Synthesis and characterization of super absorbent polymers for high-mechanical output

We report the progress of an experimental study on developing super absorbent polymers (SAP), or hydrogels for nastic structural materials that can provide large size and shape changes within a characteristic time. The goal of developing SAP materials is to produce high-mechanical output for actuation, where high stress, strain, and energy density are required and provide structural rigidity. The idea of nastic actuation centers on the synergy of three components working in concert, i.e., SAP swelling/deswelling, distributed fluid pumping using electroosmotic effects, and pH swing (controlled electrochemically). Electric input controls electroosmotic (EO) pumping and a cell pH, which in turn controls SAP swelling, and ultimately the overall actuation. When synthesized SAP is combined with EO pumping effects, the integrated SAP/EO actuator can convert electric power to mechanical power through electrochemical reactions without relying on moving parts. In this transduction, the actuation pressure is provided mostly by EO pumping and supplemented by SAP swelling/de-swelling, which helps to maintain structural rigidity and reduce back flow, while buffering the pH in the EO pump for operating stability. Systematic measurements under typical SAP stimuli of pH, ionic strength, electric field, and mechanical loading were tested for validation and efficacy. To meet high-mechanical output requirements, several SAP materials were synthesized through innovative formulation and fabrication processes to tune for targeted mechanical properties, e.g., high hydrated strength, and high swelling speed.