Dielectric relaxation studies of aqueous sodium dodecyl sulfate with some amines as co-solvents by time domain reflectometry technique

Abstract

Dielectric relaxation studies of aqueous sodium dodecyl sulfate with 1-butanol, benzyl alcohol, aniline, and tributylamine have been carried out for different concentrations at 303 K. Dielectric relaxation spectroscopy (DRS) is a versatile tool to monitor the dynamic process of micellar systems. The time domain dielectric data were obtained in the reflection mode in the frequency range of 10 MHz to 20 GHz using a HP54750A sampling oscilloscope and HP54754A TDR plug-in-module. The sample was held at 303 K in a standard military application (SMA) cell with an effective pin length of 1.35 mm. We have determined the relaxation time (τ) using the Cole–Cole method. The relative viscosity η_r of the micellar solutions was also determined. We find that η_r increases with increasing concentrations of sodium dodecyl sulfate (SDS) and there is a non-linear increase in η_r beyond 80 mM SDS. The observed relaxation time is explained by considering the superposition of two relaxation times. One is due to the rotation of the hydrated water molecule around the micelle ions and the other due to the hydrated water squeezed in the hydrophobic interior of the micelle. Our results are explained on this basis. The results on adding amines are similar to that of adding alcohols but the interaction of the amines with the head group of the micelle is not as effective as hydroxyl group of alcohols.