Route to Universally Tailorable Room-Temperature Liquid Metal Colloids via Phosphonic Acid Functionalization

Eutectic gallium-indium nanoparticles (EGaIn NPs) were produced and subsequently functionalized with decylphosphonic acid under various conditions with the goal of producing highly stable room-temperature liquid metal colloids. Fourier transform infrared spectroscopy was used to determine phosphonic acid (PA) bonding modes (e.g., bidentate, tridentate) as a function of treatment conditions. The strongest bonding modes (i.e., predominantly tridentate) were found to take place under elevated temperature (reflux in hexanes), whereas lower bulk temperature processing such as bath or probe sonication produced largely weaker modes (bidentate). It is then shown that PA ligands can be chosen, which include click-chemistry reactive functionalities, opening up a universal route to chemically bespoke self-assembled monolayers on liquid metal colloids. These results carry important implications for robust functionalization of EGaIn NPs for use in inks, composites, and other materials.