Polymer Diffusion


Recent research is actively advancing polymer science into the field of highly functional materials, such as block copolymers, protein-polymer conjugates, advanced biomaterials, and associating polymers. In addition to the structures formed by these polymers, the dynamcis are critically important for governing both transport and mechanical responses. Our group is investigating the diffusion of both rod-coil block copolymers and associative polymers. Diffusion in entangled rod-coil block copolymers interesting both scientifically and technologically because the dynamics of rodlike polymers depart significantly from those of coil polymers, which dramatically affects the processing and self-assembly of materials in the melt. Using molecular dynamics simulation, slip spring simulations, and experimental diffusion measurements by forced Rayleigh scattering, we are demonstrating that the different characteristic curvatures of the rod and coil blocks will cause the surrounding entanglements to respond to the blocks differently, resulting in fundamentally different diffusion behavior of rod-coils compared to rod and coil homopolymers. We are also proposing new modifications to the existing theories that govern the dynamics of entangled flexible polymers in order to explain our results.

In the area of associative polymers, we have demonstrated for several associative polymer systems that diffusion is accurately captured by an empirical two state model where molecules are allowed to dynamically exchange between fast and slow diffusing states. Our current work is relating this model to implications on macroscopic properties as well as trying to probe the microscopic origins of the model and why it is robust to variations in the associative group and polymer topology.