Bubble Meets Droplet: Particle-Assisted Reconfiguration of Wetting and Dewetting

Wetting in colloidal multiphase systems plays a major role in many industrial processes, including encapsulation, enhanced oil recovery, water purification, ore processing, and food technology. The wetting of a bubble or a liquid droplet by a second fluid in a third immiscible fluid medium can result in three possible wetting morphologies: non-wetting, partial engulfment, or complete engulfment. A given fluid system, however, does not always adopt the desired wetting configuration; hence there is interest in methods to tune wetting configuration on demand. Particles with suitable wettability can be strongly adsorbed to the interface of immiscible fluids. Although it was recognized more than a century ago that particles can act as stabilizers in colloidal multiphase systems, prior to this work it was still unknown whether particles can also act as wetting or progressive de-wetting modifiers. We demonstrate that wetting configuration can be dynamically tuned by selection of appropriate colloidal particles, as predicted by an effective spreading coefficient. The wetting and engulfment of an air bubble by an oil droplet in a water medium was used as a model system relevant in a wide variety of industrial processes. We demonstrate that particles can be used both to promote “bubble wetting”, thereby inducing complete bubble engulfment by an oil drop, as well as to trigger “bubble de-wetting”, i.e. substantially reducing the oil-bubble contact area. This study yields a new on demand strategy to predict and control the wetting configuration in colloidal multiphase systems, with potential benefits in a wide range of research fields, industrial processes, and commercial products.