Migration Of Micelles Research Articles

Soret effect in lyotropic liquid crystal in the isotropic phase revealed by time-resolved thermal lens

We demonstrate the Soret effect in a lyotropic liquid crystal at different temperatures across the isotropic phase detected by the time-resolved thermal lens technique. We investigate thermo-optical and mass diffusion properties of the sample and present quantitative characterization of Soret, mass and thermal diffusion coefficients. The results reveal that the temperature gradient induced in the experiments causes the migration of micelles from hotter to colder regions in the sample. The increase of the mass diffusion coefficient with temperature is related to the decrease of the radius of the micelles in the solution.

Kinetic Study of Solute Permeation across Surfactant Micelle/Bulk Solvent Interface by Moment Analysis - Chromatographic Capillary Electrophoresis (MA-CCE)

Abstract We applied moment analysis (MA) with chromatographic capillary electrophoresis (CCE) to the analytical determination of rate constants (kin and kout) of solute permeation at the interface between a bulk solvent and surfactant micelles. CE experiments were carried out in the MEKC system using thymol and sodium dodecylsulfate (SDS) as the solute and surfactant, respectively, under CCE conditions. In CCE mode, experimental conditions are controlled so that the migration of micelles, which dissolve single or plural solute molecules, is stopped in the axial direction of a capillary. Only solute molecules migrate in the capillary and are detected to record elution peak profiles. The mass-transfer kinetics of solute molecules in the capillary are determined from the elution peak profiles by the MA theory. The values of kin and kout were respectively determined as 1.5 × 10−6 and 2.6 × 10−9 m s−1 for the permeation of thymol molecules at the interfacial boundary of SDS micelle. It was demonstrated that MA-CCE was effective for the kinetic study of solute permeation across the interface between a bulk solvent and spherical molecular aggregates, e.g., surfactant micelles.

On the analytical use of the Soret-enhanced thermal lens signal in aqueous solutions

The ability of micelles or polymers to affect the thermal lens response in aqueous solutions has been investigated. It is shown that the bulk thermo-optical properties of water, and consequently the pure thermal lens signal, are only slightly changed upon the addition of macromolecular species. On the contrary, the Soret effect produced by migration of micelles or polymers in the thermal gradient can significantly enhance the probe beam signal. However, the Soret contribution depends on the measurement time scale and on the relative concentrations of both the analyte and the macromolecular species. A careful analysis of the experimental data is therefore required when an analytical use of the Soret effect is considered as well as when thermo-optical parameters of such solutions are derived from the photothermal signal.

Towards a general approach for the impurity profiling of drugs by micellar electrokinetic chromatography.

A general micellar electrokinetic chromatographic (MEKC) strategy for the impurity profiling of drugs was developed involving a sodium dodecyl sulfate (SDS) and a cetyltrimethylammonium bromide (CTAB) MEKC system. With this combination, in principle, each sample component passes the detector in at least one of the two MEKC systems provided that separation buffers of the same pH are used in both systems. In order to select the proper MEKC systems, the electroosmotic flow (EOF) and micelle migration time (t(mc)) were determined for separation buffers of several pH values, containing various amounts of surfactant and organic modifier. The selectivity of the MEKC systems was studied using a mixture of compounds with a wide range of physico-chemical properties. The final selection of two adequate MEKC systems for this approach was based on the requirements that the t(mc) (i.e., analysis time) of both systems was below 20 min and that the t(mc)/t(eof) ratio was above 3 or 2 for the SDS and CTAB system, respectively. Furthermore, the systems should provide high efficiency, exhibit differences in selectivity and use moderate concentrations of modifier and surfactant, so that, if needed, further optimization is possible. The selected MEKC systems contained 60 mM SDS or 10 mM CTAB, respectively, in a phosphate buffer (pH 7.5) with 10% acetonitrile. Some test compounds with extreme mobilities were used to demonstrate the suitability of the MEKC approach to detect each component of a sample. The potential of the proposed MEKC combination for impurity profiling was demonstrated by the analysis of fluvoxamine with several impurities at the 0.1% level.