Surfaces Slippery to Liquids: Wettability, Adhesion, and Contact Line Friction

Ensuring surfaces stay dry and clean and resistant to icing and fouling is a pervasive challenge. Historically, strategies to achieve this, such as superhydrophobicity, have focused on surface wettability. Recently, research has shifted to minimizing surface heterogeneity using slippery liquid-infused porous and slippery covalently attached liquid-like surfaces. Here, we discuss a conceptual approach to contact line friction that provides design principles underlying practical surfaces. This brings an understanding of how contact angles, on both solid and liquid-film surfaces, combined with contact angle hysteresis can predict contact line friction. This leads to reconsideration of the long-accepted wettability "spectrum". Finally, we speculate on opportunities for new coatings free from poly- and perfluoroalkyl substances to address the societal and environmental challenges of "Forever Chemicals".