Understanding flow characteristics of fluid near rough contact is important for the design of fluid-based lubrication and basic of tribology physics. In this study, the spreading and seepage processes of anhydrous ethanol in the interface between glass and rough PDMS are observed by a homemade optical in-situ tester. Digital image processing technology and numerical simulation software are adapted to identify and extract the topological properties of interface and thin fluid flow characteristics. Particular attention is paid to the dynamic evolution of the contact interface morphology under different stresses, the distribution of microchannels in the interface, the spreading characteristics of the fluid in contact interface, as well as the mechanical driving mechanism. Original surface morphology and the contact stress have a significant impact on the interface topography and the distribution of interfacial microchannels, which shows that the feature lengths of the microchannels, the spreading area and the spreading rate of the fluid are inversely proportional to the load. And the flow path of the fluid in the interface is mainly divided into three stages: along the wall of the island, generating liquid bridges, and moving from the tip side to the root side in the wedge-shaped channel. The main mechanical mechanism of liquid flow in the interface is the equilibrium between the capillary force that drives the liquid spreading and viscous resistance of solid wall to liquid. In addition, the phenomenon of “trapped air” occurs during the flow process due to the irregular characteristics of the microchannel. This study lays a certain theoretical foundation for the research of microscopic flow behavior of the liquid in the rough contact interface, the friction and lubrication of the mechanical system, and the sealing mechanism.
