between elements. We demonstrate that the temporal electromagnetic radiation distribution of two serial antennas is sensitive to the three-dimensional pattern of the optical excitation source. One can, in turn, vary this distribution continuously by optical means to reconfigure the array. ã 1999 Optical Society of America OCIS codes: 160.5140, 260.5150, 140.0140, 060.4230, 350.4010.

]]> Everett E. Crisman et al. Numerical investigation of boundary conditions for moving contact line problems http://digitalcommons.uri.edu/che_facpubs/19 http://digitalcommons.uri.edu/che_facpubs/19 Fri, 15 Feb 2013 13:35:23 PST When boundary conditions arising from the usual hydrodynamic assumptions are applied, analyses of dynamic wetting processes lead to a well-known nonintegrable stress singularity at the dynamic contact line, necessitating new ways to model this problem. In this paper, numerical simulations for a set of representative problems are used to explore the possibility of providing material boundary conditions for predictive models of inertialess moving contact line processes. The calculations reveal that up to Capillary number Ca=0.15, the velocity along an arc of radius 10Li (Li is an inner, microscopic length scale)from the dynamic contact line is independent of the macroscopic length scale a for a>103Li , and compares well to the leading order analytical ‘‘modulated-wedge’’ flow field [R. G. Cox, J. Fluid Mech. 168, 169 (1986)] for Capillary number Ca168, 169 (1986)] is used as a boundary condition along an arc of radius R =10-2a from the dynamic contact line, agree well with those using two inner slip models for Ca2000 American Institute of Physics.@ [S1070-6631~00!00402-5]

]]> Sandesh Somalinga et al. Hydrophobic silver nanoparticles trapped in lipid bilayers: Size distribution, bilayer phase behavior, and optical properties http://digitalcommons.uri.edu/che_facpubs/18 http://digitalcommons.uri.edu/che_facpubs/18 Mon, 04 Feb 2013 09:39:05 PST Background: Lipid-based dispersion of nanoparticles provides a biologically inspired route to designing therapeutic agents and a means of reducing nanoparticle toxicity. Little is currently known on how the presence of nanoparticles influences lipid vesicle stability and bilayer phase behavior. In this work, the formation of aqueous lipid/nanoparticle assemblies (LNAs) consisting of hydrophobic silver-decanethiol particles (5.7 ± 1.8 nm) embedded within 1,2-dipalmitoyl-sn-glycero-3- phosphocholine (DPPC) bilayers is demonstrated as a function of the DPPC/Ag nanoparticle (AgNP) ratio. The effect of nanoparticle loading on the size distribution, bilayer phase behavior, and bilayer fluidity is determined. Concomitantly, the effect of bilayer incorporation on the optical properties of the AgNPs is also examined.

Results: The dispersions were stable at 50°C where the bilayers existed in a liquid crystalline state, but phase separated at 25°C where the bilayers were in a gel state, consistent with vesicle aggregation below the lipid melting temperature. Formation of bilayer-embedded nanoparticles was confirmed by differential scanning calorimetry and fluorescence anisotropy, where increasing nanoparticle concentration suppressed the lipid pretransition temperature, reduced the melting temperature, and disrupted gel phase bilayers. The characteristic surface plasmon resonance (SPR) wavelength of the embedded nanoparticles was independent of the bilayer phase; however, the SPR absorbance was dependent on vesicle aggregation.

Conclusion: These results suggest that lipid bilayers can distort to accommodate large hydrophobic nanoparticles, relative to the thickness of the bilayer, and may provide insight into nanoparticle/biomembrane interactions and the design of multifunctional liposomal carriers.

]]> Geoffrey D. Bothun Surface etching of YBCO films by xenon difluoride http://digitalcommons.uri.edu/che_facpubs/17 http://digitalcommons.uri.edu/che_facpubs/17 Mon, 04 Feb 2013 09:33:18 PST We have demonstrated that xenon difluoride (XeF2) etches thin films of YBa2Cu3O7−x, the superconducting form of yttrium–barium–copper–oxide (YBCO), during dry etch processing. Both c-axis and mixed a/c-axis YBCO films show evidence of such etching with a axis being more reactive. Profiles of YBCO films examined by ESCA show that the surfaces of both etched and unetched films are barium rich at the expense of yttrium. After XeF2 etching, fluorine was found to be present to a depth of at least 40 nm. Despite the etching and the presence of fluorine in the YBCO films, the superconducting transition temperature, Tc, was unaffected by the XeF2 treatment. © 2005 American Vacuum Society. [DOI: 10.1116/1.1978894]

]]> Benjamin L. Crossley et al. Large Pyroelectric Response from Reactively Sputtered Aluminum Nitride Thin Films http://digitalcommons.uri.edu/che_facpubs/16 http://digitalcommons.uri.edu/che_facpubs/16 Mon, 04 Feb 2013 09:19:53 PST We report the pyroelectric response of c-axis oriented, undoped, wurtzite, aluminum nitride reactively sputtered onto polished silicon wafers. The voltage between a metallic contact on the AlN surface and the n+-doped silicon substrate was monitored during pulsed infrared, radiant heating. From analysis of the data, a pyroelectric voltage coefficient, PV, in excess of 0.5 􏰆 106 V/m/K was extracted for films in the 600 to 2500 Å thickness range.

]]> Everett E. Crisman et al. A Multiscale Gibbs-Helmholtz Constrained Cubic Equation of State http://digitalcommons.uri.edu/che_facpubs/15 http://digitalcommons.uri.edu/che_facpubs/15 Mon, 09 Jul 2012 06:13:48 PDT This paper presents a radically new approach to cubic equations of state (EOS) in which the Gibbs-Helmholtz equation is used to constrain the attraction or energy parameter, a. The resulting expressions for a(T, p) for pure components and a(T, p, x) for mixtures contain internal energy departure functions and completely avoid the need to use empirical expressions like the Soave alpha function. Our approach also provides a novel and thermodynamically rigorous mixing rule for a(T, p, x).When the internal energy departure function is computed using Monte Carlo or molecular dynamics simulations as a function of current bulk phase conditions, the resulting EOS is a multiscale equation of state. The proposed new Gibbs-Helmholtz constrained (GHC) cubic equation of state is used to predict liquid densities at high pressure and validated using experimental data from literature. Numerical results clearly show that the GHC EOS provides fast and accurate computation of liquid densities at high pressure, which are needed in the determination of gas hydrate equilibria.

]]> Angelo Lucia Engineering Fabrication of High-Conductivity, Transparent Electrodes with Trenched Metal Bus Lines http://digitalcommons.uri.edu/che_facpubs/14 http://digitalcommons.uri.edu/che_facpubs/14 Mon, 09 Jul 2012 04:08:23 PDT A novel transparent electrode system has been developed for thin film electroluminescent displays in which the poor conductivity of the indium-tin-oxide (ITO) electrodes has been augmented by high-conductivity buses of thick aluminum or silver. The augmented electrode system consists of patterned ITO electrodes, 200 Fm wide, centered over narrow aluminum or silver lines 40 ~m wide and separated by an intermediate diffusion barrier film of titanium to promote adhesion to the ITO and prevent blackening of the main ITO electrode by interfacial reactions. The sheet resistances of the augmented ITO electrodes (A1-Ti-ITO and Ti-Ag-Ti-ITO) were lowered by two orders of magnitude relative to the unaugmented ITO electrodes, yielding absolute values on the order of 0.1 ~/s.

]]> Otto J. Gregory et al. Piezoresistive Properties of ITO Strain Sensors Prepared with Controlled Nanoporosity http://digitalcommons.uri.edu/che_facpubs/13 http://digitalcommons.uri.edu/che_facpubs/13 Mon, 09 Jul 2012 03:57:13 PDT A ceramic strain gage based on reactively sputtered indium-tinoxide (ITO) thin films is being developed to monitor the structural integrity of components employed in aerospace propulsion systems operating at temperatures in excess of 1500°C. The hightemperature stability and piezoresistive properties depend to a large extent on the thickness of the active ITO strain elements comprising these ceramic strain gages. Scanning electron microscopy of the thick ITO sensors revealed a partially sintered microstructure consisting of a contiguous network of submicrometer ITO particles with well-defined necks and isolated nanoporosity. It appeared that densification of the ITO particles was retarded during high-temperature exposure with nitrogen playing a key role in stabilizing the nanoporosity. Based on these preliminary results, ITO strain sensors were also prepared by reactive sputtering in various nitrogen/oxygen/argon partial pressures to incorporate more nitrogen into the films. Under these conditions, sintering and densification of the ITO particles containing these nitrogen-rich grain boundaries was retarded and a contiguous network of nanosized ITO particles was established. The influence of nitrogen in the sputtered and annealed ITO films on the microstructure and the high-temperature piezoresistive properties was investigated, and the results are presented in this paper. © 2004 The Electrochemical Society. [DOI: 10.1149/1.1767839] All rights reserved.

]]> Otto J. Gregory et al. Engineering Thermoelectric Properties of ZnxInyOx+1.5y Films http://digitalcommons.uri.edu/che_facpubs/12 http://digitalcommons.uri.edu/che_facpubs/12 Mon, 09 Jul 2012 03:52:06 PDT Ceramic thin film thermocouples are being developed to replace noble metal thermocouples operating within the harsh environments of advanced turbine engines used for power generation and propulsion. Seebeck coefficients as large as 158 V/°C were determined for indium oxide (In2O3) at 950°C and 256 V/°C for zinc oxide ZnO at 1250°C relative to platinum reference electrodes. Because these Seebeck coefficients are appreciably larger than those for metallic thermocouples, alloys in the system indium zinc oxide ZnxInyOx+1.5y were investigated by cosputtering from high purity ZnO and In2O3 targets. Thermocouple libraries were patterned with platinum reference electrodes and rapidly screened using combinatorial chemistry techniques. Thermoelectric response, power, and resistivity were determined for each thermocouple in the library. Thermocouples with the optimum compositions were prepared and the resulting power factor of the biceramic junctions was determined from 75 to 650°C. © 2010 The Electrochemical Society. DOI: 10.1149/1.3518412 All rights reserved.

]]> Otto J. Gregory et al. Engineering Transition From Unilamellar to Bilameller Vesicles Induced by an Amphiphilic Biopolymer http://digitalcommons.uri.edu/che_facpubs/11 http://digitalcommons.uri.edu/che_facpubs/11 Mon, 09 Jul 2012 03:38:58 PDT We report some unusual structural transitions upon the addition of an amphiphilic biopolymer to unilamellar surfactant vesicles. The polymer is a hydrophobically modified chitosan and it embeds its hydrophobes in vesicle bilayers. We study vesicle-polymer mixtures using small-angle neutron scattering (SANS) and cryotransmission electron microscopy (cryo-TEM). When low amounts of the polymer are added to unilamellar vesicles of ca. 120 nm diameter, the vesicle size decreases by about 50%. Upon further addition of polymer, lamellar peaks are observed in the SANS spectra at high scattering vectors. We show that these spectra correspond to a co-existence of unilamellar and bilamellar vesicles. The transition to bilamellar vesicles as well as the changes in unilamellar vesicle size are further confirmed by cryo-TEM. A mechanism for the polymer-induced transitions in vesicle morphology is proposed.

]]> Jae-Ho Lee et al. Engineering Thermoelectric Power Factor of In2O3:Pd Nanocomposite Films. http://digitalcommons.uri.edu/che_facpubs/10 http://digitalcommons.uri.edu/che_facpubs/10 Mon, 09 Jul 2012 03:34:19 PDT A nanocomposite exhibiting large thermoelectric powers and capable of operating at temperatures as high as 1100 C in air was fabricated by embedding palladium nanoparticles into an indium oxide matrix via co-sputtering from metal and ceramic targets. Combinatorial chemistry techniques were used to systematically investigate the effect of palladium content in these nanocomposite films on thermoelectric response. Based on these rapid screening experiments, the thermoelectric properties of the most promising nanocomposites were evaluated as a function of post-deposition heat treatment at high temperatures. An n-type nanocomposite film was developed exhibiting a power factor of 4.5 10 4 W/m K2 at 1000 C in air. VC 2011 American Institute of Physics. [doi:10.1063/1.3607289]

]]> Otto J. Gregory et al. Engineering Relaxation Time, Diffusion, and Viscosity Analysis of Model Asphalt Systems Using Molecular Simulation http://digitalcommons.uri.edu/che_facpubs/9 http://digitalcommons.uri.edu/che_facpubs/9 Mon, 09 Jul 2012 03:30:13 PDT Molecular dynamics simulation was used to calculate rotational relaxation time, diffusion coefficient, and zero-shear viscosity for a pure aromatic compound naphthalene and for aromatic and aliphatic components in model asphalt systems over a temperature range of 298–443 K. The model asphalt systems were chosen previously to represent real asphalt. Green–Kubo and Einstein methods were used to estimate viscosity at high temperature 443.15 K. Rotational relaxation times were calculated by nonlinear regression of orientation correlation functions to a modified Kohlrausch–Williams–Watts function. The Vogel–Fulcher–Tammann equation was used to analyze the temperature dependences of relaxation time, viscosity, and diffusion coefficient. The temperature dependences of viscosity and relaxation time were related using the Debye–Stokes–Einstein equation, enabling viscosity at low temperatures of two model asphalt systems to be estimated from high temperature 443.15 K viscosity and temperature-dependent relaxation time results. Semiquantitative accuracy of such an equivalent temperature dependence was found for naphthalene. Diffusion coefficient showed a much smaller temperature dependence for all components in the model asphalt systems. Dimethylnaphthalene diffused the fastest while asphaltene molecules diffused the slowest. Neat naphthalene diffused faster than any component in model asphalts. © 2007 American Institute of Physics. DOI: 10.1063/1.2799189

]]> Liqun Zhang et al. Engineering Rotational Relaxation Times of Individual Compounds With Simulations of Molecular Asphalt Models http://digitalcommons.uri.edu/che_facpubs/8 http://digitalcommons.uri.edu/che_facpubs/8 Mon, 09 Jul 2012 03:27:05 PDT The dynamical properties of a complex system incorporate contributions from the diverse components from which it is constituted. To study this relationship in a multicomponent system, relaxation times based on rotation autocorrelation functions in molecular dynamics simulations were analyzed for molecules in two sets of unmodified and polymer-modified model asphalt/bitumen systems over 298–473 K. The model asphalt systems were proposed previously to approximate the chemical and mechanical properties of real asphalts. Relaxations were modeled using a modified Kaulrausch–Williams–Watts function and were based on the third Legendre polynomial of normal vector time correlation functions for aromatic species asphaltene, polar aromatic, naphthene aromatic. Both the end-to-end vector and the longest axis eigenvector of the radius of gyration matrix were used for time correlation functions of chain molecules C22, polystyrene. Decreases in temperature induced large increases in relaxation time consistent with the Vogel–Fulcher–Tammann equation. The presence of a polymer slowed the decay of each correlation function to some extent. The product of relaxation time and diffusion coefficient revealed qualitative differences between larger and smaller molecules in the same system. These relaxation mechanisms remained coupled for small molecules, while the larger asphaltene and polymer molecules revealed significant slowdowns in rotation compared to translational diffusion at lower temperatures. Smaller values of the stretched exponential parameter for asphaltenes compared to smaller molecules suggested a broader range of relaxation times and were consistent with this distinction. Difficulties in converging polymer chain relaxation times are discussed in terms of fluctuations in the magnitude and orientation of the end-to-end vector and chain axis eigenvector. Viscosity results suggested by the Debye–Stokes–Einstein relationship are consistent with trends shown in the literature for true bitumen systems. © 2010 American Institute of Physics. doi:10.1063/1.3416913

]]> Liqun Zhang et al. Engineering Investigation of Wetting Hydrodynamics Using Numerical Simulations http://digitalcommons.uri.edu/che_facpubs/7 http://digitalcommons.uri.edu/che_facpubs/7 Fri, 06 Jul 2012 13:24:33 PDT We report some unusual structural transitions upon the addition of an amphiphilic biopolymer to unilamellar surfactant vesicles. The polymer is a hydrophobically modified chitosan and it embeds its hydrophobes in vesicle bilayers. We study vesicle-polymer mixtures using small-angle neutron scattering (SANS) and cryotransmission electron microscopy (cryo-TEM). When low amounts of the polymer are added to unilamellar vesicles of ca. 120 nm diameter, the vesicle size decreases by about 50%. Upon further addition of polymer, lamellar peaks are observed in the SANS spectra at high scattering vectors. We show that these spectra correspond to a co-existence of unilamellar and bilamellar vesicles. The transition to bilamellar vesicles as well as the changes in unilamellar vesicle size are further confirmed by cryo-TEM. A mechanism for the polymer-induced transitions in vesicle morphology is proposed.

]]> David E. Finlow et al. Engineering Numerical Investigation of Boundary Conditions for Moving Contact Line Problems http://digitalcommons.uri.edu/che_facpubs/6 http://digitalcommons.uri.edu/che_facpubs/6 Fri, 06 Jul 2012 13:17:49 PDT When boundary conditions arising from the usual hydrodynamic assumptions are applied, analyses of dynamic wetting processes lead to a well-known nonintegrable stress singularity at the dynamic contact line, necessitating new ways to model this problem. In this paper, numerical simulations for a set of representative problems are used to explore the possibility of providing material boundary conditions for predictive models of inertialess moving contact line processes. The calculations reveal that up to Capillary number Ca50.15, the velocity along an arc of radius 10Li (Li is an inner, microscopic length scale! from the dynamic contact line is independent of the macroscopic length scale a for a.103Li , and compares well to the leading order analytical ‘‘modulated-wedge’’ flow field [R. G. Cox, J. Fluid Mech. 168, 169 (1986)] for Capillary number Ca,0.1. Systematic deviations between the numerical and analytical velocity field occur for 0.1,Ca,0.15, caused by the inadequacy of the leading order analytical solution over this range of Ca. Meniscus shapes produced from calculations in a truncated domain, where the modulated-wedge velocity field [R. G. Cox, J. Fluid Mech. 168, 169 (1986)] is used as a boundary condition along an arc of radius R 51022a from the dynamic contact line, agree well with those using two inner slip models for Ca

]]> Sandesh Somalinga et al. Engineering Synthesis of Aluminum Hydroxide Nanoparticles in Spontaneously Generated Vesicles http://digitalcommons.uri.edu/che_facpubs/5 http://digitalcommons.uri.edu/che_facpubs/5 Fri, 06 Jul 2012 12:56:37 PDT Sessile drops of aqueous electrolyte as well as cationic and anionic surfactant solutions are placed on the lower plate of a stainless steel parallel plate capacitor and the variation of static advanced contact angles with the field strength between the plates is monitored. Even at field strengths where changes in electrical body forces are negligible, these drops spreads outward, irreversibly, in response to variations in the externally applied potential gradient. Contact angles always decrease, regardless of the polarity of the applied electric field. However, the magnitude of the change is sensitive to both the polarity and strength of the field. These angles relax over time scales that are an order of magnitude higher than that predicted by diffusional resistance alone. The variation in solution surface tension in response to the externally applied electric field has been obtained experimentally from the drop shapes. For both ionic surfactant and simple electrolyte solutions, the surface tension always decreases as the electric field is increased, regardless of its polarity. For sessile drops placed on a stainless steel plate having a passivating oxide layer, reductions in both the liquid-vapour and solidliquid interfacial energy must occur to account for the observed changes in contact angle (provided Young's equation is assumed to be valid). However, for drops place on platinum coated stainless steel plates, the changes in contact angles are entirely accounted for by changes in surface tension only, implying that the solid-liquid interfacial energy does not vary with the external field.

]]> Iskandar I. Yaacob et al. Engineering Large Scale Isolation of Expression Vector Cassette by Magnetic Triple Helix Affinity Capture http://digitalcommons.uri.edu/che_facpubs/4 http://digitalcommons.uri.edu/che_facpubs/4 Fri, 06 Jul 2012 12:48:13 PDT Srinivas V. Sonti et al. Engineering A Simple Extrusion Method for the Synthesis of Aligned Silica Nanowires Using the Template of a Rigid Surface Mesophase http://digitalcommons.uri.edu/che_facpubs/3 http://digitalcommons.uri.edu/che_facpubs/3 Fri, 06 Jul 2012 12:42:36 PDT Long range alignment of silica nanowires has been accomplished by extrusion of a novel surfactant mesophase prior to silica synthesis.

]]> Limin Liu et al. Engineering Mesophase Separation and Probe Dynamics in Protein-Polyelectrolyte Coacervates http://digitalcommons.uri.edu/che_facpubs/2 http://digitalcommons.uri.edu/che_facpubs/2 Fri, 06 Jul 2012 08:48:47 PDT Protein–polyelectrolyte coacervates are self-assembling macroscopically monophasic biomacromolecular fluids whose unique properties arise from transient heterogeneities. The structures of coacervates formed at different conditions of pH and ionic strength from poly(dimethyldiallylammonium chloride) and bovine serum albumin (BSA), were probed using fluorescence recovery after photobleaching. Measurements of self-diffusion in coacervates were carried out using fluorescein-tagged BSA, and similarly tagged Ficoll, a non-interacting branched polysaccharide with the same size as BSA. The results are best explained by temporal and spatial heterogeneities, also inferred from static light scattering and cryo-TEM, which indicate heterogeneous scattering centers of several hundred nm. Taken together with previous dynamic light scattering and rheology studies, the results are consistent with the presence of extensive dilute domains in which are embedded partially interconnected 50–700 nm dense domains. At short length scales, protein mobility is unobstructed by these clusters. At intermediate length scales, proteins are slowed down due to tortuosity effects within the blind alleys of the dense domains, and to adsorption at dense/dilute domain interfaces. Finally, at long length scales, obstructed diffusion is alleviated by the break-up of dense domains. These findings are discussed in terms of previously suggested models for protein–polyelectrolyte coacervates. Possible explanations for the origin of mesophase separation are offered.

]]> A. Basak Kayitmazer et al. Engineering Hydration Repulsion Effects of the Formation of Supported Lipid Bylayers http://digitalcommons.uri.edu/che_facpubs/1 http://digitalcommons.uri.edu/che_facpubs/1 Thu, 05 Jul 2012 09:35:03 PDT When zwitterionic lipids fuse onto substrates such as silica (SiO2), the water of hydration between the two approaching surfaces must be removed, giving rise to an effective hydration repulsion. Removal of water around the polar headgroups of the lipid and the silanols (SiOH) of SiO2 allows supported lipid bilayer (SLB) formation, although an interstitial water layer remains between the lipid and surface. The importance of hydration repulsion in SLB formation is demonstrated by monitoring fusion of zwitterionic lipids onto silica (SiO2) nanoparticles heat treated to control the silanol group (SiOH) density and thus the amount of bound water. SLB formation, observed by cryo-TEM and nanodifferential scanning calorimetry, was found to be slower for the more hydrated surfaces. Although the SiOH density decreased with increasing heat treatment temperature, z-potentials were the same for all the SiO2. This arose since at the pH ¼ 8 of the experiments, only isolated silanols, with a pKa ¼ 4.9, and not hydrogen bonded silanols, with a pKa ¼ 8.5, were dissociated/charged.1 Since there were no differences in double layer forces between the SUVs and SiO2, which are the largest and most important interactions determining lipid fusion onto surfaces,2,3 the slower rate of SLB formation of DMPC onto SiO2 nanoparticles with higher silanol densities and more bound water was therefore attributed to greater hydration repulsion of the more hydrated nanoparticles. For SiO2 heated to 1000 C, with only a few isolated silanols, little adsorbed water and many hydrophobic Si–O–Si groups, particle aggregation occurred and lipid sheaths formed around the nanoparticle aggregates.

]]> Selver Ahmed et al. Engineering