Counterintuitive Wetting Transitions in Doubly Reentrant Cavities as a Function of Surface Make-up, Hydrostatic Pressure, and Cavity Aspect Ratio (Advanced Materials Interfaces)

by Sankara Arunachalam, Zain Ahmad, Ratul Das, Himanshu Mishra
Year: 2020 DOI: 10.1002/admi.202001268

Bibliography

Arunachalam, S., Ahmad, Z., Das, R., Mishra, H.*, "Counterintuitive Wetting Transitions in Doubly Reentrant Cavities as a Function of Surface Make‐Up, Hydrostatic Pressure, and Cavity Aspect Ratio". Adv. Mater. Interfaces 2020, 2001268. https://doi.org/10.1002/admi.202001268

Abstract

Surfaces that entrap air underwater can serve practical applications, such as mitigating cavitation erosion and reducing frictional drag. To achieve this, perfluorinated coatings are exploited that are non-biodegradable and fragile. Thus, coating-free, sustainable, and more robust approaches are desirable. Recently, a microtexture comprising doubly reentrant cavities (DRCs) has been demonstrated to entrap air on immersion in wetting liquids. While this is a promising approach, insights into the effects of surface chemistry, hydrostatic pressure, and cavity dimensions on wetting transitions remain unavailable. In response, we investigated Cassie-to-Wenzel transitions into circular DRCs submerged in water and compared them with cylindrical “simple” cavities (SCs). We found that at low hydrostatic pressures (~50 Pa), DRCs with hydrophilic and hydrophobic make-ups fill within 105 s and 10s, respectively, while SCs with hydrophilic make-up fill within < 10-2 s. Under elevated hydrostatic pressure ( 90 kPa), counterintuitively, DRCs with hydrophobic make-up fill dramatically faster than the commensurate SCs. This comprehensive report should provide a rational framework for harnessing microtextures and surface chemistry towards coating-free liquid repellency.

Keywords

Doubly reentrant cavities simple cavities wetting transitions Underwater hydrostatic pressure capillary condensation diffusion breakthrough pressure