Presenter: Ravi Shankar
Advisor(s): Dr. Richard J. Spontak
Author(s): Ravi Shankar,Tushar K. Ghosh and Richard J. Spontak
Graduate Program: Fiber and Polymer Science, Materials Science & Engineering, Chemical & Biomolecular Engineering
Title: Electromechanical Response of Nanostructured Polymers
Abstract: Electroactive polymers (EAPs) are emerging as a new class of lightweight and robust actuator materials with displacement capabilities that are far superior to those afforded by striction-driven ceramic materials. Moreover, EAP-based actuators enjoy additional advantages over conventional actuators in that they exhibit higher energy density, greater resilience and flexibility, higher response speed, and, perhaps most importantly, scalability. The most widely used and current benchmark EAP, an acrylic adhesive foam manufactured by 3M, exhibits an impressively high maximum actuation strain (~200% on an area basis). However, several drawbacks are associated with this acrylic foam: it is very tacky and its properties are fixed and cannot be readily tailored for particular applications. The latter shortcoming severely limits the performance range of this and other EAPs under current investigation, especially ones that derive from silicone elastomers, since all of these conventional EAPs are based on networked homopolymers. The present work describes the design of nanostructured polymer systems from the ground-up as a new avenue to highly responsive EAPs. The systems of interest here consist of incompatible block copolymers that microphase-separate into well-defined nanostructural elements, thereby providing a highly tunable avenue to desired material properties. Copolymer systems varying in molecular weight and composition have been fabricated, and their mechanical and electrical properties have been evaluated for actuator and sensory characteristics. The hysteresis behavior of these EAP materials has been measured under cyclic loading/unloading at constant strain and compares favorably with respect to the acrylic foam. Furthermore, all the copolymer systems investigated here exhibit far less nonrecoverable strain upon cyclic loading/unloading relative to the acrylic foam. In fact, nonrecoverable strain is virtually absent in some of the systems developed during the course of this study, indicating that the nanostructured polymer design could yield new and competitive materials for soft, reliable and robust actuators. An important finding in this work is that the areal actuation of the nanostructured polymer system exhibits a significantly higher maximum (> 200%) at a significantly lower breakdown electric field (~20 MV/m) compared to acrylic and silicone EAPs.