Drop friction on state-of-the-art micro/nanoengineered oil-impregnated silicon micro-pillars and micro-holes

Recently discovered micro/nanoengineered oil-impregnated surfaces have shown great promise in improving the performance of numerous engineering systems ranging from liquid handling in lab‑on-a-chip microfluidics to hydrodynamic drag reduction and heat transfer because of the remarkable droplet mobility that arises from record low contact angle hysteresis (≤2-3°). Past studies on drop friction on hemi-solid and hemi-liquid composite oil-impregnated surfaces has been limited to well-defined silicon micro-pillars. In this work, using a custom-made submicronewton accuracy cantilever force sensor, we experimentally characterize and model drop friction on oil-impregnated micro-holes. The insights gained from this work provide new understanding of the mechanism of drop friction on textured oil-impregnated surfaces and aid the rational design of surfaces that can reduce hydrodynamic drag.