Low-Temperature TSDC Studies of Molecular Dynamics in Pristine and O7+ Ion–Modified Liquid Crystalline Polyurethane

Abstract

The molecular dynamics of pristine and 100 MeV O7+ ion–modified liquid crystalline polyurethane (LCPU) was carried out using the thermally stimulated depolarization currents (TSDC) method. The TSDC spectra of pristine LCPU samples consist of current peaks appearing around 110,160, 210, and 260 K and are called the γ, β, α, and δ peaks respectively. The γ-peak is attributed to the crankshaft motion of the spacer group (but-2-ene group). The β-peak is due to the localized rotational fluctuations of C˭O groups. The α-peak is associated with the dipolar orientation of imines group present in the urethane linkage, and the δ-peak has its origin in the space charge trapping mechanism. In the TSDC spectra of O7+ ion–irradiated LCPU samples the γ-peak almost disappears, which shows that the ion induced modification in the methylene linkage. A relaxation process owing to new sub-polar groups formed due to dehydrogenation of CH2 groups and occurring in the vicinity of β-relaxation is discussed. The radiation-induced chain scissioning at NH groups in LCPU is also confirmed from the fluence effect on the α-peak. The irradiation results in the production of a large number of defect sites and an increase in the same results in the enhancement of δ-relaxation.