The phase behavior of confined, multicomponent polymer mixtures is interesting in the context of application, e.g., paints and packaging, since important film properties, such as surface roughness and hence the optical quality and friction of the film surface, change dramatically when the mixture phase separates. While this problem has been the focus of theoretical interest for the last two decades, very little experimental work exists due to the challenges in obtaining reliable data from films in the 0.01-1nm thickness range. The PI has recently extended a standard characterization technique, small angle neutron scattering, to films as thin as D=10 nm and finds that experimental measures of thin film coexistence are in qualitative disagreement with past experiments and theory on comparable systems. Resolving these discrepancies is a primary thrust of the proposed research. %%% An important element in the proper delineation of thin film behavior is a quantitative understanding of their bulk miscibility. While there is considerable research on these issues, it remains hard to a - priori predict the miscibility of two arbitrarily chosen polymers. For example, current molecular simulations which account for all of the chemical details of the molecules are limited to chain lengths which are too short to be in the range where normal polymer mixtures phase separate. As part of this research the PI has developed a quantitative lattice-based method which alleviates these concerns.
The primary focus of the proposed work, which exploits the availability of these novel and complementary theoretical and experimental tools, is to quantitatively understand the bulk phase behavior of model polymer blends, and how they are modified by the constraints and surface interactions in a thin film geometry in an integrated manner.