A new insight on the dynamics of sodium dodecyl sulfate aqueous micellar solutions by dielectric spectroscopy

Abstract

Aqueous sodium dodecyl sulfate micellar solutions were investigated by a recently developed doubledifferential dielectric spectroscopy technique in the frequency range 100 MHz-3 GHz at 22 • C, in the surfactant concentration range 29.8-524 mM, explored for the first time above 104 mM. The micellar contribution to dielectric spectra was analyzed according to three models containing, respectively, a single Debye relaxation, a Cole-Cole relaxation and a double Debye relaxation. The single Debye model is not accurate enough. Both Cole-Cole and double Debye models fit well the experimental dielectric spectra. With the double Debye model, two characteristic relaxation times were identified: the slower one, in the range 400-900 ps, is due to the motion of counterions bound to the micellar surface (lateral motion); the faster one, in the range 100-130 ps, is due to interfacial bound water. Time constants and amplitudes of both processes are in fair agreement with Grosse's theoretical model, except at the largest concentration values, where interactions between micelles increase. For each sample, the volume fraction of bulk water and the effect of bound water as well as the conductivity in the low frequency limit were computed. The bound water increases as the surfactant concentration increases, in quantitative agreement with the micellar properties. The number of water molecules per surfactant molecule was also computed. The conductivity values are in agreement with Kallay's model over the whole surfactant concentration range.

Time Domain Dielectric Spectroscopic Studies of Potassium Oleate and Cetyl Pyridinium Chloride in Acetate Buffer Solution

“…It was argued that the experimental relaxation time reflects the average dynamics of water molecules in the micelles. These assignments are in consistent with the more recent results from experiments . It is presumed that changes observed in the relaxation time of hydration water for the two surfactants are due to the different level of hydration of micelles.…”

“…The frequency dependent complex permittivity spectra of surfactants in aqueous buffer solution show up as peaks close to 1.4 GHz and 14.5 GHz, respectively in the corrected loss spectra. Both surfactant solutions exhibit a significant rise of dielectric constant with increasing concentration . As a common wisdom, the dominant process ( γ ) near 14.5 GHz which corresponds to the relaxation time of τ γ ≈ 8.5 ps is assigned to free water relaxation.…”

“…The other peak near 1.4 GHz (δ 2 ) which corresponds to the relaxation time of τ δ ≈ 55 ps for CPC and τ δ ≈ 70 ps for PO is assigned to the water hydrating the micelle. Lanzi et al attributed the relaxation time of 120 ps for SDS to the interfacial bound water. Deepu K. George et al observed the cooperative molecular dynamics in hydrated layers of DPC micelles.…”

Complexation of macrocyclic ligands in ionic SDS micellar solutions: A dielectric spectroscopy investigation

“…These authors analyzed the dielectric spectra by means of a superposition of a Cole-Cole or Debye relaxation functions for the micellar component and by a simple Debye relaxation function for the aqueous component, keeping its dielectric parameters (relaxation time and dielectric strength) fixed to the ones reported in literature [29]. The values of the parameters we obtain from our fitting procedure for SDS micellar solutions are in very good agreement with these previous data [25,28]. These two relaxations, characterized by frequencies of the order of some tens of MHz and some hundreds of MHz, respectively [26,27], are attributed to fluctuations of counterions at the micelle-aqueous phase interface.…”

“…The dielectric relaxation behavior of aqueous SDS solutions at 25 o C was previously investigated by Barchini and Pottel [25] in the frequency range between 1 MHz and 30 GHz and by many other authors [26][27][28]. These authors analyzed the dielectric spectra by means of a superposition of a Cole-Cole or Debye relaxation functions for the micellar component and by a simple Debye relaxation function for the aqueous component, keeping its dielectric parameters (relaxation time and dielectric strength) fixed to the ones reported in literature [29].…”