Modelling approaches to the dewetting of evaporating thin films of nanoparticlesuspensions

Abstract

We review recent experiments on dewetting thin films of evaporating colloidal nanoparticlesuspensions (nanofluids) and discuss several theoretical approaches to describe the ongoingprocesses including coupled transport and phase changes. These approaches range frommicroscopic discrete stochastic theories to mesoscopic continuous deterministicdescriptions. In particular, we describe (i) a microscopic kinetic Monte Carlo model, (ii) adynamical density functional theory and (iii) a hydrodynamic thin film model.Models (i) and (ii) are employed to discuss the formation of polygonal networks, spinodaland branched structures resulting from the dewetting of an ultrathin ‘postcursor film’ thatremains behind a mesoscopic dewetting front. We highlight, in particular, the presence of atransverse instability in the evaporative dewetting front, which results in highly branchedfingering structures. The subtle interplay of decomposition in the film and contact linemotion 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 particleconcentration. The model is used to discuss the self-pinning and depinning of a contact linerelated to the ‘coffee-stain’ effect.In the course of the review we discuss the advantages and limitations of the differenttheories, as well as possible future developments and extensions.