Sink dynamics of aqueous drops on lubricating fluid coated hydrophilic surfaces

Abstract

Slippery behavior of aqueous drops on lubricating oil coated solid surfaces depends strongly on the wettability of the solid substrates. Stable slippery behavior is observed, with floating aqueous drops, if underneath solid substrates are hydrophobic. For hydrophilic surfaces, lubricating oil film underneath an aqueous drop becomes unstable and ruptures due to attractive van der Waals interaction, leading to sinking of the aqueous drop. Here, we report the sinking behavior of aqueous drops on thin lubricating oil coated hydrophobic and hydrophilic surfaces. The sinking behavior of aqueous drops is analyzed in terms of change in the apparent contact angle with time. The sink time of drops depends on both the wettability of the substrate as well as viscosity of the lubricating layer, while the final apparent contact angle depends only on wettability.