Evaporative behaviour of colloidal suspension droplets on surfaces: influence of suspension characteristics on the formation of dried microstructures and films

The evaporation and wetting of a droplet on a surface is a trivial phenomenon encountered in daily life (water droplets on windows or flowers) and in many industrial processes (spraying of pesticides, micro/nano material fabrication, films coatings, DNA/RNA micro-arrays deposition, optical and electronic materials fabrication or ink jet printing). Since the addition of nanoparticles into base fluids leads to fluids with heightened physico-chemical properties (these fluids are commonly referred to as “nanofluids”); hence, it is mandatory to understand all the mechanisms at play in order to control/anticipate the stain geometry upon solvent evaporation. In fact, the specific physical phenomenon leading to well-ordered ring-like stains or films are yet to be fully uncovered. The main purpose of this experimental work is thus to enhance our current knowledge on deposit-stain formation while varying nanofluids composition. A systematic study of the evaporative behaviour and final deposit structure produced upon solvent evaporation of nanoparticle laden fluids was undertaken. An attempt to explain the mechanisms leading to the formation of different patterns is proposed to help interpret the final distribution of particles throughout the evaporating surface area. The particle shape influence was studied and two main shapes were selected: spherical and disk-like particles. For spherical nanoparticles, their addition to binary solvent mixtures and to additive laden base fluids (electrolyte and surfactant) were studied. Despite similar initial systems, various final patterns were observed from ring-like stain to films due to aggregated particles. Disk-like nanoparticle were investigated in different compositions (binary mixtures and with additives such as electrolyte and surfactant). The sol-gel transition was observed at low nanoparticles concentration in the different systems leading to final films deposits and complex structures.