18 TH INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALS 1 Introduction and Background Electric field-activated electroactive polymers (EAPs) are an attractive class of smart materials that exhibit electromechanical coupling conversion; hence they can be applied as solid-state actuators and motion or pressure sensors. EAPs have many advantages compared to other classes of materials. They are lightweight, shape conformable, generally have good energy densities, relatively high strain rates, good electromechanical coupling and high bandwidth. However, there are major obstacles to their transition to applications. Notably they require high actuation voltages, have low blocked stresses and low operating temperatures. These current limitations are linked to inherent polymer properties such as low dielectric constant and low modulus. Our recent efforts in EAP-based nanocomposites provide new avenues to significantly improve their electromechanical response. The combination of properties offered by polymer nanocomposites provides opportunities for going beyond structural reinforcement where engineered electroactive responses and enhanced electrical and dielectric properties would result in multifunctionality. In our study, we show that adding nanoparticles to a polymer system impacts the effective polarization, owing to the large interfacial area that is created. We find that, depending on the nature of the polarization enhancement, whether due to real charge injection or dipoles, the resulting nanocomposites exhibit electrostrictive actuation. With judicious selection of the polymer system, piezoelectric behavior can be observed as well. 2 Results 2.1 Electromechanical Actuation Through judicious selection of nanoparticles and polymers we can tailor the electromechanical response of polymer-based nanocomposites. For the purposes of actuation at low driving fields, single wall nanotube (SWNT)-based polymers are investigated. With increases in SWNT content and dipole moment of the polymer, the free-strain response of the polymer nanocomposites increases (Fig. 1). The magnitude of electric field required for the actuation is in the range of 0.01-0.4 MV/m, which is significantly lower than that required to drive current electronic EAPs (in the range of 100- 200 MV/m). This result demonstrates that we can manipulate the electric field required and the observed strain field to achieve it by choosing the nanoparticle content and the type of polymer matrix used. Fig. 2 shows the coefficient of electrostriction M 3333 for a number of nanocomposites systems we studied and compared to known electrostrictive polymer polyvinylide trifluoroethylene P(VDF- TrFE) [1]. The coefficient is plotted as a function of SWNT vol% for a more direct comparison between the different systems. Electrostrictive response of a polar polyimide, ( - CN) APB ODPA, in the presence of SWNTs is quantified. ( -CN) APB ODPA has a high dipole moment and also exhibits a noncovalent electron donor-acceptor relationship with SWNTs. The SWNT-( -CN) APB ODPA nanocomposites are found to have higher electrostrictive strain response, higher electrostrictive material coefficient and higher strain rate than SWNT-CP2 nanocomposites, where CP2 is a similar polyimide which is nonpolar. NANOPARTICLE-ENHANCED POLYMERS FOR ELECTROMECHANICAL ACTUATION AND ENERGY STORAGE Z. Ounaies 1* , S. Deshmukh 2 , P.Khodaparast 1 , A. Meddeb 2 1 Mechanical Engineering, The Pennsylvania State University, University Park, PA, USA 2 Aerospace Engineering, Texas A&M University, College Station, TX, USA * Corresponding author(zxo100@psu.edu ) Keywords:nanocomposites, capacitors, dielectric constant, electrostriction