Utilization of Cavity Vortex To Delay the Wetting Transition in One-Dimensional Structured Microchannels.

Frictional resistance across rough surfaces depends on the existence of slip on the liquid-gas interface; therefore, prolonging the existence of liquid-gas interface becomes relevant. In this work, we explore manipulation of the cavity shape in order to delay the wetting transition. We propose that liquid-driven vortices generated in the air cavity dissipate sufficient energy to delay the Cassie-Wenzel transition. Toward this, we fabricated cavities on the side walls of a polydimethylsiloxane-based microchannel for easy visualization and analysis of the dynamics of the liquid-gas interface. Two distinct flow regimes are identified in the experimental envelope. In the first regime, the liquid-gas interface is found to be protruding into the flow field, thus increasing the pressure drop at low Reynolds number. In the second regime, flow rate and geometry-based wetting transitions are established at moderate to high Reynolds numbers. We then investigate the effect of different cavity shapes (square, trapezoidal, and U-shape) in delaying the wetting transition by manipulating liquid-driven vortices. Out of the shapes considered in this study, trapezoidal cavities perform better than cavities with vertical walls in delaying the wetting transition due to geometrical squeezing of vortices toward the liquid-gas interface. Numerical simulations corroborate the experimental findings in that cavities with inclined walls exert more force on the liquid-gas interface, thus delaying their wetting transition. The proposed method being passive in nature appears more attractive than previous active methods.