Drop impact on a foam-coated liquid surface: Formation of antibubbles

An antibubble is a rare fluid particle that a thin air film separates the inner and outer liquid phases. This unique structure makes antibubbles a promising candidate for droplet manipulation. The controlled formation of antibubbles has attracted increasing attention in recent decades. Among the various methods, drop impact on a foam-coated liquid surface has been identified as an efficient technique. Although this method has been widely used in previous research on antibubbles, the detailed dynamics of droplet collision on the foam layer has received limited attention. This paper demonstrates a systematic study of the dynamics of drop impact on a foam layer. Experimental results show that the contact position and the diameter ratio between the droplet and the bubbles that constitute the foam layer are key factors influencing the formation of antibubbles. Regime maps based on the experimental results are built to indicate the conditions under which antibubbles form. Additionally, a novel phenomenon is introduced, wherein antibubbles are formed when the droplet collides with the surface film of the foam bubbles.