Nonequilibrium relaxation of soft responsive colloids

TL;DR

This paper develops a mean-field dynamical density functional theory to study the nonequilibrium relaxation of responsive colloids under time-dependent external fields, revealing complex, tunable relaxation behaviors validated by simulations.

Contribution

It introduces a novel DDFT model for responsive colloids that captures coupled translational and conformational dynamics during relaxation.

Findings

Rich relaxation behaviors match Brownian dynamics simulations.

Time-asymmetric relaxation of observables depends on diffusion time scales.

External field switching induces tunable relaxation dynamics.

Abstract

Stimuli-responsive macromolecules display large conformational changes during their dynamics, sometimes switching states, and are an integral property for the development of soft functional materials. Here, we introduce a mean-field dynamical density functional theory (DDFT) for a model of responsive colloids (RCs) to study the nonequilibrium dynamics of a colloidal dispersion in time-dependent external fields, with a focus on the coupling of translational and conformational dynamics during their relaxation. Specifically, we consider soft Gaussian particles with a bimodal size distribution between two confining walls with time-dependent (switching-on and off) external gravitational and osmotic fields. We find a rich relaxation behavior of the systems in excellent agreement with particle-based Brownian dynamics (BD) computer simulations. In particular, we find time-asymmetric relaxations of integrated observables (wall pressures, mean size, liquid center-of-mass) for activation/deactivation of external potentials, respectively, which are tuneable by the ratio of translational and conformational diffusion time scales. Our work paves thus the way for studying the nonequilibrium relaxation dynamics of complex soft matter with multiple degrees of freedom and hierarchical relaxations.