Characterization of the wettability of thin nanostructured films in the presence of evaporation

Vapor chambers using conventional porous membrane wicks offer limited heat transfer rates for a given thickness. This limitation can be addressed through wick nanostructuring, which promises high capillary pressures and precise control of the local porosity. This work develops a measurement technique for the wettability of nanostructured wicks based on optical imaging. Feasibility is demonstrated on a hydrophilic silicon nanowire array (SiNW) synthesized using the Vapor–Liquid–Solid (VLS) growth mechanism followed by surface plasma treatment. The wettability is determined by comparing the time-dependent liquid interface rise with a model that accounts for capillary, viscous, and gravitational forces and for evaporation. This model is demonstrated to be useful in extracting internal contact angle from thin (∼10 μm) porous films.

Graphical abstractPore level contact angle, evaporation rate, and fluid-independent structural constant of a VLS grown SiNW array were determined using a low-cost, non-contact optical tracking methodology.Figure optionsDownload full-size imageDownload high-quality image (81 K)Download as PowerPoint slideResearch highlights► Neglecting evaporation effects in wettability characterization of porous thin films can lead to significant errors. ► Proposed model accounts for evaporation in addition to capillary pressure and viscous force. ► Internal contact angle of a disordered silicon nanowire film is extracted from optical imaging measurements.