Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session H2: Polymer Physics Prize Symposium Honoring Steve Granick |
Hide Abstracts |
Sponsoring Units: DPOLY Chair: MIchael Rubinstein, University of North Carolina Room: Spirit of Pittsburgh Ballroom BC |
Tuesday, March 17, 2009 8:00AM - 8:36AM |
H2.00001: Polymer Physics Prize Talk: Polymer Mobility at Surfaces and in Confined Environments Invited Speaker: Rich new chemistry and physics emerge when one considers confined fluids, where the environment is distinctly different than in bulk. The intuition of what to expect based on bulk properties is found to break down. This talk will emphasize recent findings using a combination of single-particle imaging and fluorescence correlation spectroscopy of polymers at hard surfaces (mica), soft surfaces (phospholipid bilayers) and random network environments. A surprising dependence is found on the polymer molecular weight and concentration, as well as on the substrate makeup. [Preview Abstract] |
Tuesday, March 17, 2009 8:36AM - 9:12AM |
H2.00002: Engineered Colloids Having Particles of Controlled Size, Shape, and Chemistry Invited Speaker: This lecture will focus on opportunities for complex particles made using a novel ``top-down'' fabrication method called PRINT (Particle Replication In Non-wetting Templates). PRINT enables the production of monodisperse, shape-specific nano and micro-particles from an extensive range of organic and inorganic liquid precursors. The assembly of colloidal particles has long been a rich and continuously growing area of materials science, with great potential for a broad range of applications including electronics, control systems, optics and biotechnology. Within this field, the bulk of research has been devoted to studying the assembly of isotropic spherical particles. In spite of this, there has been a growing interest in studying the assembly of anisotropic particles due to the more complex and useful structures that these particles can potentially assemble into. There are few reports on the assembly of anisotropic particles, in part because of the lack of effective fabrication processes for the preparation of these particles with the monodispersity, control and range of compositions required for in-depth study. Herein we will discuss the use of PRINT to fabricate monodisperse, nanometer- and micron-sized particles of varying size, shape and composition. PRINT stands out because of the high degree of molding resolution, the broad range of chemistries that can be molded, and the ease with which reel-to-reel technology can be incorporated for scalability. Thus, it is ideally suited to the synthesis of unique, highly anisotropic particles in a wide range of compositions. Herein we discuss the use of dielectrophoresis to study the assembly of highly anisotropic polymer particles: rods, discs, hexnuts and boomerangs, fabricated with the PRINT process. In addition, the discussion will focus on the details and opportunities for loading shape controlled particles with magnetite and their manipulation when dispersed in various liquid media. [Preview Abstract] |
Tuesday, March 17, 2009 9:12AM - 9:48AM |
H2.00003: Polymers under Cylindrical Confinement Invited Speaker: Anodized alumina oxide (AAO) membranes offer a unique platform to investigate polymers under confinement. AAO membranes have been prepared where the diameters of the nanopores in the membrane have been varied from 8 to 50 nm by varying the anodization conditions. Capillary force is sufficiently large to draw high molecular weight polymers into the membrane, producing either nanotubes or nanorods. Polymer solutions can also be used place a thin film on the walls of the nanopores, forming nanotubes. With pore diameters less than the radius of gyration, a quantitative understanding of perturbations to chain dynamics due to geometric constraints was examined. We found a weak molecular weight-dependent mobility of polymers confined within AAO nanopores having diameters smaller than the dimension of the chains in the bulk. The measured mobility of polymers in the confined geometry was much higher than the mobility of the unconfined chain. Rayleigh instabilities in thin polymer films confined within nanoporous alumina membranes were also found where periodic undulations on the film surface were found to increase with time, eventually bridging across the cylindrical nanopore, resulting in the formation of polymer nanorods with a periodic array of encapsulated holes. With microphase separated block copolymers, where the characteristic period of the BCP morphology is comparable to the pore diameter, significant deviations from the bulk morphology as revealed by electron tomography. Small angle neutron scattering was also used to investigate the influence of cylindrical confinement on the order-to-disordered transition. This work was done in collaboration with T. J. McCarthy (UMass), K. Shin (Seoul National University), H. Jinnai (Kyoto University), D. Chen, J. Chen, H. Xiang, T. Kim, and P. Dobriyal, and was supported by the DOE, NSF MRSEC, NSF CHM. [Preview Abstract] |
Tuesday, March 17, 2009 9:48AM - 10:24AM |
H2.00004: The Challenge of Understanding the ``Complexity'' of Polymeric Fluids and Solutions Invited Speaker: It is well known that the complexity of polymer conformational shapes makes this class of molecules prone to glass formation and that high molecular mass polymers exhibit rubbery viscoelastic flow properties associated with their topological and packing interactions. Many natural and synthetic polymers also exhibit complex associative interactions arising from the variation of chemical species and the presence of charged and polar groups within the molecule that can give rise to polymer supermolecular organization into a wide range of fragile structures at the nanoscale and larger. There are changes in both the thermodynamics and dynamics of these fluids associated with these general patterns of ``complex fluid'' behavior that provide a fundamental challenge for theoretical understanding so that this field remains at the frontier of materials science. The high level of regularity observed in the relatively high frequency glassy dynamics of polymer fluids, and other glass forming liquids more broadly, and in the viscoelastic properties that define chain ``entanglement'' in high molecular mass polymers, provides some hope for a general theoretical framework describing the complex fluid dynamics of polymeric fluids. Specifically, it is argued, and supported by evidence, that the complex fluid behavior underlying glass formation, entanglement and self-assembly in polymeric fluids all involve emergent collective behavior taking the form of supermolecular polymer structures that form and disintegrate in dynamic equilibrium. This ``dynamic heterogeneity'' paradigm, which is not addressed by conventional mean field theories such as the mode-coupling model of glass formation and the reptation model, provides a framework for understanding many aspects of the linear and non-linear dynamics of polymer complex fluid behavior such as stretched exponential stress relaxation, and shear thinning and ``aging'' following cessation of flow. It also provides a framework for understanding the influence of nanoparticles, and other additives to polymeric fluids, that modify the fluid mesoscale structure, often with significant changes in material properties. [Preview Abstract] |
Tuesday, March 17, 2009 10:24AM - 11:00AM |
H2.00005: Anisotropic Self-Assembly of Nanoparticle Amphiphiles Invited Speaker: It is easy to understand the self-assembly of particles having anisotropic shapes or interactions, such as Co nanoparticles or proteins, into highly extended structures. However, there is no experimentally established strategy for creating anisotropic structures from common spherical nanoparticles. We demonstrate that spherical nanoparticles, uniformly grafted with macromolecules, robustly self-assemble into a range of anisotropic superstructures when they are dispersed in the corresponding homopolymer matrix. This phenomenon is driven by the microphase separation between the inorganic nanoparticles and the (organic) polymeric chains grafted to their surfaces in a fashion similar to block copolymers. This microphase separation driven particle self-assembly provides a unique means of controlling the global nanoparticle dispersion state in polymer nanocomposites. The relationship between the state of particle dispersion and nanocomposite properties can thus be critically examined, and in particular we focus on the mechanical reinforcement afforded when particles are added to polymers. Grafted nanoparticles are thus versatile building blocks for creating tunable and functional particle superstructures with significant practical applications. With Pinar Akcora, Hongjun Liu, Yu Li, Brian Benicewicz, Linda Schadler, Thanos Panagiotopoulos, Jack Douglas, P. Thiyagarajan and Ralph Colby. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700