Gel Filtration Chromatographic Study of Micellar Growth of Polyethylene Glycol Dodecyl Ethers

Abstract

Abstract The aggregation properties of polyethylene glycol dodecyl ethers (C12En; n=4, 5, and 8) are investigated with frontal gel (Sephadex G-200 and Sephacryl S-500) filtration chromatography (GFC) at 25 °C. At the trailing boundary of derivative GFC patterns for C12E5, unusual two peaks of micelles appear together with a peak of monomer. These micellar peaks are assigned to two types of micelle, viz., large (Rh=30 nm) and small (Rh=5 nm) micelles. As the C12E5 concentration is increased, the peak height for the large micelle increases more rapidly than that for the small micelle. Analysis of the centroid elution volume data by asymptotic theory reveals that the large micelle is the hexamer of the small micelle. This conclusion is supported by computer simulations of the GFC patterns, based on plate theory. In the derivative pattern of the trailing boundary for C12E8, the micellar peak becomes sharper and shifts to larger elution volume side, with increasing concentration. This pattern is well simulated with the assumption of linear concentration dependence of the micellar elution volume. Micelle size of C12E8 appears to remain constant. For C12E4, which is hydrophobically adsorbed on the gels, huge micelles coexist with a small amount of large micelles (Rh=33 nm).