Home > Seminars > Spring 2010 Seminar Series
Time: Fridays, 2:00 p.m. - 3:30 p.m.
Location: Aggarwal Lecture Hall, Room 130
Polymer Engineering Academic Center
250 South Forge Street, Akron, OH 44325-0301
Lectures Are Free And Open To The Public
Click here to print the schedule
Date |
Topic / Speaker |
Jan. 29 |
"Conformations of Molecular Brushes: From Flory Theorem to Fingering Instability" |
Feb. 5 |
"Commercialization of Biopolymers: New Polymers and 'Old' Polymers" |
Feb. 12 |
"Properties and Shear Alignment of Nanoparticle-Block Copolymer Hydrogels" |
Feb. 19 |
"Tailoring Nanoporous Materials for Elastic Recovery: Hybrid Silica Aerogels" |
Mar. 5 |
"Polyurethane Biomaterials" |
Apr. 2 |
"Nanofiber-Based Polymeric Composites" |
Apr. 9 |
"Instabilities in Polymer Networks" |
Apr. 16 |
"Structure-Property Relationship of Nanoclay Filled Polymer Nanocomposites" |
Apr. 23 |
"Improvements in the Simulation of Orientation in Injection Molding of Short Fiber Thermoplastic Composites" |
Apr. 30 |
"Low-Cost Carbon Fiber for Automotive Applications" |
"Conformations of Molecular Brushes: From Flory Theorem to Fingering Instability"
Dr. Andrey Dobrynin
Department of Physics
University of Connecticut
Molecular brushes are comb-like molecules consisting of a flexible backbone with short side chains grafted to it. One of the most distinctive properties of these molecules is their ability to switch conformations in response to the surrounding environment. This behavior is particularly prominent on substrates. I will present two examples of the effect of interactions on the conformations of brush-like molecules in thin films and show how conformational transitions could influence the film spreading behavior.
It is well known that the interactions between macromolecules in solution become screened as polymer concentration increases. In polymeric melts, where the interactions are completely screened, macromolecules behave as almost ideal chains obeying random walk statistics. I will show how to extend the concept of the screening of intramolecular interactions to the case of polymeric films consisting of brush molecules and linear polymer chains. Application of the screening concept demonstrates that swelling of a brush molecule is controlled not only by the degree of polymerization of the surrounding linear chains, NB, but also by the degree of polymerization of the brush's side chains, N, which determines the structural asymmetry of the mixed species. The predictions of the theoretical model are in a good quantitative agreement with the results of a direct visualization by AFM of the conformational transformations in brush molecules. These findings carry vital implications for the development of nanocomposite materials containing molecular species with different architectures.
Ability of brush molecules to adjust their conformations in response to interaction with the surrounding environment results in a new type of flow fingering (Saffman-Taylor–type) instability during spreading of a monolayer-thick brush films on a solid substrate. This instability is triggered by a conformational transition of brush-like macromolecules. The transition segregates the flowing monolayer into two conformationally different phases and simultaneously leads to an abrupt decrease in the monolayer thickness. AFM visualization of the movement of individual molecules and evolution of the instability pattern on the molecular level confirms the conformational nature of the fingering instability in spreading brush monolayers.
"Commercialization of Biopolymers: New Polymers and 'Old' Polymers"
Roger Avakian
Vice President of Scientific Development
PolyOne Corporation
Biopolymers, such as PLA (poly lactic acid or poly lactide) have recently attracted a lot of interest and publicity in both academia and industry because they are derived from renewable resources and possess many commercially desirable properties. However, compared to existing non-renewable plastics they are meant to replace, many new biopolymers have inherent weaknesses in physical properties such as impact strength and heat resistance, which dramatically limits their use in many applications.
In order to address these issues in the near term, efforts have been made to blend biopolymers with existing petroleum derived polymers to develop higher performance properties. Meanwhile many researchers are looking at ways to derive traditional polymers from sustainable sources.
This presentation discusses PolyOne's efforts to address the industry need to improve the low heat distortion temperature and impact exhibited by injection molded PLA for durable applications. Additionally it will highlight what is being done in the industry to develop traditional polymers from renewable feed stocks.
"Properties and Shear Alignment of Nanoparticle-Block Copolymer Hydrogels"
Dr. Lynn M. Walker
Department of Chemical Engineering
Carnegie Mellon University
Self-assembled block copolymer templates are used to control the nanoscale structure of materials that would not otherwise order in solution. In this work, we have developed a technique to use close-packed cubic and cylindrical mesophases of a thermoreversible block copolymer (PEO-PPO-PEO) to impart spatial order on dispersed nanoparticles. The thermoreversible nature of the template allows for the dispersion of particles synthesized outside the template. This feature extends the applicability of this templating method to many particle-polymer systems and also permits a systematic evaluation of the impact of design parameters on the structure and mechanical properties of the nanocomposites. The criteria for forming co-crystals has been fully characterized using contrast-matching small-angle neutron scatting (SANS) and the mechanical properties of these soft crystals determined. SANS experiments also demonstrate that shear can be used to align the nanocomposites into single-crystal macro-domains; the first demonstration of the formation of single-crystal nanoparticle superlattices. Numerous crystal structures have been reported for the block copolymer system and we have taken advantage of several to generate soft co-crystals. We are currently utilizing SANS to understand the flow mechanisms of several types of these co-crystals.
"Tailoring Nanoporous Materials for Elastic Recovery: Hybrid Silica Aerogels"
Jason Randall
Department of Polymer Engineering
The University of Akron
The low density and low thermal conductivity of silica aerogels makes them promising choices for use as insulation where weight is at a premium, typically the aerospace industry. However, traditional silica aerogels are fragile and friable and thus much work has been focused recently upon improving their mechanical properties. In particular, it is desirable for aerogels to exhibit robust strength as well as elastic recovery from compression to enable applications such as inflatable decelerators for planetary re-entry of spacecraft, or the next generation space suit.
In this work, a series of alkyl chain linked hybrid silanes are investigated for their ability to improve the recovery behavior of otherwise rigid epoxy reinforced silica aerogels. Sol-gel synthesis and supercritical carbon dioxide drying of these hybrid silica aerogels yields the expected "pearl necklace" nanostructure of base catalyzed silanes, with larger than typical pore size as demonstrated by SEM and nitrogen sorption porosimetry. Compression testing to 25% strain reveals aerogel formulations capable of near perfect elastic recovery while retaining a compressive modulus significantly higher than most traditional formulations. Additionally, an amine functionalized hybrid silane is demonstrated to provide both improved recovery as well as increased strength in aerogels through its use as a crosslinking site with epoxy.
"Polyurethane Biomaterials"
Dr. Stuart L. Cooper
Department of Chemical Engineering
The Ohio State University
Polyurethanes have gained acceptance in the biomedical field because they have good physical properties and biocompatibility. The name "polyurethane" describes a class of polymers that can be synthesized to possess a variety of properties, from hard to brittle to very elastic. The polyurethanes that have found use in biomedical applications have elastomeric properties accompanied by good toughness, tear resistance and abrasion resistance. They have been widely used in applications such as the artificial heart and pacemaker lead insulation, among others. The role of polyurethane's surface in the blood-material interaction will be described. Surface properties believed to affect biocompatibility include the interrelated properties of hydrophobicity, polarity and surface charge. The presence and mobility of microdomain surface morphologies may also affect protein adsorption and thrombus formation.
In an attempt to use polyurethanes in more demanding applications, we have been modifying their structure to include functional groups, which have the potential to exhibit bioactivity. Polyurethanes containing sulfonate groups exhibit hydrogel and anticoagulant behavior compared to unmodified polyurethanes. The sulfonated polyurethanes affect the ability of fibrinogen to polymerize and they consume thrombin, an important enzyme in the coagulation pathway.
Progress in understanding the interactions of the Arg-Gly-Asp (RGD) peptide sequence and integrins has stimulated a great deal of interest in the development of novel biomaterials, which may improve endothelial cell attachment and growth. Rather than immobilization of peptide to the polymer surface, an alternative approach was taken in that a polyurethane block polymer was modified so that it contained free carboxyl groups (PEU-COOH). Two cell adhesive peptides, GRGDSY (based on the fibronectin sequence, RGDS) and GRDVY (based on the vitronectin sequence RGDV), and an inactive peptide GRGESY were then grafted to the polyurethane backbone through the formation of amide linkages. The effects of peptide incorporation on polymer surface properties and endothelial cell adhesion were evaluated.
"Nanofiber-Based Polymeric Composites"
Dr. Patrick T. Mather
Director, Syracuse Biomaterials Institute
Syracuse University
It is well established that the properties of polymeric materials can be tailored at multiple scales, from macromolecular composition and architecture to macroscopic reinforcement with fillers or fibers. Reinforcement of polymeric materials at the nanometer scale offers advantages of homogeneity and synergistic effects intrinsic to the 1-100 nm scale and interphase formation. Nevertheless, preparation of nanocomposites is challenging. In the past, routes to polymeric nanocomposites have largely fallen into one of two categories: (i) top-down processing of nanocomposites by dispersion of nanofillers in monomer or polymer melts and solutions, or (ii) bottom-up synthesis of nanocomposites by polymerization of nanostructured monomers. In both cases, it has been challenging for researchers to achieve the interpenetration of matrix and reinforcement often desired for full exploitation of the two phases. In this presentation, a third alternative to the preparation of nanocomposites is presented in the context of several distinct project implementations: electrospun nanocomposites. Here, we first electrospin an interconnected (welded) polymeric nanofiber web using established methods. Then, this web is imbibed with a matrix precursor liquid and crosslinked or otherwise solidified. The result is an interpenetrating nanocomposite with tailored properties. The presentation will reveal four utilizations of such materials, including: (i) Fuel cell membranes, (ii) Shape Memory Elastomeric Composites, (iii) Triple Shape Memory Polymers, and (iv) Electrically Triggered Shape Memory Polymers.
"Instabilities in Polymer Networks"
Dr. Alfred Crosby
Department of Polymer Science & Engineering
University of Massachusetts, Amherst
Upon the development of a critical stress, many materials and geometries experience a mechanical instability, which produces significant changes in geometry with small changes in stress. In nature, mechanical instabilities are ubiquitous with the definition of shape, morphology, and function. Examples range from fingerprints to the snapping of Venus Flytrap. Inspired by these examples, we use elastic instabilities to control the morphology of soft polymer surfaces and investigate the local mechanical properties in polymer networks. Two vignettes will be presented: 1) controlling wrinkle morphology in top-constrained elastomers; and, 2) cavitation rheology for hydrogels and biological tissues. For wrinkling, we use methods with osmotic and adhesive driving forces to induce surface buckles, observing morphological transitions from dimples to wrinkles to organized folds. For cavitation rheology, we study the instantaneous expansion at the tip of a syringe needle induced at a critical pressure for a given polymer network. The critical pressure can be related to the elasticity or fracture properties of the polymer network, depending upon the needle radius. This method provides opportunities for studying mechanical properties in both synthetic polymer networks and biological tissues from molecular to macroscopic length scales at an arbitrary location.
"Structure-Property Relationship of Nanoclay Filled Polymer Nanocomposites"
Dr. Dharmaraj Raghavan
Department of Chemistry
Howard University
Our work in nanocomposites has focused on two areas: new material development and characterization of morphology and properties. Conventional synthetic routes were used to prepare organic modifiers and functionalize the layered material. Functionalized layered material filled polymer nanocomposites were formulated using different processing conditions and modified using rubber tougheners in an attempt to understand the parameters that influence clay and rubber dispersion, and thermal/ mechanical properties. Research showed that functionalized clay along with good processing conditions does improve dispersion of clay in polymer matrix. The amounts of clay platelet separation and dispersion of clay aggregates in the resin matrix were found to be sensitive to clay and toughener concentration, and clay platelets preferentially adsorb to the rubber particles. It was found that particle concentration and dispersion influence reinforcement. It was also observed that the non-uniformly dispersed clay filler promotes heterogeneous regions of lightly crosslinked regions which lower the overall thermal stability of nanocomposite. Special organically modified nanoclays were prepared by treating clays with organic group with thermal decomposition temperature far greater than 300 degrees C. Improved thermo-oxidative stability was noticed when the modified organoclay was well dispersed in the resin.
"Improvements in the Simulation of Orientation in Injection Molding of Short Fiber Thermoplastic Composites"
Dr. Donald G. Baird
Department of Chemical Engineering
Virginia Tech University
The mechanical properties of injection molded short-fiber reinforced thermoplastic composite parts are highly dependent on the orientation distribution of the fibers. A simulation tool capable of predicting fiber orientation accurately as a function of mold design and processing conditions is required as the predicted fiber orientation capabilities in commercial software show large discrepancies when compared with experimentally measured orientation. In this work a two dimensional coupled Hele-Shaw approximation for predicting the flow-induced orientation of glass fibers in injection molded composite parts is presented. In addition to coupling the stresses to fiber orientation for a highly concentrated short glass fiber PBT suspension, the model considers the slowdown of the evolution of orientation due to fiber interaction. Material parameters in the model are determined from basic rheometry rather than using data from injection molding experiments. The equation of motion coupled with stress equations are discretized using the discontinuous Galerkin Finite Element Method. Flow simulations are performed using a measured orientation profile at the gate instead of random orientation assumed in previous studies. Finally, the evolution of fiber orientation in the cavity is determined experimentally using a modified version of the method of ellipses and results are compared against the predicted values of orientation. The fiber orientation predicted in the entry region and the core layer structure at the end of fill region are now in closer agreement with the experimental values, but there are still some discrepancies. These discrepancies may be associated with flow at the advancing front and the non-isothermal nature of the flow near the mold walls.
"Low-Cost Carbon Fibers for Automotive Applications"
Dr. Amit K. Naskar
Materials Science & Technology Division
Oak Ridge National Laboratory
Carbon fibers are conducting and high performance materials used in a variety of structural composite applications. Historically, carbon fiber usage was limited to high end specialty applications. A lower end, high volume utilization, such as widespread use in passenger vehicles, will require significant cost reduction and new technology development. This presentation will give an overview of a cost analysis and research approaches that are being conducted at Oak Ridge National Laboratory (ORNL).
Cost analysis data on conventional polyacrylonitrile (PAN)-based carbon fibers shows that the precursor fiber contributes to 50% of the overall manufacturing cost of carbon fiber. Therefore, identifying suitable lower-cost precursors is a major objective to enable the widespread commercialization of carbon fibers. Inexpensive precursors that were considered include polyolefins, textile grade PAN, lignin, and melt-processible PAN. This presentation will focus on melt-processible precursors. Melt-processibility, however, precludes direct thermal stabilization of these polymeric fibers. To enhance the production rate, UV-radiation assisted crosslinking and chemical functionalization routes have been adopted. In joint work by ORNL-Virginia Tech-Clemson University a melt-processible terpolymer was developed that showed significant promise to produce low-cost carbon fiber. Melt-spun fibers were stabilized and carbonized to yield carbon fibers. Spectroscopic techniques were used to identify the crosslinking reactions. A generalized structure-property relationship of carbonized fibers will be presented.
For further information on any of the above seminars, please contact the faculty host:
Dr. Robert Weiss at rweiss@uakron.edu.
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