Relaxation to steady states of a binary liquid mixture around an optically heated colloid

TL;DR

This study investigates the asymmetric relaxation dynamics of a binary liquid mixture around an optically heated colloid, revealing distinct behaviors during heating and cooling phases through experiments and models.

Contribution

It provides a combined experimental and theoretical analysis of the relaxation processes near a heated Janus particle, highlighting the asymmetry and two-step nature of the approach to steady states.

Findings

Relaxation to steady state is slower than return to thermal equilibrium.

Concentration fluctuations follow a power law during illumination switch-on.

Energy out-flow after switch-off is described by a stretched exponential.

Abstract

We study the relaxation dynamics of a binary liquid mixture near a light-absorbing Janus particle after switching on and off illumination using experiments and theoretical models. The dynamics is controlled by the temperature gradient formed around the heated particle. Our results show that the relaxation is asymmetric: the approach to a nonequilibrium steady state is much slower than the return to thermal equilibrium. Approaching a nonequilibrium steady state is a two-step process leading to the behavior of the spatial variance of concentration field similar to the initial overshoot in response to an external field found in diverse soft materials. The initial growth of concentration fluctuations after switching on illumination follows a power law in agreement with the hydrodynamic and purely diffusive model. The energy out-flow from the system after switching off illumination is well described by a stretched exponential function of time with characteristic time proportional to the ratio of the energy stored in the steady state to the total energy flux in this state.