9505599 Fredrickson With the advent of powerful new surface characterization techniques, a number of experimental groups have reported on the surface segregation and wetting behavior of multicomponent polymer blends, as well as block and random copolymers. Surface energy differences between components are generally assumed to be responsible for producing the inhomogeneous composition profiles in such systems. Very recent experiments on model polyolefin blends and copolymers, however, have shown that a strong correlation exists between interfacial thermodynamics and the difference in conformational properties (i.e., backbone flexibilities) of the components, leading to an alternative entropic explanation for surface segregation. Theoretical calculations based on the self-consistent field theory of Edwards will be performed to place these experimental observations on a sound theoretical footing. Besides exploring surface enrichment in such "conformationally asymmetric" polymer blends and copolymers with small heats of mixing (e.g., polyolefins), calculations will be performed to investigate interfacial thermodynamics and wetting behavior in blends of "architecturally asymmetric" polymers, such as mixtures of linear and star polymers composed of the same chemical repeat unit. An examination of surface enrichment is also planned for molten polymer blends that contain star-block copolymers, and for which broken conformational and architectural symmetries may compete. The objective of these studies if to develop structure-property relations that will facilitate the rational design of polymer interfaces for engineering applications. The theoretical work proposed will be coordinated with parallel experimental efforts currently underway. %%% Theoretical research will be conducted on the properties of polymer surfaces. In particular, the question of why certain types of polymers tend to migrate to the surfaces of polymer mixtures and solids will be explored. While having fundamental interest, this problem is also of high technological interest since it impacts our ability to coat and paint plastics. ***
