Chain Diffusion in Lamellar Block Copolymers

TL;DR

This study uses molecular dynamics simulations to analyze how symmetric diblock copolymer chains diffuse in lamellar structures, revealing anisotropic diffusion behaviors aligned with theoretical models and comparing to disordered phases.

Contribution

It provides detailed simulation data on diffusion constants in lamellar block copolymers, confirming theoretical predictions and comparing anisotropic diffusion to disordered phases.

Findings

D_parallel nearly independent of χ for given chain lengths

D_perp is strongly suppressed as χ increases

Isotropic diffusion approximated by (2D_parallel + D_perp)/3

Abstract

Diffusion of symmetric diblock copolymer chains in macroscopically oriented lamellar block copolymers are studied in a molecular dynamics simulation. Results for diffusion constant both parallel $D_\parallel$ and perpendicular $D_\perp$ to the lamellar planes are compared to results in the disordered one phase region. For diblocks of length N=40 (1.1 N_e) and $100 (3N_e)$, where $N_e$ is the entanglement length of a homopolymer melt at the same density, $D_\parallel$ is nearly independent of $\chi$, while $D_\perp$ is strongly suppressed as $\chi$ is increased. These results are in agreement with theoretical predictions based on the Rouse model. The isotropic diffusion constant of quenched disordered systems is approximated fairly well by $(2D_\parallel+D_\perp)/3$ of the corresponding lamellar system.