Cho Yoonkyung, Park Chung Hee
Department of Textiles, Merchandising and Fashion Design, Seoul National University Seoul 08826 Republic of Korea
RSC Adv. 2020 Aug 24;10(52):31251-31260. doi: 10.1039/d0ra03137b. eCollection 2020 Aug 21.
This study proposes new optical roughness parameters that can be objectively quantified using image processing techniques, and presents an analysis of how these parameters are correlated with the degree of superhydrophobicity. To this end, photolithography and dry etching processes were used to form regular square pillars with different heights and spacings with a length of tens of micro-meters on silicon wafers. Optical roughness parameters of the specimens were obtained using image processing, and surface wettability was characterized using static contact angle and sliding angle measurements for water droplets of volume = 3.5 μl or 12 μl. As a result, seven optical roughness parameters were derived to describe the surface roughness topography in a multi-faceted way. Between the Cassie-Baxter state and the Wenzel state, two distinct wetting states intermediate state I, and intermediate state II were observed. Multiple linear regression of optical roughness parameters and superhydrophobicity demonstrated that in the stable Cassie-Baxter state, the contact angle can be increased or sliding angle decreased more effectively by adjusting the spacing between pillars than by just tuning the solid area fraction. However, in the metastable state where the Cassie-Baxter state can be changed to intermediate state I and by adjusting or surface geometry, reducing the solid area fraction is a priority to ensure a stable Cassie-Baxter state. Horizontal-perspective roughness parameters had a great effect on dynamic wettability in the Cassie-Baxter state. The results confirmed that the proposed optical roughness parameters may be useful for quantitative analysis of the complex effects of roughness on superhydrophobic surfaces.
本研究提出了可通过图像处理技术进行客观量化的新光学粗糙度参数，并分析了这些参数与超疏水性程度之间的相关性。为此，采用光刻和干法蚀刻工艺在硅片上形成了长度为几十微米、具有不同高度和间距的规则方柱。通过图像处理获得了试样的光学粗糙度参数，并使用体积为3.5 μl或12 μl的水滴的静态接触角和滑动角测量来表征表面润湿性。结果，推导出了七个光学粗糙度参数，以多方面描述表面粗糙度形貌。在Cassie-Baxter状态和Wenzel状态之间，观察到了两种不同的润湿中间状态，即中间状态I和中间状态II。光学粗糙度参数与超疏水性的多元线性回归表明，在稳定的Cassie-Baxter状态下，通过调整柱间距比仅调整固体面积分数能更有效地增加接触角或减小滑动角。然而，在Cassie-Baxter状态可转变为中间状态I的亚稳态中，通过调整 或表面几何形状，降低固体面积分数是确保稳定Cassie-Baxter状态的首要任务。水平视角粗糙度参数对Cassie-Baxter状态下的动态润湿性有很大影响。结果证实，所提出的光学粗糙度参数可能有助于对粗糙度对超疏水表面的复杂影响进行定量分析。
