Are the Imidazole Ionic Liquids Suitable Lubricants for Slippery Coatings?

Abstract

The results of an investigation of an impact of the structure of recently synthesized bis(trifluoromethylsulfonyl)imide mono- and dicationic ionic liquids on their properties and behavior as lubricants for slippery liquid infused superhydrophobic coatings are presented for a wide temperature range. In this study, a new approach based on monitoring the surface tension of a liquid sessile droplet on top of a coating was exploited for the analysis of the evolution of the coating properties in prolonged contact with the liquid. It was found that the continuous contact with water flow results in slippery property degradation according to two different scenarios. In the first one, the washing out of lubricant eventually led to the transition from water droplets sliding to them rolling with the establishment of a superhydrophobic state. The second scenario was revealed in di- and monocationic ILs with a siloxane linker or both siloxane tails through the continuous lubricant depletion from the texture, increase in sliding angle value, loss of slippery properties, and establishing of a homogeneous wetting regime by aqueous droplets with the contact angle around 140°. The obtained experimental data allowed concluding that, among studied ILs, the monocationic bis(trifluoromethylsulfonyl)imide ionic liquids with alkyl or mixed alkylene/siloxane tails are better suitable for application as lubricants for slippery, regularly refilled surfaces.