Exploring the impact of pillar edge effects on water drop evaporation

A water drop placed on a small pillar unveils an edge effect, which amplifies volume accumulation within the same contact area. This effect stems from an increased apparent contact angle, resembling hydrophobic surfaces. This emphasizes the influence of surface geometry beyond chemical properties. This study explores the characteristics of the drop by dissecting the interplay between surface forces, geometric attributes, and the evaporation process, enabling a comprehensive understanding of their combined impact on drop behavior. Two distinct evaporation stages were identified: the first stage, characterized by a constant contact line along the pillar edge, and the second stage, involving the detachment of edges and shape alterations influenced by surface roughness. The evaporation rate from the pillar is determined by applying the D² law and empirical observations. Moreover, the interplay among the key parameters in the process—namely, the evaporation rate, contact angle, volume, and pillar diameter—has been elucidated.