3 research outputs found
Dynamical model for the formation of patterned deposits at receding contact lines
We describe the formation of deposition patterns that are observed in many different experiments where a three-phase contact line of a volatile nanoparticle suspension or polymer solution recedes. A dynamical
model based on a long-wave approximation predicts the deposition of irregular and regular line patterns
due to self-organized pinning-depinning cycles corresponding to a stick-slip motion of the contact line.
We analyze how the line pattern properties depend on the evaporation rate and solute concentration
Modelling the formation of structured deposits at receding contact lines of evaporating solutions and suspensions
When a film of a liquid suspension of nanoparticles or a polymer solution is deposited on a surface, it may dewet from the surface and as the solvent evaporates the solute particles/polymer can be deposited on the surface in regular line patterns. In this paper we explore a hydrodynamic model for the process that is based on a long-wave approximation that predicts the deposition of irregular and regular line patterns. This is due to a self-organised pinning–depinning cycle that resembles a stick–slip motion of the contact line. We present a detailed analysis of how the line pattern properties depend on quantities such as the evaporation rate, the solute concentration, the Péclet number, the chemical potential of the ambient vapour, the disjoining pressure, and the intrinsic viscosity. The results are related to several experiments and to depinning transitions in other soft matter systems
Modelling approaches to the dewetting of evaporating thin films of nanoparticle suspensions
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