Open Access. Powered by Scholars. Published by Universities.®
- Discipline
-
- Polymer Science (159)
- Other Chemical Engineering (58)
- Biochemical and Biomolecular Engineering (54)
- Materials Science and Engineering (34)
- Polymer and Organic Materials (19)
-
- Physical Sciences and Mathematics (15)
- Catalysis and Reaction Engineering (13)
- Thermodynamics (13)
- Biomedical Engineering and Bioengineering (11)
- Chemistry (11)
- Transport Phenomena (11)
- Membrane Science (10)
- Life Sciences (9)
- Mechanical Engineering (9)
- Electrical and Computer Engineering (8)
- Other Materials Science and Engineering (8)
- Medicine and Health Sciences (7)
- Aerospace Engineering (5)
- Civil and Environmental Engineering (5)
- Complex Fluids (5)
- Polymer Chemistry (5)
- Biomaterials (4)
- Biotechnology (4)
- Chemicals and Drugs (4)
- Engineering Science and Materials (4)
- Heat Transfer, Combustion (4)
- Materials Chemistry (4)
- Process Control and Systems (4)
- Keyword
-
- Corrosion (19)
- Polymer (13)
- Electrospinning (11)
- 1 (9)
- Filtration (8)
-
- Polymers (8)
- Nanoparticles (7)
- Water (6)
- Electrochemistry (5)
- Surfactants (5)
- 3D printing (4)
- APTES (4)
- Coatings (4)
- Hydrogels (4)
- PVME (4)
- Polymer Blends (4)
- Recycling (4)
- Sustainability (4)
- 3D Printing (3)
- Absorption (3)
- Additive Manufacturing (3)
- Aluminum (3)
- Bacteria (3)
- Concrete (3)
- Contact angle (3)
- Crystallisation (3)
- Inhibitor (3)
- Magnesium (3)
- Membrane (3)
- PET (3)
- Publication Year
- Publication
- Publication Type
Articles 241 - 270 of 289
Full-Text Articles in Chemical Engineering
Designing A Nanotube Using Naturally Occurring Protein Building Blocks, Jie Zheng
Designing A Nanotube Using Naturally Occurring Protein Building Blocks, Jie Zheng
Chemical, Biomolecular, and Corrosion Engineering Faculty Research
Here our goal is to carry out nanotube design using naturally occurring protein building blocks. Inspection of the protein structural database reveals the richness of the conformations of proteins, their parts, and their chemistry. Given target functional protein nanotube geometry, our strategy involves scanning a library of candidate building blocks, combinatorially assembling them into the shape and testing its stability. Since self-assembly takes place on time scales not affordable for computations, here we propose a strategy for the very first step in protein nanotube design: we map the candidate building blocks onto a planar sheet and wrap the sheet around …
Porous Fiber Formation In Polymer-Solvent System Undergoing Solvent Evaporation, Pratyush Dayal, Thein Kyu
Porous Fiber Formation In Polymer-Solvent System Undergoing Solvent Evaporation, Pratyush Dayal, Thein Kyu
College of Polymer Science and Polymer Engineering
Temporal evolution of the fiber morphology during dry spinning has been investigated in the framework of Cahn-Hilliard equation [J. Chem. Phys. 28, 258 (1958)] pertaining to the concentration order parameter or volume fraction given by the Flory-Huggins free energy of mixing [P. J. Flory, Principles of Polymer Chemistry (Cornell University Press, Ithaca, NY, 1953), p. 672] in conjunction with the solvent evaporation rate. To guide the solvent evaporation induced phase separation, equilibrium phase diagram of the starting polymer solution was established on the basis of the Flory-Huggins free energy of mixing. The quasi-steady-state approximation has been adopted to account for …
Breakup Of Spiral And Concentric Ringed Spherulites In Polymer Crystallization, Haijun Xu, Hao-Wen Chiu, Yoshifumi Okabe, Thein Kyu
Breakup Of Spiral And Concentric Ringed Spherulites In Polymer Crystallization, Haijun Xu, Hao-Wen Chiu, Yoshifumi Okabe, Thein Kyu
College of Polymer Science and Polymer Engineering
Recently, the breakup of spiral and concentric ringed spherulites has been observed experimentally in isothermal crystallization of poly(vinylidene fluoride) in its blends with ethylene vinyl acetate copolymer. To elucidate the phenomenon of spiral breakup in polymer spherulites, a theoretical simulation has been undertaken in the framework of the phase field model of solidification based on time-dependent Ginzburg-Landau equations (TDGL model C) pertaining to the conserved concentration and nonconserved phase field order parameters. The concentration order parameter was described in terms of the Landau-type potential, while the crystal order parameter was expressed in terms of an asymmetric double-well potential to account …
Crystal-Liquid Crystal Binary Phase Diagrams, P Dayal, Ra Matkar, Thein Kyu
Crystal-Liquid Crystal Binary Phase Diagrams, P Dayal, Ra Matkar, Thein Kyu
College of Polymer Science and Polymer Engineering
We propose a new theoretical scheme for the binary phase diagrams of crystal-liquid crystal mixtures by a combination of a phase field model of solidification, the Flory-Huggins theory for liquid-liquid mixing and Maier-Saupe-McMillan (FH-MSM) model for nematic and smectic liquid crystal orderings. The phase field theory describes the crystal phase transition of anisotropic organic crystal and/or side chain liquid crystalline polymer crystals while the FH-MSM model explains isotropic, nematic and smectic-A phase transitions. Self-consistent calculations reveal several possible phase diagram topologies of the binary crystal-liquid crystal mixtures. The calculated phase diagrams were found to accord well to the reported experimental …
Coupling Between Lysozyme And Trehalose Dynamics: Microscopic Insights From Molecular-Dynamics Simulations, Taner E. Dirama, Joseph E. Curtis, Gustavo A. Carri, Alexei P. Sokolov
Coupling Between Lysozyme And Trehalose Dynamics: Microscopic Insights From Molecular-Dynamics Simulations, Taner E. Dirama, Joseph E. Curtis, Gustavo A. Carri, Alexei P. Sokolov
College of Polymer Science and Polymer Engineering
We have carried out molecular-dynamics simulations on fully flexible all-atom models of the protein lysozyme immersed in trehalose, an effective biopreservative, with the purpose of exploring the nature and extent of the dynamical coupling between them. Our study shows a strong coupling over a wide range of temperatures. We found that the onset of anharmonic behavior was dictated by changes in the dynamics and relaxation processes in the trehalose glass. The physical origin of protein-trehalose coupling was traced to the hydrogen bonds formed at the interface between the protein and the solvent. Moreover, protein-solvent hydrogen bonding was found to control …
Coupling Between Helix-Coil And Coil-Globule Transitions In Helical Polymers, Vikas Varshney, Gustavo A. Carri
Coupling Between Helix-Coil And Coil-Globule Transitions In Helical Polymers, Vikas Varshney, Gustavo A. Carri
College of Polymer Science and Polymer Engineering
We explore the coupling between the helix-coil and coil-globule transitions of a helical polymer using Monte Carlo simulations. A very rich state diagram is found. Each state is characterized by a specific configuration of the chain which could be a helix, a random coil, an amorphous globule, or one of various other globular states which carry residual helical strands. We study the boundaries between states and provide further insight into the physics of the system with a detailed analysis of the order parameter and other properties.
Confinement-Induced Ordering Of Alkanes Between An Elastomer And A Solid Surface, Kumar Nanjundiah, Ali Dhinojwala
Confinement-Induced Ordering Of Alkanes Between An Elastomer And A Solid Surface, Kumar Nanjundiah, Ali Dhinojwala
College of Polymer Science and Polymer Engineering
We have studied the molecular structure of liquid alkanes confined between a flexible elastomeric poly(dimethyl siloxane) lens and a rigid sapphire substrate using surface-sensitive infrared-visible sum frequency generation spectroscopy. The reduction in the gauche defects suggests ordering of liquid alkanes under confinement. The cooling of confined liquid below the freezing temperature leads to crystallization with alkane molecules lying on the substrate with the symmetry axis parallel to the surface normal. This structure is very different from the bulk alkane crystals next to sapphire or air interfaces.
Effect Of Thermal Transport On Spatiotemporal Emergence Of Lamellar Branching Morphology During Polymer Spherulitic Growth, Haijun Xu, Wirunya Keawwattana, Thein Kyu
Effect Of Thermal Transport On Spatiotemporal Emergence Of Lamellar Branching Morphology During Polymer Spherulitic Growth, Haijun Xu, Wirunya Keawwattana, Thein Kyu
College of Polymer Science and Polymer Engineering
Spatiotemporal emergence of lamellar branching morphology of polymer spherulite has been investigated theoretically in the framework of a phase field model by coupling a crystal solidification potential pertaining to a nonconserved crystal order parameter with a temperature field generated by latent heat of crystallization. A local free-energy density having an asymmetric double well has been utilized to account for a first-order phase transition such as crystallization. To account for the polymorphous nature of polymer crystallization, the phase field order parameter of crystal at the solidification potential of the double-well local free-energy density is modified to be supercooling dependent. The heat …
Rupture Of A Two-Dimensional Alkane Crystal, Shishir Prasad, Ali Dhinojwala
Rupture Of A Two-Dimensional Alkane Crystal, Shishir Prasad, Ali Dhinojwala
College of Polymer Science and Polymer Engineering
We have studied the breaking of a two-dimensional alkane crystal above the disordered melt using an oscillating bubble rheometer. Surface tension changes abruptly during the expansion and contraction cycle. We postulate that this is due to rupture of the 2D crystal at grain boundaries. The magnitude of the abrupt change in surface tension decreases with a decrease in the rate of change of bubble surface area with a power law exponent of 0.8. The interfacial area formed after rupture decreases with a decrease in rate. These results provide new insights in understanding defect-mediated rupture in confined geometry.
Branching In Electrospinning Of Nanofibers, A. L. Yarin, W. Kataphinan, Darrell Hyson Reneker
Branching In Electrospinning Of Nanofibers, A. L. Yarin, W. Kataphinan, Darrell Hyson Reneker
College of Polymer Science and Polymer Engineering
Electrospinning of polymer nanofibers often begins with a single, straight, elongating, and electrified fluid jet that emanates from a droplet tip when the electric field at the surface is high enough. After some distance an electrically driven bending instability of the elongating jet occurs. For a polymer solution suitable for electrospinning, capillary instability does not cause the jet to become a spray of droplets. Under some conditions, a sequence of secondary jet branches emanates from the primary jet. This paper describes an experiment in which many closely spaced branches along the jet were observed during the electrospinning of a polycaprolactone …
Phase-Field Modeling On Morphological Landscape Of Isotactic Polystyrene Single Crystals, Haijun Xu, Rushikesh Matkar, Thein Kyu
Phase-Field Modeling On Morphological Landscape Of Isotactic Polystyrene Single Crystals, Haijun Xu, Rushikesh Matkar, Thein Kyu
College of Polymer Science and Polymer Engineering
Spatio-temporal growth of isotactic polystyrene single crystals during isothermal crystallization has been investigated theoretically based on the phase field model by solving temporal evolution of a nonconserved phase order parameter coupled with a heat conduction equation. In the description of the total free energy, an asymmetric double-well local free energy density has been adopted to represent the metastable melt and the stable solid crystal. Unlike the small molecule systems, polymer crystallization rarely reaches thermodynamic equilibrium; most polymer crystals are kinetically stabilized in some metastable states. To capture various metastable polymer crystals, the phase field crystal order parameter at the solidification …
Coupling Between Lysozyme And Glycerol Dynamics: Microscopic Insights From Molecular-Dynamics Simulations, Taner E. Dirama, Gustavo A. Carri, Alexei P. Sokolov
Coupling Between Lysozyme And Glycerol Dynamics: Microscopic Insights From Molecular-Dynamics Simulations, Taner E. Dirama, Gustavo A. Carri, Alexei P. Sokolov
College of Polymer Science and Polymer Engineering
We explore possible molecular mechanisms behind the coupling of protein and solvent dynamics using atomistic molecular-dynamics simulations. For this purpose, we analyze the model protein lysozyme in glycerol, a well-known protein-preserving agent. We find that the dynamics of the hydrogen bond network between the solvent molecules in the first shell and the surface residues of the protein controls the structural relaxation (dynamics) of the whole protein. Specifically, we find a power-law relationship between the relaxation time of the aforementioned hydrogen bond network and the structural relaxation time of the protein obtained from the incoherent intermediate scattering function. We demonstrate that …
Role Of Hydrogen Bonds In The Fast Dynamics Of Binary Glasses Of Trehalose And Glycerol: A Molecular Dynamics Simulation Study, Taner E. Dirama, Gustavo A. Carri, Alexei P. Sokolov
Role Of Hydrogen Bonds In The Fast Dynamics Of Binary Glasses Of Trehalose And Glycerol: A Molecular Dynamics Simulation Study, Taner E. Dirama, Gustavo A. Carri, Alexei P. Sokolov
College of Polymer Science and Polymer Engineering
Trehalose-glycerol mixtures are known to be effective in the long time preservation of proteins. However, the microscopic mechanism of their effective preservation abilities remains unclear. In this article we present a molecular dynamics simulation study of the short time, less than 1 ns, dynamics of four trehalose-glycerol mixtures at temperatures below the glass transition temperature. We found that a mixture of 5% glycerol and 95% trehalose has the most suppressed short time dynamics (fast dynamics). This result agrees with the experimental analysis of the mean-square displacement of the hydrogen atoms, as measured via neutron scattering, and correlates with the experimentally …
Statistical Mechanics Of Worm-Like Polymers From A New Generating Function, Gustavo A. Carri, Marcelo Marucho
Statistical Mechanics Of Worm-Like Polymers From A New Generating Function, Gustavo A. Carri, Marcelo Marucho
College of Polymer Science and Polymer Engineering
We present a mathematical approach to the worm-like chain model of semiflexible polymers. Our method is built on a novel generating function from which all the properties of the model can be derived. Moreover, this approach satisfies the local inextensibility constraint exactly. In this paper, we focus on the lowest order contribution to the generating function and derive explicit analytical expressions for the characteristic function, polymer propagator, single chain structure factor, and mean square end-to-end distance. These analytical expressions are valid for polymers with any degree of stiffness and contour length. We find that our calculations are able to capture …
Onset Of Tethered Chain Overcrowding, William Y. Chen, Joseph X. Zheng, Stephen Z. D. Cheng, Christopher Y. Li, Ping Huang, Huiming Xiong, Qing Ge, Ya Guo, Roderic P. Quirk, Bernard Lotz, Lingfeng Deng, Chi Wu, Edwin L. Thomas
Onset Of Tethered Chain Overcrowding, William Y. Chen, Joseph X. Zheng, Stephen Z. D. Cheng, Christopher Y. Li, Ping Huang, Huiming Xiong, Qing Ge, Ya Guo, Roderic P. Quirk, Bernard Lotz, Lingfeng Deng, Chi Wu, Edwin L. Thomas
College of Polymer Science and Polymer Engineering
We proposed an approach to precisely control the density of tethered chains on solid substrates using PEO-b-PS and PLLA-b-PS. As the crystallization temperature T-x increased, the PEO or PLLA lamellar crystal thickness d(L) increased as well as the reduced tethering density (σ) over tilde of the PS chains. The onset of tethered PS chains overcrowding in solution occurs at (σ) over tilde*similar to3.7-3.8 as evidenced by an abrupt change in the slope between (d(L))(-1) and T-x. This results from the extra surface free energy created by the tethered chain that starts to affect the growth barrier of the crystalline blocks.
Role Of Curvature Elasticity In Sectorization And Ripple Formation During Melt Crystallization Of Polymer Single Crystals, Rujul Mehta, Wirunya Keawwattana, Andrew L. Guenthner, Thein Kyu
Role Of Curvature Elasticity In Sectorization And Ripple Formation During Melt Crystallization Of Polymer Single Crystals, Rujul Mehta, Wirunya Keawwattana, Andrew L. Guenthner, Thein Kyu
College of Polymer Science and Polymer Engineering
The present article focuses on theoretical elucidation of possible effect of mechanical deformation on spatio-temporal emergence of unusual polymer morphology subjected to quiescent isothermal crystallization conditions. The present theory developed is based on a phase field model consisted of non-conserved time dependent Ginzburg-Landau equation having an asymmetric double well potential in the crystal order parameter signifying metastability for crystallization, coupled with the chain tilt angle involving curvature elasticity and strain recovery potentials. Under quiescent crystallization conditions, the curvature elasticity term is needed to discern the emergence of sectorized single crystals. Upon coupling with the strain recovery potential, the numerical calculation …
Modification Of Statistical Threading In Two-Component Pseudorotaxane Melts Using The Amphiphilic Approach And Variations In The Confinement Geometry, Sagar S. Rane, Wayne L. Mattice, Coleen Pugh
Modification Of Statistical Threading In Two-Component Pseudorotaxane Melts Using The Amphiphilic Approach And Variations In The Confinement Geometry, Sagar S. Rane, Wayne L. Mattice, Coleen Pugh
College of Polymer Science and Polymer Engineering
Recently we described a coarse-grained model of poly(ethylene oxide) and then employed that model to study the amount of spontaneous threading of cyclic molecules by linear chains in the melt [C. A. Helfer, G. Xu, W. L. Mattice, and C. Pugh, Macromolecules 36, 10071 (2003)]. Since the amount of statistical threading at equilibrium is small, there is interest in identifying physical changes in the system that will increase the threading. We now use that coarse-grained model to investigate the effect on threading of various hypothetical (but feasible) modifications to the two-component system of macrocycles and linear chains in the melt, …
Growth Dynamics Of Isotactic Polypropylene Single Crystals During Isothermal Crystallization From A Miscible Polymeric Solvent, Rujul Mehta, Wirunya Keawwattana, Thein Kyu
Growth Dynamics Of Isotactic Polypropylene Single Crystals During Isothermal Crystallization From A Miscible Polymeric Solvent, Rujul Mehta, Wirunya Keawwattana, Thein Kyu
College of Polymer Science and Polymer Engineering
The present article presents a spatiotemporal growth of isotactic polypropylene (iPP) single crystals, melt crystallized from a polymeric solvent, i.e., poly (ethylene octene) copolymer that is known to be miscible with iPP. Optical and atomic force microscopic investigations reveal that the melt grown single crystals of iPP develop in the form of two parallel rows of crystal lamellae, but these crystals merge at the tips. To elucidate the mechanism of these emerging parallel rows of iPP crystals, a phase field model pertaining to solidification phenomena has been employed that involves a nonconserved crystal order parameter and a chain-tilting angle. This …
On The Generalized Borel Transform And Its Application To The Statistical Mechanics Of Macromolecules, Marcelo Marucho, Gustavo A. Carri
On The Generalized Borel Transform And Its Application To The Statistical Mechanics Of Macromolecules, Marcelo Marucho, Gustavo A. Carri
College of Polymer Science and Polymer Engineering
We present a new integral transform called the generalized Borel transform (GBT) and show how to use it to compute distribution functions used to describe the statistical mechanics of macromolecules. For this purpose, we choose the random flight model (RFM) of macromolecules and show that the application of the GBT to this model leads to the exact expression of the polymer propagator (two-point correlation function) from which all the statistical properties of the model can be obtained. We also discuss the mathematical simplicity of the GBT and its applicability to macromolecules with other topologies. (C) 2003 American Institute of Physics.
Yieldlike Constitutive Transition In Shear Flow Of Entangled Polymeric Fluids, Prashant Tapadia, Shi-Qing Wang
Yieldlike Constitutive Transition In Shear Flow Of Entangled Polymeric Fluids, Prashant Tapadia, Shi-Qing Wang
College of Polymer Science and Polymer Engineering
We describe an unexpected constitutive transition in entangled polymer solutions. At and beyond a critical stress, the initial spatially homogeneous and well-entangled sample transforms from its entangled (coiled) state into a fully disentangled (stretched) state over a period during which the resulting shear rate increases in a spatially inhomogeneous fashion. In the mode of controlled shear rate, the sample exhibits a stress plateau over three decades. Flow birefringence and normal stress observations unravel additional features of these flow phenomena.
Observation Of Novel Liquid-Crystalline Phase Above The Bulk-Melting Temperature, Keshav S. Gautam, Satyendra Kumar, Didier Wermeille, Doug Robinson, Ali Dhinojwala
Observation Of Novel Liquid-Crystalline Phase Above The Bulk-Melting Temperature, Keshav S. Gautam, Satyendra Kumar, Didier Wermeille, Doug Robinson, Ali Dhinojwala
College of Polymer Science and Polymer Engineering
In this paper, we show that a noncrystalline but ordered smectic-like phase exists above the bulk-melting temperature (T-m) at poly(n-alkyl acrylates)-air interface. The surface ordered phase is one monolayer thick and undergoes a sharp transition from order to disorder 10degreesC above T-m for n=22. The presence of a surface phase that does not exist in the bulk has important implications in the design of thermally responsive adhesives.
Relaxation Of A Rubbed Polystyrene Surface, Alexander D. Schwab, Ali Dhinojwala
Relaxation Of A Rubbed Polystyrene Surface, Alexander D. Schwab, Ali Dhinojwala
College of Polymer Science and Polymer Engineering
The relaxation dynamics of a rubbed polystyrene (PS) surface have been characterized using infrared-visible sum frequency generation spectroscopy (SFG). The SFG results were compared with previous relaxation of retardation measurements, and the results show that the rubbed PS surface has the same T(g) as the bulk where T(g) is defined as tau(T(g))=5 s, however, the surface has a lower activation energy (DeltaE) and a larger stretching exponent (beta(KWW)) than bulk PS. This indicates that the surface region relaxes more quickly than the bulk. The thickness of this region of lower DeltaE and larger beta(KWW) is estimated to be roughly 12 …
Poly(Meta-Phenylene Isophthalamide) Nanofibers: Coating And Post Processing, Wenxia Liu, Mathew Graham, Edward A. Evans, Darrell Hyson Reneker
Poly(Meta-Phenylene Isophthalamide) Nanofibers: Coating And Post Processing, Wenxia Liu, Mathew Graham, Edward A. Evans, Darrell Hyson Reneker
College of Polymer Science and Polymer Engineering
Electrospun nanofibers have applications in the areas of filtration, composites; biomaterials, and electronics. Controlling the surface properties of these nanofibers is important for many applications. Nanofibers can also be used as unique substrates for observing the growth of deposited films and creating nanoscale structures. In this work, electrospun poly(meta-phenylene isophthalamide) (MPD-I) nanofibers were used as substrates for creating nanoscale structures out of carbon-based materials and metals. MPD-I was used because it can be electrospun into nanofibers with diameters smaller than 10 nm and it has good thermal stability. MPD-I nanofibers were coated with carbon, copper, and aluminum using plasma enhanced …
A Device For Surface Study Of Confined Micron Thin Films In A Total Internal Reflection Geometry, Sergey Mamedov, Alexander D. Schwab, Ali Dhinojwala
A Device For Surface Study Of Confined Micron Thin Films In A Total Internal Reflection Geometry, Sergey Mamedov, Alexander D. Schwab, Ali Dhinojwala
College of Polymer Science and Polymer Engineering
A device to probe the molecular structure of materials next to a solid interface in a thin film geometry has been developed. The device can produce controlled thicknesses as small as 1 mum with parallelity better than 0.003degrees. We have shown that the thickness and the parallelity of the film produced between two optical surfaces can be quantified using white light and monochromatic light interferometry, respectively. In addition, this apparatus allows the study of these films in a static state or under shear using spectroscopic techniques involving transmission or reflection measurements. (C) 2002 American Institute of Physics.
Melting At Alkyl Side Chain Comb Polymer Interfaces, K. S. Gautam, Ali Dhinojwala
Melting At Alkyl Side Chain Comb Polymer Interfaces, K. S. Gautam, Ali Dhinojwala
College of Polymer Science and Polymer Engineering
Infrared visible sum frequency generation (SFG) spectroscopy has been used to study structure and melting transition temperatures of alkyl-side chain-acrylate comb polymers at air and solid interfaces. At the air interface, the SFG spectra show methyl bands and two transitions are observed: the first, near the bulk melting temperature, T-m, and the second 10-20degreesC higher than T-m. The shorter the alkyl side chain, the larger the difference between the two transition temperatures. In contrast, methylene bands are observed at sapphire interface with a single transition near T-m (C18).
Motion Of Droplets Along Thin Fibers With Temperature Gradient, Alexander L. Yarin, Wenxia Liu, Darrell Hyson Reneker
Motion Of Droplets Along Thin Fibers With Temperature Gradient, Alexander L. Yarin, Wenxia Liu, Darrell Hyson Reneker
College of Polymer Science and Polymer Engineering
Liquid n-decane, n-undecane, n-dodecane, and n-hexadecane formed tiny symmetrical droplets on a partially wettable cylindrical fiber. When a temperature gradient was created along the fiber, the droplets began to move along the fiber toward the cold region. An explanation of the phenomenon is related to the thermocapillary motion. Other possible mechanisms were ruled out. The theoretical results and experimental data agree reasonably well. (C) 2002 American Institute of Physics.
Two-Photon-Excited Green Emission And Its Dichroic Shift Of Oriented Thin-Film Cds On Glass Formed By Laser Deposition, B. Ullrich, R. Schroeder, H. Sakai, A. Zhang, Stephen Z. D. Cheng
Two-Photon-Excited Green Emission And Its Dichroic Shift Of Oriented Thin-Film Cds On Glass Formed By Laser Deposition, B. Ullrich, R. Schroeder, H. Sakai, A. Zhang, Stephen Z. D. Cheng
College of Polymer Science and Polymer Engineering
The photoluminescence of oriented thin-film CdS on glass formed by laser deposition was investigated employing 200 fs, 1.54 eV laser pulses at room temperature. The ultrafast excitation caused a two-photon absorption process, which results in purely green emission at the band gap. The spectra are fitted very well by the application of the van Roosbroeck-Shockley relation, density of states, and Urbach's rule demonstrating the intrinsic character of the radiative recombination. It is further shown that the energy position of the emission peak depends on the polarization of the impinging laser beam due to the dichroism of the highly oriented films. …
Taylor Cone And Jetting From Liquid Droplets In Electrospinning Of Nanofibers, Alexander L. Yarin, S Koombhongse, Darrell Hyson Reneker
Taylor Cone And Jetting From Liquid Droplets In Electrospinning Of Nanofibers, Alexander L. Yarin, S Koombhongse, Darrell Hyson Reneker
College of Polymer Science and Polymer Engineering
Sessile and pendant droplets of polymer solutions acquire stable shapes when they are electrically charged by applying an electrical potential difference between the droplet and a flat plate, if the potential is not too large. These stable shapes result only from equilibrium of the electric forces and surface tension in the cases of inviscid, Newtonian, and viscoelastic liquids. In liquids with a nonrelaxing elastic force, that force also affects the shapes. It is widely assumed that when the critical potential phi (0*) has been reached and any further increase will destroy the equilibrium, the liquid body acquires a conical shape …
Dislocation-Controlled Perforated Layer Phase In A Peo-B-Ps Diblock Copolymer, Lei Zhu, Ping Huang, Stephen Z. D. Cheng, Qing Ge, Roderic P. Quirk, Edwin L. Thomas, Bernard Lotz, Jean-Claude Wittmann, Benjamin S. Hsiao, Fengji Yeh, Lizhi Liu
Dislocation-Controlled Perforated Layer Phase In A Peo-B-Ps Diblock Copolymer, Lei Zhu, Ping Huang, Stephen Z. D. Cheng, Qing Ge, Roderic P. Quirk, Edwin L. Thomas, Bernard Lotz, Jean-Claude Wittmann, Benjamin S. Hsiao, Fengji Yeh, Lizhi Liu
College of Polymer Science and Polymer Engineering
Small angle x-ray analyses show that the shear-induced hexagonal perforated layer phase in a poly(ethylene oxide)-b-polystyrene diblock copolymer consists of trigonal (R3(overbar)m) twins and a hexagonal (P6(3)/mmc) structure, with trigonal twins being majority components. Transmission electron microscopy reveals that the hexagonal structure is generated through sequential intrinsic stacking faults on the second layer from a previous edge dislocation line, while the trigonal twins are formed by successive intrinsic stacking faults on neighboring layers due to the plastic deformation under mechanical shear.
Bending Instability In Electrospinning Of Nanofibers, A. L. Yarin, S. Koombhongse, Darrell Hyson Reneker
Bending Instability In Electrospinning Of Nanofibers, A. L. Yarin, S. Koombhongse, Darrell Hyson Reneker
College of Polymer Science and Polymer Engineering
A localized approximation was developed to calculate the bending electric force acting on an electrified polymer jet, which is a key element of the electrospinning process for manufacturing of nanofibers. Using this force, a far reaching analogy between the electrically driven bending instability and the aerodynamically driven instability was established. Continuous, quasi-one-dimensional, partial differential equations were derived and used to predict the growth rate of small electrically driven bending perturbations of a liquid column. A discretized form of these equations, that accounts for solvent evaporation and polymer solidification, was used to calculate the jet paths during the course of nonlinear …