凹槽状PDMS基底上水滴的挥发及Cassie-Wenzel转变行为

Evaporation of Sessile Droplet on Grooved PDMS Substrate and Resultant Cassie-Wenzel Transition

通过在线跟踪水滴在凹槽状聚二甲基硅氧烷(PDMS)基底上的挥发行为,研究了蒸馏水的挥发规律Cassie-Wenzel转变行为.结果表明,初始阶段,水滴处于Cassie状态,且在垂直于凹槽方向(V)和平行于凹槽方向(P)上存在显著的各向异性.水滴的挥发过程依次表现出接触直径不变模式、接触角不变模式及共同减小模式,与平滑基底上水滴的挥发规律类似.在挥发过程中,发生了Cassie-Wenzel转变,转变发生的时间与PDMS基底上突起部分的面积分数(即固相率)呈现良好的线性关系.随着挥发的进行,水滴的各向异性在接触角不变模式阶段消失,即挥发导致水滴从开始的椭球缺状变为球缺状.

The evaporation of sessile droplets （water） on grooved polydimethylsiloxane （PDMS） substrate was investigated in detail. The contact angles and diameters of the droplet show clear difference between vertical （V） and parallel （P） directions, indicating the anisotropy of the droplet. Upon evaporation, three stages including constant diameter mode（CDM）, constant contact-angle mode（CCM） and combination mode of them have been tracked as well as the results on the flat PDMS. The transition from Cassie to Wenzel state, leading to the simultaneous quick increase of the contact diameter and the sudden decrease of the height and contact angle, was observed in the first stage （CDM）. The transition time depends crucially on the area fraction of the protrusion. Furthermore, the anisotropy of the droplet disappears, resulting in the equal diameters in P and V directions in the second stage （CCM）. The results are significant for the control of superhydrophobicity surface.