Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session W24: Microphysical Properties of Block Copolymer Aggregates, Going Beyond Structure |
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Sponsoring Units: DPOLY Chair: Steve Hudson, National Institute of Standards and Technology Room: Colorado Convention Center 201 |
Thursday, March 8, 2007 2:30PM - 3:06PM |
W24.00001: Solvated Block Copolymers as a Novel Class of Electroactive Nanostructured Polymers Invited Speaker: Microphase-ordered block copolymers serve as model systems to elucidate the potential of molecular self-assembly and organic templates to fabricate functionalized polymer materials. Both aspects are related to the incorporation of secondary species such as low-molar-mass compounds or nanoparticles within copolymer matrices. Since the resulting properties of such functionalized copolymers depend on the morphology of the blend or composite, the nonrandom distribution of such inclusions within the copolymer matrix must be understood. Using a self-consistent field theoretical approach, we first evaluate the segregation and interfacial excess of low-molar-mass and nanoscale species in ordered triblock copolymers as functions of block selectivity and inclusion size. The predictions are found to agree with the morphology observed in a model triblock copolymer/nanoparticle composite, suggesting a wide correspondence in the structure-forming effect of molecular and nanoscale inclusions that will have implications in the design of functional nanostructured polymers such as conformable electroactive actuators. Such responsive materials, stimulated by electric fields, are required for emergent technologies such as microrobotics, micro air vehicles and responsive prosthetics. High actuation strains ($>$50{\%}) are currently afforded by dielectric elastomers at relatively high electric fields ($>$50 V/$\mu $m). In this work, we demonstrate that incorporation of a low-volatility solvent into a triblock copolymer yields physical networks that exhibit excellent displacement under an external field. Ultrahigh actuation strains ($>$200{\%}) accompanied by low cyclic hysteresis are realized at significantly reduced electric fields ($<$40 V/$\mu $m). Use of nanostructured polymers whose properties can be tailored by varying copolymer characteristics or blend composition represents an innovative and tunable avenue to reduced-field actuation for advanced engineering, biomimetic and biomedical applications. [Preview Abstract] |
Thursday, March 8, 2007 3:06PM - 3:18PM |
W24.00002: Self-Assembled Micro-Phase Separated Semi-Permeable Membranes. Dale Handlin, Scott Trenor, Carl Willis Anionic polymerization of block copolymers affords superior microstructure control and thus morphology management through precise control of block structures. Numerous researchers have studied sulfonated styrenic block copolymers as semi-permeable membranes for various applications. Traditionally, the styrenic endblocks of triblock copolymers are sulfonated, as was first practiced by Kraton polymers in the late 1960's. Once endblock sulfonated polymers are hydrated, water plasticizes the endblocks which results in a significant degradation in the mechanical properties. We have recently designed new sulfonated block copolymer structures that have continuous ionic phases and retain their strength when fully hydrated. We have used known structure-property relationships to tailor the properties of the sulfonated polymer membranes via polymer structure, placement of sulfonic acid functionality, and membrane formation techniques. This ability to control membrane morphology allows us to decouple the degree of sulfonation from the amount of water swelling as well as the water swelling from the transport properties. The initial characterization and the ability to manipulate the mechanical and transport properties of these polymers will be discussed. [Preview Abstract] |
Thursday, March 8, 2007 3:18PM - 3:30PM |
W24.00003: Toward structure-property relationships in block copolymer electrolytes Enrique Gomez, Mohit Singh, Vincent Chen, Nitash Balsara Polymer membranes with high ionic conductivity are important for applications such as solid-state batteries and fuel cells. These polymer electrolytes must have a high modulus to prevent the catastrophic formation of dendrites. However, current approaches rely on poly(ethylene oxide) (PEO)/lithium-salt mixtures whose conductivity is inversely proportional to their modulus. Our strategy is to decouple the mechanical and ionic transport properties by utilizing PEO-based block copolymers comprising of soft, nanoscale conducting channels in a hard, non-conducting glassy matrix. In order to determine the role of structure on the ionic conductivity of these materials, we perform various transmission electron microscopy (TEM) experiments. Three-dimensional reconstructions provide important structural information regarding the manner in which the conductive phase percolates through the copolymer electrolyte. Energy-filtered electron microscopy allows for the direct imaging of lithium. Current efforts are focused on using these TEM experiments to determine the structure-property relationships of block copolymer battery electrolytes. [Preview Abstract] |
Thursday, March 8, 2007 3:30PM - 3:42PM |
W24.00004: Phase Behavior of Block Copolymers containing Poly(vinyl pyridine) by Coordination with Metal Chloride Dong Hyun Lee, Hwang Yong Kim, Jin Kon Kim, Du Yeol Ryu, June Huh We studied, via small angle X-ray scattering, rheology, and transmission electron microscopy, the change of the domain spacing (D) and the order-to-disorder transition temperature (T$_{ODT})$ with the amount of cadmium chloride (CdCl$_{2})$ for polystyrene-\textit{block}-poly(2-vinyl pyridine) copolymers (PS-P2VP) and polystyrene-\textit{block}-poly(4-vinyl pyridine) copolymers (PS-P4VP). With increasing amount of CdCl$_{2}$, both D and T$_{ODT}$ of PS-P2VP increased greatly. On the other hand, with increasing amount of CdCl$_{2}$, D of PS-P4VP decreased, whereas T$_{ODT}$ of PS-P4VP increased dramatically. These results are due to different types of the coordination between CdCl$_{2}$ and nitrogen atoms in the 2-position of pyridine ring (intra-chain coordination) in PS-P2VP, compared with nitrogen atoms in the 4-position (inter-chain coordination) in PS-P4VP. This work was supported by Creative Research Initiative Program supported by KOSEF [Preview Abstract] |
Thursday, March 8, 2007 3:42PM - 3:54PM |
W24.00005: Brownian Dynamics Simulation of ABA Block Copolymer in Selective Solvent: Kinetics of HEX Cylinders to BCC Spheres Transition Minghai Li, Yongsheng Liu, Rama Bansil A Brownian Dynamics simulation was performed on 200 bead spring chains of triblock copolymer, A$_{10}$B$_{10}$A$_{10}$. The repulsive interactions of A monomers (in good solvent) are modeled by the Weeks-Chandler-Anderson potential. The poor solvent attraction of the B monomers is described by a Lennard-Jones (LJ) potential. We have determined the phase diagram of 30{\%} ABA block copolymer in a selective solvent for the A block. At temperature T=1 (in units of $\varepsilon $/k$_{B}$, where $\varepsilon $ is the well depth of the LJ interaction potential and k$_{B}$ the Boltzmann constant) the equilibrium state is HEX cylinder; at T=1.5 the system is in BCC spheres. We follow the time evolution of the HEX to BCC transition by jumping from T=1 to 1.5. The Fourier transform is calculated at each time-step in the simulation and compared to time-resolved small angle x-ray scattering data from triblock copolymer solution (Kraton G1650 in mineral oil). The simulation is also compared with a calculation based on a geometric model of coupled anisotropic fluctuations to describe the transition from HEX cylinders to BCC spheres. [Preview Abstract] |
Thursday, March 8, 2007 3:54PM - 4:06PM |
W24.00006: Symmetric Diblock Copolymers in Nanopores: Monte Carlo Simulations and Strong-Stretching Theory Qiang Wang We have performed lattice Monte Carlo simulations to study the self-assembled morphology of symmetric diblock copolymers in nanopores. The pore diameter and surface preference are systematically varied to examine their effects on the chain conformations, structures of various morphologies and their phase transition. Various ensemble-averaged profiles and quantities are used to provide detailed information about the system. The simulation results are also compared with the predictions of a strong-stretching theory commonly used in the literature. Such comparisons reveal the deficiencies of this theory in describing the morphologies under cylindrical confinement, and call for further theoretical studies using more accurate formalisms. [Preview Abstract] |
Thursday, March 8, 2007 4:06PM - 4:18PM |
W24.00007: Self-assembly of a diblock a copolymer melt absorbed in porous materials. Panagiotis Maniadis, Ioannis Tsimpanogiannis, Edward Kober Self-consistent field theory is used to study the self-assembly of a diblock copolymer melt absorbed in a porous material. We find that self-assembly is affected when the characteristic length scales of the porous material are of the same order as the polymer ratio of gyration (Rg). When the porous size is much larger than Rg, then the polymer self-assembly is affected only locally close to the contact with the pore surface. Interesting new morphologies appear when the size of the pores and the distance between them is comparable to the diblock characteristic lengths. In this case the polymer structure changes according to the constrains from the porous. We will present results for two types of regular pores arrangement a) checkers board and b) staggered lattice. [Preview Abstract] |
Thursday, March 8, 2007 4:18PM - 4:30PM |
W24.00008: Effective Control of Pore Size in the Block Copolymer by Matrix Crosslinking E. Kim, C. Shin, D.Y. Ryu, J. Bang, C. Hawker, T. Russell Thin films of block copolymer with nano-sized morphology have great attention for their potential use. Especially, the control of block copolymer pore size in the cylindrical microdomain has been studied by many research groups. Previously, pores of PS-b-PMMA thin films with diameters as low as 3nm only via crosslinking by ozone the matrix surrounding the cylindrical microdomains are reported, in which the diameters of the pores are found to increase by increasing ozone exposure with the pore size limitation, only to 8 nm. The main objective of our study is to find out the condition of controlling the pore size widely as well as tunability by using BCB crosslinking unit. PS-b-PMMA copolymers were synthesized with reactive benzocyclobutene (BCB) functionality which is randomly incorporated into the PS backbone, having PMMA volume fraction of $\sim$0.3 with various BCB amount from 3\% to 16\%. We investigated the optimal thermal annealing condition, time dependence to get the ordered cylindrical nanostructure with controlled size, where nanostructures of block copolymer are oriented normal to the substrate due to balanced interfacial interaction on the surface. [Preview Abstract] |
Thursday, March 8, 2007 4:30PM - 4:42PM |
W24.00009: Superelastic materials based on multigraft copolymers U. Staudinger, R. Weidisch, Y. Zhu, S. P. Gido, D. Uhrig, J. W. Mays, M. Klueppel, G. Heinrich PI-PS-multigraft copolymers with tri- tetra- and hexafunctional PS branches have been studied to investigate the influence of molecular architecture on morphological and tensile properties and to find novel material concepts. The materials form nanostructures ranging from spheres to cylinders to lamellae. Thus these materials show excellent transparency. Mechanical properties are strongly depending on functionality of the graft copolymer and on the number of branch points per molecule. Increasing functionality and a larger number of branch points cause a distinct increase in tensile strength due to enhanced physical crosslinking in such multigrafts. Tetra- and hexafunctional multigrafts show surprising high strain at break values up to 1550 {\%} and excellent elasticity far exceeding that of commercial elastomers. Simulation of hysteresis behavior revealed that the deformation mechanism can be explained by the flocculation model based on filled elastomers. [Preview Abstract] |
Thursday, March 8, 2007 4:42PM - 4:54PM |
W24.00010: Mesoscopic Archimedian Tiling Patterns in ABC Star-Shaped Terpolymers Atsushi Takano, Kenichi Hayashida, Tomonari Dotera, Yushu Matsushita Microphase-separated structures formed by ABC star-shaped terpolymers were investigated by transmission electron microscopy (TEM), electron tomography (3D-TEM), and small-angle X-ray scattering (SAXS). The samples are composed of polystyrene (S), polyisoprene (I) and poly(2-vinylpyridine) (P), their volume ratios of I:S:P are 1:1:X, where 0.2$<$X$<$4.9. From morphological observations by TEM, it was found that ISP stars show characteristic cylindrical structures when X is within the range 0.7$\mathbin{\lower.3ex\hbox{$\buildrel<\over {\smash{\scriptstyle=}\vphantom{_x}}$}} $X$\mathbin{\lower.3ex\hbox{$\buildrel<\over {\smash{\scriptstyle=}\vphantom{_x}}$}} $1.9. By the careful investigation of the ISP stars by TEM and 3D-TEM, it was confirmed that the cross-sections of cylindrical structures of four samples show two-dimensional tiling patterns consisting of regular polygons, that is, [6.6.6], [4.8.8], [3.3.4.3.4], and [4.6.12], which are families of the Archimedian tiling patterns. Furthermore the SAXS patterns of four samples are quite consistent with structural observation of TEM. [Preview Abstract] |
Thursday, March 8, 2007 4:54PM - 5:06PM |
W24.00011: Hierarchical Structures of a Multiblock Copolymer Melt Weihua Li, An-Chang Shi Hierarchical structures of a multiblock copolymer melt are investigated using real-space self-consistent mean-field theory. The polymer, $A(BC)_nBA$, is composed of three species A, B, and C. The parameter n indicates the number of short BC blocks with equal lengths. Hierarchical lamellar structures with parallel double periodicity have been observed in very recent experiments done by Masuda, et al. in this type of multiblock copolymer melts. These heirachical structures are reproduced in our one-dimensional calculations. We locate the transitions between hierarchical lamellar phase and single lamellar phase as the composition $f_A$ is varied for two types of hierarchical lamellae with five and seven thin layers, respectively. In addition, we explore hierarchical cylindrical structures using two-dimensional calculations. [Preview Abstract] |
Thursday, March 8, 2007 5:06PM - 5:18PM |
W24.00012: Whispering Gallery Modes in Highly Hexagonal Symmetric Structures of Three Dimensional SBA-1 Mesoporous Silica Chih-Wei Chen, Yang-Fang Chen An interesting optical resonant mode, called whispering gallery mode (WGM), has been discovered, inside the three dimensional highly hexagonal symmetry of SBA-1. The hexagonal structure provides a suitable environment for the light wave to circulate around due to multiple total internal reflection at the resonator's boundary and generates the resonant states. By means of the Fourier transform infrared transmittance, we observed the optical WGMs in mesoporous silica SBA-1 decaoctahedron for the first time. Based on the hexagonal total internal reflecting model, the observed eigenmodes can be explained quite well. We also discovered that under the condition of WGMs, the absorption of CO$_{2}$ and H$_{2}$O molecules can be greatly enhanced. [Preview Abstract] |
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