Sustainable Non-PFAS Hydrophobic Surfaces from Naturally Derived Sepiolite, Myristic Acid, and Ethyl Cellulose for Stable Dropwise Condensation

Non-wettable surfaces are widely used across a range of applications, from energy systems and water harvesting to self-cleaning materials and biomedical devices. However, increasing environmental and regulatory concerns surrounding per- and polyfluoroalkyl substances (PFAS) have prompted a shift towards sustainable alternatives. In this study, near-superhydrophobic, PFAS-free aluminum surfaces are developed using a scalable dip-coating technique involving sepiolite nanoparticles, myristic acid, and ethyl cellulose. Sepiolite, a naturally occurring fibrous clay mineral, is chemically modified with myristic acid to enhance its interfacial bonding with the metal substrate and impart hydrophobicity to the nanoparticles, while ethyl cellulose acts as an additional hydrophobic modifier that improves mechanical resilience and coating adhesion to the metal surface. Condensation experiments demonstrate stable dropwise condensation on the developed surfaces, along with enhanced heat transfer performance compared to filmwise behavior observed on uncoated aluminum. Notably, the condensation heat transfer performance of the sepiolite-based coatings is comparable to that of state-of-the-art superhydrophobic surfaces fabricated using PFAS-based chemistries. Thus, the work highlights the potential of naturally derived, biodegradable materials to replace fluorinated compounds in energy, water treatment, and related industrial applications, offering a promising pathway toward environmentally sustainable surface engineering.