Yu Ying-Song, Wang Ming-Chao, Huang Xianfu
Department of Mechanics, School of Civil Engineering, Architecture and Environment, Hubei University of Technology, Wuhan, 430068, China.
State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing, 100190, China.
Sci Rep. 2017 Oct 26;7(1):14118. doi: 10.1038/s41598-017-14593-5.
Evaporation of water and ethanol/water droplets containing large polystyrene (PS) microparticles on polydimethylsiloxane (PDMS) surface was experimentally investigated. It is found that no matter with or without small addition of ethanol, a compact monolayer deposition is formed for lower microparticle concentration while mountain-like deposition for higher concentration. Since the more volatile compound (ethanol) evaporates more quickly than the less volatile compound (water), evaporation of ethanol/water mixture droplet exhibits different characteristics from pure water. When the concentration of microparticle is low, the contact radius of ethanol/water mixture droplet decreases throughout the whole process, while the contact angle increases at first to a maximum, then keeps almost constant, and finally decreases sharply. However, the evaporation of ethanol/water mixture droplet with higher concentration of microparticle behaviors more complex. The settling time of microparticles was estimated and its theoretical value agrees well with the experimental one. Moreover, a mechanism of self-pinning of microparticles was used to elucidate the deposition behavior of microparticles, indicating that as the contact line is depinning, the liquid film covering the outmost microparticle becomes thicker and thicker, and the microparticles have to move spontaneously with the depinning contact line under the action of capillary force.
对含有大尺寸聚苯乙烯（PS）微粒的水和乙醇/水滴在聚二甲基硅氧烷（PDMS）表面的蒸发过程进行了实验研究。结果发现，无论是否添加少量乙醇，较低微粒浓度时会形成致密的单层沉积，而较高浓度时则会形成山状沉积。由于挥发性更强的化合物（乙醇）比挥发性较弱的化合物（水）蒸发得更快，乙醇/水混合液滴的蒸发表现出与纯水不同的特性。当微粒浓度较低时，乙醇/水混合液滴的接触半径在整个过程中减小，而接触角先增大到最大值，然后几乎保持不变，最后急剧减小。然而，微粒浓度较高的乙醇/水混合液滴的蒸发行为更为复杂。估算了微粒的沉降时间，其理论值与实验值吻合良好。此外，采用微粒自钉扎机制来解释微粒的沉积行为，表明随着接触线脱钉，覆盖最外层微粒的液膜变得越来越厚，微粒在毛细力作用下不得不随着脱钉的接触线自发移动。
