Simulation of the thermocapillary assembly of a colloidal cluster during the evaporation of a liquid film in an unevenly heated cell

TL;DR

This paper models the thermocapillary-driven assembly of colloidal clusters during liquid evaporation in an uneven heat environment, revealing how heat flux influences particle clustering behavior.

Contribution

It introduces a two-dimensional mathematical model to analyze particle transfer and cluster formation driven by thermocapillary flow during evaporation.

Findings

Higher heat flux reduces particle clustering at low concentrations.

Thermocapillary flow increases with heat flux, affecting particle entry into clusters.

Gravity-to-drag ratio determines whether particles join the cluster.

Abstract

The control of the thermocapillary assembly of colloidal particle clusters is important for a variety of applications, including the creation of photonic crystals for microelectronics and optoelectronics, membrane formation for biotechnology, and surface cleaning for laboratory-on-chip devices. It is important to understand the main mechanisms that influence the formation of such clusters. This article considers a two-dimensional mathematical model describing the transfer of particles by a thermocapillary flow in an unevenly heated cell during the evaporation of a liquid. This gave us the opportunity to study one of the main processes that triggers the formation of a particle cluster. Whether the particle will move with the flow or stop at the heater, becoming the basis for the cluster, is determined by the ratio between gravity and the drag force. The results of numerical calculations show that, for small particle concentrations, their fraction entering the cluster decreases as the volumetric heat flux density $Q$ increases. The reason for this is an increase in the thermocapillary flow with an increase in the volumetric heat flux $Q$. It reduces the probability of particles entering the cluster.