ИСТИНА

PARAMETERS OF SELF-ASSEMBLED MOLECULAR AGGREGATES OF NONIONIC SURFACTANTS IN THE TERNARY SYSTEMS TWEEN-80 – WATER - TOLUENE. Poteshnova M.V., Zadymova N.M., Rudelev D.S. Department of Chemistry, Moscow State University, Leninskie Gory, 119899 Moscow, Russia, poteshnova@colloid.chem.msu.ru, zadymova@colloid.chem.msu.ru The elucidation of mechanisms of modifying effect of solubilizates of different nature (aliphatic and aromatic hydrocarbons, oleophilic surfactants, perfluorocarbons and etc.) on self-organized molecular ensembles (micelles) of hydrophilic surfactants in aqueous solutions is the basic problem of colloid chemistry. Earlier in our experiments [1] the influence of solubilizate (toluene) on structural transformations of Tween-80 micelles in aqueous solutions into opalescent microemulsions of first type according to Winsor classification was found. In this work 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) was studied. MSR is number of moles of toluene per mole Tween-80 in surfactant molecular aggregate (mol/mol). 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 for estimation of MSR of transparent micellar systems to toluene [2]. To determine Rh and N the methods of dynamic and static light scattering were correspondently used and the combination of these methods was also used for nW/EO estimation. The nature of the toluene microenvironment in micelles and microemulsions was examined by UV- and NMR-spectroscopy. It was found that for Tween-80 micelles without solubilizate Rh = 3,6 nm, N = 36 and the value of nW/EO is 5,7 water molecules per EO segment. The increasing of toluene solubilization (up to MSR=1,1 mol/mol) results in increasing of Rh up to 4,7 nm, and N up to 40, nW/EO up to14,5. In microemulsions saturated by toluene MSR=7,7 mol/mol and Rh= 11,2 nm. Aggregation number for the last case was calculated on assumption that nW/EO =14,5 and it was N=489. It was shown that toluene localized in micellar hydrophobic core when the solubilizate contents were low and both in hydrophobic core and oxyethylene shell of surfactant molecular aggregate when these contents were high. On the base of received data the mechanism of transformation of micellar systems into microemulsions under the solubilizate influence was suggested. This work is supported by the Russian Fond 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.