Abstract
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.
Highlights
Preparation and shape transformation mechanism of the binary cooperative hydro/organo copolymer films The hydro/organo Janus copolymer films were prepared from a bilayer solution resulting from the immiscibility of a hydrophilic monomer solution (AA) and a hydrophobic monomer solution (BMA) (Figure 1a)
The results showed that sodium was hardly detected in the upper surface (PBMA network) and the atom ratio of C to O was ~ 4.6 (Figure 2b), which is similar to the calculated value of PBMA (4.0), whereas the atom ratio of C, O, Na was ~ 1.13: 1: 0.32 (Figure 2c, the calculated value of sodium polyacrylate was 1.5: 1: 0.5) in the lower surface
In conclusion, we successfully synthesized shape-transformable Janus films composed of a binary hydro/organo copolymer film via one-step polymerization of layered immiscible monomer solutions
Summary
The shape transformations of biological organisms[1,2,3,4,5,6] have been the inspiration for many products in the field of artificial muscles,[7,8,9,10,11,12,13] soft robotics,[14,15,16,17,18,19] sensors[20] and complex shape engineering.[21,22] For example, the leaves of the Venus flytrap snap together to capture insects by virtue of the synergy between the hydroelastic instability and asymmetric expansion of the inner and outer surfaces at the cellular level.[2]. By mimicking the sophisticated hierarchical structures present in nature, the motion of polymer films has been successfully demonstrated in several cases.[23,24,25,26,27,28,29,30] For example, hydrogel bilayers embedded with intersecting inorganic platelets or cellulose fibrils have exhibited pine-cone-like bending and pod-like twisting motions.[24,31] the practical applications of these actuators were limited because of the low modulus and weak mechanical strength of the hydrogels.[32] Elastomer single layer films, such as azobenzene polymer films synthesized using an elaborate molecular design,[13,27] can achieve smart responsive curving These films require a unidirectional stimulus to generate anisotropic contraction/expansion of their two sides; this factor limits the film thickness to the micrometer or sub-millimeter level.[27,33,34,35] there is great opportunity and challenge in exploring new strategies to synthesize robust intelligent polymer actuators
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