Modifying the MRI, elastic stiffness and electrical properties of polyvinyl alcohol cryogel using irradiation

The aim of this work was to study the effect of radiation on the elastic stiffness, electrical and MRI properties of polyvinyl alcohol (PVA)-based cryogel (PVA-C). The PVA-C samples were irradiated with a 60C0 γ-source, at 2.18×106Rads. The indentation measurements (an indication of elastic stiffness) reduced by about 14.6% for PVA-3C and 5.7% PVA-6C after irradiation, indicating that the material became harder/stiffer. It was found that MRI relaxation times provide an alternative and non-destructive method to evaluate the radiation effect on PVA-C. The T1 of PVA-C that had undergone three freeze thaw cycles decreased with irradiation by 10%, 25% and 35% at 1T, 1.89T and 3T respectively. The T1 of PVA-C that had undergone six freeze thaw cycles decreased with irradiation by 18%, 15% and 11% at 1T, 1.89T and 3T respectively. The T2 of PVA-C decreased with irradiation only at 1T, however this change is hypothesized to be due to the interaction of two spin pools in the gel. The electrical conductivity (σ) and permittivity constant (ε) of the unirradiated and γ-irradiated PVA-C samples were measured at different frequencies in the range 40Hz to 1MHz. The results demonstrated that the conductivity increased with irradiation by 50% for PVA-3C (three freeze thaw cycles) and 75% for PVA-6C (six freeze thaw cycles) at frequencies greater than 1KHz.The permittivity decreased with irradiation up to 25% for 3C and 35% for 6C at frequencies less than 1KHz.