Abstract
This thesis dicusses the formation and development of periodic patterns of separated phases in polymer thin films, and also the patterned nanowire distributions in polymer blend thin films. First, the preferential partition of silver nanowires in thin films of PS/PVP blends, that induces drastic blend morphology variation, was reported. The silver nanowires were fabricated with the anodic aluminum oxide templating method, and had a diameter of 300 nm and length of 10 mm. At a higher nanowire loading of 10%, the silver nanowires were entangled and selectively concentrate within the continuous PVP domain. If surface modified by thiols carrying hydrophobic tails, the silver nanowires became hydrophobic and preferred to stay within the discrete hydrophobic PS domains. At a lower nanowire loading of 5%, the nanowires stayed non-entangled and concentrated at regions near the interfaces of the PS and PVP phases, which induced the formation of interconnected PS domains. Second, patterns of parallel strips were observed in thin films spin cast from the PS/PVP/chloroform solution on un-patterned substrates. The formation of anisotropic patterns, manifested not only in thickness variation but also in composition variation, was found to be driven by the Marangoni instability, with the PS and PVP streams flowing toward the preferred regions as the phase separation induced by solvent evaporation proceeded. On the other hand, periodic patterns were obtained for PS/PVP blend films, solution cast on tilted glass substrates. Regular arrays of the separated phases and strip patterns of separated phases were observed. The initial viscosity of the polymer solution and the thickness of blend films were lumped into one single parameter to study the phase morphology development at various initial polymer solution concentrations. Third, parallel striations made of silver nanowires were formed through the Marangoni instability induced during spin cast of nanowire/polymer solutions. The silver nanowires were found to concentrate at the valleys of the striation pattern to balance the non-uniform surface tension distribution in the polymer thin film. The resulting nanowire striation patterns were found to depend on polymer concentration, rotation speed, nanowire loading, and polymer characteristics. The van der Waals interactions between silver nanowires suspended in several different polymer solutions were estimated to correlate with the quality of the nanowire striation pattern achieved for different polymers. Nanowire agglomeration occurred in polymers giving large van der Waals interactions such that no nanowire striation pattern was formed in these systems. The distribution of nanowires in the spin-cast polymer thin films was found to be governed by the coupling competition among the Marangoni convection, van der Waals attractive forces, and centrifugal force.