Structure and electric properties of Poly(vinylidene cyanide-tetracyanoethylene) copolymer predicted with density functional theory

Abstract

The geometry, energy, internal rotation barrier, dipole moments, and molecular polarizabilities of poly (vinylidene cyanide-tetracyanoethylene) (P(VDCN-TeCN)) of a-and b-chain models were studied with DFT at B3PW91/6-31G(d) level. The effects of chain length and TeCN content on the copolymer chain stabilities, chain conformations, and electric properties were examined and compared with those of the poly(vinylidene fluoride-tetrafluoroethylene) (P(VDF-TeFE)) copolymer and the polyvinylidene cyanide (PVDCN) homopolymer to explore whether P(VDCN-TeCN) possess an expected good piezoelectricity or not. Based on the internal rotation potential curves of P(VDCN-TeCN) dimer models (H[CH 2 C(CN) 2 -C(CN) 2 C(CN) 2 ]H and H[C(CN) 2 CH 2 -C(CN) 2 C(CN) 2 ]H), the conformational angles, relative stabilities of a-and b-conformations and the transition energy barriers of b?a and a?b were discussed. The results show that the stability of the b-conformation increases and the b?a transition in P(VDCN-TeCN) is more difficult than that in PVDCN. The energy difference per monomer unit between the b-and a-chains decreases with increasing TeCN content. The contribution of average dipole moment per monomer unit in the b-chain is affected by the chain curvature and TeCN content, and there is a weakly parabolic dependence on the VDCN content. For the same chain length, the calculations show that the dipole moment contribution per monomer unit in the P(VDCN-TeCN) with 0.5 molar fractions TeCN is smaller than either the b-chain PVDCN or the b-chain P(VDCN-TeFE). The chain length does not produce a significant change in the mean polarizability for either the a-or the b-P(VDCN-TeCN); however, the value increases with increasing the TeCN content in P(VDCN-TeCN)s.

Piezoelectric approaches to organic polymeric materials

“…For instance, incorporation of nitrile (-CN) groups in copolymers of poly(vinylidene cyanide) (PVDCN), such as PVDCN-vinyl acetate, PVDCN-tetracyanoethylene, and PVDCN-tetrafluoroethylene, could induce cooperativity, wherein multiple CN dipoles cohesively react to the electric field applied, rather than each dipole functioning independently, leading to improved piezoelectric response. [115][116][117] In addition, some morphologies might not sustain the electric field or heat required for poling without experiencing physical damage or alteration in their structure, limiting the application of the process. The value of the electric field is limited by the dielectric breakdown of the polymeric material.…”

“…7(b)). A comprehensive data analysis method for dielectric spectra analysis has been summarized by Mellinger 115 . The approach involves fitting the experimental data to appropriate mathematical models and extracting the key material parameters such as permittivity, elastic modulus, and electromechanical coupling factor from the fitting results.…”