Self-organization of Microhydrogels

Abstract

Polymeric hydrogel particles (microgels) have “stimuli-responsiveness” and their physicochemical properties can be controlled by external stimuli such as temperature and pH. Moreover, microgels are swollen by water, which show Brownian motion, and also possess colloidal properties such as dispersing/flocculating. The authors have been studying microgels under the concept of “dimension and function control of polymeric hydrogel particles in microscopic spatial fields”, and it includes function control by utilizing self-organization in non-equilibrium system. In particular, when thermoresponsive poly(N-isopropyl acrylamide) (pNIPAm) microgel dispersions are dried, non-closepacked ordered structure of microgels are assembled on substrate. We focused on this phenomenon, and clarified the spontaneous structure formation process of pNIPAm microgels by observing the drying process. Furthermore, different from a very simple system such as “droplet drying”, we succeeded in the development of novel microgels (autonomously oscillating microgels) which periodically change their volume and interparticle interaction by coupling the pNIPAm microgels with chemical oscillation reaction (Belousov-Zhabotinsky (BZ) reaction). In this paper, we will mainly explain the study about “self-organization of microgels”, especially, the development of the autonomously oscillating microgels.