Front instabilities in evaporatively dewetting nanofluids

Abstract

Various experimental settings that involve drying solutions or suspensions of nanoparticles-often called nanofluids-have recently been used to produce structured nanoparticle layers. In addition to the formation of polygonal networks and spinodal-like patterns, the occurrence of branched structures has been reported. After reviewing the experimental results we use a modified version of the Monte Carlo model first introduced by Rabani [Nature 426, 271 (2003)] to study structure formation in evaporating films of nanoparticle solutions for the case that all structuring is driven by the interplay of evaporating solvent and diffusing nanoparticles. After introducing the model and its general behavior we focus on receding dewetting fronts which are initially straight but develop a transverse fingering instability. We analyze the dependence of the characteristics of the resulting branching patterns on the driving effective chemical potential, the mobility and concentration of the nanoparticles, and the interaction strength between liquid and nanoparticles. This allows us to understand the underlying instability mechanism.

Patterned deposition at moving contact lines

“…In general, most authors agree that patterns of lines that are parallel to the receding contact line result from a stick-slip motion of the contact line that is caused by pinning/depinning events [30,45,55,87]. Branched structures and patterns of lines orthogonal to the contact line (the latter are sometimes called spoke patterns [44,47,55,67,88]) are thought to result from transversal instabilities of the receding contact line (sometimes called fingering instabilities) [51,[89][90][91].…”

Evaporation-induced self-assembling of few-layer graphene into a fractal-like conductive macro-network with a reduction of percolation threshold

“…[1][2][3][4][5] The micro(nano-)graphenes originating from a top-down approach synthesis (exfoliation of graphite-based materials) usually exhibit a lower conductivity and their (transparent) conductive films formed by spin coating, hot-spray or other techniques show a few-dozen kO sheet resistance. [20][21][22] Initially, this was described by hydrodynamic instabilities and solute-transport phenomena. ); 11 this relationship can be modified by the film thickness within a given matter.…”

“…A variant is a low surface coverage, e.g. 20,21 The recently reported ''open'' domain simulations also consider particle aggregation during the evaporation process, assisted by shrinking of the drying fronts from the edges toward the center. [12][13][14][15] At present, we propose an evaporation-induced self-assembling method as an alternative way to achieve a highly conductive graphene (few-layer graphene) network on a macroscale.…”

Modelling the evaporation of thin films of colloidal suspensions using dynamical density functional theory

“…To model these processes, simple two-dimensional (2d) lattice kinetic Monte-Carlo (KMC) models were proposed [28,26,23,29]. Vancea et.…”

“…al. [29] made a detailed investigation of the characteristics of the branched structures and their dependence on the model parameters. They observed that as in the experiments the fingering instability becomes stronger the smaller the nano-particle mobility gets.…”