The current paradigm of self-propelled motion of liquid droplets on surfaces with chemical or topographical wetting gradients is always mono-directional. In contrast, here, we demonstrate bidirectional droplet motion, which we realize using liquid infused surfaces with topographical gradients. The deposited droplet can move either toward the denser or the sparser solid fraction area. We rigorously validate the bidirectional phenomenon using various combinations of droplets and lubricants, and different forms of structural/topographical gradients, by employing both lattice Boltzmann simulations and experiments. We also present a simple and physically intuitive analytical theory that explains the origin of the bidirectional motion. The key factor determining the direction of motion is the wettability difference of the droplet on the solid surface and on the lubricant film.

具有化学或地形湿润梯度的表面上的液滴自推进运动的当前范例始终是单向的。相反，在这里，我们演示了双向液滴运动，这是使用具有地形梯度的液体注入表面实现的。沉积的液滴可以朝较密或较稀疏的固体部分区域移动。通过同时使用晶格Boltzmann模拟和实验，我们使用液滴和润滑剂的各种组合以及不同形式的结构/形貌梯度来严格验证双向现象。我们还提出了一种简单且物理上直观的分析理论，该理论解释了双向运动的起源。