Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session A20: Spatially Confined Polymer Materials |
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Sponsoring Units: DPOLY Chair: Joanne Budzien, Sandia National Laboratories Room: 321 |
Monday, March 16, 2009 8:00AM - 8:36AM |
A20.00001: Field-Based Simulations of Confined Block Copolymers Invited Speaker: This presentation will discuss field-theoretic simulation methods that can be used to analyze the self-assembly behavior of thin block copolymer films, including films that are laterally confined on a flat substrate and curved films on a spherical manifold. Our studies of lateral confinement have revealed strategies for epitaxially templating microdomain patterns with long-range in-plane order and minimal defects (``graphoepitaxy"), and methods for diversifying the set of stable 2D lattice structures. On the sphere, we have found defective ground state block copolymer morphologies that are analogous to spherical crystalline packings in other contexts, e.g. the Thompson problem and viruses. The methods and findings have applications in block copolymer lithography and in dispersion technology of polymer-stabilized nanoparticles and colloids. [Preview Abstract] |
Monday, March 16, 2009 8:36AM - 8:48AM |
A20.00002: Diblock copolymers in thin films Marianne Heckmann, Barbara Drossel We investigate the phase behaviour of diblock copolymers which are confined to thin films. We employ both self-consistent field (SCFT) theory and Strong Stretching Theory (SST) in order to compute the free energies of different possible morphologies. We show that only the simplest structures which are combinations of the bulk morphologies are stable when cylinder- or sphere-forming copolymers are confined between hard walls interacting with the monomers. We present and compare phase diagrams computed with SCFT and SST for different sets of parameters. [Preview Abstract] |
Monday, March 16, 2009 8:48AM - 9:00AM |
A20.00003: Block copolymers confined in nano-pores Andrei Zvelindovsky, Marco Pinna Using cell dynamics simulation we investigate morphologies block copolymers confined in the nano-pores of various geometries such as spherical cavities, cylinder pores and confinement formed by concentric spheres and cylinders. We examine the influence of molecular composition, parameters of confinement such as curvature and characteristic size, as well as preferential interaction of copolymer blocks with the surfaces. Several block copolymer morphologies are investigated: lamellae, cylinders, spheres and bicontinuous. Deviation from the bulk structure develops under influence of confinement. [Preview Abstract] |
Monday, March 16, 2009 9:00AM - 9:12AM |
A20.00004: Order and Disorder in a Lamella Forming Fluid Near an Attractive Substrate Andrew Croll, An-Chang Shi, Kari Dalnoki-Veress By using wedged thin films, we have measured the effect of interfaces on the ordering of a diblock copolymer in real space. Symmetric diblocks can form lamellae and the strong preference of the substrate for one of the blocks can induce this ordering well above the order-disorder transition (ODT) temperature. However, the induced order is decays away from the substrate $\sim \exp (-x/\xi)$. The lengthscale, $\xi$, diverges as the temperature is decreased at ODT, and two distinct regions are observed in the scaling of $\xi$ with the temperature attributable to the two interfaces of the film (air and substrate). The dynamics of ordering and disordering near the substrate is found to be exponential in time, though the mechanisms differ. In disordering the distance from the substrate is unimportant, and all layers relax identically. However, the timescale of the formation of lamellae is found to vary significantly with the distance from the substrate. [Preview Abstract] |
Monday, March 16, 2009 9:12AM - 9:24AM |
A20.00005: Crystallization behavior of polyethylene under nanoscopic cylindrical confinement Woojung Cho, Euntaek Woo, June Huh, Younggyu Jeong, Kyusoon Shin Due to the increasing usage of nanoscopic materials, fundamental understanding of the crystallization is more and more demanded. In this presentation, we will discuss the crystallization behavior of linear polyethylene confined in cylindrical nanopores. We observed the crystallization mechanism transition from homogeneous nucleation to heterogeneous nucleation upon the tightening of the confinement. We also found that the crystalline structure, examined by x-ray diffraction and calorimetry, shows deviations from those of bulk and the crystal formation is severely influenced by the imposed confinement. [Preview Abstract] |
Monday, March 16, 2009 9:24AM - 9:36AM |
A20.00006: Managing bond tension in spreading macromolecules. Sergey Sheyko, Insun Park, Alper Nese, Krzysztof Matyjaszewski, David Shirvaniants, Michael Rubinstein Mechanical activation of chemical bonds plays a vital role in biology, chemistry, and engineering. Unlike other activation stimuli, such as light and temperature, mechanical activation is site and direction specific. However, in a typical experiment, macroscopic stress is distributed over myriads of different molecules. This results in significant and ill-defined variation of both the magnitude and direction of forces at individual chemical bonds. Here, we show how to achieve a great degree of control over bond tension in flowing polymer films. The distinctive feature of this finding is that the mechanical tension is controlled on three different length scales. First, chemical bonds are activated within a narrowly defined area of a macroscopic film. Second, only certain molecules are activated within a mixture of molecules. Third, the tension can be focused to a specific bond within a flowing macromolecule. It is demonstrated that the focused tension breaks covalent bonds with a molecular-scale precision. [Preview Abstract] |
Monday, March 16, 2009 9:36AM - 9:48AM |
A20.00007: Spreading of Polymer Films at the Molecular Scale: Conformation, Orientation, and Fractionation. Michael Barrett, Alper Nese, Krzysztof Matyjaszewski, Sergei Sheiko Previously, we have reported that comb-like polymer macromolecules undergo a plug-flow with an insignificant contribution of molecular diffusion (\textit{Phys. Rev. Lett}. \underline {93}, 206103, \textbf{2004}). It was also suggested that the composition of the flowing polymer melt was the same both inside the fluid reservoir (drop) and in the precursor film. This work called into question the macroscopic picture of polymer spreading. Through molecular imaging by AFM, we observe that macromolecules spread at different velocities depending on their size. We show that flow causes the molecules to align perpendicular to the flow direction We have also identified specific molecular conformations, such as hairpins, that become more abundant in spreading films. Lastly, we demonstrate that chain entanglements hinder permeation of long macromolecules from the drop to precursor film. These findings shed light on the molecular mechanism of spreading of polymer melts on natural, i.e. heterogeneous, substrates. [Preview Abstract] |
Monday, March 16, 2009 9:48AM - 10:00AM |
A20.00008: Polarization Anisotropy of DNA in Nanochannels Fredrik Persson, Fredrik Westerlund, Jonas Tegenfeldt, Anders Kristensen Studies of DNA in nanoscale confinement, where the dynamics and statics of the DNA extension or position is investigated as a function of e.g. DNA contour length, degree and shape of the confinement as well as buffer conditions, has yielded new insight in the physical properties of DNA. Our work extends this field by not only studying the location of fluorescent dyes along a confined DNA molecule but also monitor the orientation of the dyes by measuring the polarization of the fluorescence emission. By choosing a dye which fluorescence polarization is related to the DNA backbone and measuring the emission that is polarized parallel and perpendicular to the extension axis of the stretched DNA, information on the local spatial distribution of the DNA backbone can be obtained. The result is analogous to linear dichroism (LD) on a single-molecule level, and obtained in a highly parallel fashion. [Preview Abstract] |
Monday, March 16, 2009 10:00AM - 10:12AM |
A20.00009: ABSTRACT WITHDRAWN |
Monday, March 16, 2009 10:12AM - 10:24AM |
A20.00010: Newtonian drop deformation in a viscoelastic matrix under shear Shahriar Afkhami, Pengtao Yue, Yuriko Renardy When a Newtonian drop is sheared in a viscoelastic matrix, the direct numerical simulation produces a viscoelastic ``wake'' at the interface at the front and back of the drop. In the case of a drop reaching a stationary state, the stresses in the wake and the viscous shear balance out the interfacial tension force. When a viscoelastic drop is sheared in a Newtonian matrix, numerical simulations exhibit an overshoot in the transient evolution of drop deformation. Experimental observations also show that an overshoot can occur when a Newtonian drop is sheared in a viscoelastic matrix. However, these overshoots do not appear for 3D drop computations. In this work, we investigate why drop simulations in 3D do not display overshoots. [Preview Abstract] |
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