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

Abstract

a b s t r a c t a r t i c l e i n f oThe influence of two different macrocyclic ligands, [2.2.2] cryptand (C222) and 18-crown-6 (18C6) ether on the structural properties of sodium dodecyl sulfate (SDS) micellar solutions has been investigated by means of dielectric spectroscopy, in a frequency range from 1 kHz to 50 GHz. The dielectric spectra of SDS micellar solutions present three relaxation processes. In the MHz region, two different relaxations centered at about 30 MHz and 300 MHz, can be attributed to the micelle contribution, while, close to 20 GHz, the contribution of the bulk water orientational polarization is observed. The addition of ligands causes relevant changes in the overall dielectric relaxation spectrum. Significantly, the relaxation processes corresponding to the micelle component are largely modified by the presence of the different ligands investigated both in the relaxation frequency and in the dielectric strength, thus indicating a reorganization of the charged interface of ligand-decorated micelles. These changes are briefly discussed in the light of the phenomenology observed in attractive colloids, where the presence of a long-range electrostatic repulsive interaction and a short-range attractive interactions results in the presence of a well-defined cluster phase.

Cluster Phases of Decorated Micellar Solutions with Macrocyclic Ligands

“…From dielectric spectroscopy measurements, − three relaxation processes have been found in SDS micellar solutions both with and without complexation with macrocyclic ligands, K222 and 18C6. Two relaxations are of micellar origin, at 30 and 300 MHz, as a result of the radial and lateral motions of the diffuse ion cloud around the micelle; the third relaxation, close to 20 GHz, corresponds to bulk water contribution .…”

Aggregation processes in micellar solutions: a Raman study

“…The study of aggregation processes is a topic of broad interest in the physical research, because the understanding of the interactions involved in the aggregation mechanisms is fundamental in many industrial processes, in medicine, and for modeling biological systems …”

“…Recently, the aggregation dynamics have been extensively investigated by theoretical, computational and experimental methods in different systems, ranging from chemical reactive mixtures, colloids, biomaterials . In colloidal charged particles suspension the aggregation can be induced by the addition of ligands: particles or polymers, that alter the charge distribution on the particle surface.…”