Surface directed spinodal decomposition of fluids confined in cylindrical pore

TL;DR

This study uses molecular dynamics to explore how binary fluids confined in cylindrical pores undergo surface-directed spinodal decomposition, revealing different domain structures and growth dynamics depending on wetting conditions.

Contribution

It provides detailed insights into the morphology and growth behavior of phase separation in cylindrical confinement with varying wetting interactions.

Findings

Partial wetting leads to plug-like metastable domains.

Full wetting results in tube-like, complete phase separation.

Wetting species exhibits 2D growth dynamics with a 1/2 exponent.

Abstract

The surface directed spinodal decomposition of a binary liquid confined inside cylindrical pore is investigated using molecular dynamics simulation. One component of the liquid wets the pore surface while the other remains neutral. A variety of wetting conditions are studied. For the partial wetting case, after an initial period of phase separation, the domains organize themselves into plug-like structure and the system enters into a metastable state. Therefore, a complete phase separation is never achieved. Analysis of domain growth and the structure factor suggests an one-dimensional growth dynamics for partial wetting case. As the wetting interaction is increased beyond a critical value, a transition from the plug-like to tube-like domain formation is observed which corresponds to the full wetting morphology. Thus, a complete phase separation is achieved as the wetting species moves towards the pore surface and forms layers enclosing the non wetting species residing around the axis of the cylinder. The coarsening dynamics of both the species are studied separately. The wetting species is found to follow a two-dimensional domain growth dynamics with a growth exponent 1/2 in the viscous hydrodynamic regime. This was substantiated by the Porod tail of the structure factor. On the other hand, the domain grows linearly with time for the non wetting species. This suggests that the non wetting species behaves akin to a three-dimensional bulk system. An appropriate reasoning is presented to justify the given observations.