Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session N30: Block Copolymer Phase Behavior |
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Sponsoring Units: DPOLY Chair: Thomas Epps, National Institute of Standards and Technology Room: Baltimore Convention Center 327 |
Wednesday, March 15, 2006 8:00AM - 8:12AM |
N30.00001: Equilibrium Phase Diagram of a Model Rod-Coil Block Copolymer B.D. Olsen, R.A. Segalman Rod-coil block copolymers can be used to form important self-assembled structures containing functional blocks such as helical polypeptides or conducting polymers. The thermodynamics of these materials is distinct from classical block copolymers due to the conformational asymmetry of the polymer chain and the effect of liquid crystallinity on the microphase structure. We have recently developed a weakly segregated model system, poly(alkoxyphenylene vinylene-b-isoprene) (PPV-b-PI), in which rod-rod and rod-coil interactions are modulated by the presence of short side chains on the rod. We present the phase diagram for rod-coil block copolymers in the weak segregation limit, demonstrating equilibrium lamellar, nematic, and isotropic phases. As molecular weight is increased, subtle order-order transitions in the lamellar phase become obvious. In particular, we will discuss the relative stabilities of smectic phases based on scattering data. Finally, we will discuss the non-lamellar hexagonal phases that are observed as the relative rod-fraction of the block copolymer is decreased. [Preview Abstract] |
Wednesday, March 15, 2006 8:12AM - 8:24AM |
N30.00002: Phase behavior of linear ABC triblock copolymer Joon Chatterjee, Frank S. Bates We report the study of melt phase behavior of poly(isoprene-$b$-styrene-$b$-ethylene oxide) as our model ABC triblock copolymer. Previous investigations on this system have discovered a network phase with O$^{70}$ space group symmetry in an orthorhombic lattice adjacent to network phases with cubic lattice symmetries, namely, alternating gyroid and core-shell gyroid. The present study investigates and expands the phase diagram with varying monomer compositions and temperature. Nearly monodisperse triblock copolymers with controlled molecular weights and block compositions are synthesized by anionic polymerization techniques. Blending of homopolymers with the triblock copolymer is used to refine the phase boundaries. Dynamic mechanical spectroscopy, small angle x-ray scattering, TEM and optical experiments are used to characterize the equilibrium morphologies. Other new phases such as hexagonal cylinders and bcc spheres have been observed. We observe that the phase diagram is not symmetric across the $f_{A}=f_{C}$ isopleth. [Preview Abstract] |
Wednesday, March 15, 2006 8:24AM - 8:36AM |
N30.00003: Electron tomography of a novel non-cubic network phase in ABC copolymers Gerd E. Schroeder, Stephen T. Hyde, Hermis Iatrou, Nikos Hadjichristidis, Satoshi Akasaka, Hirokazu Hasegawa We report the discovery of a novel bicontinuous tetragonal phase in the linear ABC triblock terpolymer system polystyrene (PS), polyisoprene (PI) and polydimethylsilocane (PDMS). The data is consistent with spacegroup Fddd and is distinctly non-cubic. The channel topology is distinct from the better-known cubic bicontinuous mesophases (diamond and gyroid types, with channels). It consists in 2 identical intertwined labyrinths with 3- and 4-connected nodes. Our mesophase differs from an earlier report of a copolymer phase (also in a linear terpolymer system) with the same spacegroup by Epps {\em et al} (Macromolecules {\bf 37}, 8325-41, 2004), who deduced a single channel morphology, based on TEM and SAXS data. Our proposal is based on 3D $e^-$-tomography data. The channel geometry is identified via a medial surface (MS) algorithm. For a labyrinth, the MS is a generalised channel graph consisting in surface patches. In contrast to line graphs, the MS is a complete descriptor of both topology and geometry. It provides robust shape characteristics, and is a useful tool for visualisation of complicated hyperbolic mazes. [Preview Abstract] |
Wednesday, March 15, 2006 8:36AM - 8:48AM |
N30.00004: Phase behavior of poly(pentafluorostyrene-b-methyl methacrylate) block copolymers Tracy Bucholz, Yueh-Lin Loo Fluorine-containing polymers have garnered interest for properties such as chemical inertness, high thermal stability, and low dielectric constants. Previously, the controlled synthesis of fluoropolymers has been difficult due to the electron-withdrawing nature of fluorinated monomers. This issue, however, has been addressed with the development of atom transfer radical polymerization. Using this technique, we have been able to synthesize diblock copolymers containing polypentafluorostyrene (PPfS) and poly(methyl methacrylate), PMMA. The resulting diblock copolymers exhibit narrow molecular weight distributions ($\le $1.1) and undergo microphase separation to form highly-ordered nanostructures at moderate molecular weights. Comparisons of order-disorder transition temperatures with anionically synthesized poly(styrene-b-isoprene), PS/PI, diblocks of comparable molecular weights and compositions suggest that the segregation strength of PPfS/PMMA is within a factor of two of that of PS/PI. This observation is surprising given the chemical uniqueness of PPfS and PMMA but is in fact in agreement with the theoretical segregation strength relative to PS/PI predicted by differences in their solubility parameters. [Preview Abstract] |
Wednesday, March 15, 2006 8:48AM - 9:00AM |
N30.00005: Perforated layer structures in liquid crystalline block copolymers Kishore Tenneti, Xiaofang Chen, Christopher Li, Yingfeng Tu, Xinhua Wan, Qi-Feng Zhou, Igors Sics, Benjamin Hsiao Phase structures of a series of poly(styrene-block-(2,5-bis-(4- methoxyphenyl)oxycarbonyl)styrene) (PS-b-PMPCS) liquid crystalline “rod-coil” block copolymers (LCBCPs) were investigated using thermal analysis, X-ray analysis and transmission electron microscopy. In the low molecular weight asymmetric BCP system, perforated layer structures were observed where the excessive PS molecules punctured the PMPCS domains and these perforations uniquely possess tetragonal in- plane symmetry. In the high molecular weight system, these perforated layer structures were observed in symmetric samples. Randomly initiated perforations became more regular and uniform upon blending with PS homopolymer in symmetric BCPs. These regular perforations also possess tetragonal in-plane symmetry. [Preview Abstract] |
Wednesday, March 15, 2006 9:00AM - 9:12AM |
N30.00006: Self-assembly of polydisperse acrylic block copolymers Anne-Valerie Ruzette, Ludwik Leibler, Florence Chauvin, Denis Bertin, Pierre Gerard Self-assembled block copolymers present great interest since they combine at the nanometer scale intrinsic properties of different homopolymers. Over the past decade, remarkable progress in synthetic chemistry has unveiled new opportunities to prepare tailored block copolymers of judiciously chosen monomer type and architecture at reasonable cost. In particular, controlled radical polymerizations (CRP) are suitable to all kinds of vinyl monomers in common mass, suspension or even emulsion processes. Most synthetic efforts in this field have focused on developing a ``living'' character of free radical chain-ends and control polydispersity in length and composition. Here, we discuss a different, though quite common, situation where only one of the copolymer blocks is controlled. Overall composition and molecular weight polydispersities are thus large. Self-assembly and mesoscopic order in these ``asymmetrically polydisperse'' block copolymers and their blends is discussed. [Preview Abstract] |
Wednesday, March 15, 2006 9:12AM - 9:24AM |
N30.00007: Electrospun poly(styrene-b-isoprene) fibers that exhibit internal structure Sergio Mendez, Vibha Karla, Prashant Kakad, Marleen Kamperman , Yong Joo We have used the elelctrospinning process to fabricate fibers from THF / poly(styrene-b-isoprene) (PS-PI) diblock copolymer solutions. We spun fibers with copolymers that had various volume fractions of PI. These fibers had diameters ranging from 200 nm to 5 microns depending on the processing conditions such as solution concentration, needle size, electric field, etc.. The goal of this investigation was to observe the formation of self-assembled microstructures within the fibers. SAXS data indicates that the copolymer microphase separates and that there is some degree of globally ordered domains; however, TEM images indicate that this order is more local which might be due to the short residence time in the electrospinning process. By comparison, SAXS and TEM data of PS-PI films exhibits unambiguous global ordering. In an attempt to improve the long range order within the fibers, we performed various annealing treatments, and found that heating at temperatures below the glass transition temperature only had a small effect. [Preview Abstract] |
Wednesday, March 15, 2006 9:24AM - 9:36AM |
N30.00008: Confinement induced novel morphologies of block copolymers An-Chang Shi, Bin Yu, Baohui Li Self-assembly of block copolymers confined in cylindrical nanopores is studied systematically using a simulated annealing method. For diblock copolymers which form two-dimensional hexagonally-packed cylinders with period $L_{0}$ in the bulk, novel structures such as helices and stacked toroids spontaneously form inside the cylindrical pores. These confinement induced morphologies have no counterpart in the bulk system and they depend on the pore diameter ($D$) and the surface-polymer interactions, reflecting the importance of structural frustration and interfacial interactions. On tightening the degree of confinement, transitions from helices to toroids to spheres are observed. Mechanisms of the morphological transitions can be understood based on the degree of structural frustration parametrized by the ratio $D/L_{0}$. [Preview Abstract] |
Wednesday, March 15, 2006 9:36AM - 9:48AM |
N30.00009: Self-assembly of three-dimensional morphologies in a diblock copolymer melt confined in a cylindrical nanopore Weihua Li, Robert A. Wickham The microdomain morphologies of an AB diblock copolymer melt confined in a cylindrical nanopore are investigated using three- dimensional real-space self-consistent mean-field theory. We find that many structures self-assemble in the pore, including cylinders, helices, toroids, disks, and spheres. We compute the relative stability of these structures and locate transitions between phases as the diameter of the pore is varied. We focus on narrow pores for simplicity since it appears that the number and complexity of the structures formed increases as the pore size increases. For each of our morphologies, we measure the inter-domain distance, the degree of chain stretching, the area of A/B interface, and the A/B interfacial curvature. We identify which of these factors are driving the structural transitions. Our results will be compared with recent experiments and simulations. [Preview Abstract] |
Wednesday, March 15, 2006 9:48AM - 10:00AM |
N30.00010: Effects of confinement on the order-disorder transitionin diblock copolymer melts and crystallization Dadong Yan, Bing Miao, Charles C. Han, An-Chang Shi The effects of confinement, in terms of size and geometry, on the order-disorder transition (ODT) in diblock copolymer melts are studied theoretically. Confinements are applied by restricting diblock copolymers in given geometries of slab, cylinder and sphere, respectively. Within the frame of self- consistent field theory, the second-order fluctuation of free energy functional is studied, and its minimum determines the spinodal point of the homogeneous phase. For the slabs and cylindrical cases the spinodal point $(\chi N)_s$ of the homogeneous phase is independent of the confinement, while in spherical case $(\chi N)_s$ is increased except some suitable radius of the sphere. In addition, using the idea that before nucleation there are fluctuations of the orientation of polymer chains, the puzzling direction of lamellae in the crystallization under confinement can be explained. [Preview Abstract] |
Wednesday, March 15, 2006 10:00AM - 10:12AM |
N30.00011: Effect of Cross-linking on the Structure and Thermodynamics of Lamellar Block Copolymers Enrique Gomez, Nitash Balsara, Jayajit Das, Arup Chakraborty The effect of cross-linking on the structure and thermodynamics of a lamellar poly(styrene-\textit{block}-isoprene) copolymer was studied using small angle X-ray scattering (SAXS), depolarized light scattering (DPLS) and transmission electron microscopy (TEM). The selective cross-linking of the polyisoprene block took place either in the disordered state, in an isotropic ordered state, or in a shear-aligned ordered state. Using DPLS and TEM, the grain structure as a function of cross-linking density was studied. The order-disorder transition temperature for various block copolymer networks was determined as function of cross-linking density, and comparisons are made to a mean-field theory. [Preview Abstract] |
Wednesday, March 15, 2006 10:12AM - 10:24AM |
N30.00012: Influence of Conformational Asymmetry on the Phase Behavior of Ternary Homopolymer/Block Copolymer Blends around the Bicontinuous Microemulsion Channel Ning Zhou, Timothy Lodge, Frank Bates We have developed a new ternary polymeric system, poly(ethylene-alt-propylene) (PEP) / poly(butylene oxide) (PBO) / PEP-PBO, to study the complex phase behavior near the bicontinuous microemulsion phase channel. The molecular weights of the PEP and PBO homopolymers are 2600 and 3050 g/mol, respectively, and copolymer is 23.4 kg/mol with volume fraction composition fPBO = 0.49. A combination of small-angle neutron scattering, small-angle X-ray scattering, rheology, optical microscopy and visual oil bath measurements was employed to map out the phase diagrams at five fixed homopolymer PBO/PEP ratios, ranging from 40/60 to 60/40 by volume, with copolymer concentrations ranging from 0 to 100\%. It was found that the bicontinuous microemulsion channel is consistently cut off at low temperature by a hexagonal phase. We attribute this phenomenon to the effect of the conformational asymmetry between the PEP and PBO species, whereby the more flexible PBO component induces a spontaneous curvature toward the PBO domains. These findings complement previous descriptions of the isopleth phase diagrams for the A/B/A-B systems, and identify a new design variable for preparing bicontinuous phases. [Preview Abstract] |
Wednesday, March 15, 2006 10:24AM - 10:36AM |
N30.00013: Swelling and Shrinkage of Lamellar Domain of Conformationally Restricted Block Copolymers by Metal Chloride Dong Hyun Lee, Jin Kon Kim, June Huh, Du Yeol Ryu The lamellar domain spacing (D) of symmetric polystyrene-block- poly(2-vinyl pyridine) copolymer (PS-P2VP) and PS-block-poly(4- vinyl pyridine) copolymer (PS-P4VP) with cadmium chloride (CdCl2) were studied by using rheometry, small angle X-ray scattering and transmission electron microscopy. With increasing amount of CdCl2, D of PS-P2VP increased greatly, but it decreased for PS-P4VP. This is due to different types of the coordination between CdCl2 and nitrogen atoms in the 2-position of pyridine ring (intra-chain coordination), compared with nitrogen atoms in the 4-position (inter-chain coordination). [Preview Abstract] |
Wednesday, March 15, 2006 10:36AM - 10:48AM |
N30.00014: Azimuthal Orientational Correlations due to Excluded Volume Epitaxy in Growing Anisotropic Grains Ashoutosh Panday, Samuel Gido The understanding of the microstructure of anisotropically shaped grains can have a strong influence on a range of material properties, including transport, mechanical and electro-optical properties. A grain-structure related phenomenon, called Excluded Volume Epitaxy (EVE) is reported in this study. EVE is a local, inter-grain orientational correlations effect, which results from a combination of sporadic nucleation of anisotropic grains and impingement of growing grains. Due to EVE, the anisotropically shaped grains have a tendency to be similarly aligned in a local neighborhood, despite the fact that there is no global orientation in the sample. This effect has been verified by transmission electron microscope (TEM) images of lamellar block copolymers and optical micrographs of small molecule crystals. Additionally, to quantify the effect of EVE, a modeling and simulation study involving random nucleation and subsequent growth of anisotropic grains was performed. The simulation study revealed a tendency for azimuthal, inter-grain orientational correlation and re-confirmed the experimental observation of EVE. [Preview Abstract] |
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