ИСТИНА

The experimental researches of the micelle transformations to microemulsions are of great interest not only from scientific point of view, but also of their importance in practice because of their application in pharmacology, food and cosmetic industry, oil recovery and ecology. In recent works [1] we have shown the modifying action of solubilizate (toluene) on micelles of nonionic polyoxyethylenated surfactant Tween-80 (20 oxyethylene (EO) units per molecule) in aqueous solutions, resulting in the transition from micelles to microemulsions of the first type according to Winsor classification. In order to clear the mechanism of these structural transitions in ternary systems Tween-80-toluene-water the toluene concentration influence on the parameters of micellar and microemulsion systems (molar solubilization ratio - MSR, hydrodynamic radius - Rh, aggregation number - N, the amount of water molecules per EO segment - nW/EO, and microenvironment of solubilized toluene) were studied in this work. The concentration of toluene in the investigated systems was determined by refractometric technique and UV-spectroscopy. We suggested the special procedure based on spectrophotometry of extremely diluted microemulsions [2] for estimation of MSR micellar systems to toluene. To determine Rh and N the methods of dynamic and static light scattering were correspondently used and the combination of these methods was used for nW/EO estimation. The nature of the toluene microenvironment in miselles and microemulsions is examined by UV- and NMR-spectroscopy. It was shown that when concentration ratio of toluene and surfactant Ctol/Csurf <0,7 the solubilizate is localized inside hydrophobic core of micelles, at Ctol/Csurf >1 the toluene begins to accumulate in oxyethylene part of micelles. It was found that for micelles without solubilizate the value of nW/EO is 5,7 water molecules per EO segment and for micelles with toluene (MSR=1,1 mol toluene per mol micellar surfactant) nW/EO value is 8,8. The discovered increasing of Tween-80 micelle hydration degree with solubilizate is probably connected with changing of poly(ethylene oxide) chains conformation. The further increasing of toluene solubilization results in micelles enlarge (Rh=3,6nm) up to microemulsion droplets sizes (Rh=11,2nm) and increasing of aggregation numbers (N=36 for micelles, N=681 for microemulsions). It was shown with NMR-spectroscopy that toluene is localized in OE part of microemulsion droplets. Thus the structural transitions of micellar systems into microemulsions under solubilizate effect and their mechanism are determined by the condition of surface of self-organized molecular aggregates. This work is supported by the Russian Found of Basic Researches, project No. 01-03-32408. [1] M.V.Poteshnova, N.M. Zadymova, Vestnik MGU, ser 2, khimiya, 43(2002) 185. [2] N.M. Zadymova, N.V. Karmasheva, Kolloidnyi Zhurnal, 64(2002) 449.