Effect of gamma-irradiation on liquid crystalline properties of cholesteryl pelargonate (nonanoate)

Effect of Co-60 gamma-irradiation at a dose 500 kGy on dielectric and thermodynamic properties of cholesteryl pelargonate (nonanoate) (ChP) has been studied by differential scanning calorimeter (DSC) and electric impedance analyzer. From UV spectra of irradiated ChP a charge transfer complex peak has been observed at 290 nm besides the peak of pure ChP at 240 nm making it a bicomponent mixture. Irradiated sample shows depression in crystal-cholesteric (K-Ch) transition by 4.0 degrees C and cholesteric-isotropic (Ch-I) transition by 9.8 degrees C while cholesteric-smectic A (Ch-SmA) by 15.4 degrees C. Enthalpies (Delta H) of the K-Ch, Ch-I and Ch-SmA transitions are found to decrease on irradiation. The dielectric constants (epsilon(perpendicular to)' and epsilon(parallel to)') and losses (epsilon(perpendicular to)'' and epsilon(parallel to)'') in planar and homeotropic alignments of the sample have been measured in the frequency range 100 Hz to 10 MHz at different temperatures between 30 to 100 degrees C. The dielectric losses (epsilon(perpendicular to)'' and epsilon(parallel to)'') Of the irradiated sample are observed to increase significantly (150%) whereas the dielectric anisotropy Delta epsilon (=epsilon(perpendicular to)' - epsilon(parallel to)') decreases.