Nanobending of the microscopic liquid-gas interface on the solid surface and its potential impact on nanobubbles

Young contact angle is widely applied to evaluate liquid wetting phenomena on solid surfaces. For example, it gives a truncated-spherical shape prediction of a droplet/bubble profile through the Young-Laplace equation. However, recent measurements have shown the deviation of a microscopic droplet profile from the spherical shape, indicating that the conventional Young contact angle as the boundary condition is insufficient to describe the microscopic liquid wetting phenomena which play a critical role when nanobubbles on the wall. Here, we reveal a liquid-gas interface nano-bending, which is caused by the nonlinear coupling between the effects of the microscopic interface geometry and solid-liquid interactions and is responsible for this deviation. Based on molecular dynamics simulations and mathematical modeling, we describe the structure of the nano-bending and explain the mechanism of the nonlinear-coupled effect. We further apply our findings to illustrate the saddle-shaped profile in the vicinity near the contact region. The interface nano-bending, rather than the Young contact angle, acts as the boundary at the contact line and dictates the liquid wetting system. In this way, we succeed in accurately predicting the microlayer profile (µm thickness liquid film beneath a nucleation bubble) captured by different experiments. These findings not only provide insight into recent nano-scale droplet- and bubble-related wetting phenomena, but are also helpful for surface engineering concerning nano-scale wetting control.