Bio-inspired and Advanced Energy Research Center, School of Mechanics, Civil Engineering and Architecture, Northwestern Polytechnical University, Xi'an 710129, P. R. China.
Soft Matter. 2019 Dec 11;15(48):10055-10064. doi: 10.1039/c9sm01783f.
Understanding the mechanisms of controlling vapor condensation on surfaces is of significant importance in many fields. Despite many efforts made in the investigation of vapor condensation, few studies concern the condensation on flexible substrates, especially in microscale. In this paper, the condensation of high temperature water vapor on substrate with various flexibilities and wettabilities is investigated using molecular dynamics simulation. The results indicate that when substrates with the same flexibility vary from hydrophobic to hydrophilic, the condensation rate increases and the condensation mode changes from no-condensation to dropwise condensation, incomplete filmwise condensation and filmwise condensation, and meanwhile, the heat exchange between the water vapor and the substrate becomes more efficient; when substrates with the same wettability vary from rigid to flexible, the nucleation density, the condensation rate and the heat exchange efficiency increase significantly. In particular, the condensation modes on rigid and flexible substrates with the same wettability are generally the same except for the substrates with εwater-Cu = 0.4 kcal mol-1; and the critical values of substrate spring constant for the condensation mode transition are about 80-100 kcal mol-1 Å-2 when εwater-Cu = 0.4 kcal mol-1. Therefore, changing the flexibility of the substrate is proposed as a new way to control the condensation mode at the initial stage of water vapor condensation to meet design requirements.
理解控制表面蒸汽凝结的机制在许多领域都具有重要意义。尽管在蒸汽凝结的研究方面已经做出了许多努力，但很少有研究涉及到柔性基底上的凝结，特别是在微尺度上。本文采用分子动力学模拟研究了不同柔性和润湿性基底上水蒸汽的凝结。结果表明，当具有相同柔性的基底从疏水性变为亲水性时，凝结速率增加，凝结模式从无凝结变为滴状凝结、不完全膜状凝结和膜状凝结，同时，水蒸汽和基底之间的热交换变得更加高效；当具有相同润湿性的基底从刚性变为柔性时，成核密度、凝结速率和热交换效率显著提高。特别是，在具有相同润湿性的刚性和柔性基底上的凝结模式通常是相同的，除了εwater-Cu = 0.4 kcal mol-1 的基底；对于εwater-Cu = 0.4 kcal mol-1 的基底，凝结模式转变的基底弹簧常数的临界值约为 80-100 kcal mol-1 Å-2。因此，改变基底的柔性被提出作为一种在水蒸汽凝结的初始阶段控制凝结模式的新方法，以满足设计要求。
