Crossover in Topologically Driven Surface Segregation of Cyclic/Linear Polymer Blends

In comparison to the surface segregation that occurs in polymer blends due to chemical differences between the two types of repeat units or in blends with different chain sizes, where shorter chains are preferred at the surface, topologically driven surface segregation is more difficult to describe theoretically. We report experimental observation and theoretical consideration of a crossover in the surface segregation of blends of linear and cyclic polymers from control by a universal topological driving force for long chains to control by surface packing for short chains. For a 37k cyclic/linear polystyrene blend the surface is enriched in cyclic chains in quantitative agreement with self-consistent field theory. For a 2k cyclic/linear polystyrene blend the surface is enriched in linear chains, consistent with Wall Polymer Reference Interaction Site Model theory. While the surface segregation seen in blends of linear and branched chains can be described using a conventional surface potential, the topological driving force important here cannot be.