Autophobic Retraction on Charged Solids from Milliseconds to Minutes: A Multisystem Study of Adsorption-Controlled Kinetics

Abstract Autophobic wetting refers to the self-induced retraction of a liquid from a surface whose wettability has been reduced by adsorption or deposition of molecules supplied by the liquid itself. It involves coupling between interfacial adsorption, lateral transport, and capillary-driven flow. Yet the time scale and extent of surfactant influence on droplet spreading and retraction remain incompletely understood. Previous studies were often limited to vertical geometries, single surfactant–substrate pairs, and indirect modeling of near-contact-line gradients. These limitations prevented a clear analysis of how adsorption kinetics and surface charge regulate the full droplet lifetime. We address this gap with a combined experimental and theoretical study. We present a time-resolved sessile-droplet experiment and describe the kinetics with an adaptive Cox-Voinov-type model that includes time-dependent surface energies. Together, they resolve the entire dewetting time evolution, from initial contact and early spreading, through autophobic retraction, to late-time relaxation. We study both cationic and anionic surfactants on charge-regulating silica and permanently charged mica. The model reproduces the measured contact line motion across a wide range of concentrations and times. Using high-speed imaging, we directly detect surfactant adsorption ahead of the moving contact line. This is evidenced by a surfactant-rich track on the solid substrate, which we quantify using the newly introduced Surfactant Carryover Length (SCL). The SCL measures the lateral extent of surfactant transfer ahead of the contact line and its dependence on concentration. Our findings show how this carried-over surfactant and the evolving surface energies slow spreading and trigger autophobic retraction. This framework unifies kinetic wetting, adsorption kinetics, and substrate charge effects, offering a general description of surfactant-laden droplet evolution relevant to coatings, agriculture, and biomedical applications.