Method for Studying Micelle Formation Using Size Exclusion Chromatography, Light Scattering, and UV Spectroscopy

Abstract

A method for the direct observation and measurement of micelles has been developed. At higher solution concentrations, multi-angle laser light scattering in batch mode was used, and at lower concentrations, Size Exclusion Chromatography with dual detection (Light Scattering and Refractive Index) was employed. Micelle formation for PEG and a copolymer of PEG with lactate and acrylate groups (8KLX) were observed using this method. The critical concentrations for the micelle formation were determined for the PEG and 8KLX macromolecules. Confirmation of the results was obtained using an independent spectrophotometric method.The phenomena of macromolecular association, complexation and micelle formation occupy a very important place in polymer and biopolymer chemistry. All of these phenomena are strongly dependent upon the concentration of the macromolecules in solution. The size and number of the macromolecular aggregates in solution increase with increasing concentration.Size Exclusion Chromatography (SEC) l\l is one of the most reliable methods for the determination of molecular weight and size of macromolecules in solution. In principle, this method may be used for the corresponding characterization of macromolecular aggregates. However, aggregation normally occurs at concentration levels higher than those used in SEC. Common SEC solute concentrations range from 1% to 5%, and after passing through the chromatographic system, are diluted by a factor of 30-50. As a result, when the solutions reach the detector cell, their concentration is less 0.1%. Frequentiy, such concentration levels are not enough for aggregate formation, and direct determination of molecular weights and sizes of these macromolecular aggregates becomes impossible.The use of SEC with two detectors on line (multi-angle light scattering, LS, and refractive index, RI) affords a new opportunity to observe these aggregates directly in