Evaporation of water drops on polymer surfaces: Pinning, depinning and dynamics of the triple line

In this study, the evaporation of water drops on four distinctive polymeric substrates, acrylonitrile butadiene styrene, polycarbonate, poly(methylmethacrylate) and poly(vinyl chloride), typified by unlike superficial morphologies, was investigated using the sessile drop method coupled with a video-enhanced image digitization technology and a best-fitting algorithm. The correlations between the observed dissimilar dynamics of the three phases contact line during the water drop evaporative process and the aforementioned surface topographies were deeply analyzed and discussed. The evaporation dynamics were measured and intensively illustrated in terms of the variation of contact angle, wetting diameter, drop height, drop volume, and drop shape. While the drops sitting on surfaces characterized by numerous defects and inhomogeneities showed a pinned triple line for almost their whole lifetime, for drops deposited on smoother substrates, after an initial pinning stage, the three phases contact line was observed receding freely until the drop disappearance.