Atomistic modeling of flexoelectricity in amorphous polymers

In this paper, the amorphous PVDF (Polyvinylidene Fluoride) and PE (Polyethylene) models are established. The relationship between configuration density and temperature is calculated by molecular dynamics simulation. The rationality of model is determined by comparing with the experimentally determined glass transition temperature T_g. Secondly, the strain gradient is applied to the main chain carbon atoms of the amorphous PVDF and PE equilibrium configuration. Electric polarization occurs when the microstructure of the configuration changes. The transverse flexoelectric coefficients μ₁₂ of amorphous PVDF and PE configurations are 1.24×10^-9 C/m and -2.63×10^-9 C/m, respectively, obtained by fitting the relationship between polarization and strain gradient. Finally, through the micromechanical analysis, the CF₂ and CH₂ dipoles rotate around the main chain along the inner side of the curved surface under the strain gradient, accompanied by some small structural adjustments. This leads to the electric polarization of the amorphous PVDF and PE configuration. Due to the difference in charge number and electronegativity between the amorphous PVDF and PE groups, the calculated transverse flexoelectric coefficients of the amorphous PVDF and PE are opposite, and the absolute value of the transverse flexoelectric coefficient of PE is greater than that of PVDF.