The smart valve for micro flow-velocity regulation based on the “Interfacial Barrier” effect of wettability-patterned surfaces

In fluid control, traditional valves are limited in their applications due to reliance on external power sources and complex structures. Current research focuses on passive driving mechanisms through structural design or surface design/enhancement. Among these, passive regulation of fluid transport through surface wettability gradient differences is a hot topic. This study constructed patterned surfaces through ordered/disordered combinations of hydrophilic/hydrophobic/superhydrophobic (wettability/hydrophobicity) properties and investigated fluid flow behavior. A "Smart" valve design was proposed, which utilizes changes in contact angle hysteresis force (<i>F</i>_h) caused by interfacial wettability differences to achieve micro flow-velocity regulation. The results showed that when water flowed through pattern I, the flow rate experienced a two-stage surge (667% and 2200%), while at pattern II, it triggered a stepwise deceleration (reductions of 79% and 75%). Furthermore, a mechanism of "Interfacial Barrier" was proposed, where gravitational force, viscous force (<i>F</i>_<i>η</i>), and <i>F</i>_h jointly contribute to energy storage and dissipation across the interface. Additionally, droplet impact experiments validated that the greater the interfacial wettability difference, the stronger the energy storage or dissipation effect. This study establishes the "Smart" valve as an efficient and precise fluid control solution that requires no external power, applicable in fields such as chemical engineering, biomedicine, and microfluidics.