Entrapment of gas in the spreading of a liquid over a rough surface

Abstract Conditions for the incomplete displacement of gas from the valley between two parallel ridges by a liquid‐drop front advancing over the ridges are calculated. The significant parameters are found to be the liquid density, surface tension, contact angle, and geometry of the ridges. The solution may be obtained analytically or, more conveniently, graphically. Surface roughnesses are divided into four classes, one of which can stably switch from liquid—to gas—fill, and another vice versa. This may account for some of the hysteresis effects reported in bubble nucleation. It is pointed out that surfaces consisting predominately of cavities are more likely to follow these considerations than grooved surfaces, owing to displacement of gas by advance of liquid along the grooves. An example important in boiling and cavitation theory is worked out, and qualitative agreement with the literature is shown.