Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session H30: Padden Award Symposium |
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Sponsoring Units: DPOLY Chair: Anne Mayes, Massachusetts Institute of Technology Room: Baltimore Convention Center 327 |
Tuesday, March 14, 2006 11:15AM - 11:27AM |
H30.00001: Electrochemically Controlled Self-Assembly of an Organometallic Block Copolymer Hany Eitouni, Nitash Balsara We have established a technique for exerting localized reversible control over the formation of block copolymer microphases. The application of electrical fields as low as 2 V/cm across a 17 weight {\%} solution of a disordered, partially oxidized poly(isoprene-\textit{block}-ferrocenyldimethylsilane) copolymer in dichlorobenzene results in the formation of ordered domains near the positive electrode. Spatially- and temporally-resolved small-angle neutron scattering (SANS) and birefringence measurements on the sample in the presence of the electric field were used to follow the order formation process. After reversal of the electrical bias on the system, the ordered regions underwent order-to-disorder transitions and new ordered regions were formed at the opposite electrode. Optical birefringence measurements indicated that the ordered regions possessed significant long-range orientational order. [Preview Abstract] |
Tuesday, March 14, 2006 11:27AM - 11:39AM |
H30.00002: Anomalous Segregation of Deuterium Labeled PS at hPS:dPS/hPMMA Interfaces as Characterized by SIMS and Mean-Field Theory Shane Harton, Fred Stevie, Harald Ade Secondary ion mass spectrometry (SIMS) was used to measure real- space depth profiles of deuterium labeled polystyrene (dPS) in hPS:dPS/poly(methyl methacrylate) (hPMMA) bilayers, with the hPS:dPS blend being well within the single-phase region of the phase diagram. Profound changes in the thermodynamic behavior of this system at the polymer/polymer interface are observed in the form of significant segregation of dPS to the hPS:dPS/hPMMA interface. Furthermore, a depletion hole was observed during the early stages of formation of an equilibrium excess of dPS, implying that the energetic gain at the interface per dPS chain has to be $>$ kT. The observed interfacial excess is quantified by generating theoretical profiles, using self-consistent mean- field theory (SCMF), and fitting an effective interaction energy parameter $\Delta$$\chi$ as a function of temperature. The temperature dependency of $\Delta$$\chi$ was found to be a factor of 3$-$4 greater than any of those reported for $\chi$ of PS/PMMA. It was also found that SCMF accurately describes the concentration dependency of dPS segregation at a constant dPS molecular weight using a concentration independent $\Delta$$\chi$, however $\Delta$$\chi$ was found to be dependent on dPS molecular weight. A novel method of using carbon-13 labeling is demonstrated as an alternative to deuterium labeling, providing a true tracer for investigations of such phenomena as polymer chain mobility near surfaces and interfaces and reactive coupling at polymer/polymer heterogeneous interfaces. [Preview Abstract] |
Tuesday, March 14, 2006 11:39AM - 11:51AM |
H30.00003: Toward Single-Chain Crystallisation Kinetics Michael V. Massa, Kari Dalnoki-Veress By dewetting a thin film of a crystallisable polymer on an unfavourable substrate, one can create an ensemble of isolated and impurity-free droplets, in which homogeneous crystal nucleation can occur. Previously we have demonstrated (PRL, 92, 255509, 2004) that for bulk-like droplets (containing on the order of 10\^{}9 chains) the homogenous nucleation rate scales with the \textit{volume} of the droplet. However, as the domain size is reduced far below these length scales, the confinement of polymer chains to dimensions less than the radius of gyration, the increase in the ratio of surface area to volume, and the decrease in the number of neighbouring chains can all potentially lead to changes in the crystallisation kinetics. With the same sample geometry, we extend our study of homogeneous nucleation to smaller droplet length scales. Crystallisation is monitored using ellipsometry, which offers a very sensitive probe to changes in the sample density, even for extremely small quantities of material. With complimentary results from atomic force microscopy, we follow the homogeneous crystallisation of a supercooled melt, from bulk length scales down to single-chain dimensions. [Preview Abstract] |
Tuesday, March 14, 2006 11:51AM - 12:03PM |
H30.00004: Fabrication of Three-Dimensional Nanostructures from Self-Assembling Block Copolymers on Two-Dimensional Chemically Patterned Templates with Mismatched Symmetry Mark Stoykovich, Kostas Daoulas, Harun Solak, Sang-Min Park, Yioryos Papakonstantopoulos, Juan de Pablo, Marcus Mueller, Paul Nealey A combined experimental and theoretical approach is used to examine the direct fabrication of complex three-dimensional (3D) nanostructures by the self-assembly of block copolymer materials on two-dimensional templated surfaces. Here a lamella-forming ternary block copolymer -- homopolymer blend is considered on periodically patterned substrates consisting of square arrays of spots. The blend follows the substrate pattern and forms a quadratically perforated lamella (QPL). At intermediate film thicknesses necks connect this QPL to the film surface, resulting in a bicontinuous morphology. For thicker films bicontinuous morphologies are observed that consist of a sequence of parallel lamellae with disordered perforations. The principal concept of this work extends beyond this initial demonstration and can be generalized to the fabrication of complex 3D structures that have potential applications in nanoelectronics, separation membranes, and catalysis. [Preview Abstract] |
Tuesday, March 14, 2006 12:03PM - 12:15PM |
H30.00005: Slaved Diffusion in Phospholipid Bilayers Liangfang Zhang, Steve Granick Dual-color fluorescence correlation spectroscopy (FCS) was employed to simultaneously investigate the translational diffusion of phospholipids in supported fluid bilayers and polymers which adsorb on these bilayers at incomplete surface coverage. It was found that the translational diffusion of phospholipids split into two populations due to polymer adsorption. A slow mode, whose magnitude was the same as that of adsorbed polymers, coexisted with a fast mode characteristic of naked lipid diffusion. Using 2-color fluorescence, cross-correlation between the diffusion of phospholipids and polymers suggested the plausible interpretation that polymer adsorption created nanodomains of lipid whose mobility was determined by the occluded area of the adsorbed polymer. That is, those lipids inside the nanodomains were enslaved by the adsorbed polymers and diffused collectively. Variations of the polymer molar mass showed that the slow mode of phospholipid diffusion varied inversely with molar mass of the adsorbate, as predicted by our notion of slaved diffusion. This work offers a new mechanism to explain how naonsized domains with reduced mobility arise in lipid membranes. [Preview Abstract] |
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