Domain Growth and Aging in a Phase Separating Binary Fluid Confined Inside a Nanopore

TL;DR

This study investigates how hydrodynamics influence phase separation in confined binary fluids within nanopores, revealing inertial growth and aging behaviors that differ from bulk fluids, with implications for understanding confined fluid dynamics.

Contribution

It provides the first detailed molecular dynamics analysis of phase separation kinetics and aging in a confined binary fluid, highlighting the effects of confinement and hydrodynamics.

Findings

Domain growth follows a t^{2/3} power law before freezing.

Aging dynamics exhibit a temperature-independent power-law with exponent ~2.55.

Confined systems form striped morphologies that become frozen.

Abstract

Hydrodynamics is known to have strong effects on the kinetics of phase separation. There exist open questions on how such effects manifest in systems under confinement. Here, we have undertaken extensive studies of the kinetics of phase separation in a two-component fluid that is confined inside pores of cylindrical shape. Using a hydrodynamics-preserving thermostat, we carry out molecular dynamics simulations to obtain results for domain growth and aging for varying temperature and pore-width. We find that all systems freeze into a morphology where stripes of regions rich in one or the other component of the mixture coexist in a locked situation. Our analysis suggests that, irrespective of the temperature the growth of the average domain size, $\ell(t)$, prior to the freezing into stripped patterns, follows the power law $\ell(t)\sim t^{2/3}$, suggesting an inertial hydrodynamic growth, which typically is applicable for bulk fluids only in the asymptotic limit. Similarly, the aging dynamics, probed by the two-time order-parameter autocorrelation function, also exhibits a temperature-independent power-law scaling with an exponent $\lambda \simeq 2.55$, much smaller than what is observed for a bulk fluid.