Triple-Pillar Wetting Regulates Capillary Wicking in High-Aspect-Ratio Micropillar Arrays

Capillary wicking in high-aspect-ratio micropillar arrays is significantly influenced by the wetting topology adopted by the advancing meniscus. Here, we investigate capillary imbibition in micropillar arrays with a fixed geometry ratio (h/(l - d) = 2.86) while systematically varying surface wettability and working-fluid composition. High-speed visualization and a geometry-informed capillary-pressure model show that triple-pillar wetting (TPW) provides a stronger capillary-driving state than double-pillar wetting (DPW) by increasing the effective wetted perimeter. The TPW fraction ϕTPW is positively correlated with front velocity and decreases markedly as the interfacial driving parameter σ cos θ decreases, suggesting a possible shift from TPW-dominated to DPW-dominated transport. Compared with square arrays, equilateral-triangular arrays promote TPW and exhibit superior pumping performance under favorable wetting conditions; however, they are more susceptible to contact-line pinning at larger contact angles. These findings clarify how pore-scale meniscus topology controls liquid-gas interfacial propagation and apparent imbibition dynamics in structured porous media.