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Controlling polymer thin film structures by tuning interfacial interactions
The utilization of poly(styrene-random-methyl methacrylate), P(S-r-MMA), random copolymer brush surfaces to control the structure of polymer films is demonstrated. Random copolymer brush layers were generated by end anchoring the copolymers onto silicon substrates. By dictating the chemical composition of the random copolymer, the resultant brush layer could be precisely tuned to have properties ranging from pure PS to pure PMMA. This was determined by experiments where PS and PMMA homopolymer films showed dewetting behavior characteristic of the interactions between the homopolymer film and the underlying brush layer. Brushes having a styrene fraction of 0.58 have balanced interactions with PS and PMMA and constitute surfaces that are nonpreferential or neutral to PS and PMMA. The influence of interactions between polymer films and random copolymer brush layers is addressed for three systems. First, the interfacial structures of dPS and dPMMA homopolymer films with the brush layer were examined with neutron reflectivity (NR). The interfacial width between the two layers strongly depended upon the interactions between them. Furthermore, it is observed that penetration of dPMMA to the silicon substrate can occur for cases where the brush layer does not provide a sufficient enthalpic or entropic barrier. Second, atomic force microscopy studies (AFM) show that PS/PMMA demixed films had morphologies that varied greatly with substrate interactions. With annealing, some of these structures rearranged significantly while others remained relatively unchanged. The third type of polymer film examined in this study, diblock copolymers constitutes the main focus of this work. Normally, preferential interactions of one block at an interface induce a parallel orientation of the block copolymer domains. By utilizing neutral random copolymers, preferential segregation of each block is eliminated resulting in a perpendicular orientation of block copolymer domains. This was shown for poly(styrene-block-methyl methacrylate), P(S-b-MMA), block copolymers having lamellar and cylindrical morphologies. Using a wide variety of techniques the structural dependence of these films with annealing time and the effects of commensurability were examined. By controlling the growth of these domains, the generation of novel film structures comprised of perpendicular lamellar and cylindrical domains was achieved.
Huang, Elbert E, "Controlling polymer thin film structures by tuning interfacial interactions" (2000). Doctoral Dissertations Available from Proquest. AAI9960760.