Modelling approaches to the dewetting of evaporating thin films of nanoparticle suspensions

TL;DR

This paper reviews experimental and theoretical approaches to understanding the dewetting behavior of evaporating thin films of nanoparticle suspensions, highlighting models from microscopic to hydrodynamic scales and their insights into pattern formation.

Contribution

It provides a comprehensive comparison of microscopic, mesoscopic, and hydrodynamic models for nanoparticle film dewetting, emphasizing their applications and limitations.

Findings

Identification of transverse instabilities leading to fingering patterns.

Explanation of the formation of polygonal networks and branched structures.

Discussion of contact line pinning and depinning related to the coffee-stain effect.

Abstract

We review recent experiments on dewetting thin films of evaporating colloidal nanoparticle suspensions (nanofluids) and discuss several theoretical approaches to describe the ongoing processes including coupled transport and phase changes. These approaches range from microscopic discrete stochastic theories to mesoscopic continuous deterministic descriptions. In particular, we describe (i) a microscopic kinetic Monte Carlo model, (ii) a dynamical density functional theory and (iii) a hydrodynamic thin film model. Models (i) and (ii) are employed to discuss the formation of polygonal networks, spinodal and branched structures resulting from the dewetting of an ultrathin 'postcursor film' that remains behind a mesoscopic dewetting front. We highlight, in particular, the presence of a transverse instability in the evaporative dewetting front, which results in highly branched fingering structures. The subtle interplay of decomposition in the film and contact line motion is discussed. Finally, we discuss a simple thin film model (iii) of the hydrodynamics on the mesoscale. We employ coupled evolution equations for the film thickness profile and mean particle concentration. The model is used to discuss the self-pinning and depinning of a contact line related to the 'coffee-stain' effect. In the course of the review we discuss the advantages and limitations of the different theories, as well as possible future developments and extensions.