Block Copolymer Reptation


Recent research is actively advancing polymer science into the field of highly functional materials, such as block copolymers, protein-polymer conjugates, advanced biomaterials, and semiconducting polymers. Functional polymer domains typically deviate from the familiar Gaussian chain conformations of traditional polymers. For example, extended π-conjugation means semiconducting polymers are rodlike, and specific protein folds mean peptide sequences in active enzymes must adopt a predetermined 3-dimensional shape. While the dynamics and viscoelastic properties of traditional flexible polymers has been well-studied, little is known about how these increasingly prevalent conformational restrictions can affect material properties such as mechanics, processing, and self-assembly kinetics.

Our group is investigating the dynamics of entangled rod-coil block copolymers as a model for this wider class of functional polymeric materials. Diffusion in the entangled regime is especially 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 both molecular dynamics simulation 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.