Diffusion and Segregation in Polymer Films

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We will continue our experiments on diffusion and segregation in polymer films, exploiting the complementary depth profiling capabilities of forward recoil spectrometry, nuclear reaction analysis, dynamic secondary ion mass spectrometry and neutron reflectometry for polymer molecules labelled with deuterium. Emphasis will be placed on understanding diffusion in microphase- separated block copolymer melts with spherical morphologies, where we will investigate both the diffusion of individual block copolymer chains and the diffusion of micelles. Emphasis will also be placed on understanding surface segregation in model mixtures of polymers, with both the details of the equilibrium concentration profile and the kinetics with which such equilibrium profiles are approached being of interest. Finally the influence of a surface attraction on phase separation by spinodal decomposition in polymer films will be further explored. The goals of this research are to develop new experimental methods for investigating the fundamental aspects of diffusion in polymers and to use these methods to critically test models of these processes. Diffusion of one polymer into another plays an important role in a variety of industrial processes ranging for melt blending of miscible polymers to friction welding and heat sealing of plastics. Basic information on diffusion rates is also required to allow predictions on the kinetics of phase separation in partially compatible polymers and to permit comparison between theory and experiments on polymer crystallization. On an even more basic level, diffusion measurements in polymers are of interest for the light they can shed on the fundamentals of viscoelastic processes ("molecular rheology") in polymer melts.