Effect of surface peak-valley features on the fluid flow performance in rough contact interface

In this work, two kinds of microtextured surfaces with different surface peak-valley features, namely positively skewed surface with micropillar array and negatively skewed surface with micropit array, are prepared to explore the effect of peak-valley features on the fluid flow performance in rough contact interface. The distribution and connectivity of microchannels is analyzed, and the physical mechanism of peak-valley features inducing different fluid flow processes is also derived through constructing a kinetic model of fluid spreading. It is found that when the surface skewness Ssk > 0, the positively skewed surface forms the void regions with better connectivity in the interface compared with the negatively skewed surface (Ssk < 0), despite both the surfaces having nearly the same roughness (Sa ∼ 3.6 mm). The formed microchannels are defined as crossed open microchannel and semi-closed microchannel, respectively, and the feature length of the microchannel decreases with the increase in load. The quantitative results of fluid flow demonstrate that the liquid has a better spreading and flow ability in the contact interface of the positively skewed surface. Even under the same microchannel feature length (nearly 48 mm), the fluid spread area ratio of the positively skewed surface has an order of magnitude higher than that of the negatively skewed surface. The mechanism of different flow characteristics induced by surface peak-valley features is believed as the variation of the microchannel shape, leading to the change in the capillary pressure at the meniscus. We believe the present work would lay a theoretical foundation for regulating the microscopic flow behavior in the contact interface.