Autonomously Oscillating Hydrogel Microspheres with High-Frequency Swelling/Deswelling and Dispersing/Flocculating Oscillations.

Fast swelling/deswelling and dispersing/flocculating oscillations of autonomously oscillating hydrogel microspheres (microgels) at periods of single-order seconds were accomplished. The design of the oscillating microgels is based on the incorporation of neutral and hydrophilic acrylamide monomers into conventional microgels to suppress the irreversible aggregation of the microgels during oscillation at high substrate concentrations and high temperatures in the Belousov-Zhabotinsky (BZ) reaction. In contrast to conventional microgels, the aforementioned microgels can carry out the BZ reaction under optimized conditions without irreversible aggregation at higher temperature, resulting in short oscillation periods (∼7 s) that were obtained from optical transmittance measurements. Furthermore, a macrogel composed of organized microgels was prepared, which also showed a remarkably fast swelling/deswelling oscillation (oscillation period: ∼23 s). This new type of oscillating microgel could be applied to advanced materials, e.g. to autonomously oscillating micropumps that imitate the human heartbeat.