Mixed Cassie-Baxter wetting states on a porous material stabilized by electrowetting

¹ Institut de Physique de Rennes, UMR CNRS 6251, Université de Rennes 1, campus de Beaulieu 35042 Rennes cedex, France
² LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, Univ. Paris Diderot UPMC Univ. Paris 06, Sorbonne Paris Cité - 5 place Jules Janssen, 92195 Meudon, France

Received: 13 June 2017
Accepted: 1 September 2017

Abstract

Electrowetting is used to force imbibition in model porous plates. These porous plates are sintered disordered bronze bead packings that are homogeneously coated with a constant-thickness layer of parylene. Cycles of increasing and decreasing voltage trigger the imbibition of a ionized water sessile drop by changing its contact angle with the porous material from non-wetting to wetting shapes. During a cycle, a drop experiences partial imbibition and a strong hysteresis of its contact angle with the porous plate. Since the imbibition process quickly stabilizes, we adopt an equilibrium description of the wetting properties of the drop on the porous plate. Our model, based on the Cassie-Baxter approach, shows that three different wetting states are experienced by the drop, one of which being made possible only by the modification of the contact angle inside the pores. Our model describes the experimental results very well.