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Articles 1 - 14 of 14
Full-Text Articles in Polymer Science
Exploring Stress Overshoot Phenomenon Upon Startup Deformation Of Entangled Linear Polymeric Liquids, Yangyang Wang, Shi-Qing Wang
Exploring Stress Overshoot Phenomenon Upon Startup Deformation Of Entangled Linear Polymeric Liquids, Yangyang Wang, Shi-Qing Wang
College of Polymer Science and Polymer Engineering
This work explores the picture associated with stress overshoot during sudden continual (i.e., startup) external deformation of entangled polymeric liquids and proposes a specific scaling form to depict the intermolecular interactions responsible for chain deformation. Following a previously proposed idea that the stress overshoot in startup deformation is a signature of yielding, we search for ingredients that should go into the description of the force imbalance at the yield point and show that the expression for the intermolecular locking force f(iml), derived from the characteristics associated with the yield point, can be tested against experiment. New rate-switching experiments support the …
Nature Of Steady Flow In Entangled Fluids Revealed By Superimposed Small Amplitude Oscillatory Shear, Pouyan E. Boukany, Shi-Qing Wang
Nature Of Steady Flow In Entangled Fluids Revealed By Superimposed Small Amplitude Oscillatory Shear, Pouyan E. Boukany, Shi-Qing Wang
College of Polymer Science and Polymer Engineering
We carry out a systematic investigation into steady-state shear behavior of six entangled solutions based on a superposition of continuous shear and small amplitude oscillatory shear (SAOS). During steady shear in the shear thinning regime, the superimposed SAOS frequency sweep measurements reveal characteristics of viscous liquids, e. g., terminal dynamics, on the experimental time scale of the reciprocal shear rate. The residual entanglement network retains the same level of elastic stiffness as the equilibrium system does. Consistent with the convective constraint release idea, chains in the network are forced to pass around each other as they must do so to …
Nonlinearity In Large Amplitude Oscillatory Shear (Laos) Of Different Viscoelastic Materials, Xin Li, Shi-Qing Wang, Xiaorong Wang
Nonlinearity In Large Amplitude Oscillatory Shear (Laos) Of Different Viscoelastic Materials, Xin Li, Shi-Qing Wang, Xiaorong Wang
College of Polymer Science and Polymer Engineering
The present work investigates nonlinear behavior in large amplitude oscillatory shear (LAOS) of four different polymeric materials using simultaneous conventional rheometric measurements and particle-tracking velocimetric observations. In contrast to most studies in the literature that treat nonlinearity in LAOS in steady state, we emphasize by the present four examples that nonlinearity in LAOS often arise in complex fluids due to time-dependent rearrangement of their microstructures in response to LAOS. Consequently, no correlation is obvious between strain dependence of the steady-state stress response and the time-dependent characteristics of the steady-state response. For instance, a highly viscoelastic material made of nano-sized polybutadiene …
Synthesis And Characterization Of Some Rhenium Complexes, Joseph Brian Scott
Synthesis And Characterization Of Some Rhenium Complexes, Joseph Brian Scott
Masters Theses & Specialist Projects
Plastics or polymers are thought to behave oppositely from metals. Ideally, polymers behave as insulators while metals conduct electricity. Shirakawa and coworkers discovered conductive polymers in 1977.1 These conductor polymers have been extensively studied, discovering that charge transfer oxidative doping of polyacteylene could increase its conductivity by 12 orders of magnitude. Polyacetylene, although showing promise as an organic conductor, because it is highly air-sensitive and oxidizes when exposed to molecular oxygen, therefore making this an unattractive use for commercial products. Attention has been focused on heterocylic aromatic polymers such as polythiophene and polypyrrole, in efforts to produce conductive polymers that …
Electrospinning Route For The Fabrication Of P-N Junction Using Nanofiber Yarns, A. F. Lotus, S. Bhargava, E. T. Bender, E. A. Evans, R. D. Ramsier, Darrell Hyson Reneker, G. G. Chase
Electrospinning Route For The Fabrication Of P-N Junction Using Nanofiber Yarns, A. F. Lotus, S. Bhargava, E. T. Bender, E. A. Evans, R. D. Ramsier, Darrell Hyson Reneker, G. G. Chase
College of Polymer Science and Polymer Engineering
Electrospinning is a simple, versatile, and cost effective method for generating nanoscale fibers, wires, and tubes. Nanowires and nanotubes could be important building blocks for nanoscale electronics, optoelectronics, and sensors as they can function as miniaturized devices as well as electrical interconnects. We report on a simple method to fabricate free standing ceramic nanofiber heterostructures, which exhibit rectifying behavior of a p-n junction.
Nonlinear-Optical Studies Of A Fluorinated Poled Polyimide Guest-Host System, S. F. Hubbard, K. D. Singer, F. Li, Stephen Z. D. Cheng, F. W. Harris
Nonlinear-Optical Studies Of A Fluorinated Poled Polyimide Guest-Host System, S. F. Hubbard, K. D. Singer, F. Li, Stephen Z. D. Cheng, F. W. Harris
College of Polymer Science and Polymer Engineering
We report on poling of a low dielectric constant preimidized fluorinated fully aromatic guest-host polyimide nonlinear optical material including thermal stability of optical nonlinearities and waveguiding properties. We measured a second-harmonic coefficient (d33 = 4.9 +/- 0.5 pm/V at 1217 nm fundamental wavelength) which is accurately predicted by a thermodynamic model of poled polymers. The optical nonlinearity of a poled sample was thermally stable at 80-degrees-C for over 300 h. Films were observed to have negative birefringence. Optical losses for slab waveguides in lowest order TE and TM modes were greater-than-or-equal-to 7.7 dB/cm for doped waveguides at 800 nm wavelength …
Universal Scaling Behavior In Startup Shear Of Entangled Linear Polymer Melts, Pouyan E. Boukany, Shi-Qing Wang, Xiaorong Wang
Universal Scaling Behavior In Startup Shear Of Entangled Linear Polymer Melts, Pouyan E. Boukany, Shi-Qing Wang, Xiaorong Wang
College of Polymer Science and Polymer Engineering
We have studied stress overshoot behavior in startup shear of four monodisperse polymer melts with a range of chain entanglement from Z = 24 to 160 entanglement points per chain. In the elastic deformation regime defined by (gamma)over dot tau(R) > 1 where tau(R) is the Rouse relaxation time, (i) the peak shear stress sigma(max) scales with the time t(max) at the peak to -1/2 power, in contrast to an exponent of -1/4 in the viscoelastic regime (for (gamma)over dot tau(R) < 1), (ii) sigma(max) changes linearly with the elapsed strain at the stress peak gamma(max), which scales with the applied shear rate as (gamma)over dot(1/3), (iii) a supermaster curve collapses time-dependent shear stress growth curves up to the stress maximum at all shear rates for all the four styrene-butadiene rubber samples. (C) 2009 The Society of Rheology. [DOI: 10.1122/1.3086872]
Effects Of Photointensity Gradient On Directional Crystal Growth In Blends Of Crystalline Polymer And Photoreactive Monomer Undergoing Photopolymerization-Induced Phase Transformation, Pankaj Rathi, Soo Jeoung Park, Thein Kyu
Effects Of Photointensity Gradient On Directional Crystal Growth In Blends Of Crystalline Polymer And Photoreactive Monomer Undergoing Photopolymerization-Induced Phase Transformation, Pankaj Rathi, Soo Jeoung Park, Thein Kyu
College of Polymer Science and Polymer Engineering
Effects of light intensity gradient on development of intricate hierarchical morphology of semicrystalline polyethylene oxide (PEO) and photoreactive diacrylate (DA) blends undergoing photopolymerization-induced crystallization have been demonstrated experimentally and theoretically. The melting temperature of PEO was found to decline upon addition of DA monomer. A solid-liquid phase diagram has been established by self-consistently solving the combined phase field free energy of crystal solidification and Flory-Huggins (FH) free energy of liquid-liquid demixing. Dynamic calculations were performed using time-dependent Ginzburg-Landau (model C) equations by incorporating the combined phase field and FH free energy densities coupled with the photopolymerization kinetics. The spatiotemporal development …
Application Of The Thermal Flash Technique For Low Thermal Diffusivity Micro/Nanofibers, Michael T. Demko, Zhenting Dai, Han Yan, William P. King, Miko Cakmak, Alexis R. Abramson
Application Of The Thermal Flash Technique For Low Thermal Diffusivity Micro/Nanofibers, Michael T. Demko, Zhenting Dai, Han Yan, William P. King, Miko Cakmak, Alexis R. Abramson
College of Polymer Science and Polymer Engineering
The thermal flash method was developed to characterize the thermal diffusivity of micro/nanofibers without concern for thermal contact resistance, which is commonly a barrier to accurate thermal measurement of these materials. Within a scanning electron microscope, a micromanipulator supplies instantaneous heating to the micro/nanofiber, and the resulting transient thermal response is detected at a microfabricated silicon sensor. These data are used to determine thermal diffusivity. Glass fibers of diameter 15 mu m had a measured diffusivity of 1.21x10(-7) m(2)/s; polyimide fibers of diameters 570 and 271 nm exhibited diffusivities of 5.97x10(-8) and 6.28x10(-8) m(2)/s, respectively, which compare favorably with bulk …
Effects Of Prior Aging At 316°C In Argon On Inelastic Deformation Behavior Of Pmr-15 Polymer At 316°C: Experiment And Modeling, Ozgur Ozmen
Theses and Dissertations
The inelastic deformation behavior of PMR-15 neat resin, a high-temperature polymer, was investigated at 316 deg C. The experimental program was designed to explore the influence of strain rate on tensile loading, unloading, and strain recovery behaviors. In addition, the effect of the prior strain rate on the relaxation response of the material, as well as on the creep behavior following strain controlled loading were examined. The material exhibits positive, nonlinear strain rate sensitivity in monotonic loading and unloading. Early failures occur in the inelastic regime. The recovery of strain at zero stress and creep response are strongly affected by …
Theory And Computation Of Photopolymerization-Induced Phase Transition And Morphology Development In Blends Of Crystalline Polymer And Photoreactive Monomer, Pankaj Rathi, Thein Kyu
Theory And Computation Of Photopolymerization-Induced Phase Transition And Morphology Development In Blends Of Crystalline Polymer And Photoreactive Monomer, Pankaj Rathi, Thein Kyu
College of Polymer Science and Polymer Engineering
A hypothetical phase diagram of a crystalline polymer/photoreactive monomer mixture has been calculated on the basis of phase field (PF) free energy of crystal solidification in conjunction with Flory-Huggins (FH) free energy of liquid-liquid demixing to guide the morphology development during photopolymerization of poly(ethylene oxide)/triacrylate blend. The self-consistent solution of the combined PF-FH theory exhibits a crystalline-amorphous phase diagram showing the coexistence of solid+liquid gap bound by the liquidus and solidus lines, followed by an upper critical solution temperature at a lower temperature. When photopolymerization was triggered in the isotropic region, i.e., slightly above the crystal melting transition temperatures, the …
Shear Banding Or Not In Entangled Dna Solutions Depending On The Level Of Entanglement, Pouyan E. Boukany, Shi-Qing Wang
Shear Banding Or Not In Entangled Dna Solutions Depending On The Level Of Entanglement, Pouyan E. Boukany, Shi-Qing Wang
College of Polymer Science and Polymer Engineering
Entangled DNA solutions are ideal as a model system to examine nonlinear shear flow behavior. Even when the number of entanglements per chain, Z, is higher than 100, the solution is still soft enough with an elastic plateau modulus under 100 Pa and is thus amenable to experimental study by commercial rotational rheometry without ambiguity and uncertainty. We have investigated nonlinear flow behavior of three entangled DNA solutions with Z=24, 60, and 156, respectively, using a combination of particle-tracking velocimetric (PTV) and conventional rheometric measurements. We explore questions such as (a) whether shear banding also occurs in moderately entangled solutions, …
Understanding Rubber Friction In The Presence Of Water Using Sum-Frequency Generation Spectroscopy, Kumar Nanjundiah, Ping Yuan Hsu, Ali Dhinojwala
Understanding Rubber Friction In The Presence Of Water Using Sum-Frequency Generation Spectroscopy, Kumar Nanjundiah, Ping Yuan Hsu, Ali Dhinojwala
College of Polymer Science and Polymer Engineering
Infrared-visible sum-frequency-generation spectroscopy (SFG) was used to study the molecular structure of water between a poly(dimethylsiloxane) (PDMS) and a sapphire substrate. The observation of SFG peaks associated with the dangling surface hydroxyl groups (3690 cm(-1)) and water bands (3000-3400 cm(-1)) indicates that the contact spot between the PDMS lens and the sapphire substrate is heterogeneous. Within the contact spot there are regions where the methyl groups of the PDMS chains are in direct contact with the surface hydroxyl groups on the sapphire substrate. In the other regions, a thin water layer is trapped between the two surfaces with spectral features …
Inhomogeneous Degradation Of Polymer Electrolyte Membrane In Pem Fuel Cells, Xinyu Huang, Wonseok Yoon
Inhomogeneous Degradation Of Polymer Electrolyte Membrane In Pem Fuel Cells, Xinyu Huang, Wonseok Yoon
Faculty Publications
Membrane durability is one of the technical barriers for the commercialization of polymer electrolyte membrane (PEM) fuel cells. Membrane embrittlement (a form of mechanical weakening) can lead to the frequently observed “sudden death” behavior of PEM fuel cells. It is the objective of this study to explore the fundamental mechanisms of the mechanical weakening of perfluorosulfonic acid (PFSA) based electrolyte membranes during the accelerated degradation test.