Manipulating Gas Micro-Volumes with Submerged Meshes of Controlled Wettability

In the last century, much attention has been given to the study of surface wettability, and many techniques have been developed to produce superhydrophobic (water-repelling) and superhydrophilic (water-attracting) substrates. On the other hand, much less effort has been put in the analysis of the interaction between a solid surface and an air bubble. Nevertheless, the interaction between a solid substrate and gas bubbles is important when the substrate is submerged in water or any other liquid containing dissolved gas, and it can be relevant in many industrial applications, such as those involving two-phase column reactors. Few studies concerning underwater superhydrophobicity and superaerophobicity have been published in the last two decades, but none of them focus on the interaction between gas bubbles and a submerged permeable substrate, such as a metal mesh. The present work demonstrates the possibility of employing submerged metal meshes with super air-attracting/repelling properties to manipulate micro-volumes of air, in the form of bubbles, rising at terminal velocity. Superaerophobic meshes selectively allow the passage of an air bubble depending on the mesh pore-size and the bubble equivalent diameter. Superaerophilic meshes reduce or amplify the volume of a stream of incoming bubbles covering a wide range of amplification factors. Mainly two cases are considered hereafter: in the first one, uniform superaerophilic or superaerophobic meshes are analyzed; in the second one, a wettability-pattern is imparted on the top and bottom surfaces of the mesh. In the latter case, a relation to predict the volume of a bubble resulting from a given mesh is proposed.