Diffusion of block copolymers

Block copolymers have been attracting the attention of a great number of scientists and engineers with their beautiful ordered structures on a nanometer scale. Repulsion between dissimilar blocks of block copolymers drives micro-phase separation on the length scale—the radius of gyration of the block copolymer chains. Due to the presence of such nano-domains, the diffusion of block copolymers in the melt is significantly reduced in the direction perpendicular to the interface between the domains. In this direction, block copolymer chains diffuse by an activated hopping mechanism in which the shorter block is pulled out from its domain into the majority domain. Consequently, in this direction the diffusion coefficients of block copolymers decrease exponentially with the activation energy of the hopping process χNskBT, where χ is the Flory parameter, Ns is the degree of polymerization of the shorter block, kB is Boltzmann's constant and T is temperature. The diffusion along the domain interface is less restricted by the presence of domains. The interface diffusion coefficient depends on the degree of segregation and presence of entanglements. Experiments, theories and simulations of block copolymer diffusion in ordered structures are reviewed.