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

Abstract

We use molecular dynamics to calculate the structural, elastic, and polar properties of crystalline ferroelectric β -poly(vinylidene fluoride), PVDF (-CH 2 -CF 2 -) n with randomized trifluoroethylene TrFE (-CHF-CF 2 -) n as a function of TrFE content (0-50%) in the temperature range of 0-400 K. There is a very good agreement between the experimentally obtained and the computed values of the lattice parameters, thermal expansion coefficients, elastic constants, polarization, and pyroelectric coefficients. A continuous decrease in Young's modulus with increasing TrFE content was observed and attributed to the increased intramolecular and intermolecular repulsive interactions between fluorine atoms. The computed polarization displayed a similar trend, with the room temperature spontaneous polarization decreasing by 44% from 13.8 µC/cm 2 (pure PVDF) to 7.7 µC/cm 2 [50/50 poly(VDF-co-TrFE)]. Our results show that molecular dynamics can be used as a practical tool to predict the mechanical and polarization-related behavior of ferroelectric poly (VDFco-TrFE). Such an atomistic model can thus serve as a guide for practical applications of this important multifunctional polymer. . Fax:+1 860 486 2981; Tel:+1 860 486 2012 ‡ These authors contributed equally to this work. J o u r n a l N a me , [ y e a r ] , [ v o l . ] , 1-8 | 1

Ferroelectric Polymers Exhibiting Negative Longitudinal Piezoelectric Coefficient: Progress and Prospects

“…In most of the current models the role of chain tacticity has been, unfortunately, overlooked. For instance, most studies focus on quantifying or reproducing the ferroelectric properties of PVDF and P(VDF‐TrFE)s with the assumption that the all‐ trans conformation is the ground state of the polymers . A more recent density functional theory study ignored the contributions of chain tacticity and showed that all‐ trans conformation is the most energetically favorable for both P(VDF‐TrFE)s and PTrFE, which is in contrast to recent experimental results on P(VDF‐TrFE)s and PTrFE as well as the previous conformational energy calculations on PTrFE .…”

“…Consequently, the regioregularity was not properly described while the chain tacticity was not analyzed. This is also one of main reasons why theoretical works considered only VDF‐TrFE as the model of P(VDF‐TrFE) copolymers . The regiosequences were explicitly determined based on the assignments of 19 F NMR signals of P(VDF‐TrFE) copolymers ( Table 2 ).…”

Piezoelectric Scaffolds as Smart Materials for Neural Tissue Engineering

“…PVDF-TrFE forms the β-phase through copolymerization without the need for mechanical stretching or drawing [208]. In the case of additional annealing, mechanical stretching, or electrical poling, it is possible to further increase the crystallinity and alignment of the CF2 dipoles, thereby inducing higher piezoelectricity as compared to homopolymer PVDF, dependent on the TrFE content [209]. Electrospun PVDF-TrFE fibrous scaffolds showed higher crystallinity and β-phase content as compared to the starting powder material for neural and bone tissue engineering [101][102][103][104].…”

Energy barriers for dipole moment flipping in PVDF-related ferroelectric polymers

“…To model the inter-and intra-molecular interactions, we use the MSXX force field, 40 which is widely used for studying PVDF-related molecules. [41][42][43][44][45][46][47] The version without the shell model is used because the shell parameters for the TrFE and CFE monomers are not available. While density functional theory (DFT) calculations are more accurate than those from force fields, they are limited by large computational demands.…”