Kinetics of Phase Separation in Thin Films: Lattice versus Continuum Models for Solid Binary Mixtures

TL;DR

This paper models phase separation in thin solid binary mixtures using a lattice kinetic approach, capturing wetting and domain growth behaviors, and extends the validity of continuum models to low-temperature regimes with steep concentration gradients.

Contribution

It introduces a lattice-based kinetic model for phase separation that remains accurate at low temperatures where continuum Ginzburg-Landau models fail.

Findings

Domain size grows as t^{1/3} after quench.

Model valid at temperatures far below criticality.

Provides transparent relation between interaction parameters and free energy.

Abstract

A description of phase separation kinetics for solid binary (A,B) mixtures in thin film geometry based on the Kawasaki spin-exchange kinetic Ising model is presented in a discrete lattice molecular field formulation. It is shown that the model describes the interplay of wetting layer formation and lateral phase separation, which leads to a characteristic domain size $\ell(t)$ in the directions parallel to the confining walls that grows according to the Lifshitz-Slyozov $t^{1/3}$ law with time $t$ after the quench. Near the critical point of the model, the description is shown to be equivalent to the standard treatments based on Ginzburg-Landau models. Unlike the latter, the present treatment is reliable also at temperatures far below criticality, where the correlation length in the bulk is only of the order of a lattice spacing, and steep concentration variations may occur near the walls, invalidating the gradient square approximation. A further merit is that the relation to the interaction parameters in the bulk and at the walls is always transparent, and the correct free energy at low temperatures is consistent with the time evolution by construction.