Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session H2: Polymer Physics Prize Symposium |
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Sponsoring Units: DPOLY Chair: Richard Register, Princeton University Room: LACC 151 |
Tuesday, March 22, 2005 8:00AM - 8:36AM |
H2.00001: Routes to Frustrated Nanostructures with Block Copolymers Invited Speaker: Diblock copolymers of polystyrene and polybutadiene, PS-b-PBD were confined within nanoscopic cylindrical pores in alumina membranes. By capillary action, microphase separated symmetric and asymmetric PS-b-PBD were drawn into pores varying in diameter from 15 to several hundred nanometers. After thermal annealing, the alumina membrane was dissolved in a weak base, leaving nanorods of the PS-b-PBD that were then imbedded in epoxy, microtomed and stained with OsO$_{4}$. TEM on cross-sections taken parallel to and normal to the nanorod axis was used to investigate the morphology. For symmetric PS-b-PBD, when the pore diameter, d, was much larger than the copolymer repeat period, L$_{0}$, multiple concentric cylinders of PS and PBD oriented along the nanorod axis was obtained. When d$<$2L$_{0}$ and d/L$_{0}$ was non-integer, the morphology changed to a torroidal or stacked-disc type of morphology. For asymmetric PS-b-PBD ($\phi _{PBD}\sim $0.3) when d/L$_{0}$ was large, cylinders of PBD in a PS matrix were found where the hexagonal packing was altered by the constraints of the walls. However, if d$<$2L$_{0}$, helices of PBD in PS running along the nanopore axis were found. Thus, using simple diblock copolymers, the frustration and curvature imposed on the copolymers forces new morphologies leading to novel templates and scaffolds for nanostructured materials. Supported by the NSF, MRSEC and NIRT at UMass, the Dept. of Energy, and the Hyperstructured Organic Materials Research Center in Seoul, Korea. \textit{With K. Shin, H. Xiang, S. Moon, T. Kim and Thomas J. McCarthy} [Preview Abstract] |
Tuesday, March 22, 2005 8:36AM - 9:12AM |
H2.00002: Using polymer chemistry and block copolymers to create a viable nanopatterning strategy Invited Speaker: The fabrication of nanoscopic devices will increasingly rely on the precise control over materials properties and function on very small size scales, typically 5 nanometers to a few microns. The most promising approach to this is a `bottoms-up' approach relying on self-assembly and recent developments in `living' free radical procedures have allowed the construction of tailor-made polymer molecules that facilitate this strategy. The design and application of functionalized block copolymers in developing a viable nanopatterning strategy and their application in advanced storage devices and microelectronics for the information technology industry will be discussed. [Preview Abstract] |
Tuesday, March 22, 2005 9:12AM - 9:48AM |
H2.00003: Micellization of pH-responsive Amphiphilic Diblock Copolymers in Aqueous Media and the Formation of Metal Nanocrystals Invited Speaker: External-stimuli responsive block copolymers, usually known as double-hydrophilic copolymers, respond to changes in their environment such as pH, temperature and salt concentration and undergo micellization in aqueous media. Micellization induced by controlling the solution pH is advantageous for certain applications in particular when fully hydrophobic cores are required. A category of such systems comprise a pH-sensitive (weak) basic or acidic block that forms the micelle core surrounded by a corona formed by a neutral hydrophilic block. In this work we investigate the micellization behavior and the metal-nanoparticle formation in poly(2-(diethylamino)ethyl methacrylate)-block-poly(hexa(ethylene glycol) methacrylate), PDEAEMA-b-PHEGMA, amphiphilic block copolymers in aqueous media. The hydrophobic PDEAEMA block is pH-sensitive: at low pH it can be protonated and it becomes partially or completely hydrophilic, leading to molecular solubility, whereas at higher pH micelles are formed; the behavior is studied by dynamic light scattering, 1H-NMR and atomic force microscopy. The micelles consist of a PDEAEMA core and a PHEGMA corona, where the core can dissolve metal compounds due to coordination. In all these micellar nanoreactors, metal nanoparticles nucleate and grow upon reduction with sizes in the range of a few nanometers as observed by transmission electron microscopy whereas X-ray diffraction verifies their nanocrystalline structure. These particles exhibit significantly enhanced catalytic properties for hydrogenation and oxidation reactions. [Preview Abstract] |
Tuesday, March 22, 2005 9:48AM - 10:24AM |
H2.00004: Force Measurements Using Capillary Instabilities Invited Speaker: Planar surfaces are stabilized by the Laplace pressure, which dampens the entire capillary wave spectrum of a liquid surface. Pattern formation at surfaces and in thin films are therefore the consequence of a destabilizing pressure. The analysis of pattern formation processes can therefore be used to quantitatively measure the destabilizing force. My presentation will focus on three examples for such force measurements: \begin{enumerate} \item Electrohydrodynamic Instabilities. It is long known that electric fields destabilize liquid surfaces. An electric field applied across at thin polymer film causes the amplification of a single capillary mode, which is quantitatively predicted by a linear stability analysis. The good quantitative agreement of experimental results and theoretical predictions illustrates the usefulness of our approach. \item Acoustic Casimir Effect. We show that the confinement of thermal modes (acoustic phonons) in thin films lead toe a Casimir-type force that leads to the breakup of thin polymer films. \item Film Instabilities caused by temperature gradients. A high temperature gradient across a thin polymer film causes a amplified capillary instability. This non-convective effect is driven by the diffusion of heat across a polymer-air double layer and is a function of the acoustic impedance of the polymer-air interface. \end{enumerate} [Preview Abstract] |
Tuesday, March 22, 2005 10:24AM - 11:00AM |
H2.00005: Toughness and adhesion in an acqueous environment Invited Speaker: Highly swollen crosslinked polymers gels are normally very brittle because there are no significant energy dissipation mechanisms that operate close to the crack tip. The presence of the low molecular weight swelling agent suppresses the viscoelastic process that would normally generate resistance to crack propagation in a crosslinked elastomer. We have examined the effect of forming a random copolymer of a hydrophilic monomer with a small amount of hydrophobic monomer so that the hydrophobic monomers associate. The association was demonstrated by the rheology of the uncrosslinked material. The breakup of these hydrophobic associations gives an energy dissipation mechanism and thereby was found to increase the toughness of the swollen gel. Adhesion of a hydrophobic material, such as PDMS, to a range of substrates is expected to be very different in an aqueous environment than in air. We have used the JKR technique to examine both the work of adhesion (contact formation) and the interface toughness between PDMS lenses and a number of substrates of different hydrophilicity both in air and under water. The water was found to have a profound effect on the measured adhesion. [Preview Abstract] |
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