Development of an Electroosmosis and Ionic Polymer Based Nastic Actuator

摘要

We developed a nastic actuator based on the synergistic actuation of super-absorbent polymer (SAP) and an innovatively designed electroosmotic (EO) fluid pump. It is integrated with a deformable structure that generates size and shape changes with a high energy density. The nastic actuator contains both an active pressure source and a passive engineered deformable plate embedded with fluid channels. In nature, nastic structures change shape as a response to environmental stimuli, as exemplified by many biological species such as the Venus flytrap. The mechanical strain involved in the nastic actuators is very significant; much greater than is evident in the majority of actuation materials for example, piezoelectric ceramic. The mechanical stress produced is also orders of magnitude higher than that found in typical ionic-based electroactive polymers. As a result, the output mechanical energy density is substantial, on the order of 10~5 J/m~3. The stress-strain curve lies in a new region of high-stress/high-strain, away from both extremes of high-stress/low-strain and high-strain/low-stress. This newly exploited stress-strain region can spawn new applications. The response time for a 10% strain rate is within seconds. Significant bending and extension were demonstrated through a pumping pressure of more than 11 atmospheres. In addition to the synergistic swelling/de-swelling and pumping, the inclusion of SAP helps to hold backpressure, stabilize pH, define shape, and distribute pressure. The contribution of SAP to the overall pressure, in general, is smaller than that by EO, and depends on its chemical formulation and fabrication. We will report the performance and characterization of the developed nastic actuator.