Investigating Physico-chemo-mechanical Changes of Eutectic Gallium Indium (eGaIn) Thin Films Induced by Fluorinated Aqueous Droplets

Abstract

Herein, we demonstrate how the chemical sensitivity and mechanical stability of 2D thin films of eutectic gallium indium (eGaIn) can be leveraged to sense dilute amounts of fluorinated compounds (e.g., per- and polyfluorinated alkyl substances or PFAS). The method utilizes the interfacial interactions between 2D thin films of eGaIn and PFAS microdroplets, which induce thin film delaminations due to the perturbations in the Ga-to-O ratio at the interface. We tested three fluorinated samples – 200 ppm PFOA (perfluorooctanoic acid), 0.014 ppb PFAS, and 0.001 ppb PFAS to investigate the delamination, which exhibits sensitivities to concentrations. We leveraged energy-dispersive X-ray spectroscopy (EDS) and Raman spectroscopy to quantify and probe the shift in elemental distributions and surface dynamics of the eGaIn films. The observed delamination phenomena and the spectroscopic analyses suggest that our method provides a rapid in situ PFAS analysis tool related to total organic fluorine detection, complementing the existing technologies. Such a simplistic tool offers a fast approach to developing low-cost, field-deployable chemical sensors for total organofluorine detection.