Adsorption of copolymers at polymer/air and polymer/solid interfaces / Robert Oslanec.

Oslanec, Robert.
xxv, 293 p. ; 29 cm.
Local subjects:
Penn dissertations -- Materials science and engineering.
Materials science and engineering -- Penn dissertations.
Using mainly low-energy forward recoil spectrometry (LE-FRES) and neutron reflectivity (NR), copolymer behavior at polymer/air and polymer/solid interfaces is investigated. For a miscible blend of poly(styrene-ran-acrylonitrile) copolymers, the volume fraction profile of the copolymer with lower acrylonitrile content is flat near the surface in contrast to mean field predictions. Including copolymer polydispersity into a self consistent mean field (SCMF) model does not account for this profile shape. LE-FRES and NR is also used to study poly(deuterated styrene-block-methyl-methacrylate) (dPS-b-PMMA) adsorption from a polymer matrix to a silicon oxide substrate. The interfacial excess, $z\sp*$, layer thickness, L, and layer-matrix width, w, depend strongly on the number of matrix segments, P, for $P 2N$, the matrix chains are repelled from the adsorbed layer and the layer characteristics become independent of P. An SCMF model of block copolymer adsorption is developed. SCMF predictions are in qualitative agreement with the experimental behavior of $z\sp*$, L, and w as a function of P. Using this model, the interaction energy of the MMA block with the oxide substrate is found to be $-8k\sb{B}T.$ In a subsequent experiment, the matrix/dPS interaction is made increasingly unfavorable by increasing the 4-bromostyrene mole fraction, x, in a poly(styrene-ran-4-bromostyrene) (PBr$\sb{\rm x}$S) matrix. Whereas experiments show that $z\sp*$ slightly decreases as x increases, the SCMF model predicts that $z\sp*$ should increase as the matrix becomes more unfavorable. Upon including a small matrix attraction for the substrate, the SCMF model shows that $z\sp*$ decreases with x because of competition between PBr$\sb{\rm x}$S and dPS-b-PMMA for adsorbing sites. In thin film dewetting experiments on silicon oxide, the addition of dPS-b-PMMA to PS coatings acts to slow hole growth and prevent holes from impinging. Dewetting studies show that longer dPS-b-PMMA chains are more effective stabilizing agents than shorter ones and that 3 volume percent dPS-b-PMMA is the optimum additive concentration for this system. For a dPS-b-PMMA:PS blend, atomic force microscopy of the hole floor reveals mounds of residual polymer and a modulated contact line where the rim meets the substrate.
Supervisor: Russell J. Composto.
Thesis (Ph.D. in Materials Science and Engineering) -- University of Pennsylvania, 1997.
Includes bibliographical references.
Local notes:
University Microfilms order no.: 98-14898.
Composto, Russell J., advisor.
University of Pennsylvania.
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