Effect of nonionic surfactant on wetting behavior of an evaporating drop under a reduced pressure environment
Effect of nonionic surfactant on wetting behavior of an evaporating drop under a reduced pressure environment
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DOI：
10.1016/j.jcis.2003.10.039
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发表时间：
2004-04-15
影响因子：
9.9
通讯作者：
Sefiane, K
中科院分区：
文献类型：
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作者：
Sefiane, K
本文研究了常压下固着液滴的蒸发。比较了水滴在铝和聚四氟乙烯表面上的减压蒸发。结果发现，水滴在铝表面表现出“脱钉跳”在低于大气压。这是当钉扎液滴突然脱钉时，接触角增加，同时底部宽度减小。然后研究了添加非离子表面活性剂（Triton X-400）到铝表面的固着水滴的蒸发。初始接触角在0.001重量% Triton X-100时表现出最小值。在相同浓度下也观察到蒸发速率的最大值。发现具有低表面活性剂浓度的液滴表现出“脱钉”跳跃。据认为，表面活性剂的局部浓度引起表面张力的梯度。接触角的平衡由复杂的现象决定，包括界面处的表面活性剂扩散和吸附过程。由于三线附近的强烈蒸发，表面活性剂的积聚将导致沿界面沿着的表面张力梯度。表面张力的梯度会影响润湿行为（Marangoni效应）。在低表面活性剂浓度下，接触线脱钉在表面张力梯度的强烈作用下，由于三重线附近的表面活性剂积累，在液滴界面上自发地发展。最大蒸发速率对应于钉扎液滴的最小接触角。(C)2003年爱思唯尔公司All rights reserved.
The evaporation of sessile drops at reduced pressure is investigated. The evaporation of water droplets on aluminum and PTFE surfaces at reduced pressure was compared. It was found that water droplets on an aluminum surface exhibit a 'depinning jump' at subatmospheric pressures. This is when a pinned droplet suddenly depins, with an increase in contact angle and a simultaneous decrease in the base width. The evaporation of sessile water droplets with a nonionic surfactant (Triton X-400) added to an aluminum surface was then studied. The initial contact angle exhibited a minimum at 0.001 wt% Triton X-100. A maximum in the evaporation rate was also observed at the same concentration. Droplets with low surfactant concentrations are found to exhibit the 'depinning jump. It is thought that the local concentration of the surfactant causes a gradient of surface tension. The balance at the contact angle is dictated by complex phenomena, including surfactant diffusion and adsorption processes at interfaces. Due to the strong evaporation near the triple line, an accumulation of the surfactant will lead to a surface tension gradient along the interface. The gradient of surface tension will influence the wetting behavior (Marangoni effect). At low surfactant concentrations the contact line depins under the strong effect of surface tension gradient that develops spontaneously over the droplet interface due to surfactant accumulation near the triple line. The maximum evaporation rate corresponds to a minimum contact angle for a pinned droplet. (C) 2003 Elsevier Inc. All rights reserved.