(Super)Spreading and drying of trisiloxane-laden quantum dot nanofluids on hydrophobic surfaces

Abstract

Nanofluids hold promise for a wide range of areas of industry. However, understanding of wetting behavior and deposition formation in course of drying and spreading of nanofluids, particularly containing surfactants, is still poor. In this paper, the evaporation dynamics of quantum dot-based nanofluids and evaporation-driven self-assembly in nanocolloidal suspensions on hexamethyldisilazane-, polystyrene-, and polypropylene-coated hydrophobic surfaces have been studied experimentally. Moreover, for the very first time, we make a step to understanding of wetting dynamics of superspreader surfactant-laden nanofluids. It was revealed that drying of surfactant-free quantum dot nanofluids in contrast to pure liquids undergoes not three but four evaporation modes including last additional pinning mode when contact angle decreases whilst triple contact line is pinned by the nanocrystals. In contrast to previous studies, it was found out that addition of nanoparticles to aqueous surfactant solutions leads to deterioration of spreading rate and to formation of double coffee ring. For all surfaces examined, superspreading in presence and absence of quantum dot nanoparticles takes place. Despite the formation of coffee rings on all substrates, they have different morphology. Particularly, the knot-like structures are incorporated into the ring on hexamethyldisilazane- and polystyrene-coated surfaces