Dielectric and molecular dynamic studies of sub-Tg by thermally stimulated current (TSC) analysis for liquid crystalline epoxy thermosets

Dielectric constant (ε′), loss factor (tan δ) and molecular dynamic behavior of liquid crystalline epoxy cured with diamine were studied by thermally stimulated discharge current (TSC) technique and were compared with the conventional epoxy system. The relaxation time τ and the activation energy of reorientation of the dipoles for each TSC characteristic band were expressed as Arrhenius relationship. Liquid crystalline epoxy (LCE) monomer was diglycidyl ether of biphenyl (DGEBP) and the conventional epoxy was diglycidyl ether of bisphenol A (DGEBA). The conventional epoxy had two sub-Tg relaxations; γ-relaxation was related to the motion of glycidyl ether segment and β-relaxation was due to the crankshaft motion of the hydroxylether group. LCE thermoset exhibited another γ′-relaxation in addition to those two relaxations; the reorientation of mesogenic unit. The para-ether linkage of the biphenyl mesogenic unit allows it to rotate without disturbing neighborhood unit.