LAUSR

Abstract The morphological characteristics of the gas-liquid interfaces receding through the gap with a sharp feature in a quasi-static fashion is investigated in this paper. A series of quasi-static experiments have been performed. A theoretical model that tracks the movement of the gas-liquid interface is developed. Different from previous models, our model is developed on the mesoscopic scale and the pressure difference at every point on the interface is different because the effect of gravity cannot be ignored. A method to solve numerically the model under specific boundary conditions is proposed. The numerical result is experimentally verified, and good agreement is found between predicted and experimental behaviors of the gas-liquid interface. Through this model, the following analysis is carried out. Firstly, threshold of the model application was determined. Then, numerical results of residual liquid were obtained. It is concluded that the critical curve that determines whether liquid remains or not is independent of the receding contact angle when the gap is small (below 0.5 mm), while it is related to the receding contact angle when the gap is large (above 0.5 mm). Finally, it was carried out to understand the evolution of pressure difference and determine the maximum pressure difference. It is found that the maximum pressure difference appears at the first corner of the feature. The maximum pressure difference decreases with the increase of the gap height and decreases with the increase of the receding contact angle. This allows us to effectively design and optimize the removal structure in the immersion head. This model not only applies to the rectangular feature in this paper, but also to arbitrary features, and even to track advancing the gas-liquid interface using the advancing contact angle.