Evaporative drying of a water droplet on liquid infused sticky surfaces

Abstract

We report the evaporation dynamics of water droplets over liquid infused slippery surfaces fabricated by dispensing high viscosity silicone oil over topographically patterned substrates obtained by replication of rose petals. These replicated surfaces also exhibit sticky hydrophobicity, similar to that observed in actual rose petals due to the presence of secondary nano-folds that decorate the primary conical micro-pillars. We first show that such a surface imparts stickiness to a high viscosity slip enhancing oil layer dispensed over it, thereby suppressing hemi-wicking even at low oil layer thickness (hE). Subsequently we show that hE strongly influences the dynamics as well as morphological evolution of an evaporating water drop dispensed over such slippery surfaces, particularly in terms of the dimension and life time of the wetting ridge that forms around any liquid droplet over a slippery surface due to the balance of surface tension forces around the contact line. Our experiments reveal that the adhesive effect of the substrate patterns become more significant with progressive reduction in hE, which in turn limits the maximum height attained by the wetting ridge and thus favours rapid evaporation of the droplet, despite the surface retaining slippery Wenzel wetting state under water. We also show some interesting intermediate evolution stages such as multiple overlapping wetting ridges under certain specific conditions, due to a competition between spreading of the oil layer and restriction in its flow imposed by the substrate patterns. Finally, we show that the effect of viscosity of the slip enhancing oil layer also exemplifies as hE progressively reduces.