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Partially ordered region: a new mechanism for electromechanical response of EAPs

The understanding of the electromechanical response in electroactive polymers (EAPs) will lead the development of new materials or the improvement of existing materials. The recent development of electrostriction based high performance EAPs, such as irradiated P(VDF-TrFE) and dielectric elastomers, makes it more interesting to understand the micro-mechanism that contribute the observed strain response. However, the current widely accepted mechanisms, such as electric field induced phase transition and the Maxwell effect, could not explain some of the observed phenomena. In this paper, the structure and property of recrystallized P(VDF-TrFE) 65/35 copolymer which was previously irradiated with high-energy electrons are reported. It is found that the interfacial layer existing between the crystalline regions and amorphous regions plays an important role. This concept is further extended to explain the pre-stress dependence of the electromechanical response observed in dielectric elastomers. That is, partially ordered regions are induced in the dielectric elastomer by the pre-stress. These partially ordered regions are the key to the observed high electromechanical performance dielectric elastomers.