Acta Phys. -Chim. Sin. ›› 2013, Vol. 29 ›› Issue (08): 1762-1770.doi: 10.3866/PKU.WHXB201306033

• SOFT MATTER • Previous Articles     Next Articles

Growth Modes of Condensates on Nanotextured Surfaces and Mechanism of Partially Wetted Droplet Formation

LIU Tian-Qing, SUN Wei, LI Xiang-Qin, SUN Xiang-Yu, AI Hong-Ru   

  1. School of Chemical Engineering, Dalian University of Technology, Dalian 116024, Liaoning Province, P. R. China
  • Received:2013-04-23 Revised:2013-06-03 Published:2013-07-09
  • Contact: LIU Tian-Qing E-mail:liutq@dlut.edu.cn
  • Supported by:

    The project was supported by the National Natural Science Foundation of China (50876015).

Abstract:

The energy increasing rate (EIR) of a condensed droplet was analyzed during its growth in three different modes. The lowest EIR corresponding to one of the three ways was used as the criterion to determine the mode in which a condensed drop will increase its volume. The results show that the EIR according to the mode of increasing contact angle (CA) is much smaller than that according to the two other modes during the first period of growth of a condensate spot formed within a nanostructure. This means that the drop will grow, with CA increasing but the base area remaining constant, until a certain CA. After this, the EIR according to the mode of CA increasing becomes much higher than that according to the two other modes. The three-phase contact line of the drop starts to shift and the base area begins to increase while the CA remains constant. During this second period, the state of increased base area can be wetted; i.e., a Wenzel-state droplet forms with an apparent CA less than 160°. In contrast, the expanded base area can be in a composite state; i.e., a partially wetted droplet forms with a CA greater than 160° . The growth mode and its wetted state of a condensed droplet are strongly related to nanostructure. Partially wetted condensed drops can appear only on surfaces with nanopillars of a certain height and small pitch. The calculated results were consistent with experimental observations reported in the literature for the wetting states of condensed drops on nanotextured surfaces, with an accuracy of 91.9%, which is obviously higher than those calculated with reported formulas.

Key words: Super-hydrophobicity, Nano structure, Condensation, Drop, Growth mode, Wetted state, Mechanism, Model

MSC2000: 

  • O647