Molecular mobility of CU(II)-containing liquid crystalline ionomers: dielectric relaxation and thermally stimulated depolarization currents

Abstract

Molecular mobility of functionalized liquid crystalline (LC) copolymer (P1) containing mesogenic cyanobiphenyl groups and acrylic acid fragments (28%) as well as LC ionomers P2 (Cu 2.5() and P3 (Cu 7() with copper ions were studied by dielectric spectroscopy (DS) and by thermally stimulated depolarization current (TSDC) methods. For P1–P3, the frequency dependences of dielectric losses and temperature dependences of depolarization current were obtained and four relaxation processes γ1, β, α, and δ were found. For each of them a molecular mechanism was proposed. Moreover, for P1, P2, and P3, at high temperatures the TSDC global curves indicate the peak of depolarization current, which has no analogue in the dielectric spectrum. For P1 this peak is a ρ-process of low intensity. For P2 and P3 ionomers the intensity and temperature position of the high temperature peak increase as compared to those of P1. The mechanisms of the high temperatures peak for the P2 and P3 systems containing copper ions were attributed to the free space charge polarization and to the dipole polarization process of polymer chains included in ionic associates (multiplets). There is good correlation between the peak temperature positions obtained from the global TSDC spectrum at equivalent frequency and those obtained from DS.