Effect of Metallization on the Electromechanical Properties of Microfluidically Synthesized Hydrogel Beads

This investigation demonstrates that metallization can be used to tailor the electromechanical properties of polymer beads. Rigid ion exchange resin beads and softer microfluidically synthesized polyionic liquid hydrogel beads were metallized using an ion exchange process. Metallization increased bead stiffness and dielectric coefficient while reducing resistivity in all beads examined here. Gold-filled beads were preferable over platinum-filled beads as they generated greater changes in electrical properties with smaller increased stiffness. These properties could be further altered by performing multiple metallization steps, but diminishing returns were observed with each step. Ion exchange resin beads were always stable after multiple metallization steps, but polyionic beads would often rupture when repeatedly compressed. Polyionic beads with higher ionic liquid (IL) content were more fragile, and beads synthesized from monomer solutions containing 1% IL were mechanically robust after three metallization steps. These 1% IL beads delivered similar electrical properties as the IONAC beads that also underwent three metallization steps at a significantly reduced stiffness.