Creating cycles in polymer chains has implications for both the surface fluctuations of melts and the thermodynamics of surface segregation in blends. Since surface fluctuations are important for determining wetting/dewetting, adhesion and tribology of thin melt films, we have investigated the variation in their behavior as chain topology is varied from linear to branched to cyclic, bicyclic (8-shaped), and tadpole. As films become thinner the surface fluctuation dynamics become slower than expected from a hydrodynamic continuum theory (HCT) that works well for sufficiently thick films of unentangled chains. For cyclic chains, this slowing of fluctuations sets in at film thicknesses (relative to Rg) larger than in the case of linear chains. It is also observed that a "residual adsorbed layer" persisting after rinsing away most of the film is notably thicker for the case of the cyclic chain than for its linear analog. Star branched chains display behavior deviating from the HCT at still larger thicknesses. We also consider briefly surface segregation in a blend of chains in which the two species differ only in topology, one being linear and the other cyclic. Rationalizing the experimental results requires proper theoretical treatment of topologically driven surface segregation, which cannot be described using a conventional surface potential. We report 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 the Wall Polymer Reference Interaction Site Model theory.

How closed loops impact melt surface fluctuations and surface segregation in blends

255th National Meeting (2018)

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