Counterintuitive Wetting Transitions in Doubly Reentrant Cavities as a Function of Surface Make-Up, Hydrostatic Pressure, and Cavity Aspect Ratio

Summary

This record has been merged with an existing record at: http://hdl.handle.net/10754/666098.



Abstract
Surfaces that entrap air underwater serve numerous practical applications, such as mitigating cavitation erosion and reducing frictional drag. These surfaces typically rely on perfluorinated coatings. However, the non-biodegradability and fragility of the coatings limit practical applications. Thus, coating-free, sustainable, and 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 in DRCs remain unavailable. In response, Cassie-to-Wenzel transitions into circular DRCs submerged in water are investigated and compared with those in cylindrical “simple” cavities (SCs). It is found that at low hydrostatic pressures (≈50 Pa), DRCs with hydrophilic (θo ≈ 40°) and hydrophobic (θo ≈ 112°) make-ups fill within 105 and 107 s, respectively, while SCs with hydrophilic make-up fill within <10−2 s. Under elevated hydrostatic pressure (P ≤ 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 microtexturing and surface chemistry toward coating-free liquid repellency.

Citation
Arunachalam, S., Ahmad, Z., Das, R., & Mishra, H. (2020). Counterintuitive Wetting Transitions in Doubly Reentrant Cavities as a Function of Surface Make-Up, Hydrostatic Pressure, and Cavity Aspect Ratio. Advanced Materials Interfaces, 2001268. doi:10.1002/admi.202001268

Acknowledgements
S.A. and Z.A. contributed equally to this work. The research reported in this publication was supported by funding from King Abdullah University of Science and Technology (KAUST) under the award number BAS/1/1070-01-01. The authors thank Mr. Ulrich Buttner and Mr. Ahad A. Sayed from the KAUST Core Labs for their assistance with the microfabrication. The authors thank Dr. Wei Xu for helping with the confocal measurements and Mr. Edelberto Manalastas for his assistance in the fabrication of the pressure chamber for the confocal experiments. The authors thank Ms. Jamilya Nauruzbayeva for processing confocal images using Imaris software and proofreading the manuscript. The authors also thank Dr. Meng Shi (KAUST) and Dr. Yair Kaufman (University of California Santa Barbara) for fruitful discussions.

Publisher
Wiley

Journal
Advanced Materials Interfaces

DOI
10.1002/admi.202001268

Additional Links
https://onlinelibrary.wiley.com/doi/10.1002/admi.202001268

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