Gas Bubbles and Gas Pancakes at Liquid/Solid Interface: A Continuum Theory Incorporated with Molecular Interactions

TL;DR

This paper develops a continuum theory incorporating molecular interactions to analyze gas states at liquid-solid interfaces, predicting three distinct states including a novel coexistence of gas bubbles and pancakes.

Contribution

It introduces a theoretical framework that predicts multiple gas states at interfaces, including the first prediction of coexistence of gas bubbles with gas pancakes.

Findings

Identifies three possible gas states: complete wetting, partial wetting, and pseudopartial wetting.

Predicts the coexistence of gas bubbles and gas pancakes at the interface.

Provides nanoscale thickness estimates for gas pancakes and larger radii for gas bubbles.

Abstract

The states of gas accumulated at the liquid-solid interface are analyzed based on the continuum theory where the Hamaker constant is used to describe the long-range interaction at the microscopic scale. The Hamaker constant is always negative, whereas the gas spreading coefficient can be either sign. Despite the complexity of gas, including that the density profile may not be uniform due to absorption on both solid and liquid surfaces, we predict three possible gas states at the liquid-solid interface, i.e. complete wetting, partial wetting and pseudopartial wetting. These possible gas states correspond respectively to a gas pancake (or film) surrounded by a wet solid, a gas bubble with a finite contact angle, and a gas bubble(s) coexisting with a gas pancake. Typical thickness of the gas pancakes is at the nanoscale within the force range of the long-range interaction, whereas the radius of the gas bubbles can be large. The state of gas bubble(s) coexisting with a gas film is predicted theoretically for the first time. Our theoretical results can contribute to the development of a unified picture of gas nucleation at the liquid-solid interface.