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Dielectric relaxation studies of aqueous sodiumdodecyl sulphate with some additives as co-solvents in time domain reflectometry technique

T.Kalaivani, Prabhakar Undre, R.Sabesan, S.Krishnan

Dielectric relaxation studies of aqueous sodium dodecyl sulphate with formamide and acetamide, have been carried out for different concentrations at 303k. Dielectric Relaxation Spectroscopy (DRS) is a versatile tool to monitor the dynamic process ofmicellar systems. The time domain dielectric data were obtained in the reflection mode in the frequency range of 10MHz to 20GHz using a HP54750A sampling oscilloscope and HP54754A TDR plug-in-module. The samplewas held at 303k in a SMAcellwith an effective pin length of 1.35mm.We have determined the relaxation time () using the Cole-Cole method. The relative viscosity r of the micellar solutions was also determined.We find that r increases with increasing concentrations of SDS and there is a non-linear increase in r beyond 80mM 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 amides 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 hydroxy group of alcohols.