Effective slip length at solid-liquid interface of roughness-induced surfaces with omniphobicity

Boundary slip of the liquid-solid interface of micro/nano fluid flow are of great interest, as slippage is linked with decreased drag in many applications of mirco-/nano-fluidic channels. Previous studies have seldom included a systematic analysis of the effect of roughness on the measurement and quantification of effective boundary slip at interfaces between oil and superoleophilic/superoleophobic surfaces. This study focuses on the measurement and quantification of effective slip length on rough surfaces using atomic force microscopy (AFM). The correction to the effective slip length is analyzed, then surfaces with various degrees of roughness were fabricated. Quantitative analysis of the effective slip length is presented. Results show that the surface roughness could significantly inhibit the degree of effective boundary slip on both superoleophilic surfaces in Wenzel state and superoleophobic surfaces in Cassie state immersed in oil. The oleic systems were likely to inhibit effective boundary slip and resulted in an increasing in drag with increasing roughness at the solid-Liquid interfaces.