Association, Segregation, and Transport in Copolymer Liquids

9901087

Lodge

Multicomponent polymers in general, and block copolymers in particular, offer attractive routes to novel properties, by the incorporation of disparate chemical elements into materials with prescribed morphologies. However, the important dynamic properties of such mixtures are rather poorly understood. Complications arise due to the presence of structure, which presents barriers to transport, and by the unkown effects of mixing on the chain dynamics. The unifying philosophy of this proposal is that the collective dynamic response of a multicomponent polymer system can only be understood if the underlying structure, mechanisms of motion, and individual component contributions are known. Experimental studies addressing three fundamental issues in this area will be pursued. First, the transient states of aggregation that may exist upon disordering block copolymer melts from the sphere morphology, and upon disordering block copolymer solutions in solvents of varying selectivity, will be characterized. The former topic has received some experimental attention in the literature, but the results are controversial; the latter has not been addressed systematically. Second, the mechanisms of motion of strongly-segregated block copolymers will be delineated, particularly through measurements of chain diffusion along, and perpendicular to, the cylinder axis in oriented samples. This study builds on a previous exploration of the weakly-segregated regime, and will be relevant to most copolymer materials, which are typically more strongly-segregated. Third, the composition and temperature dependence of the monomeric friction factors of the two components of exemplary immiscible mixtures will be examined. This work exploits recently-developed approach involving disordered multiblock copolymers that circumvents the phase separation problem.

Polymers are ubiquitous in contemporary technology, but future advances in their application will rely on incorporating several different components into one material, while controlling structure on the microscopic level. Such microstructures can have profound effects on the flow properties of molten polymers, which in turn control the processing of polymers into films, fibers, and three-dimensional objects. This proposal seeks to gain fundamental insight into the way molecular parameters of the several components impact the flow properties of the resulting multicomponent polymer materials.