Thermal and hydrodynamic effects in the ordering of lamellar fluids

TL;DR

This study investigates how thermal and hydrodynamic effects influence the ordering of lamellar fluids during phase separation, revealing how thermal front speed affects morphology and orientation in different viscosities and dimensions.

Contribution

It introduces a hybrid simulation method coupling lattice Boltzmann and finite difference schemes to analyze lamellar fluid ordering under thermal fronts, highlighting the impact of thermal conductivity on morphology and orientation.

Findings

High thermal conductivity leads to frozen entangled configurations at high viscosity.

Low thermal conductivity results in well-ordered lamellae parallel to thermal fronts.

Orientation of lamellae varies with dimensionality and thermal conductivity.

Abstract

Phase separation in a complex fluid with lamellar order has been studied in the case of cold thermal fronts propagating diffusively from external walls. The velocity hydrodynamic modes are taken into account by coupling the convection-diffusion equation for the order parameter to a generalised Navier-Stokes equation. The dynamical equations are simulated by implementing a hybrid method based on a lattice Boltzmann algorithm coupled to finite difference schemes. Simulations show that the ordering process occurs with morphologies depending on the speed of the thermal fronts or, equivalently, on the value of the thermal conductivity {\xi}. At large value of {\xi}, as in instantaneous quenching, the system is frozen in entangled configurations at high viscosity while consists of grains with well ordered lamellae at low viscosity. By decreasing the value of {\xi}, a regime with very ordered lamellae parallel to the thermal fronts is found. At very low values of {\xi} the preferred orientation is perpendicular to the walls in d = 2, while perpendicular order is lost moving far from the walls in d = 3.