Smart actuators based on electroactive fluorinated polymers: relationship between molecular organization and electroactive response

Abstract

Electroactive polymers (EAP) show a change of properties (size, shape, temperature…) when an electric field is applied. Poly(vinylidene fluoride-ter-trifluoroethylene-ter-chlorotrifluoroethylene) P(VDF-ter-TrFE-ter-CTFE) terpolymers have been extensively studied since the 2000s and they found various applications in organic printed and flexible electronics, such as smart actuators. They exhibit different electroactive properties depending on the CTFE content. For %CTFE = 0, copolymers are ferroelectric and piezoelectric at room temperature (RT), while terpolymers are relaxor-ferroelectric and electrostrictive at RT for %CTFE > 6%. On the top of the processing conditions, the chemical composition (%CTFE) have a strong impact on the crystalline structure and morphology, and consequently on the electroactive properties. Unimorph actuators with two different chemical compositions were studied by in-situ Wide Angles X-Ray Scattering (WAXS) and by measuring their macroscopic deformation under an increasing electric field (up to 110 V/µm). These techniques were used to extract their electromechanical coefficients (��31 and ��31) at the macroscopic scale and to relate the crystalline scale to the macroscopic properties. By comparing the evolution of the crystalline unit cell dimensions and of the macroscopic strain of the actuator under an electric field, interesting information on the mechanisms involved were deduced and will be discussed.