Hydrodynamic Effects in Kinetics of Phase Separation in Binary Fluids: Critical versus off-critical compositions

TL;DR

This study uses hydrodynamics-preserving molecular dynamics simulations to analyze phase separation kinetics in binary fluids, revealing different growth mechanisms near and far from the critical composition, with results matching theoretical predictions.

Contribution

It identifies and characterizes the diffusive coalescence growth mechanism near off-critical compositions, contrasting it with viscous hydrodynamic growth at critical composition.

Findings

Diffusive droplet motion observed between collisions.

Power-law growth exponent matches theoretical value.

Growth mechanisms differ near and far from critical composition.

Abstract

Via hydrodynamics preserving molecular dynamics simulations we study growth phenomena in a phase separating symmetric binary mixture model. We quench high-temperature homogeneous configurations to state points inside the miscibility gap, for various mixture compositions. For compositions around the symmetric or critical value we capture the rapid linear viscous hydrodynamic growth due to advective transport of material through tube-like interconnected domains. The focus of the work, however, is on compositions close to any of the branches of the coexistence curve. In this case, the growth in the system, following nucleation of droplets of the minority species, occurs via coalescence mechanism. Using state-of-the-art techniques we have identified that these droplets, between collisions, exhibit diffusive motion. The value of the exponent for the power-law growth, related to this diffusive coalescence mechanism, as the composition keeps departing from the critical value, has been estimated. This nicely agrees with a theoretical number. These results are compared with the growth that occurs via particle diffusion mechanism, in non-hydrodynamic environment.