Robust and rapid responsive organic-inorganic hybrid bilayer hydrogel actuators with silicon nanoparticles as the cross-linker

Abstract

Hydrogel actuators belong to a type of smart soft materials which can take place anisotropic thrust and/or displacement under various environmental stimuli including thermal, light, pH, humidity etc. Robust strength and rapid response are of critical importance to high-performance hydrogel actuators. Here we report the syntheses and investigations of mechanical properties for series novel organic-inorganic hydrogels by using vinyl functionalized silicon nanoparticles (SiNPs) as the cross-linker. The doped SiNPs significantly enhance the mechanical strength of polyacrylamide (PAAm) hydrogels. Furthermore, the SiNPs composite poly-N-isopropylacrylamide (PNIPAm) hydrogels exhibit rapid response in deswelling and swelling behaviours. The excellent mechanical and responsive properties are attributed to the enhanced rigidity via SiNPs doping into the hydrogel network and the improved water diffusion through mPEG branch chains on the surface of nanoparticles, respectively. As a proof of concept, a bilayer PNIPAm@PAAm hydrogel actuator is facilely synthesized via an in-situ polymerization process. This composite hydrogel actuator shows extremely fast response rate of directional bending in hot water, about 6 times faster than the control without doping of SiNPs. This work demonstrates that these SiNPs composite hydrogels provide enhanced mechanical and responsive performances and may expand the future applications in smart hydrogel materials.