润湿
接触角
下降(电信)
压力降
毛细管压力
跌落冲击
毛细管作用
旋滴法
材料科学
机械
坐滴法
流体体积法
化学
复合材料
机械工程
分手
物理
多孔介质
工程类
多孔性
作者
Abrar Ahmed,Raymond Sanedrin,Thomas Willers,Prashant R. Waghmare
标识
DOI:10.1016/j.jcis.2021.10.003
摘要
The drop deposition technique can impact contact angle measurements. We hypothesized that the drop pinch-off, during the traditionally used pendant drop technique, significantly alters the static contact angle. The capillary waves and dynamic wetting pressure generated during the pendant drop deposition are the source for forced spreading, which can be circumvented by alternative liquid-needle drop deposition techniques.To compare the role of drop pinch-off and resultant dynamic wetting pressure, we meticulously observed and quantified the entire drop deposition process using high speed imaging until the drop attains the static contact angle in both cases, namely pendant drop and liquid needle deposition technique. Conventionally used standard substrates are compared using both techniques and further compared using literature data. The capillary waves and corresponding drop shape variations are analysed for quantifying the dynamic wetting pressure by measuring drop base diameter, contact angle and centre of mass.We compared three parameters - drop pinch-off, spreading behaviour and respective static contact angles along with the resultant dynamic wetting pressure for both the techniques, i.e., pendant drop and liquid-needle. For the pendant drop technique we observed a pronounced drop volume dependency of these parameters even though the corresponding Bond numbers are less than unity. In contrast, for the liquid needle there is no such dependency. With a theoretical argument corroborating experimental observations, this work highlights the importance of a well controlled drop deposition, with a minimum wetting pressure, in order to guarantee contact angle data that is independent of drop deposition effects, thereby only reflecting the substrate properties.
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