Effect of surface wettability on evaporation rate of droplet array

Abstract

The evaporation of droplets in an array is hindered by adjacent droplets because of vapor-mediated interactions. Existing theoretical models for predicting the evaporation rate of droplets in the array neglect the important factor of surface wettability. In this work, we developed a model involving a contact angle function to accurately predict the evaporation rate of droplets with an arbitrary contact angle in the array. Fick's first and second laws were solved for evaporating droplets in the array by using steady-state three-dimensional numerical simulations, to derive the contact angle function. The proposed model was experimentally validated for arrayed droplets evaporating on flat hydrophilic and hydrophobic surfaces. We show that the contact angle function approaches unity on hydrophilic surfaces, which implies that the proposed model coincides with Wray et al.'s model. On the other hand, the contact angle function is much lower than unity on hydrophobic surfaces, indicating a low evaporation rate of droplets in the array. The findings of this study are expected to advance our understanding of droplet evaporation in arrays in a wide range of scientific and engineering applications.