Dynamic self-consistent field approach for studying kinetic processes in multiblock copolymer melts

TL;DR

This paper develops a semi-analytical dynamic self-consistent field approach to study kinetic ordering in multiblock copolymer melts, enabling analysis without simulations and aiding in designing nonequilibrium materials.

Contribution

It introduces a semi-analytical method to calculate mobility functions for multiblock copolymers, extending dynamic self-consistent field theory to complex sequences without simulations.

Findings

Identified different dynamical regimes during ordering after quenches.

Derived an approximate expression for the single-chain dynamic structure factor.

Showed the approach can inform quenching protocols for material design.

Abstract

The self-consistent field theory is a popular and highly successful theoretical framework for studying equilibrium (co)polymer systems at the mesoscopic level. Dynamic density functionals allow one to use this framework for studying dynamical processes in the diffusive, non-inertial regime. The central quantity in these approaches is the mobility function, which describes the effect of chain connectivity on the nonlocal response of monomers to thermodynamic driving fields. In a recent study [Mantha et al, Macromolecules 53, 3409 (2020)], we have developed a method to systematically construct mobility functions from reference fine-grained simulations. Here we focus on melts of linear chains in the Rouse regime and show how the mobility functions can be calculated semi-analytically for multiblock copolymers with arbitrary sequences without resorting to simulations. In this context, an accurate approximate expression for the single-chain dynamic structure factor is derived. Several limiting regimes are discussed. Then we apply the resulting density functional theory to study ordering processes in a two-length scale block copolymer system after instantaneous quenches into the ordered phase. Different dynamical regimes in the ordering process are identified: At early times, the ordering on short scales dominates; at late times, the ordering on larger scales takes over. For large quench depths, the system does not necessarily relax into the true equilibrium state. Our density functional approach could be used for the computer-assisted design of quenching protocols in order to create novel nonequilibrium materials.