Diffusion of Entangled Rod-Coil Block Copolymers

The diffusion of entangled rod-coil block copolymers is investigated by molecular dynamics (MD) simulations, and theories are introduced that describe the observed features and underlying physics. The reptation of rod-coil block copolymers is dominated by the mismatch between the curvature of the rod and coil entanglement tubes, which results in dramatically slower diffusion of rod-coils compared to the rod and coil homopolymers. For small rods, a local curvature-dependent free energy penalty results in a rough energy surface inside the entanglement tube, causing diffusivity to decrease with rod length. For large rods, rotational hindrances on the rod dominate, causing the coil block to relax by an arm retraction mechanism and diffusivity to decrease exponentially with coil size.