# Oleoplaning droplets on lubricated surfaces

## TL;DR

This paper visualizes and explains how droplets slide effortlessly on lubricated surfaces due to a continuous lubricant film, revealing oleoplaning behavior similar to hydroplaning, with implications for designing liquid-repellent surfaces.

## Contribution

It provides the first experimental visualization of the intercalated lubricant film under droplets and demonstrates how hydrodynamic forces enable oleoplaning on lubricated surfaces.

## Key findings

- Visualization of the lubricant film using confocal interferometry
- Droplets can oleoplaning with minimal force and no pinning
- Hydrodynamic forces transform partial dewetted films into continuous layers

## Abstract

Recently, there has been much interest in using lubricated flat and nano-/micro-structured surfaces to achieve extreme liquid-repellency: any foreign droplet immiscible with the underlying lubricant layer was shown to slide off at a small tilt angle $<$ 5$^{\circ}$. This behavior was hypothesized to arise from a thin lubricant overlayer film sandwiched between the droplet and solid substrate, but this has not been observed experimentally. Here, using confocal optical interferometry, we are able to visualize the intercalated film under both static and dynamic conditions. We further demonstrate that the lubricant flow entrained by droplet motion can transform a partially dewetted film into a continuous layer, by generating a sufficient hydrodynamic force to lift the droplet over the solid substrate. The droplet is therefore oleoplaning, akin to tires hydroplaning on a wet road, with minimal dissipative force (down to 0.1 $\mu$N for 1 $\mu$l droplet when measured using a cantilever force sensor) and no contact line pinning. The techniques and insights presented in this study will inform future work on the fundamentals of wetting for lubricated surfaces and enable their rational design.