Size characterization of commercial micelles and microemulsions by Taylor dispersion analysis

In this work, Taylor dispersion analysis was applied to the measurement of micelles (or microdroplets) molecular diffusion coefficient in micellar (or microemulsion) systems based on neutral/anionic/cationic or zwitterionic surfactants. The choice of the micellar marker and the influence the surfactant/marker concentrations on this determination are studied. Experimental results are compared to those derived from the literature using other experimental techniques. Taylor dispersion analysis, experienced in narrow capillaries, was found to be an efficient and suitable method for micelle (or microdroplet) size measurement due to: the low sample consumption, the absence of filtration requirement of the sample, the broad range of size determination (with no lower limit down to angstroms), the simplicity of the protocol, the possibility to measure the viscosity of surfactant solutions in given conditions and the determination of the weight-average micelle hydrodynamic radius. Application to the size-characterization of commercial microemulsions (Gelucire(®) 44/14), used as an excipient in the pharmaceutical formulation, is provided with a comparison to DLS measurements. It was found that the polydispersity in size of the micelle did not influence the Gaussian peak shape of the taylorgram due to rapid surfactant exchange compared to the time-scale of the experiments (a few minutes).