Imaging the Thermal Dynamic Panorama for Volume Phase Transition and Water-Molecule Communication of Single Microhydrogels

Abstract

Thermal volume phase transition of thermosensitive hydrogels, the intrinsic stress-stimulated response of the microstructure, is widely utilized to fabricate flexible smart devices. However, their stability and responsiveness are limited by mechanical properties linked to size, water content, and polymer chain deformation. Herein, we employed a synchronous thermal–optical imaging technique to in situ investigate the volume phase transition behaviors of a single microhydrogel under thermal cycling. At the single-microhydrogel level, we found that hysteretic dynamics within the low critical solution temperature region revealed distinct collapse/swell mechanisms tied to water-molecule communication and microscale morphology. Furthermore, the hydrophilicity of a substrate regulates the microgel mobility, affecting water transport and intermicrogel communication. Additionally, microgel water-molecule communication enables infiltration on superhydrophobic surfaces like lotus leaves. This thermal-controlled optical imaging methodology greatly develops a serviceable characterization of flexible stimuli-driven materials and devices at the microentity level, decoding their detailed dynamic processes, transient intermediate states, and intrinsic mechanisms.