Study by Small-Angle Neutron Scattering of Sodium Dodecyl Sulfate Micelles with the Macrocyclic Ligand [2.2.2]Cryptand

Abstract

The addition of [2.2.2]cryptand (C222) to sodium dodecyl sulfate (SDS) micelles in aqueous solution is studied by small-angle neutron scattering (SANS). Hydrogenated and perdeuterated SDS micelles with 8% (wt/wt) concentration have been studied in the presence of 0.5, 1.0, and 1.5 mole ratio C222/surfactant. SANS analysis was performed using a two-shell model for the micelle form factor (core plus interfacial layer) and a screened Coulomb interactive potential for the interparticles potential. For both deuterated and hydrogenated surfactant, C222 ligand complexes the sodium micellar counterion and is mainly located at the interface partially screening the micelle surface charge. Counterion complexation produces, as compared to pure SDS micellar solutions, an increase of the interfacial layer thickness and a decrease of the micellar surface charge, of the contact potential, and of the average aggregation number. We report a detailed analysis of the micelle structure and intermicellar interaction potential.

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

“…This investigation revealed that, in spite of the good solubility of the cryptand in water, C222 molecule is partitioned at micellar surface and penetrates below the polar head group region [14]. Interestingly, C222 molecule is able to decrease the effective micellar charge and the average aggregation number, as well as to increase the shell thickness.…”

“…According to small-angle neutron scattering [SANS] measurements [14,21], both ligands solubilize at the micellar surface with the effect of increasing the thickness of the polar head region at the micelle interface, accompanied by a decrease of both the micellar surface charge and the micellar aggregation number.…”

“…The size and the aggregation number of the micelles are decreased, as well as the thickness of the interfacial micellar layer [5,14]. In the case of C222, the interfacial adsorption of the ligand is driven by the hydrophobic repulsion of the exposed surfaces in the presence of an intermolecular repulsive electrostatic contribution due to the sodium ion trapped inside the ligand cage [14]. The dielectric spectra of the LD-micelles appear modified as a consequence of the reorganization of the interfacial micellar layer in terms of surface charge, size and counterion mobility.…”

“…Recently, the behavior of sodium and lithium dodecyl sulfate micelles [14] upon the complexation of counterions by macrocyclic [2.2.2] cryptand was studied by small-angle neutron scattering. This investigation revealed that, in spite of the good solubility of the cryptand in water, C222 molecule is partitioned at micellar surface and penetrates below the polar head group region [14].…”

“…In this work, we investigated the radiowave dielectric properties of a two-component aqueous ionic micellar solutions of SDS in the presence of two macrocyclic ligands, [2.2.2]cryptand [C222] and 18-crown-6 [18C6] ether, which are recognized to be specific complexing agents for sodium [20] and are able to modify the structural and the dynamic properties of the SDS micellar system [14,21].…”