First principle calculations of molecular polarization switching in P(VDF–TrFE) ferroelectric thin Langmuir–Blodgett films

Abstract

This paper reports first principle calculations and analysis of the molecular mechanism of the polarization switching in polyvinylidene fluoride and its copolymer with trifluoroethylene (P(VDF–TrFE)) using semi-empirical and ab initio quantum chemical methods based on the HyperChem 7.5 and Gaussian98 programs. The simulations were performed for different copolymer contents in P(VDF–TrFE)—(70:30), (60:40) and pure PVDF. The calculated values of the dipole moment and average polarization of the molecular chains show a clear hysteresis under varying electric field with polarization saturated at ∼0.1–0.14 C m−2. The calculated coercive fields (corresponding to the rotation of molecular chains to opposite orientation) are consistent (within an order of magnitude) with experimental data obtained for thin films (Ec = 5–18 MV cm−1). In the absence of external electric fields, the interactions between several molecular chains lead to the orientation of all dipole moments along one direction parallel to the chain plane. This model corresponds to the PVDF layer on the dielectric surface. For the electric field in the perpendicular direction, all chains are rotated along this direction corresponding to the model of conductive substrate.

Анализ Вычислительных И Экспериментальных Исследований Переключения Поляризации В ПВДФ И П (Вдф-ТрФЭ) Сегнетоэлектрических Пленках На Наноуровне

“…These studies continue the series of our previous investigations of ferroelectric and nanoscale properties of thin LB PVDF copolymer films [8,[16][17][18][19][20][21]. The analysis of computational and experimental data and new computed evaluations obtained allow us to estimate the sizes of possible transition region approximately to be of the order of 10 nm.…”

“…Computational studies of the polarization switching mechanism in such polymer films were performed on an idealized model, consisting of one, two and four polymer chains with limited structural units by means of the first-principles quantum theory [15][16][17][18][19][20][21].…”

“…Now these LB polymer films are widely explored experimentally, using various techniques, including nanoscale characterization by atomic force microscopy (AFM) and piezoresponse force microscopy (PFM) method [4][5][6][7][8][9][10][11], and theoretically, using various computational methods [12][13][14][15][16][17][18][19][20][21]. These novel ferroelectric nano-materials are very promising for nanobiotechnology, nanobiomedicine, bio-and microelectronics, and as a prospective component of various nanocomposites and "intellectual" templates with "smart surface" properties.…”

Exclusive self-aligned β-phase PVDF films with abnormal piezoelectric coefficient prepared via phase inversion

“…First principle calculations by Bystrov et al have shown that interaction between molecular chains of PVDF leads to the orientation of each molecular dipole moment along one direction parallel to the chain plane. [35] It is noteworthy that although β-phase crystals do not have preferential orientation in PVDF films formed by phase inversion 15 or by drying in air; 12 the PVDF membranes obtained may still exhibit a certain degree of piezoelectric effect as shown by our results in Figure 3h. However, this aspect has been largely ignore in the literature with the porous PVDF films formed by phase inversion usually considered unsuitable for poling and electroactive applications.…”

Significant triboelectric enhancement using interfacial piezoelectric ZnO nanosheet layer

“…As water is a dipolar molecule, the electric field acts on the initial surface, inducing aligned -crystals, which in turn causes the alignment of the -phase crystals in the sequential crystallisation. Using first-principle calculations, Bystrov et al have shown that the interaction between PVDF molecular chains leads to the orientation of each molecular dipole moment along one direction parallel to the chain plane [36]. On the other hand, the molecular interaction in PVDF will lead to the same orientation direction as ZnO growth direction [22], thus they increase the charge density more profoundly, hence increasing the overall efficiency of TENG devices.…”