Dynamic swelling performance of hydrophobic hydrogels

ABSTRACT Conventional gels manifest monotonous swelling or shrinking performance upon immersing in solvents until reaching an equilibrium state. Recently, we discovered that the “hydrophobic hydrogels” prepared from hydrophobic polymer networks demonstrated dynamic swelling performance without equilibrium states. Upon water immersion, the gels expanded tremendously at the first stage until reaching a swelling peak; subsequently, the gels shrunk at an extremely slow rate. While this phenomenon endows the material with an unusual feature, more efforts are highly demanding for the full understanding of this performance. Herein, we systematically investigate the hydrophobic hydrogels’ swelling kinetics by screening the organic solvent dependence, polymer effect, and temperature impact. It is revealed that the chemical structure of gels greatly influences the swelling kinetics. The higher the networks’ hydrophobicity, the slower the swelling kinetics. Meanwhile, organic solvents demonstrate a limited effect on the dynamic swelling performance. Moreover, higher temperature significantly accelerates the whole volume change process. Based on the swelling performance, we further develop hydrogel-based soft devices with time-programmable two-dimensional and three-dimensional shape-shifting performances.