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Articles 511 - 540 of 608

Full-Text Articles in Chemical Engineering

Mechanical Characterization Of Polymer Electrolyte Membrane With Optical Methods, Xinyu Huang, Luis Alva, Jay Neutzler Jan 2011

Mechanical Characterization Of Polymer Electrolyte Membrane With Optical Methods, Xinyu Huang, Luis Alva, Jay Neutzler

Faculty Publications

Mechanical properties of polymer electrolyte membrane have important implications in the endurance of many electrochemical energy conversion devices [1]. Mechanical experiments are effective method to reveal discrete damage developed in the membrane by quantifying the change of mechanical strength and toughness. Regular strain measurement methods are overly intrusive to the thin and relatively fragile polymer electrolyte membrane; hence optical-based minimal invasive stress/strain measurement methods are studied.

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Effect Of Surface Freezing On Meniscus Relaxation In Side Chain Comb Polymers, Shishir Prasad, Zhang Jiang, Michael Sprung, Sunil K. Sinha, Ali Dhinojwala Apr 2010

Effect Of Surface Freezing On Meniscus Relaxation In Side Chain Comb Polymers, Shishir Prasad, Zhang Jiang, Michael Sprung, Sunil K. Sinha, Ali Dhinojwala

College of Polymer Science and Polymer Engineering

We have observed a sharp slowing down of the relaxation of the liquid meniscus for polydn-alkyl acrylate) at temperatures where there are no abrupt changes in bulk viscosity or surface tension. This slowing down is due to the formation of a surface-ordered monolayer above the bulk melting temperatures. X-ray photon correlation spectroscopy measurements reveal that the surface capillary fluctuations are also significantly slower due to the formation of the ordered monolayer for film thicknesses comparable to that of the precursor films. The slowing down of the precursor film dynamics is responsible for slower meniscus relaxation below the surface ordering transition …

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Preparation Of Styrene Acrylic Copolymer Toner Resin By Solution Polymerization., Neo Su Siang Apr 2010

Preparation Of Styrene Acrylic Copolymer Toner Resin By Solution Polymerization., Neo Su Siang

Student Works (2010-2019)

This project has investigated solution polymerization to produce toner resins. There are three stages: (i) synthesis of low molecular weight styrene acrylic copolymer; (ii) synthesis of high molecular weight styrene acrylic copolymer; (iii) mixing high and low molecular weight copolymers. Gel Permeation Chromatography (GPC) was used to study molecular weight distributions, Melt Flow Index (MFI) Instrument to study the flowability of resin, Differential Scanning Calorimetry (DSC) to study the thermal properties of resin, and acid number to quantitate the amount of acidic group in the resin. A comparison of properties between the experimental samples, patent’s claims, and commercial resins had …

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Characteristics Of Proton Conducting Pva-Chitosan Polymer Blend Electrolytes., Mohd Fakhrul Zamani Abdul Kadir Jan 2010

Characteristics Of Proton Conducting Pva-Chitosan Polymer Blend Electrolytes., Mohd Fakhrul Zamani Abdul Kadir

Student Works (2010-2019)

The main focus of this present work is to build a good conducting solid polymer electrolyte (SPE) based on chitosan and poly(vinyl alcohol)(PVA) blend. Solution cast technique has been employed to produce sample films in this work. From the scanning electron micrographs (SEM) the surface morphology of the blend containing 40 wt.% chitosan and 60 wt.% PVA (C4P6) is homogenous and miscible in one and another. The C4P6 film is the most amorphous and is the best candidate for the polymer host in the electrolyte systems studied in the present work. Ammonium Nitrate (NH4NO3) is the doping salt that provides …

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Synthesis Of Urethane Acrylate Macromer From Palm Oil-Based Polyol And Its Application As A Resin For Dental Composite., Fadhel A. A. Alsanabani Jan 2010

Synthesis Of Urethane Acrylate Macromer From Palm Oil-Based Polyol And Its Application As A Resin For Dental Composite., Fadhel A. A. Alsanabani

Student Works (2010-2019)

A slightly branched urethane acrylate macromer (UAM) was synthesized by reacting palm oil-based polyol with excess amounts of polymeric methylene diphenyl diisocyanate (MDI) to form urethane prepolymer, then reacted with 2-hydroxyethyl methacrylate (HEMA) and FT-IR spectroscopy confirmed the urethane and grafted acrylate groups. 0.2% by weight of camphoroquinone (CQ) and 0.8% by weight of ethyl-4-N,N-dimethylamino-benzoate (4EDMAB) by weight were added to render the experimental resins light-curable. Their viscosity, percentage of degree of conversion (%DC) and cross-linking density (CLD), percentage of volumetric polymerization shrinkage (%VPS), water sorption and solubility, flexural strength, modulus of elasticity and toughness were determined and compared to …

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Thermo-Electrical And Mechanical Studies On Polymer-Organically Modified Montmorillonite Composite., Norhana Abdul Halim Jan 2010

Thermo-Electrical And Mechanical Studies On Polymer-Organically Modified Montmorillonite Composite., Norhana Abdul Halim

Student Works (2010-2019)

The field of polymer-nanoclay composite has attracted a lot of attention in materials studies due to the dramatic improvement on polymers characteristics. For example mechanical and thermal properties, chemical resistance as well as the reduced gas permeability. However, structural changes and the mechanisms that may contribute to these improvements are not fully understood. In this work, the study on polymer nanoclay composite concentrates on the effects of OMON inclusion within different polymer matrix systems. The matrixes are a series of natural rubbers (Standard Malaysia Rubber – Latex grade (SMRL); Deproteinized Natural Rubber (DPNR) and Epoxidized Natural Rubber (ENR-50)), plasticized Polyvinyl …

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Electrical And Structural Studies Of Polyacrylonitrile (Pan) Complexed With Inorganic Salts., Khairul Bahiyah Md Isa Jan 2010

Electrical And Structural Studies Of Polyacrylonitrile (Pan) Complexed With Inorganic Salts., Khairul Bahiyah Md Isa

Student Works (2010-2019)

In the present study, polymer electrolyte films composed of polyacrylonitrile (PAN) as a host polymer, ethylene carbonate (EC) as the plasticizer and lithium triflate (LiCF3SO3) and sodium triflate (NaCF3SO3) as dopant salts were prepared by the solution cast technique. Five systems of polymer electrolytes films have been prepared; these systems are the plasticized-PAN system i.e. PAN-EC system, two salted-PAN systems i.e. PAN-LiCF3SO3 and PAN-NaCF3SO3, and two plasticized-salted PAN systems i.e. PAN-EC-LiCF3SO3 and PAN-EC-NaCF3SO3. The pure PAN film was prepared as a reference. The ionic conductivity for each system is characterized using impedance spectroscopy. The room temperature conductivity of the pure …

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Synthesis Of Chromium-Based Ziegler-Natta Catalysts And Thier Application In Ethylene Polymerization And Copolymerization., Wong Jun Xuan Jan 2010

Synthesis Of Chromium-Based Ziegler-Natta Catalysts And Thier Application In Ethylene Polymerization And Copolymerization., Wong Jun Xuan

Student Works (2010-2019)

Four chromium-based oxo-trinuclear carboxylate complexes were prepared by reacting Cr(NO3).9H2O with acetic acid and substituted carboxylic acids to produce [Cr3O(CH3COO)6.3H2O]NO3.7H2O,[Cr3O(ClCH2COO)6.3H2O]NO3.3H2O, [Cr3O(Cl2CHCOO)6.3H2O]NO3.H2O and [Cr3O(Cl3CCOO)6.3H2O]NO3.2H2O, which alysis (TGA).Chromium content in each complex was determined by titrimetry method and the result was in good agreement with that from TGA. Chromium(III)monochloroacetate complex[Cr3O(ClCH2COO)6.3H2O]NO3.3H2O in combination with diethylaluminium chloride formed heterogeneous catalyst system for ethylene polymerization and ethylene-propylene copolymerization. Both Al/Cr ratio and temperature influenced the catalytic activity. The maximum activity of ethylene polymerization was 1768 gPE/gCr/hr/atm, achieved by polymerizing ethylene at 29°C with Al/Cr ratio 30.8. Effect of chloro-substituent groups on carboxylic ligand was studied …

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Exploring Stress Overshoot Phenomenon Upon Startup Deformation Of Entangled Linear Polymeric Liquids, Yangyang Wang, Shi-Qing Wang Dec 2009

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 …

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Nature Of Steady Flow In Entangled Fluids Revealed By Superimposed Small Amplitude Oscillatory Shear, Pouyan E. Boukany, Shi-Qing Wang Dec 2009

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 …

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Nonlinearity In Large Amplitude Oscillatory Shear (Laos) Of Different Viscoelastic Materials, Xin Li, Shi-Qing Wang, Xiaorong Wang Oct 2009

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 …

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Synthesis And Characterization Of Some Rhenium Complexes, Joseph Brian Scott Aug 2009

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 …

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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 Jul 2009

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.

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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 Jun 2009

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 …

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Universal Scaling Behavior In Startup Shear Of Entangled Linear Polymer Melts, Pouyan E. Boukany, Shi-Qing Wang, Xiaorong Wang Jun 2009

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]

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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 May 2009

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 …

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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 Mar 2009

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 …

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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 Mar 2009

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 …

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Theory And Computation Of Photopolymerization-Induced Phase Transition And Morphology Development In Blends Of Crystalline Polymer And Photoreactive Monomer, Pankaj Rathi, Thein Kyu Mar 2009

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 …

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Shear Banding Or Not In Entangled Dna Solutions Depending On The Level Of Entanglement, Pouyan E. Boukany, Shi-Qing Wang Feb 2009

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, …

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Understanding Rubber Friction In The Presence Of Water Using Sum-Frequency Generation Spectroscopy, Kumar Nanjundiah, Ping Yuan Hsu, Ali Dhinojwala Jan 2009

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 …

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Inhomogeneous Degradation Of Polymer Electrolyte Membrane In Pem Fuel Cells, Xinyu Huang, Wonseok Yoon Jan 2009

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.

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Photopolymerization-Induced Crystallization And Phase Separation In Poly(Ethylene Oxide)/Triacrylate Blends, Soo Jeoung Park, Thein Kyu Dec 2008

Photopolymerization-Induced Crystallization And Phase Separation In Poly(Ethylene Oxide)/Triacrylate Blends, Soo Jeoung Park, Thein Kyu

College of Polymer Science and Polymer Engineering

The present article describes experimental and theoretical investigations of miscibility and crystallization behavior of blends of poly(ethylene oxide) (PEO) and triacrylate monomer (TA) using differential scanning calorimetry and optical microscopy. The PEO/TA blends manifested a single T(g) varying systematically with composition suggestive of a miscible character in their amorphous states. Moreover, there occurs melting point depression of PEO crystals with increasing TA. A phase diagram was subsequently established that exhibited a solid+liquid coexistence region bound by the liquidus and solidus lines, followed by an upper critical solution temperature (UCST) at a lower temperature. The emerging phase morphology was investigated to …

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From Elastic Deformation To Terminal Flow Of A Monodisperse Entangled Melt In Uniaxial Extension, Yangyang Wang, Shi-Qing Wang Dec 2008

From Elastic Deformation To Terminal Flow Of A Monodisperse Entangled Melt In Uniaxial Extension, Yangyang Wang, Shi-Qing Wang

College of Polymer Science and Polymer Engineering

Using a well-entangled monodisperse styrene-butadiene random-copolymer (SBR) melt as a model system, we illustrate generic features of uniaxial extension behavior that may be shared by all well-entangled thermoplastic and elastomeric materials. Depending on the imposed extensional rate, the same sample may behave like a viscous liquid or an elastic "solid." Analogous to the recently revealed shear inhomogeneity, the SBR melt inevitably undergoes cohesive failure in the form of sample breakage whenever the Weissenberg number is much greater than unity, making it challenging to reach steady state. In the elastic deformation regime where the external deformation rate is faster than Rouse …

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Partial Crystallinity In Alkyl Side Chain Polymers Dictates Surface Freezing, Shishir Prasad, Zhang Jiang, Sunil K. Sinha, Ali Dhinojwala Aug 2008

Partial Crystallinity In Alkyl Side Chain Polymers Dictates Surface Freezing, Shishir Prasad, Zhang Jiang, Sunil K. Sinha, Ali Dhinojwala

College of Polymer Science and Polymer Engineering

We have studied the structure of a novel crystalline surface monolayer on top of a disordered melt of the same material [poly(n-alkyl acrylate)s] using grazing incidence x-ray diffraction. The grazing incidence x-ray diffraction, surface tension, and bulk latent heat results show that side chains crystallize except the nine methylene units of the alkyl side chains closest to the polymer backbone. The partial crystallinity along with a thicker surface layer, due to the additional length of the linker group, explains why the difference between the surface order-to-disorder transition temperature and bulk melting temperature increases with a decrease in the length of …

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Steady State Measurements In Stress Plateau Region Of Entangled Polymer Solutions: Controlled-Rate And Controlled-Stress Modes, Sham Ravindranath, Shi-Qing Wang Aug 2008

Steady State Measurements In Stress Plateau Region Of Entangled Polymer Solutions: Controlled-Rate And Controlled-Stress Modes, Sham Ravindranath, Shi-Qing Wang

College of Polymer Science and Polymer Engineering

Despite decades of efforts, reliable measurements of nonlinear flow behavior of well-entangled polymers in continuous shear have been challenging to obtain. The present work attempts to accomplish three important tasks: (A) overcome this challenge by adopting a strategy of decoupling theological measurements from the outer meniscus region in a cone-partitioned plate (C/PP) setup; (B) determine whether well-entangled solutions indeed undergo a flow transformation under creep that can be taken to phenomenologically define an entanglement-disentanglement transition (EDT); (C) provide the velocity profiles of such solutions undergoing either controlled-stress or controlled-rate shear by carrying out in situ particle-tracking velocimetric (PTV) measurements. Upon …

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Universal Scaling Characteristics Of Stress Overshoot In Startup Shear Of Entangled Polymer Solutions, Sham Ravindranath, Shi-Qing Wang Jun 2008

Universal Scaling Characteristics Of Stress Overshoot In Startup Shear Of Entangled Polymer Solutions, Sham Ravindranath, Shi-Qing Wang

College of Polymer Science and Polymer Engineering

We have carried out conventional theological measurements to explore the well-known stress overshoot behavior in startup shear of eight entangled polybutadiene solutions. In the elastic deformation regime with (gamma)over dot tau(R)> 1, we have identified universal scaling features associated with the stress maximum sigma(max) for samples of different levels of entanglements per chain ranging from 27, 40 to 64. Specifically, at the moment t(max) of the peak stress sigma(max) where the applied strain is gamma(max) = (gamma)over dott(max): (a) sigma(max) varies linearly with gamma(max), (b) sigma(max) scales with t(max) as sigma(max)similar to(t(max))-1/2. The combination of (a) and (b) yields a …

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Sticky Gecko Feet: The Role Of Temperature And Humidity, Peter H. Niewiarowski, Stephanie Lopez, Liehui Ge, Emily Hagan, Ali Dhinojwala May 2008

Sticky Gecko Feet: The Role Of Temperature And Humidity, Peter H. Niewiarowski, Stephanie Lopez, Liehui Ge, Emily Hagan, Ali Dhinojwala

College of Polymer Science and Polymer Engineering

Gecko adhesion is expected to be temperature insensitive over the range of temperatures typically experienced by geckos. Previous work is limited and equivocal on whether this expectation holds. We tested the temperature dependence of adhesion in Tokay and Day geckos and found that clinging ability at 12 degrees C was nearly double the clinging ability at 32 degrees C. However, rather than confirming a simple temperature effect, our data reveal a complex interaction between temperature and humidity that can drive differences in adhesion by as much as two-fold. Our findings have important implications for inferences about the mechanisms underlying the …

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Large Amplitude Oscillatory Shear Behavior Of Entangled Polymer Solutions: Particle Tracking Velocimetric Investigation, Sham Ravindranath, Shi-Qing Wang May 2008

Large Amplitude Oscillatory Shear Behavior Of Entangled Polymer Solutions: Particle Tracking Velocimetric Investigation, Sham Ravindranath, Shi-Qing Wang

College of Polymer Science and Polymer Engineering

Large amplitude oscillatory shear (LAOS) has been employed widely to probe the nonlinear behavior of complex fluids. Typically, the system undergoing LAOS has been assumed to experience homogeneous shear in each cycle so that material functions can be introduced to analyze the nonlinear dependence of these functions on the amplitude and frequency. Using particle-tracking velocimetric technique, we have carried a more systematic investigation on four different entangled polybutadiene (PBD) solutions with the number of entanglements per chain Z=13, 27, 64 and 119, extending well beyond the initial observations of shear banding in entangled PBD solutions under LAOS [Tapadia , Phys. …

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Thermal Damage Approach Of Concrete: Application To Specimens Subjected To Combined Compressive And High Temperature Loads, Abdellah Menou, Ghassan Mounajed, Hocine Boussa, Christian La Borderie, Khalid Lafdi Feb 2008

Thermal Damage Approach Of Concrete: Application To Specimens Subjected To Combined Compressive And High Temperature Loads, Abdellah Menou, Ghassan Mounajed, Hocine Boussa, Christian La Borderie, Khalid Lafdi

Chemical and Materials Engineering Faculty Publications

Within the framework of study of concrete structures subjected to fire, .a theoretical and experimental work was conducted. The aim of this study was to investigate and to model the damage mechanisms of concrete after their exposure to high temperatures. The multiphase Digital Concrete Model as well as the damage model, MOD EV, which were both implemented on the finiteelem~ rit software package, SYMPHONIE, were used simμltaneously to assess the thermal damage of the concrete. In order to validate the thermal damage model, an experimental investigation was performed. The mechanical characteristics of 5 cementitious materials, which included cement paste, mortar, …

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