Probing PFAS-induced interfacial disturbances with self-propelled camphor motors

Per- and polyfluoroalkyl substances (PFAS) are persistent contaminants that strongly accumulate at air-water interfaces, where they influence fate, transport, and treatment efficiency. However, experimental access to their dynamic interfacial effects remains limited. Here, camphor-driven Marangoni motors were employed as macroscopic probes to translate molecular adsorption of PFAS into measurable propulsion dynamics. Using perfluorooctanoic acid (PFOA) as a model PFAS and sodium dodecyl sulfate (SDS) as a hydrocarbon benchmark, systematic comparisons revealed distinct interfacial signatures. Increasing PFOA concentration induced a progression from continuous propulsion to oscillatory motion and confinement, with 0.4 mM PFOA suppressing the propulsion velocity by approximately 72 % relative to the control. In contrast, SDS transitioned from fast propulsion to long-period oscillations and complete arrest, particularly in the presence of Ca²⁺. Quantitative analysis of speed, oscillation period, and peak velocity demonstrated that PFOA exerted more persistent suppression of Marangoni propulsion and retained oscillatory dynamics under ionic perturbation, highlighting its strong and resilient interfacial activity. Localized interactions between PFOA and camphor may modulate interfacial stress renewal in the camphor diffusion zone, supporting sustained oscillatory propulsion compared with SDS. This framework provides a physically transparent model linking amphiphile adsorption to macroscopic interfacial mobility and establishes motion metrics as diagnostic observables for probing amphiphile-interface interactions under non-equilibrium conditions, offering a low-cost platform for mechanistic insight into interfacial processes relevant to water and wastewater treatment.