Elastic properties of poly(vinyldene fluoride) (PVDF) crystals: A density functional theory study

Abstract

We computed structural and elastic properties of totally nine phases of poly(vinyldene fluoride) (PVDF) crystals using the density-functional theory (DFT) method with and without inclusion of the dispersion corrections. In addition to the four known crystalline forms, mechanic properties of five theoretically predicted crystalline forms of PVDF are also investigated. The all-trans form I p exhibits the largest cohesive energy, bulk, and Young's modulus among the nine crystalline forms. The DFT calculations suggest that the d crystalline forms (III au , III pu , III pd , and III ad ) possess poor chain rigidity among the nine PVDF crystalline forms. In contrast, a change of relative orientation of PVDF chains does not lead to significant change in cohesive energy and mechanic properties. A comparison of the cohesive energies of nine crystalline forms of PVDF suggests that the theoretically proposed crystalline forms of PVDF are quite stable.

Temperature dependent structural, elastic, and polar properties of ferroelectric polyvinylidene fluoride (PVDF) and trifluoroethylene (TrFE) copolymers

“…The aforementioned FF model has already been employed for simulations of the ferroelectric-to-paraelectric phase transitions in PVDF. 33,36,37,39 The computed spontaneous polarization exhibits a similar trend with increasing TrFE content as already predicted with the DFT calculations at 0K, 33 but its magnitude is underestimated by about 20%. The obtained structural and elastic properties are in good agreement with previous computational studies.…”

“…57 The dependence of the values of the elastic stiffness tensor components of poly(VDF-co-TrFE) on composition are shown in Fig. 36,37,39,57,58 This discrepancy can be explained by the fact that the type of randomness present even in large computational models of β -PVDF crystals includes only ro- tational disordering of the polymer chains, which still remain perfectly aligned and connected along the backbone direction. As expected, for all TrFE concentrations, the elastic stiffness component along backbone chain direction C 33 remains about an order of magnitude larger, compared to the other two principal direction components C 11 and C 22 .…”

“…13,28,29 During the two decades following the discovery of ferroelectricity in PVDF, a variety of classical interacting-dipole approaches had been used to evaluate the polarization and piezoelectric properties of this polymer family. Furthermore, Pei et al 36 have recently computed the structural and elastic properties for nine different polymorphs of PVDF. Nakhmanson et al 33 have applied density functional theory (DFT) to study the polar properties of β -PVDF as a function of TrFE and TFE copolymer content, showing a large polarization enhancement within the crystal (as compared to the properties of individual all-trans PVDF chains) when quantummechanical effects are fully taken into account.…”

Hydroxyl-decorated graphene systems as candidates for organic metal-free ferroelectrics, multiferroics, and high-performance proton battery cathode materials

“…The first ferroelectric crystal, Rochelle salt, which was discovered in 1920 [2], is an organic ferroelectric material containing organic tartrate ion. At present, the study of ferroelectricity in organic solids has been limited to some well-known polymer ferroelectrics [3] like polyvinylidene difluoride (PVDF) [4][5][6][7][8][9][10], or a few low-molecular-mass compounds like thiourea [11], tetrathiafulvalene (TTF) complexes with p-bromanil (tetrabromo-p-benzoquinone) [12] and pchloranil (tetrachloro-p-benzoquinone) [13], croconic acid [14] and so on. Multiferroicity, i.e., coexistence of magnetism and ferroelectricity, is even more desirable for constructing multifunctional devices [15,16] where electrical polarization can be controlled by applied magnetic fields and magnetization by applied voltage.…”

Exceptional enhancement of ductility and toughness in poly(vinylidene fluoride)/carbon nanotubes composites

“…Apart from void pinning effect of CNTs, the complex polymorphs of PVDF with different crystalline structures have to be considered. Owing to the substantial difference in modulus and ductility among each crystalline phases, any variations in the ratio of PVDF crystal structures is expected to exert considerable influence on physical properties of PVDF composites . There are altogether five forms of chain arrangements of PVDF, among which, α, β, and γ phases are the most frequently observed and studied.…”