סמינר לפיזיקה של מערכות ביולוגיות וחומרים רכים: Drying of Liquid Droplets
Prof. Xingkun Man, Center of Soft Matter Physics and Its Applications, Beihang University, Beijing, China
The drying of liquid droplets is a common daily life phenomenon that has long held a special interest in scientific research. We propose an Onsager variational principle theory that describes the droplet shape evolution and predicts the deposit distribution of nonvolatile components on the substrate. It is shown that for the drying of a single droplet, the deposition pattern changes continuously from a coffee ring to volcanolike and to mountainlike depending on the mobility of the contact line and the evaporation rate. We also show that added surfactants can change the deposition pattern from mountainlike to volcanolike and then to coffee ring patterns. Specially, a two-ring formation is formed due to the contact line motion undergoing a clear receding-advancing transition induced by surfactants. Moreover, we show that as droplets evaporate many concentric rings of deposits are formed but are taken over by a solid-circle pattern in the final stage of drying. When drying of two neighboring droplets, asymmetrical ring-like deposition patterns are formed, including fanlike and eclipse-like deposition patterns.