A new EAP based on electroosmotic flow: nastic actuators

Abstract

A new type of polymeric actuator has been developed based on a micro-scale hydraulic mechanism, in which electroosmotic flow (EOF) is used to pump a fluid from one place to another in the device. This "nastic" actuator is in principle capable of producing both large displacements and high forces at reasonable speeds. Prototypes were fabricated from polydimethylsiloxane (PDMS) by micro-molding a fluid supply chamber, an expansion chamber, and connecting channels, and then topping this layer with a thin PDMS membrane. Upon applying a voltage across the two chambers, fluid flowed into the expansion reservoir, deflecting the membrane upward by hundreds of μm within a few seconds. The performance of these prototypes have been characterized in terms of deflection under load at various applied voltages, deflection vs. time upon input of a step potential, and repeatability. The performance of the actuator has been modeled, and the experimental and theoretical results are in reasonable agreement. The modeling work predicts that as the channel size is scaled down, the actuation stress will increase substantially, up to GPa for nanochannels, rivaling piezoelectrics and shape memory alloys but with much higher strain. Future applications of these actuators may include valves, shape-changing materials, and soft robotics.