Droplet evaporation dynamics on microstructured biphilic, hydrophobic, and smooth surfaces

Understanding liquid evaporation on surfaces is of utmost importance due to its impact on a plethora of industrial and natural processes. Over the past several decades, through chemical functionalization or surface structuring, wetting and non-wetting surfaces have been extensively developed and studied in an attempt to control liquid-surface interactions. More recently, surfaces with wettability patterns comprising of local wetting/non-wetting regions have received considerable attention. Although quantitative analytical models in parallel with scaling arguments have been developed to predict and understand liquid droplet evaporation on such micro-structured surfaces, consensus in the wider community is sparse. Developing a better understanding of the evaporation performance on structured surfaces is imperative for selecting optimal structure length scales and designs for specific applications. Here, we develop dual wettability or biphilic micropillar surfaces having various dimensions by utilizing lift-off microfabrication. We focus on studying the evaporation dynamics of sessile water droplets on such micropillared biphilic as well as hydrophobic surfaces. We start by investigating the evaporation of water droplets having a wide range of diameter (100<D<500 mu m) using the traditional classical method, where the droplet volume decreases in time. We then employ the steady method to study the droplet evaporation dynamics on the micropillared surfaces. We elucidate the mechanisms governing the observed behavior using scaling analysis, demonstrating the steady method to be particularly advantageous for microdroplet evaporation studies. Our work not only characterizes the evaporation dynamics on structured wettability-patterned functional surfaces but also demonstrates the advantages of the steady method to study droplet evaporation. [GRAPHICS]