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Omniphobic surfaces, which repel polar and non-polar liquids alike, have proven of value in a myriad of applications ranging from piping networks, textiles, food and electronics packaging, the construction industry, and underwater drag reduction. A limitation of currently employed omniphobic surfaces is their reliance on perfluorinated coatings/chemicals, increasing cost and environmental impact and preventing applications in harsh environments. Thus, there is a keen interest in rendering conventional materials, such as hydrocarbon-based plastics, omniphobic by micro/ nanotexturing rather than via chemical makeup, with notable success having been achieved for silica surfaces with doubly reentrant pillars (DRPs). These surfaces exhibit superomniphobicity against droplets of polar and apolar liquids, characterized by apparent contact angles θr > 150° and contact angle hysteresis < 10°). However, we discovered a critical limitation of DRPs – they catastrophically lose superomniphobicity in the presence of localized physical damages/defects or on immersion in wetting liquids. In response, we pioneered bio-inspired gas-entrapping microtextured surfaces (GEMS) architecture composed of doubly reentrant cavities (DRCs). DRCs are capable of robustly entrapping air when brought into contact with liquid droplets or on immersion, which prevents catastrophic wetting transitions even in the presence of localized structural damage/defects. This dissertation talk presents our multifaceted wetting characterization of DRCs via custom-built pressure cells, confocal laser scanning microscopy, environmental scanning electron microscopy, contact angle goniometry, high-speed imaging, and upright optical microscopy.
Sankara Arunachalam (ORCID iD: 0000-0003-3685-3913) is pursuing graduate research in Professor Himanshu Mishra’s group at King Abdullah University of Science and Technology (KAUST). He received his Bachelor’s degree in Aeronautical Engineering from Anna University, India (2005-09), followed by a Master’s degree in Aerospace Engineering from the Indian Institute of Science (IISc), Bangalore (2009-11). He started his carreer as a Research Engineer at BEML Ltd, India (2011-15), and relocated to KAUST to work as a Research Specialist (2015-20) and later as a graduate student. His research focuses on developing sustainable gas-entrapping microtextured surfaces and understanding their interactions with droplets and bulk liquids. He has successfully demonstrated proof-of-concept applications of this bio-inspired approach for coating-free frictional drag reduction, mitigating cavitation erosion, and separation technologies. He has co-authored over 11 peer-reviewed articles with over 400 citations and holds one patent.