【摘要】 从超疏水表面(SHS)上初始冷凝液核长大、合并、形成初始液斑开始,分析计算了冷凝液斑变形成为Wenzel或Cassie液滴过程中界面能量的变化,并以界面能曲线降低、是否取最小值为判据,确定冷凝液滴的最终稳定状态.计算结果表明:在只有微米尺度的粗糙结构表面上,冷凝液滴的界面能曲线一般都是先降低再升高,呈现Wenzel状态;而当表面具有微纳米二级粗糙结构,且纳米结构的表面空气面积分率较高时,冷凝液滴的能量曲线持续降低,直至界面能最小的Cassie状态,因此可以自发地形成Cassie液滴.还计算了文献中具有不同结构参数的SHS上冷凝液滴的状态和接触角,并与实验结果进行了比较,结果表明,计算的冷凝液滴状态与实验观察结果完全吻合.因此,微纳二级结构是保持冷凝液滴在SHS上呈现Cassie状态的重要因素.更多还原

【Abstract】 The interface free energy of a local condensate from the growth and combination of numerous initial condensation nuclei was calculated during its shape changes from an early flat shape to a Wenzel or Cassie state on the super-hydrophobic surface (SHS). The final state of the condensed drop was determined according to whether the interface free energy continuously decreased or it had a minimum value. Our calculations indicate that condensation drops on a surface only with micro roughness display Wenzel state because the interface free energy curve of a condensed drop first decreases and then increases, existing a minimum value corresponding to Wenzel drop. On a surface with appropriate hierarchical roughness, however, the interface energy curve of a condensed drop will constantly decline until it reaches the Cassie state. Therefore, a condensed drop on a hierarchical roughness surface can spontaneously reach the Cassie state. In addition, the states and apparent contact angles of condensed drops on a SHS with different structural parameters were calculated and compared with experimental observations. Results show that the calculated condensed drop states agree well with the experimental results. It can be concluded that micro and nano hierarchical roughness is the key structural factor responsible for sustaining condensed drops in the Cassie state on a SHS.更多还原