Theories of surface-driven segregation in polymer fluids /
Three polymer interfacial systems-thin films of diblock copolymer melts, polymer blends near surfaces, and surface segregation of athermal polymer blends-are studied by density functional theory. We analyze the weak-segregation, thermodynamic predictions of a simple mean-field model of diblock copo...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
1998.
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| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=737708081&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | Three polymer interfacial systems-thin films of diblock copolymer melts, polymer blends near surfaces, and surface segregation of athermal polymer blends-are studied by density functional theory. We analyze the weak-segregation, thermodynamic predictions of a simple mean-field model of diblock copolymer melts sandwiched between surfaces that interact weakly with melts. These films may not exhibit a phase transition although the segregation that develops within them resembles ordering in the bulk. When transitions occur, they result from a competition between surface and bulk effects and have no bulk analogue. Thin films confined by identical surfaces or surfaces having equal-in-magnitude but opposite affinities for the monomers may exhibit first-and second-order transitions when the melt-surface interactions are small. Second-order transitions do not occur in films with large surface affinities. The instabilities that lead to the second-order transitions in films disappear with increases in the film thickness. We also investigate the long-wavelength features of near-surface composition profiles of monomers in a binary, symmetric blend with an external field gradient expansion. The gradient expansion includes information about correlations of polymer chains with the surface. Relative to simpler theories of polymer-surface adsorption, our theory predicts a small increase of the interfacial width. We illustrate a derivation of a surface-boundary condition on the composition profile directly from the monomer-surface Hamiltonian. This boundary condition, when combined with our density functional analysis, leads to first-order wettingtransitions. Finally, our work on surface segregation of athermal blends is presented. We study the effect on surface segregation due to disparity in molecular weights, stiffness of polymer chains, and sizes of the monomers. Our results suggest that disparity in molecular weights do not lead to a profound surface segregation. In the study of stiff and flexible polymer chains near surface, we find that stiffness in chains does not cause segregation. In this work, we have also demonstrated the surface segregation of polymer blends near surfaces due to the disparity in monomeric sizes. An attractive surface is found to repel larger segments and adsorb smaller segments, and vice versa. |
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| Item Description: | Vita. "Major Subject: Chemistry". |
| Physical Description: | xi, 148 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilms Inc. |
| Bibliography: | Includes bibliographical references: pages 112-120. |