A monolithic hydro/organo macro copolymer actuator synthesized via interfacial copolymerization

Synthetic polymer actuators have attracted increasing attention for their potential applications in artificial muscles, soft robotics and sensors. The majority of previous efforts have focused on smart hydrogels with bilayer structures that can change their shape in response to environmental stimuli, such as temperature, light and certain chemicals. However, the practical application of hydrogels is limited because of their low modulus and weak mechanical strength. Here we synthesized a robust monolithic actuator of a macro-scale hydro/organo binary cooperative Janus copolymer film. The process involves direct, one-step interfacial polymerization of immiscible hydrophilic and hydrophobic vinyl monomer solutions, and the resultant product exhibited binary cooperative shape transformation to multiple external stimuli. The Janus copolymer film can work in both aqueous solutions and organic solvents, with bidirectional and site-specific bending arising from cooperative asymmetric swelling/shrinking of the hydrogel and organogel networks. In addition, the as-prepared Janus copolymer film can act as a sensor element for solvent leakage detection. This binary cooperative strategy is applicable to most immiscible monomer systems and provides a general approach to developing novel functional copolymer materials. Combining water-based and organic gels into one polymer produces muscle-like devices with solvent-specific bending capabilities. Many biological organisms, such as the Venus flytrap, can activate movement through cooperative action of inner and outer cell surfaces. Inspired by such designs, Shutao Wang from the Chinese Academy of Sciences and colleagues synthesized a two-sided copolymer with hydrophilic acrylic acid and hydrophobic butyl methacrylate components. The mechanically tough, millimeter-thick film expanded significantly on the acrylic acid side when immersed in water, leading to reversible coiling due to non-uniform internal stresses. Similarly, the film bent in the opposite direction when placed into an organic solvent. By exploiting these effects, the team produced a prototype leak sensor that leans over and contacts different electrodes in the presence of specific liquids. Shape transformation of hydro/organo Janus films: A hydro/organo Janus copolymer film has been designed and fabricated via a novel strategy, an unconventional one-step interfacial polymerization of the immiscible hydrophilic vinyl monomer solution and hydrophobic vinyl monomer solution. Under the binary cooperative effect of the hydrogel network and organogel network, the Janus film is able to work both in the aqueous solutions and organic solvents, and exhibit excellent shape-transformation performance, such as bidirectional and site-specific bendings.