Super Tough Bilayer Actuators Based on Multi-Responsive Hydrogels Crosslinked by Functional Triblock Copolymer Micelle Macro-Crosslinkers
ABSTRACT: Intelligent hydrogels responsive to external stimuli have been widely studied for great potentials for artificial muscles, soft robotics, sensors and actuators. However, the weak mechanical properties, narrow response range, and slow response speed of many responsive hydrogels have hindered practical applications. In this paper, tough multi-responsive hydrogels were synthesized by using vinyl functionalized triblock copolymer micelles as macro-crosslinkers and N-isopropyl acrylamide (NIPAM) and acrylamide (AAm) or 2-(dimethylamino)ethyl methacrylate (DMAEMA) and 2-acrylamido-2-methyl-1-propane-sulfonic acid (AMPS) as monomers. The P(NIPAM-co-AAm) hydrogels have tensile strength up to 1.6 MPa and compressive strength up to 127 MPa, which are tunable by changing the formulations. Moreover, the lower critical solution temperature (LCST) of the thermosensitive hydrogels has been manipulated in a wide range by changing the molar ratio of NIPAM to AAm. Responsive hydrogel bilayers were fabricated through a two-step synthesis. A second layer of P(DMAEMA-co-AMPS) was synthesized on the first P(NIPAM-co-AAm) layer to obtain a bilayer hydrogel, which was responsive to temperature, pH and ionic strength changes to undergo fast and reversible shape transformation a few minutes. This kind of multi-responsive hydrogel device with strong and tough properties has broad prospects in soft actuators.