Li Yifan, Pan Yunlu, Zhao Xuezeng
Key Laboratory of Micro-Systems and Micro-Structures Manufacturing, Ministry of Education and School of Mechatronics Engineering, Harbin Institute of Technology, Harbin, 150001, P.R. China.
Beilstein J Nanotechnol. 2017 Nov 27;8:2504-2514. doi: 10.3762/bjnano.8.250. eCollection 2017.
Interface conditions are an important property that can affect the drag of fluid flow. For surfaces with different oleophobicity, the boundary slip at the solid-oil interface is mostly larger than that at the solid-water interface. Roughness is a key factor for the wettability of superoleophilic/superoleophobic surfaces, and it has been found to affect the effective value of slip length in measurements. Moreover, there are no studies on the effect of roughness on slip at interfaces between oil and superoleophilic/superoleophobic surfaces. A theoretical description of the real surface roughness is yet to be found. Results show that the effective slip length is negative and decreases with an increasing root mean squared (RMS) roughness of surfaces, as the increasing roughness enhances the area with discontinuous slip at the solid-liquid interface. The underlying mechanisms are analyzed. The amplitude parameters of surface roughness could significantly inhibit the degree of boundary slip on both superoleophilic surfaces in Wenzel state and superoleophobic surfaces in Cassie state immersed in oil. The oleic systems were likely to enhance boundary slip and resulted in a corresponding reduction in drag with decreasing roughness on the solid-oil interfaces.
界面条件是影响流体流动阻力的一个重要特性。对于具有不同疏油性的表面，固-油界面处的边界滑移大多大于固-水界面处的边界滑移。粗糙度是超亲油/超疏水表面润湿性的关键因素，并且已发现它会影响测量中滑移长度的有效值。此外，尚无关于粗糙度对油与超亲油/超疏水表面之间界面处滑移影响的研究。尚未找到对实际表面粗糙度的理论描述。结果表明，有效滑移长度为负，且随着表面均方根（RMS）粗糙度的增加而减小，因为粗糙度的增加会增大固-液界面处滑移不连续的区域。对其潜在机制进行了分析。表面粗糙度的幅度参数可显著抑制处于文泽尔状态的超亲油表面以及浸没在油中的处于卡西状态的超疏水表面上的边界滑移程度。油酸体系可能会增强边界滑移，并导致固-油界面上粗糙度降低时阻力相应减小。
