Terpolymers of vinylidene fluoride (VDF), trifluoroethylene (TrFE), and chlorotrifluoroethylene (CTFE) were synthesized as potential materials for electromechanical transduction.
These terpolymers had relatively high molecular weights (∼30 kg/mol) and CTFE levels in
the range of 5−10 mol %. The presence of the bulky CTFE units disrupts the sequence length
of the crystal, which lowers both the melting and Curie transitions; however, the degree of
crystallinity remains high. The formation of smaller, more mobile polar domains gives rise
to good electromechanical response. At low electric fields (7 MV/m), longitudinal strains as
high as 0.5% are attained. This is significantly higher than the strains achieved with the
same terpolymer obtained by bulk polymerization. The present materials exhibit a low
mechanical modulus (ca. 0.2 GPa) relative to other VDF−TrFE copolymers. This might limit
their use, depending on the application.
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An electrostatic model introduced earlier for predicting the heats of formation and dipole moments of fluorinated and chlorinated methanes is extended with success to longer straight-chain saturated compounds. The results are compared with the group and trigonal additivity approaches and shown to be an improvement in many cases. Discussion of the incremental methylene contribution to the heat of formation is presented for fluorinated and chlorinated species.
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