A monolithic anti-freezing hydro/organo Janus actuator with sensitivity to the polarity of solvents.

Hydrogels with bilayer structures, known as actuators, have attracted increasing attention in recent years due to their sophisticated intellectual functions such as pine-cone-like bending and pod-like twisting in response to temperature, light, pH, special solvents Herein, we synthesized a monolithic hydro/organic actuator by a direct one-step interfacial-incompatible polymerization of hydrophilic and hydrophobic vinyl macromolecular monomers, PEGMA and PPGMA, which were dissolved in water and ethyl acetate solutions, respectively. We found that the hydro/organo actuator exhibited directional, bidirectional, and site-specific bending behaviour under a single stimulus. In water and non-polar organic solvents, the hydro/organo actuator exhibited opposite bending behaviour as expected. However, in organic solvents, the hydro/organo actuator also exhibited quite different bending behaviour, depending on the polarity of the organic solvent. The hydro/organo actuator even experienced a dual responsive action in response to a single stimulus. We also found that such a hydro/organo actuator could be used effectively at low temperatures. The mechanism and potential applications of hydro/organo actuators based on PEGMA--PPGMA were also discussed and provided.