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Polymers on nanoperiodic, heterogeneous surfaces
Abstract
Herein we establish a relationship between controlled nanoscale surface interactions and subsequent macromolecular ordering. Chemically heterogeneous striped surfaces of polar silicon oxide and non polar gold are generated over large areas, via glancing angle evaporation on facetted silicon substrates. The processing conditions required for generation of stripe widths comparable to the size of a polymer molecule are outlined. Substrates with 20–30 nm metal linewidths and 40–60 rim stripe periods are prepared. Spin and solution casting of incompatible polymer mixtures of polystyrene (PS) and polymethylmethacrylate (PMMA) on heterogeneous surfaces are found to generate films with unique, substrate directed morphologies dependant on the kinetics of the casting process. Spin cast films posses a surface adsorbed layer of blended composition due to rapid polymer adsorption from solution, while solution cast films phase separate at the substrate/polymer interface on a molecular level. Preferential adsorption of PS to the non polar gold stripes and PMMA to polar silicon oxide stripes is observed at the substrate beneath the macroscopically phase separated domains of the blend components. Preferential adsorption occurs over a large molecular weight range, with a molecular weight dependence on the morphology of the adsorbed polymer lines found. Solution cast films of the symmetric copolymer poly(styrene-block-methylmethacrylate), P(S-b-MMA), on heterogeneous surfaces show lamellar microdomain orientations perpendicular to the substrate plane, parallel to the striping. Commensurability of the block copolymer and substrate stripe periods is found to be essential for producing such a surface directed morphology. The commensurability window depends inversely on the degree of confinement of the morphology, with unconfined films requiring more stringent conditions for surface directed morphology reorientation. The distance over which the orientation of the microdomains persists in thick films is found to depend on the ordering kinetics, scaling with copolymer molecular weight. Confinement effects such as tension and compression and defects in the lateral long range orientation of surface directed lamellar morphologies are observed for slightly incommensurate morphologies, with the amount of strain and defect concentration found to increase with the loss of commensurability.
Subject Area
Polymers|Condensation|Materials science
Recommended Citation
Rockford, Lee David, "Polymers on nanoperiodic, heterogeneous surfaces" (2001). Doctoral Dissertations Available from Proquest. AAI3000338.
https://scholarworks.umass.edu/dissertations/AAI3000338