Active alignment-driven coarsening in confined near-critical fluids

TL;DR

This study explores how activity driven by alignment interactions influences phase separation and coarsening in confined near-critical fluids, revealing that activity can overcome kinetic arrest and accelerate domain growth.

Contribution

It introduces a novel investigation of active near-critical fluids under confinement, demonstrating how alignment activity modifies coarsening dynamics and morphology.

Findings

Passive system exhibits spinodal decomposition and arrested coarsening.

Activity induces collective transport, leading to phase separation.

Late-stage growth transitions to faster, ballistic coarsening with exponent 2/3.

Abstract

We investigate vapor-liquid phase separation of an active near critical Lennard-Jones fluid confined within a cylindrical pore using molecular dynamics simulations. Activity is introduced via Vicsek-type alignment interactions, enabling a systematic study of how self-propulsion modifies domain morphology and coarsening kinetics under quasi-one-dimensional confinement. In the passive limit, the system undergoes early-time spinodal decomposition (diffusive growth characterized by the Lifshitz-Slyozov exponent $\alpha = 1/3$), followed by the formation of periodically modulated, plug-like liquid domains along the pore axis. At late times, coarsening becomes kinetically arrested, and the system remains trapped in a metastable striped state. Introducing activity destabilizes this arrested morphology by enhancing collective domain transport, leading to frequent domain mergers and complete phase separation at sufficiently high activity. The late-stage coarsening then exhibits a crossover to faster, ballistic growth with an effective exponent $\alpha = 2/3$, consistent with a cluster-coalescence mechanism. Analysis of two-point correlation functions and structure factors confirms dynamic scaling across all activity regimes. Our results demonstrate that alignment-induced activity can overcome confinement-driven kinetic arrest, providing new insight into phase separation in confined active fluids. The relevant growth laws are analyzed and interpreted using appropriate theoretical frameworks.