Inner structure of oxyethylated diisononylphenol in water

Abstract
Micellar solutions of different concentrations (0.1-5% wt) of oxyethylated diisononylphenols (OEDNP) (C₉H₁₈)₂C₆H₄(OC₂H₄)_nOH with different mean numbers of ethylene-oxide (EO) groups (18, 20 and 24) were investigated by means of SAXS and DLS (and SANS for OEDNP-20). The mean hydrodynamic diameters (using DLS data) and equivalent uniform sphere diameter distributions (using the initial part of SAXS curves) were calculated. Both methods gave consistent results. The characteristic functions of micellar particles are quite similar for all investigated concentrations and numbers of EO groups. These results make clear that the micelles are very stable and can be refered to as spherical particles. Three maxima of characteristic functions persuade us to refuse the simple core - shell model and to propose a more complicated model of spherical particles with a hydrophobic core and two successsive covers (core - inner layer - outer layer). One of the two alkyl chains of the molecule from the internal layer is included into the core and another is directed outside in contact with the alkyl groups of the molecules from the outer layer and the EO groups of the molecules from the inner layer.