Article Cite This: J. Phys. Chem. C XXXX, XXX, XXX−XXX
pubs.acs.org/JPCC
Route to Universally Tailorable Room-Temperature Liquid Metal Colloids via Phosphonic Acid Functionalization Zachary J. Farrell,†,‡ Nina Reger,§ Ian Anderson,† Ellen Gawalt,*,§ and Christopher Tabor*,† †
Air Force Research Laboratory, Dayton, Ohio 45433, United States UES, Inc., Dayton, Ohio 45432, United States § Duquesne University, Pittsburgh, Pennsylvania 15282, United States
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ABSTRACT: 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.
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INTRODUCTION Gallium-based room-temperature liquid metal alloys such as eutectic gallium indium (EGaIn) have gained increasing popularity over the last decade for use in applications that include reconfigurable electronics, conformal electrodes, flexible electrical interconnects, and self-healing circuitry among others.1−4 Although most of these applications have harnessed EGaIn in its bulk form, for stimuli-responsive applications (including self-healing circuitry and medicine), there is focused interest in colloidal forms of EGaIn.4−7 Additionally, in many advanced additive manufacturing techniques (e.g., aerosol jet printing and ink jet printing), colloidal suspensions are used in conjunction with a large variety of stabilizing agents to enhance colloidal stability and particle/solvent compatibility. For these application areas, it is of paramount importance to be able to tailor the particle surface chemistry specifically to the target material system, as has been done with other nanomaterials.8−11 A unique property of gallium alloys in both nano- and bulk forms is their tendency to form a thin (
