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Articles 541 - 570 of 608

Full-Text Articles in Chemical Engineering

Electrical, Structural, And Chemical Properties Of Semiconducting Metal Oxide Nanofiber Yarns, A. F. Lotus, E. T. Bender, E. A. Evans, R. D. Ramsier, Darrell Hyson Reneker Jan 2008

Electrical, Structural, And Chemical Properties Of Semiconducting Metal Oxide Nanofiber Yarns, A. F. Lotus, E. T. Bender, E. A. Evans, R. D. Ramsier, Darrell Hyson Reneker

College of Polymer Science and Polymer Engineering

The electrical, structural, and chemical properties of twisted yarns of metal-oxide nanofibers, fabricated using a modified electrospinning technique, are investigated in this report. In particular, synthesized zinc oxide and nickel oxide yarns having diameters in the range of 4-40 mu m and lengths up to 10 cm were characterized, whose constituent nanofibers had average diameters of 60-100 nm. These yarns have one macroscopic dimension for handling while retaining some of the properties of nanofibers. (C) 2008 American Institute of Physics.

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Sublethal And Killing Effects Of Atmospheric-Pressure, Nonthermal Plasma On Eukaryotic Microalgae In Aqueous Media, Ying Zhong Tang, Xin Pei Lu, Mounir Laroussi, Fred C. Dobbs Jan 2008

Sublethal And Killing Effects Of Atmospheric-Pressure, Nonthermal Plasma On Eukaryotic Microalgae In Aqueous Media, Ying Zhong Tang, Xin Pei Lu, Mounir Laroussi, Fred C. Dobbs

OES Faculty Publications

In-depth studies on the interaction of nonthermal plasmas with microorganisms usually focus on bacteria; only little attention has been given to their effects on more complex eukaryotic cells. We report here nonthermal plasma's effects on cell motility, viability staining, and morphology of eukaryotic microalgae, with three marine dinoflagellates and a marine diatom as major targets. The effects on motility and viability staining depended on the time of exposure to plasma and the species of microalgae. We observed a strong pH decrease in aqueous samples (marine and freshwater algal cultures, their culture media, and deionized water) after exposure to plasma, and …

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Structure Property Relationships In Electron Donating Systems For Potential Photovoltaic Applications., Jonathan Moghal Jan 2008

Structure Property Relationships In Electron Donating Systems For Potential Photovoltaic Applications., Jonathan Moghal

Doctoral

Conjugated polymers are considered to be one-dimensional semiconductors. In conjugated polymers single and double bonds alternatively bond the carbon atoms along the polymer chain. The loosely bound electrons determine the electronic properties of conjugated polymers. In order to utilise the properties of conjugated polymers in terms of a photovoltaic (PV) device application an acceptor material must be added. The acceptor material used in this study is used in buckminsterfullerence (C60). C60 was selected for this purpose due to its size and the fact that it can accept up to six additional electrons. Ultrafast charge transfers from a conducting polymer onto …

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Plasma Medicine, Mounir Laroussi, Alexander Fridman Jan 2008

Plasma Medicine, Mounir Laroussi, Alexander Fridman

Electrical & Computer Engineering Faculty Publications

Recent demonstrations of plasma technology in the treatment of living cells, tissues, and organs are creating a newfield at the intersection of plasma science and technology with biology and medicine - Plasma Medicine.

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Elastic Breakup In Uniaxial Extension Of Entangled Polymer Melts, Yangyang Wang, Pouyan Boukany, Shi-Qing Wang, Xiaorong Wang Dec 2007

Elastic Breakup In Uniaxial Extension Of Entangled Polymer Melts, Yangyang Wang, Pouyan Boukany, Shi-Qing Wang, Xiaorong Wang

College of Polymer Science and Polymer Engineering

Five entangled melts, with the number of entanglements per chain ranging from 25 to 160, have been studied to illustrate how cohesive strength can be overcome in either continuous or interrupted extension (i.e., during or after uniaxial stretching). The internal elastic stress due to chain deformation from imposed strain appears to be the cause of the observed yielding behavior that reveals scaling laws. The visual signature of the elastic breakup is the occurrence of nonuniform extension. The yield phenomena may be understood at a force level.

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New Theoretical Considerations In Polymer Rheology: Elastic Breakdown Of Chain Entanglement Network, Shi-Qing Wang, Sham Ravindranath, Yangyang Wang, Pouyan Boukany Aug 2007

New Theoretical Considerations In Polymer Rheology: Elastic Breakdown Of Chain Entanglement Network, Shi-Qing Wang, Sham Ravindranath, Yangyang Wang, Pouyan Boukany

College of Polymer Science and Polymer Engineering

Recent experimental evidence has motivated us to present a set of new theoretical considerations and to provide a rationale for interpreting the intriguing flow phenomena observed in entangled polymer solutions and melts [P. Tapadia and S. Q. Wang, Phys. Rev. Lett. 96, 016001 (2006); 96, 196001 (2006); S. Q. Wang , ibid. 97, 187801 (2006)]. Three forces have been recognized to play important roles in controlling the response of a strained entanglement network. During flow, an intermolecular locking force f(iml) arises and causes conformational deformation in each load-bearing strand between entanglements. The chain deformation builds up a retractive force f(retract) …

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Photopolymerization-Induced Directional Crystal Growth In Reactive Mixtures, Soo Jeoung Park, Pankaj Rathi, Thein Kyu May 2007

Photopolymerization-Induced Directional Crystal Growth In Reactive Mixtures, Soo Jeoung Park, Pankaj Rathi, Thein Kyu

College of Polymer Science and Polymer Engineering

Photopolymerization-induced crystallization has been demonstrated in blends of polyethylene oxide-diacrylate at temperatures above the depressed melting temperature of the crystalline component. Upon exposure to ultraviolet irradiation, the melting transition curve moves upward and eventually surpasses the reaction temperature, thereby inducing phase separation as well as crystallization. The present paper demonstrates the occurrence of directionally solidified interface morphologies of polymer crystals subjected to a photointensity gradient. The epitaxially grown seaweed or degenerate structures were observed at the circumference (low-intensity region) while the dense branched spherulites developed at the core high-intensity region.

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Discrepancy In Determination Of Chi Parameters By Melting Point Depression Versus Small-Angle Neutron Scattering In Blends Of Deuterated Polycarbonate And Isotactic Poly(Methyl Methacrylate), Thein Kyu, Rushikesh A. Matkar, Dong Soo Lim, Chechian Ko Apr 2007

Discrepancy In Determination Of Chi Parameters By Melting Point Depression Versus Small-Angle Neutron Scattering In Blends Of Deuterated Polycarbonate And Isotactic Poly(Methyl Methacrylate), Thein Kyu, Rushikesh A. Matkar, Dong Soo Lim, Chechian Ko

College of Polymer Science and Polymer Engineering

The discrepancy in the chi interaction parameters of deuterated polycarbonate/isotactic poly(methyl methacrylate) blends as determined by the melting point depression approach and the small-angle scattering technique is reported. We have modified the Flory diluent theory by removing the inherent assumption of complete rejection of the solvent from the crystal solid by taking into consideration the crystal-amorphous, amorphous-crystal, and crystal-crystal interactions. The discrepancy in chi values obtained by the two methods is discussed.

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A Correlation Between Velocity Profile And Molecular Weight Distribution In Sheared Entangled Polymer Solutions, Pouyan E. Boukany, Shi-Qing Wang Apr 2007

A Correlation Between Velocity Profile And Molecular Weight Distribution In Sheared Entangled Polymer Solutions, Pouyan E. Boukany, Shi-Qing Wang

College of Polymer Science and Polymer Engineering

In this work we attempt to answer several questions concerning the flow characteristics of entangled polymer solutions in a sliding plate shearing cell. We explore (a) how the molecular weight distribution affects the velocity profile in simple shear, (b) whether the observed shear banding is consistent with a nonmonotonic constitutive model, (c) whether the flow response and velocity profiles are different in simple shear depending on the different modes of shear. Our results provide a comparison with recent reports on a polydisperse polymer sample [Tapadia and Wang, Phys. Rev. Lett. 96, 016001 (2006); Tapadia, et al., Phys. Rev. Lett. 96, …

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How Does The Coupling Of Secondary And Tertiary Interactions Control The Folding Of Helical Macromolecules?, Vikas Varshney, Gustavo A. Carri Jan 2007

How Does The Coupling Of Secondary And Tertiary Interactions Control The Folding Of Helical Macromolecules?, Vikas Varshney, Gustavo A. Carri

College of Polymer Science and Polymer Engineering

The authors study how the simultaneous presence of short-range secondary and long-range tertiary interactions controls the folding and collapse behavior of a helical macromolecule. The secondary interactions stabilize the helical conformation of the chain, while the tertiary interactions govern its overall three-dimensional shape. The authors have carried out Monte Carlo simulations to study the effect of chain length on the folding and collapse behavior of the chain. They have calculated state diagrams for four chain lengths and found that the physics is very rich with a plethora of stable conformational states. In addition to the helix-coil and coil-globule transitions, their …

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Nonquiescent Relaxation In Entangled Polymer Liquids After Step Shear, Shi-Qing Wang, Sham Ravindranath, Pouyan Boukany, Michael Olechnowicz, Roderic P. Quirk, Jimmy Mays Nov 2006

Nonquiescent Relaxation In Entangled Polymer Liquids After Step Shear, Shi-Qing Wang, Sham Ravindranath, Pouyan Boukany, Michael Olechnowicz, Roderic P. Quirk, Jimmy Mays

College of Polymer Science and Polymer Engineering

Large step shear experiments revealed through particle tracking velocimetry that entangled polymeric liquids display either internal macroscopic movements upon shear cessation or rupturelike behavior during shear. Visible inhomogeneous motions were detected in five samples with the number of entanglements per chain ranging from 20 to 130 at amplitudes of step strain as low as 135%.

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Interfacial Stick-Slip Transition In Simple Shear Of Entangled Melts, Pouyan E. Boukany, Prashant Tapadia, Shi-Qing Wang Oct 2006

Interfacial Stick-Slip Transition In Simple Shear Of Entangled Melts, Pouyan E. Boukany, Prashant Tapadia, Shi-Qing Wang

College of Polymer Science and Polymer Engineering

This article describes a systematic investigation of a discontinuous interfacial stick-slip transition (SST) in simple shear of monodisperse entangled 1,4-polybutadiene (PBD) and polyisoprene (PIP) melts with different molecular weights and architecture, using a specially designed controlled-force shear rheometer. The magnitude of the transition is found to be determined by the level of chain entanglement. Specifically, the dependence of extrapolation length b on molecular weight as b similar to M-w(3.4) and of the melt viscosity as b similar to eta is consistent with the observations based on capillary rheometric studies [X. Yang et al., Rheol. Acta 37, 415-423 (1998)]. The interfacial …

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Porous Fiber Formation In Polymer-Solvent System Undergoing Solvent Evaporation, Pratyush Dayal, Thein Kyu Aug 2006

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 …

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Breakup Of Spiral And Concentric Ringed Spherulites In Polymer Crystallization, Haijun Xu, Hao-Wen Chiu, Yoshifumi Okabe, Thein Kyu Jul 2006

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 …

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Crystal-Liquid Crystal Binary Phase Diagrams, P Dayal, Ra Matkar, Thein Kyu Jun 2006

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 …

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Coupling Between Lysozyme And Trehalose Dynamics: Microscopic Insights From Molecular-Dynamics Simulations, Taner E. Dirama, Joseph E. Curtis, Gustavo A. Carri, Alexei P. Sokolov Jan 2006

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 …

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Coupling Between Helix-Coil And Coil-Globule Transitions In Helical Polymers, Vikas Varshney, Gustavo A. Carri Oct 2005

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.

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Confinement-Induced Ordering Of Alkanes Between An Elastomer And A Solid Surface, Kumar Nanjundiah, Ali Dhinojwala Oct 2005

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.

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Effect Of Thermal Transport On Spatiotemporal Emergence Of Lamellar Branching Morphology During Polymer Spherulitic Growth, Haijun Xu, Wirunya Keawwattana, Thein Kyu Sep 2005

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 …

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Rupture Of A Two-Dimensional Alkane Crystal, Shishir Prasad, Ali Dhinojwala Sep 2005

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.

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Branching In Electrospinning Of Nanofibers, A. L. Yarin, W. Kataphinan, Darrell Hyson Reneker Sep 2005

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 …

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Phase-Field Modeling On Morphological Landscape Of Isotactic Polystyrene Single Crystals, Haijun Xu, Rushikesh Matkar, Thein Kyu Jul 2005

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 …

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Coupling Between Lysozyme And Glycerol Dynamics: Microscopic Insights From Molecular-Dynamics Simulations, Taner E. Dirama, Gustavo A. Carri, Alexei P. Sokolov Jun 2005

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 …

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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 Mar 2005

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 …

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Results Of An Interlaboratory Study Of The Astm Standard Test Method For Tensile Properties Of Polymer Matrix Composites D 3039, Margaret Pinnell, Richard Fields, Ronald Zabora Jan 2005

Results Of An Interlaboratory Study Of The Astm Standard Test Method For Tensile Properties Of Polymer Matrix Composites D 3039, Margaret Pinnell, Richard Fields, Ronald Zabora

Mechanical and Aerospace Engineering Faculty Publications

An investigation was conducted on the ASTM Standard Test Method for Tensile Properties of Polymer Matrix Composites (D 3039). This investigation consisted of both preliminary testing and an interlaboratory test program. Information generated from preliminary testing was used to determine the effects of various parameters and to optimize the interlaboratory test plan and test protocol. The interlaboratory study portion of this investigation was conducted on six composite material systems in a variety of lay-up configurations. The number of participating labs ranged from five to nine depending on the material type. Precision statistics were determined for the ASTM D 3039 standard …

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Statistical Mechanics Of Worm-Like Polymers From A New Generating Function, Gustavo A. Carri, Marcelo Marucho Sep 2004

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 …

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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 Jul 2004

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.

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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 Jun 2004

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 …

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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 Jun 2004

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, …

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Growth Dynamics Of Isotactic Polypropylene Single Crystals During Isothermal Crystallization From A Miscible Polymeric Solvent, Rujul Mehta, Wirunya Keawwattana, Thein Kyu Feb 2004

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 …

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