Effective Dielectric Constant and Refractive Index of Quasi-Two-Dimensional Polydomain Film of Conjugated Polymer in Absorption Region

Aver’yanov, E.M.// Zhidkie Kristally i Ikh Prakticheskoe Ispol'zovanie//


An uniaxial film of a conjugated polymer consisting of statistically equivalent uniaxial domains of the average dimension a is considered in the plane XY with the optical axis Z. The optical axes n_d of domains are randomly oriented in the plane XY. In the region of light absorption, the domains are characterized by the dielectric constants epsilon_j = epsilon_1j + iepsilon_2j and the refractive indices N_j = n_j + ik_j for an ordinary (j = o) and extraordinary (j = e) light waves. For the waves with wavelength lambda >> a, wave vector k*perpendZ and polarization EperpendZ, such polydomain film is two-dimensional composite medium with effective dielectric constant epsilon* = epsilon_1* + iepsilon_2* and effective refractive index N* = n* + ik*. In this work, the relations which connect the components epsilon_1*, epsilon_2*, n*, k* with the components n_j, k_j were established. For testing the relations and calculating the components epsilon_1*, epsilon_2*, n*, k*, the experimental values n_oA, k_oA (n_eA, k_eA) were used instead of values n_o, k_o (n_e, k_e) in the transparency and electronic absorption regions for the uniaxial monodomain films of the conjugated polymer F8BT with axial orientation (O_A) of macromolecules with respect to the optical axis n_A in the XY plane. The calculated components epsilon_1*, epsilon_2*, n*, k* were compared with the experimental components epsilon_1oP, epsilon_2oP, n_oP, k_oP in the same spectral regions for an ordinary light wave with lambda >> a, k*perpendZ, EperpendZ in the uniaxial polydomain F8BT films with in-plane orientation (O_P) of macromolecules. The relations epsilon_1* = epsilon_1oP, epsilon_2* = epsilon_2oP, n* = n_oP, k* = k_oP established here with good precision show that the polydomain F8BT films are close to the ideal two-dimensional polycrystal.