Slipperiness and stability of hydrophilic surfaces coated with a lubricating fluid

Abstract

In recent years, many research groups have studied the slipperiness of rough or porous hydrophobic surfaces infused with a lubricating fluid. Here, we alternatively present a simple method to fabricate stable slippery surfaces on hydrophilic samples, which are more commonly and widely used. At room temperature, hydrophilic samples lubricated with silicone oil did not present a slippery surface for water drops, which were observed to sink into the oil layer due to the inherently hydrophilic surface. Annealing these samples at higher temperatures, however, caused the silicone molecules to covalently bind the silicon surface, hence making the surface hydrophobic. At an optimized annealing temperature and annealing time, the surfaces showed excellent slipperiness, with negligible contact angle hysteresis and low sliding angles. Water drops on the slippery surfaces were found to be enveloped, or cloaked, in a thin layer of the lubricating oil, which minimized the oil–water interfacial energy. Upon sliding, these oil-cloaked water drops slowly removed lubricating oil, which resulted in the degradation of the slipperiness. This degradation was prevented when using large water drops or a continuous flow of water.