Controlling self-assembly and anisotropy of block copolymer materials with nanorods.

摘要

The detailed nanostructure of composites formed from block copolymers and nanoparticles is known to depend sensitively on the preferred morphology of the block copolymer, on the shapes of the particles, and on interactions between the two components. But it can also depend on the kinetics of self-assembly in the polymer, and there are circumstances under which the kinetics of morphologically selective domain nucleation and growth determine the overall nanostructure of the composite. To study the mechanism of morphological seeding in block copolymer nanocomposites, cylindrical polystyrene- block-polyisoprene diblock (as a solution in dibutylphthalate) and poly(styrene-block-isoprene-block-styrene) triblock (as a blend with homopolystyrene) copolymers were combined with gold nanorods of different diameters and surface treatments. Polarized optical microscopy, transmission electron microscopy, and small angle X-ray analysis on these composites demonstrate that the nanorods selectively nucleate coaxial domains of copolymer cylinders (i.e., domains of cylinders aligned along the same axis as the nanorod). These single nucleation events occur regardless of nanorod diameter and surface character, and determine the order of most of the surrounding polymer. Mesoscale modeling of the nucleation process, performed with nanorods of different diameters and with different polymer-surface interactions, illustrates the mechanism by which copolymer-dispersed nanorods with different sizes and surface chemistry can template organization of cylindrical copolymer domains.; This thesis also describes a simple method for preparing conductive films from single-wall nanotube-polymer composite materials. This approach involves a two step procedure of (1) suspending nanotubes in concentrated solutions of poly(styrene-b-isoprene-b-styrene) and tackifier resin and (2) coating the composite solutions onto polymer substrates. Films with surface resistivity values of ∼103 O/square were prepared by controlling the concentration of nanotubes in solution. The effect of mechanical deformation on the conductivity of composite films was investigated. In addition, confocal Raman microscopy was used to understand the origin of electrical conductivity in the composite films.