Chemical Engineering Commons^™

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 …

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 …

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

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

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

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

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

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

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

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

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

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

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

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

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

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. …

Compostability Of Degradable Plastics And Its Use In Solid Waste Disposal / Putri Nadzrul Faizura Bt Megat Khamaruddin., Putri Nadzrul Faizura Megat Khamaruddin

Student Works (2000-2009)

Plastic waste generation and quantity generated is a growing concern in many countries including Malaysia. Plastic waste contributes the third highest waste volume in Malaysian municipal solid waste (MSW) next to putrescible waste and paper. ln the year 2000, plastic waste in MSW of Kuala Lumpur was 24.4% by weight from the MSW and most of the plastic waste was dumped into landfills. Landfills in Malaysia are reducing in its useful life as the amount of waste generated is growing every year by 2% and they have become an undesirable option of getting rid of plastic waste because of the …

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

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

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 …

Effects Of Compression Processing Parameters And Antioxidants On Molecular Degradation Of Biodegradable Poly-L-Lactide (Plla), Thomas J. Hannan Jr.

Masters Theses

The purpose of this research was to find a combination of poly (L-lactic acid), also known as poly-L-lactide or (PLLA) and antioxidants that would, together, produce a product whose degradation rate would be advantageous for use in biodegradable medical implants. Intrinsic viscosity tests were conducted on compression molded samples of PLLA that were molded at various processing parameters in order to find optimal parameters. The optimal processing parameters were found to be time 10 minutes, temperature 220°C, and pressure 1000 psi.

The molecular weight of PLLA sample was taken while pressure, time, and temperature were varied. As pressure increased, no …

The Effects Of Incorporation Of Polyethylene Glycol On Properties Of Silica-Carbon Black-Filled Rubber Compound, Yoke Cheng Tang

Student Works (2000-2009)

The use of polyethylene glycol (PEG) to modify the surface of precipitated silica by means of physical adsorption was investigated. The effects of adding PEG on processing, cure and physical properties of a silica-carbon black-filled natural rubber truck tread compound were examined. For each series of investigation, two sets of experiments were conducted. Set I was to check the effects of both physical adsorption due to PEG and chemical modification due to a silane coupling agent, Si-69 on the surface of silica. Set 2 was to check the effects of physical adsorption due to PEG alone on the surface of …

Molecular Structure Of Polystyrene At Air/Polymer And Solid/Polymer Interfaces, K. S. Gautam, Alexander D. Schwab, Ali Dhinojwala, D. Zhang, S. M. Dougal, M. S. Yeganeh

College of Polymer Science and Polymer Engineering

IR-visible sum-frequency generation(SFG) spectroscopy has been used in a total internal reflection geometry to study the molecular structure of polystyrene (PS) at PS/sapphire and PS/air interfaces, simultaneously. The symmetric vibrational modes of the phenyl rings dominate the SFG spectra at the PS/air interface as compared to the antisymmetric vibrational modes at the PS/sapphire interface. This indicates approximately parallel orientation of the phenyl rings at the PS/air interface while nearly perpendicular orientation at the PS/sapphire interface, with respect to the surface normal.

Theoretical Investigation On Dynamics Of Photopolymerization-Induced Phase Separation And Morphology Development In Nematic Liquid Crystal/Polymer Mixtures, Domasius Nwabunma, Hao-Wen Chiu, Thein Kyu

College of Polymer Science and Polymer Engineering

A theoretical investigation of the dynamics of photopolymerization-induced phase separation (PIPS) and morphology development in a nematic liquid crystal (LC) polymer network mixture has been undertaken by incorporating photopolymerization kinetics into the coupled time-dependent Ginzburg-Landau (TDGL-Model C) equations. The simulation on the spatio-temporal evolution of the coupled LC concentration and orientation order parameters reveals that both morphological and scattering patterns for the orientation order parameter initially lag behind those of the concentration order parameter. However, the two fields evolve to the same spatial topologies with the progression of time. The PIPS dynamics is characterized only by the late stage of …

Bending Instability Of Electrically Charged Liquid Jets Of Polymer Solutions In Electrospinning, Darrell Hyson Reneker, Alexander L. Yarin, Hao Fong, Sureeporn Koombhongse

College of Polymer Science and Polymer Engineering

Nanofibers of polymers were electrospun by creating an electrically charged jet of polymer solution at a pendent droplet. After the jet flowed away from the droplet in a nearly straight line, it bent into a complex path and other changes in shape occurred, during which electrical forces stretched and thinned it by very large ratios. After the solvent evaporated, birefringent nanofibers were left. In this article the reasons for the instability are analyzed and explained using a mathematical model. The rheological complexity of the polymer solution is included, which allows consideration of viscoelastic jets. It is shown that the longitudinal …

Spatiotemporal Growth Of Faceted And Curved Single Crystals, Thein Kyu, Rujul Mehta, Hao-Wen Chiu

College of Polymer Science and Polymer Engineering

The spatiotemporal growth of single crystals in a crystalline polymer has been investigated theoretically based on a nonconserved time dependent Ginzburg-Landau equation (known as TDGL model A). In the description of the total free energy, a double-well local foe energy density signifying metastability of crystal ordering is combined with a nonlocal free energy term representing an interface gradient. The resulting nonlinear reaction diffusion equation after renormalization possesses a solitary wave property. Two-dimensional numerical calculations were performed to elucidate the faceted single crystal growth including square, rectangular, diamond-shaped, and curved single crystals. A three-dimensional simulation was also undertaken for the emergence …

Double Twist In Helical Polymer "Soft" Crystals, Christopher Y. Li, Stephen Z. D. Cheng, Jason J. Ge, Feng Bai, John Z. Zhang, Ian K. Mann, Frank W. Harris, Lang-Chy Chien, Donghang Yan, Tianbai He, Bernard Lotz

College of Polymer Science and Polymer Engineering

In natural and synthetic materials having non-racemic chiral centers, chirality and structural ordering each play a distinct role in the formation of ordered states. Configurational chirality can be extended to morphological chirality when the phase, structures possess low liquid crystalline order. In the crystalline states the crystallization process suppresses the chiral helical morphology due to strong ordering interactions, In this Letter, we report the first observation of helical single lamellar crystals of synthetic non-racemic chiral polymers. Experimental evidence shows that the molecular chains twist along both the long and short axes of the helical lamellar crystals, which is the first …

Helical Single-Lamellar Crystals Thermotropically Formed In A Synthetic Nonracemic Chiral Main-Chain Polyester, Christopher Y. Li, Donghang Yan, Stephen Z. D. Cheng, Feng Bai, Jason J. Ge, Bret H. Calhoun, Tianbai He, Liang-Chy Chien, Frank W. Harris, Bernard Lotz

College of Polymer Science and Polymer Engineering

Phase structures and transformation mechanisms of nonracemic chiral biological and synthetic polymers are fundamentally important topics in understanding their macroscopic responses in different environments. It has been known for many years that helical structures and morphologies can exist in low-ordered chiral liquid crystalline (LC) phases. However, when the chiral liquid crystals form highly ordered smectic liquid crystal phases, the helical morphology is suppressed due to the crystallization process. A double-twisted morphology has been observed in many liquid crystalline biopolymers such as dinoflaggellate chromosomes (in Prorocentrum micans) in an in vivo arrangement. Helical crystals grown from solution have been reported in …

Phase Structures And Morphologies Determined By Competitions Among Self-Organization, Crystallization, And Vitrification In A Disordered Poly(Ethylene Oxide)-B-Polystyrene Diblock Copolymer, Lei Zhu, Yan Chen, Anqui-Q. Zhang, Bret. H. Calhoun, Moonseok Chun, Stephen Z. D. Cheng, Benjamin S. Hsiao, Fengji Yeh, Takeji Hashimoto

College of Polymer Science and Polymer Engineering

A poly(ethylene oxide)-b-polystyrene (PEO-b-PS) diblock copolymer having a number-average molecular weight ((M) over bar(n)) of 11000 g/mol in the PEO blocks and an (M) over bar(n) of 5200 g/mol in the PS blocks has been synthesized (with a volume fraction of the PEO blocks of 0.66 in the molten state). Differential scanning calorimetry results show that this copolymer possesses a single endotherm, which is attributed to the melting of the PEG-block crystals. Based on real-time resolved synchrotron small-angle x-ray scattering (SAXS) observations, the diblock copolymer is in a disordered state above the glass transition temperature of the PS-rich phase (T-g(PS)) …

Rhythmic Growth Of Target And Spiral Spherulites Of Crystalline Polymer Blends, Thein Kyu, Hw Chiu, Aj Guenthner, Y Okabe, H Saito, T Inoue

College of Polymer Science and Polymer Engineering

Numerical calculations reveal that the target and spiral growth patterns in spherulites can be generated from the time-dependent Ginzburg-Landau equations (model C) by coupling a conserved compositional order parameter and a nonconserved crystal ordering parameter. Of particular interest is that the periodic concentric rings (target) or the spirals at the spherulitic core remain stationary in both the crystal (orientational) ordering field and the concentration field. Another intriguing observation is that the growth of target and spiral spherulites occurs in a stepwise fashion in synchronism with the rhythmic energy dissipation during crystallization.