ИСТИНА

To work out colloid-chemical principles of the application of surfactant environmentally safe ultramicroheterogeneous dispersions to purify water from toxic hydrophobic pollutions (which solubility in water is several orderes higher than limiting permissible concentration) has become very actual now. A study was made of peculiarity of solubilization of aromatic compounds in aqueous solutions of nonionic surfactants at different temperatures as compared with ionic surfactants. Solubilizers: anionic surfactant (sodium dodecyl sulfate), cationic surfactant (cetylpyridinium chloride), nonionic surfactants (Tween-80, sorbitane (polyoxyethylene)monooleate, 20 oxyethylene groups per molecule and Neonol AF 9-12, para-nonylphenol polyoxyethylene, 12 oxyethylene groups per molecule), solubilizates: toluene and octane were used. Solubilization was determined by refractometric technique according to the rule of additivity of specific refractions at hydrocarbon optimum quantities, necessary to achieve solubilization equilibrium and by UV-spectroscopy. Molar solubilization ratio (MSR) of the spherical micelles (i.e. the number of moles of organic compound solubilized per mole of micellar surfactant) was calculated from equilibrium isotherms of solubilization. MSR in respect to octane was shown to be close to nonionic and ionic surfactants (MSR < 1), and octane reside in hydrophobic core of micelle. Several peculiarities for solubilization of toluene in aqueous solutions of nonionic surfactants in comparison with ionic surfactants were found: anomalous high value of MSR, increase in MSR with increasing oxyethylene part length of nonionic surfactant molecule, decrease in MSR for nonionic surfactants with increasing pH of solution, anomalous high value of MSR of nonionic surfactants for toluene in respect to octane. The analysis of these results and UV-spectroscopy data justify that toluene molecules are solubilized predominantly in oxyethylene part of nonionic surfactant micelles (for example, for Tween-80 ~ 85-90%), while insignificant portion of toluene is localized in micellar hydrophobic core. One can assume that protonic segments of oxyethylene chains interact with -electrons of an aromatic ring of the solubilizate. Partition coefficients of solubilizate between water and micellar pseudophase and thermodynamic functions of solubilization for investigated systems and for model systems discussed in literature (solubilizer - sodium oleate, which hydrophobic part of molecule is identical with hydrophobic part of Tween-80, solubilizates – benzene, ethylbenzene, octane) were calculated at temperature 293-333K. Solubilization was shown to possess entropy nature for investigated systems (|TS| > |H|) and increase with increasing temperature, independent of surfactant or solubilizate nature, i.e. independent of solubilizate preferential localization in hydrophobic core or in oxyethylene part of micelles. Free energy of transfer of CH-fragment of aromatic ring from water into hydrophobic core of micelle and from water into oxyethylene part of micelle was found to be close (CH ~ - 3,1kJ/mole).