Micellar Properties of Nonionic Surfactant Tween 40® in Water: Small-Angle X-Ray Scattering Study†

Marija Bešter-Rogač
Faculty of Chemistry and Chemical Technology, University of Ljubljana, SI-1000 Ljubljana, Slovenia.
E-mail: marija.bester@fkkt.uni-lj.si

Abstract
The structural properties of a nonionic surfactant polyoxyethylenesorbitan monopalmitate (C₆₂H₁₂₂O₂₆, commercial names Tween 40^®, Polysorbate 40) in aqueous solutions in the temperature range between 15 and 45 °C have been studied by small-angle X-ray scattering (SAXS) technique. Low concentration experimental data were evaluated using the model free indirect Fourier transformation method (IFT), whereas at higher concentration a generalized indirect Fourier transformation method (GIFT) based on the simultaneous determination of intra- and interparticle scattering contributions was applied. It was found that in Tween 40^® aqueous solutions globular micelles with maximum distance within one particle of about 9 nm and radii of the hydrophobic core between 2.1–2.4 nm are present. The concentration and the temperature do affect neither the size nor the shape of the micelles considerably, however the presence of the non-spherical and/or elongated aggregates at higher concentrations at all temperatures could be assumed.

Keywords: Tween 40^®, water solutions, small-angle X-ray scattering, structural investigation