(6eh) Dynamics of Entangled Rod-Coil Block Copolymers

Polymer science is exploring advanced materials which combine functional domains such as proteins and semiconducting polymers with traditional flexible polymers onto the same molecule. While thermodynamic assemblies of different geometries introduce many interesting new phenomena such as entropic packing and liquid crystalline interactions, dynamic effects are also important to understand for optimal design of material mechanics, processing kinetics, and because of the new physics that directly arises from the motion of multiple domains of dissimilar geometries. 

We have recently proposed a theory for the molecular mechanisms of motion in entangled rod-coil block copolymers as a model for this wider class of functional polymeric materials. The large geometrical differences between rigid rods and Gaussian coils cause significant nonlinearities in dynamical behavior as these two motifs are combined on the same molecule. In particular, our theory hypothesizes that the motion of rod-coils is slowed relative to rod and coil homopolymers because of a mismatch between the curvature of the rod and coil entanglement tubes. Dual relaxation mechanisms are predicted in the small and large rod limits, where either the rod or the coil block is expected to determine the motion of the overall molecule. 

In this poster we describe the mechanisms of rod-coil block copolymers in detail, while providing significant evidence from both simulation and experiment in support of our theory. We first consider the tracer diffusion of symmetric coil-rod-coil triblocks using molecular dynamics simulation and forced Rayleigh scattering experiments. These results are then generalized to consider rod-coil diblock copolymers, whose asymmetry requires additional analysis. Self-diffusion studies then provide an important step in translating the new physics into practical applications. Finally, additional simulations using coarse-grained models provide a more direct understanding of the underlying mechanisms.