Flexoelectric effect and statistical properties in polar liquid crystals

The structural properties and flexoelectric coefficients e ₁ and e ₃ of polar liquid crystals (LCs) such as 4-n-pentyl-4′-cyanobiphenyl (5CB) are studied in the nematic phase by the molecular-dynamics and statistical-mechanics methods. A number of order parameters, $\bar P_{2L} (L = 1,2,3)$ and $\bar P_2 (r)$ , and orientational correlations ξ_λ for the nearest and next-nearest neighbors were investigated. The calculations show the absence of spontaneous polarization $(\bar P_1 \simeq 0)$ in the nondeformed polar 5CB liquid crystal over the entire range of temperatures corresponding to the nematic phase. The origination of spontaneous polarization (characterized by two independent flexoelectric coefficients e ₁ and e ₃) in response to an external deformation of a 5CB sample is studied. The calculated e ₁ and e ₃ coefficients agree well with the experimental data for 5CB obtained by the pyroelectric method.