Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session V18: Focus Session: Physics of Green Polymers and of Biocompatibility |
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Sponsoring Units: DPOLY DBP Chair: John Torkelson, Northwestern University Room: 319 |
Thursday, March 19, 2009 8:00AM - 8:36AM |
V18.00001: Spectroscopic Analyses of Microstructures Associated with Plant Based Polymers Invited Speaker: Currently, less than 0.02\% of polymers used are plant based with the rest originating from petroleum feedstock. There are a number of applications that require some of these new polymers, independent of the cost of the petroleum. Because of their size scale, it is most appropriate to use vibrational and NMR spectroscopy to characterize the microstructure of these plant based polymers. We present a number of examples in order to illustrate the use of these alternative polymers. Soybean is one of the most promising alternatives. Both its saturated and unsaturated components can be utilized. In various applications, the saturated component is important because the rapid crystallization directly controls the rheological behaviors. This is especially significant if cocrystallization with other polymers, especially statistically random copolymers, is an important consideration. Crystallization kinetics and subsequent morphological units formed have yet to be characterized. In addition, the unsaturated component can be modified to form various polyols for use in reactive mixtures. The miscibility behavior of such polymers with other oligomers or polymers strongly influences the reaction kinetics and the products formed. The extreme hydrophobic nature of soybean based polymers is reflected in that it has opposite physical properties to that of the hydrophilic polyols used in the current formulations. We also have significant interest in poly(lactic acid). We have characterized the inherent structural rigidity, correlating the changes in chain conformation to the chain conformation. We have identified the intermolecular forces which stabilized the crystalline units. In addition, we have been able to control the crystallization process resulting from addition configurational defects. These applications illustrate the opportunities we have available in a world which may embrace such a set of polymers. [Preview Abstract] |
Thursday, March 19, 2009 8:36AM - 8:48AM |
V18.00002: Toughening and reinforcing degradable polymers to extend their properties and applications SuPing Lyu, Jianbin Zhang, Adam Buckalew, Jim Schley, Bryant Pudil, Lian Luo, Chris Hobot, Mike Benz, Randy Sparer, Julie Trudel Polymer materials made from renewable feedstocks mainly are cellulose derivatives and aliphatic polyesters such as polylactide. There are two challenges in the use of these materials to replace petroleum based polymers. One is how to easily process these materials to make them into needed shapes and other is how to broaden the properties of these materials so that they can be used for applications where petroleum based polymers play major roles. Most of the renewable source based materials are brittle. This abstract presents a method of how to toughen and reinforce polylactide to make a family of polymers that cover broad ranges of toughness and strength for various applications such as biomedical device manufacturing. [Preview Abstract] |
Thursday, March 19, 2009 8:48AM - 9:00AM |
V18.00003: A QCM-D Study of the Enzymatic Degradation of Cellulose Thin Films Dan Glickman, Oleh Tanchak, Michael Reid, Amanda Quirk, Darrell Cockburn, Colin Macdougall, Anthony Clarke, Jacek Lipkowski, John Dutcher A sophisticated surface-sensitive technique, the quartz crystal microbalance with dissipation monitoring (QCM-D), was used to study the interaction of a mixture of cellulolytic enzymes from the fungus T. reesei with cellulose thin films deposited onto polycrystalline gold surfaces. It was found that the QCM experiment was sensitive to two processes that occur during the enzyme mixture-cellulose thin film experiment: adsorption of the enzyme to the film surface, and the subsequent degradation of the cellulose thin film. A model describing the measured frequency shift in the QCM data will be described, which gives excellent fits to the experimental data. [Preview Abstract] |
Thursday, March 19, 2009 9:00AM - 9:12AM |
V18.00004: An Atomic Force Microscopy Study of the Mechanism of Cellulose Biodegradation Amanda Quirk, Maohui Chen, Darrell Cockburn, Sarah Regli, Anthony Clarke, John Dutcher, Jacek Lipkowski, Sharon Roscoe Cellulose, a biopolymer consisting of long chain $\beta $-(1$\to $4) linked glucose sugars, is used as structural material by plants and bacteria. Degradation of cellulose to glucose, a sugar easily fermented to ethanol, occurs by the enzymatic hydrolysis of cellulose by cellulase enzymes. The enzymes have a~complex structure including carbohydrate binding modules and catalytic domains responsible for the binding and degradation of cellulose, respectively. Atomic force microscopy (AFM) was used to study native cellulose films prepared from Acetobacter xylinum using a novel application of the Langmuir-Blodgett technique. These films allowed AFM images of single fibers and their microfibril structure to be obtained. Further \textit{in situ} AFM studies of single fibers were performed in solution using cellulolytic enzymes. The \textit{in situ} degradation of cellulose fibers was monitored over 20-hours using AFM. These studies provided insight into the degradation timeline of a single fiber. Complementary studies of proteins adsorbed on cellulose fibers revealed information about the binding of the enzymes to the substrate. Studying the modular enzyme action separately will provide insight into the mechanism of cellulose binding and contribute to our understanding of the degradation process. [Preview Abstract] |
Thursday, March 19, 2009 9:12AM - 9:24AM |
V18.00005: Observation of Biodegradation of Cellulose Fibers Using Surface Plasmon Resonance Imaging Oleh M. Tanchak, Scott Allen, Darrell Cockburn , Anthony J. Clarke, Jacek Lipkowski, John R. Dutcher Cellulose is the most abundant biopolymer on Earth and can provide a renewable supply of ethanol fuel to replace fossil fuels. A fundamental understanding of the mechanisms of the biodegradation of cellulose is essential to the development novel enzyme systems that can efficiently and selectivity degrade a variety of biomass substrates. A novel Surface Plasmon Resonance Imaging (SPRI) instrument was used to study the biodegradation of cellulose fibers anchored to a thiolated gold surface. The kinetics of binding of the inactive enzymes to cellulose fibers and their digestion by catalytically-active homologs will be presented. [Preview Abstract] |
Thursday, March 19, 2009 9:24AM - 9:36AM |
V18.00006: Sustainable Engineering and Improved Recycling of PET for High-Value Applications: Transforming Linear PET to Lightly Branched PET with a Novel, Scalable Process Cynthia Pierre, John Torkelson A major challenge for the most effective recycling of poly(ethylene terephthalate) concerns the fact that initial melt processing of PET into a product leads to substantial degradation of molecular weight. Thus, recycled PET has insufficient melt viscosity for reuse in high-value applications such as melt-blowing of PET bottles. Academic and industrial research has tried to remedy this situation by synthesis and use of ``chain extenders'' that can lead to branched PET (with higher melt viscosity than the linear recycled PET) via condensation reactions with functional groups on the PET. Here we show that simple processing of PET via solid-state shear pulverization (SSSP) leads to enhanced PET melt viscosity without need for chemical additives. We hypothesize that this branching results from low levels of chain scission accompanying SSSP, leading to formation of polymeric radicals that participate in chain transfer and combination reactions with other PET chains and thereby to in situ branch formation. The pulverized PET exhibits vastly enhanced crystallization kinetics, eliminating the need to employ cold crystallization to achieve maximum PET crystallinity. Results of SSSP processing of PET will be compared to results obtained with poly(butylene terephthalate). [Preview Abstract] |
Thursday, March 19, 2009 9:36AM - 9:48AM |
V18.00007: Spontaneously Formed Biocompatible Surfaces in Water by Segregation of Amphiphilic Block Copolymers Hideaki Yokoyama, Takashi Ishizone, Naoya Torikai, Jaroslaw Majewski, Ayako Oyane Reduction of hydrophobic interaction in water is important in biological interfaces. We have found that poly(styrene-\textit{b}-oligo ethylene glycol methyl ether methacrylate) (PS-PMENMA) segregates the PMENMA block to the surface in hydrophobic environment such as in air or in a vacuum, and shows remarkable resistance against adsorption or adhesion of proteins, platelets and cells in water. We studied the interfacial structures between PS modified by the spontaneous segregation of PS-PMENMA and water using neutron reflectivity and adhesion force measurement using atomic force microscope with hydrophobic probes. The interfacial structure and hydrophobic interaction depend on the number of ethylene glycol (EO) units in PMENMA. PMENMAs with two or more EO units show distinct swollen layers with two sharp interfaces at polymer/water interfaces, which effectively reduce hydrophobic interaction in water, while PMENMA with one unit of EO diplays broader single interface with unsatisfactory reduction. [Preview Abstract] |
Thursday, March 19, 2009 9:48AM - 10:24AM |
V18.00008: Electrospun Nanofibers for Neural and Tissue Engineering Invited Speaker: Electrospinning has been exploited for almost one century to process polymers and other materials into nanofibers with controllable compositions, diameters, porosities, and porous structures for a variety of applications. Owing to its small size, high porosity, and large surface area, a nonwoven mat of electrospun nanofibers can serve as an ideal scaffold to mimic the extra cellular matrix for cell attachment and nutrient transportation. The nanofiber itself can also be functionalized through encapsulation or attachment of bioactive species such as extracellular matrix proteins, enzymes, and growth factors. In addition, the nanofibers can be further assembled into a variety of arrays or architectures by manipulating their alignment, stacking, or folding. All these attributes make electrospinning a powerful tool for generating nanostructured materials for a range of biomedical applications that include controlled release, drug delivery, and tissue engineering. This talk will focus on the use of electrospun nanofibers as scaffolds for neural and bone tissue engineering. [Preview Abstract] |
Thursday, March 19, 2009 10:24AM - 10:36AM |
V18.00009: Control of Protein Adsorption on Surfaces with Grafted Polymers Igal Szleifer, Jan Genzer Non-specific protein adsorption is the first process in the foreign body response. The molecular design of surface modifiers that prevent non-specific adsorption requires the understanding of the factors that determine protein adsorption. The hierarchy of time and length scales present in the adsorption requires a multiscale approach to treat the complexity of the process. We will discuss the driving forces that determine protein adsorption and how end-grafted polymers can be used to modify the ability of the proteins to reach the surface. We will show the differences between preventing protein adsorption thermodynamically and kinetically. For practical applications the relevant time scales are hours or days. We will show how a molecular approach can be used to study these time scales. In particular we will show two different levels of approximations based on a molecular understanding of the adsorption process that enables, through the proper integration of degrees of freedom, to determine the kinetics of adsorption over 16 orders of magnitude in time. This approach is applied to explain recent experimental observations carried out on orthogonal modified surfaces that suggest that protein adsorption is a universal function of the product of grafted polymer surface coverage and molecular weight. [Preview Abstract] |
Thursday, March 19, 2009 10:36AM - 10:48AM |
V18.00010: Optimization of Polymer Surfaces for Specific Targeting Elena Dormidontova, Matthew Hagy, Shihu Wang Using Monte Carlo simulations we studied reversible binding between a polymer layer functionalized by ligands and a receptor surface. By analyzing distance-dependent profiles for the average number of ligands bound to receptors, the total free energy of polymer layer-cell surface interaction and the interaction force the influence of different design parameters of a polymer layer on the affinity and specificity of binding were investigated. We show that planar polymer layers with a smaller chain length and grafting density, larger degree of functionalization, and larger absolute binding energy exhibit higher affinity to the cell surfaces with a large density of mobile receptors. A high binding specificity can be achieved by the polymer layers with intermediate ligand-receptor binding energies or an intermediate number of ligands, as a larger binding energy or number of ligands lacks specificity while a smaller binding energy or number of ligands provides inadequate affinity. As a result, the optimal design of the polymer layers can be achieved by using several different strategies, which will be discussed. [Preview Abstract] |
Thursday, March 19, 2009 10:48AM - 11:00AM |
V18.00011: Cluster structure in urea aqueous solution and it's effect on DNA denature He Cheng, Charles C. Han, Boualem Hammouda The existence of large cluster structure in urea aqueous solution is proved by Small Angle Neutron Scattering (SANS). Our results indicate that urea is a water- structure-breaker, and large urea cluster will be formed when it's concentration is higher than 20 w{\%}. This cluster is very stable, and almost do not change with temperature. The helix-to-coil denaturation transition of DNA was studied with various urea concentrations, to testify the solvent structure influence on this process. [Preview Abstract] |
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