An isotopic effect in the dielectric spectra of Ark. 9/water systems

Dielectric spectra of H₂O and D₂O molecules in the L_α liquid crystalline phase of nonylphenoxy-poly(ethylenoxy)ethanol(Ark. 9)/water lyotropic systems have been investigated by dielectric time domain spectroscopy in the frequency range from 10 MHz to 10 GHz. By fitting the Cole-Cole formula to the dielectric spectra, obtained at different temperatures the dielectric increments, the relaxation times and the distribution parameters have been calculated. A strong retardation of water molecules has been found for the lamellar phase with low water content, i.e. 10 water molecules (H₂O or D₂O) per one Ark. 9 molecule. The relaxation times obtained at room temperature for the light and heavy water are 63 and 93 ps, respectively. It means that the retardation factor for D₂O molecules in the L_α phase is close to 1.5 and higher than that found for pure heavy water (1.25). Any decomposition of the dielectric spectra obtained seems to be unsubstantiated. The temperature dependences of the relaxation times acquired for both kinds of water obey the Arrhenius behaviour.