Aggregation and surface properties of synthetic double-chain non-ionic surfactants in aqueous solution

Double-chain non-ionic surfactants have been synthesized with the general formula 2CnMPEG750, where n is the number of carbons in the alkyl chains and 750 is the molecular weight of the monomethoxypolyoxyethylene (MPEG) head group. The aggregation and surface properties in dilute aqueous solution (< 1.0% w/w) of surfactants with n = 8, 10 and 12 have been determined. Each of the surfactants formed clear, foaming, non-birefringent solutions. Total-intensity light scattering indicated the presence of micelles with aggregation numbers of 36, 68 and 74 for the 2C8, 2C10 and 2C12 surfactants, respectively, whereas photon-correlation studies yielded radii, assuming spherical aggregates, of 59-103 A. Surface-tension measurements gave critical micelle concentrations for the surfactants in the range 1.15-7.24 x 10(-6) M; these, as expected, decreased when the number of carbon atoms in the alkyl chains was increased. Such studies are important in the design of new surfactants as vehicles for drug delivery because it is imperative to be able to predict the type of aggregate formed by a surfactant.