Tuning the Surface Properties of Liquid Metal Particles via Non-Native Shells for Stimuli-Responsive Electronics

Emerging gallium-based liquid metal (LM) particles are attractive candidates for stimuli-responsive electronics and therapeutics. These core-shell materials consisting of a solid oxide skin and a deformable core can be ruptured to form conductive pathways under an external applied force. While there are many advantages in utilizing the oxide skin for LM processing, the intrinsic properties of the gallium oxide impose limitations on their long-term stability. For instance, the oxide thickness gradually increases when aged under ambient conditions. When exposed to water, gallium oxide hydroxide crystallites form on the LM oxide skin, affecting its mechanical properties while further consuming gallium in the process.¹ Highly acidic or basic environments etch the oxide, causing the LM particles to coalesce into a bulk droplet. The accompanying changes in the LM particle properties are directly correlated to changes in their native oxide, which can either positively or negatively influence the overall material performance. Thus, expanding the capabilities of LM particles beyond the properties of the native gallium oxide shell would offer better stability and tunability of these materials. In this work, we discuss strategies by which to modify the surface properties of LM particles through various non-native coatings. Specifically, we investigate coating these particles with inorganic materials such as silica or 2D graphene oxide, which improve the surface properties of LM particles. These coatings serve as a protective barrier against undesirable environmental conditions (i.e., pH, reactive oxygen species, etc.) while providing additional mechanical stability to LM particles.² Currently, other 2D materials are being explored as surface modifiers for improving the optical response of LM particles. We have also investigated the use of phosphonic acid organic ligands in functionalizing the surface of the LM oxide which can lead to polymerized LM networks or hydrophobic surface properties, depending on the terminal groups chosen.^3,4 By purposefully selecting the materials that mediate the surface interactions of LM particles, we can expand the palette of non-native coatings that enable previously unattainable properties for LM-based responsive, multifunctional electronics.<br/>References:<br/>1. Creighton, Megan A., et al. "Oxidation of Gallium-based Liquid Metal Alloys by Water." Langmuir 36.43 (2020): 12933-12941.<br/>2. Creighton, Megan A., et al. "Graphene-based encapsulation of liquid metal particles." Nanoscale 12.47 (2020): 23995-24005.<br/>3. Farrell, Zachary J., et al. "Route to universally tailorable room-temperature liquid metal colloids via phosphonic acid functionalization." The Journal of Physical Chemistry C 122.46 (2018): 26393-26400.<br/>4. Thrasher, Carl J., et al. "Mechanoresponsive polymerized liquid metal networks." Advanced Materials 31.40 (2019): 1903864.