Electrowetting of evaporating extended meniscus

Abstract

The natural tendency of the contact line of an extended curved meniscus to retract on application of heat is countered using electrowetting. The effect of electrowetting during evaporation is experimentally evaluated by measuring the thickness profile of a meniscus near the microscopic contact line region using image analyzing interferometry. The system consists of a meniscus of surfactant (SDS) laden water film over a silicon substrate (with native oxide) subjected to heating followed by incremental imposition of electric fields. Results show that the resultant electrostatic pressure enhances suction towards the hot spot and the subsequent spreading can offset meniscus retraction. Additional insights into the related microscale transport processes including in situ evaluation of the Hamaker constant are obtained through a comprehensive model using the augmented Young–Laplace equation, interfacial phase transfer and lubrication theory. A comparison of average heat flux for conditions with and without electric field (∼8 V) demonstrates substantial (more than 100%) enhancement, highlighting the potential of electrowetting in micro-cooling applications.