ISSN 1061-933X, Colloid Journal, 2006, Vol. 68, No. 6, pp. 757–760. © Pleiades Publishing, Inc., 2006. Original Russian Text © A.G. Ramazanova, V.V. Korolev, E.V. Ivanov, 2006, published in Kolloidnyi Zhurnal, 2006, Vol. 68, No. 6, pp. 829–832. 757 INTRODUCTION It has been shown earlier [1, 2] that, upon the adsorption of oleic, linolic, and linolenic acids on finely dispersed magnetite from solutions in n-hexane and carbon tetrachloride, molecules of solute and solvent compete for the active sites on the adsorbent surface. In this case, the decisive effect on the adsorption of afore- mentioned unsaturated fatty acids (UFAs) is imparted by the number of double bonds in their molecules, as well as by the desolvation of adsorbent surface and adsorbate molecules. With allowance for the latter cir- cumstance, the conclusion drawn in [2–4] that, upon the passage from one solvating medium (n-C 6 H 14 ) to another (CCl 4 ), the inversion occurs in the sequence of the position of isotherms of adsorption on magnetite for this series of acids, seems to be most interesting. For example, upon the adsorption from carbon tetrachlo- ride (hexane) solutions, the values of limiting adsorp- tion a m , characteristic energy of adsorption E a , and vol- ume of porous space V p of magnetite increase (decrease) in the oleic, linolic, and linolenic acids series. Evidently, the effect of the nature of apolar solvent on the processes occurring on the ferroparticle surface is directly related with the specific features of intermolecu- lar interaction between the adsorbate and solvation envi- ronment. At a macroscopic level, these features are exhibited in the thermodynamic characteristics of disso- lution (solvation) of UFAs. The most important among them are the volumetric or packing effects that depict structural changes in a solvent due to the desolvation of acid molecules and the formation of UFA–n-C 6 H 14 (CCl 4 ) solvation complexes with different sizes (vol- umes) and compositions [5, 6]. The elucidation of corre- lations in changes of adsorption and partial volumetric characteristics of studied UFAs in n-hexane and tetra- chloride should promote the understanding of processes that are responsible for the stability and efficiency of dif- ferent magnetite-containing colloidal systems. In this work, we analyzed volume effects of dissolu- tion (solvation) of oleic, linolic, and linolenic acids in n-C 6 H 14 and CCl 4 at 298.15 K to establish interrelations between these thermodynamic parameters and adsorp- tion properties of studied UFAs on the surface of finely dispersed magnetite. RESULTS OF EXPERIMENTS AND CALCULATIONS We used n-hexane, high purity grade, and tetrachlo- ride, special purity grade, additionally purified from admixtures by the corresponding procedures [7, 8]. The purity of solvents was verified by the IR spectrometry (in cells made of CaF 2 ) and densimetry. Densities of sol- vents (n-C 6 H 14 and CCl 4 ) prepared for experiments were equal at 298.15 K to 0.655195 and 1.584995 g cm –3 , respectively, that is well consistent with reliable pub- lished data [9]. Oleic, linolic, and linolenic acids (with general structural formula C 18:n , where n is the number of C=C bonds in cis-9-, cis-6-, and cis-3- positions with respect to “end” methyl group) were purified in accordance with the procedure described in [3] to the residual con- tent of impurities of no higher than 0.1 wt %. The qual- ity of UFAs was estimated by the integral intensity of IR absorption bands in thin films on plates made of KRS-5. Data on the properties and structure of acids studied are listed in Table 1. ρ 1 * Interrelation between Parameters of Isotherms of Adsorption of Fatty Acids on the Surface of Magnetite and Volume Effects of Their Dissolution in n-Hexane and Carbon Tetrachloride at 298.15 K A. G. Ramazanova, V. V. Korolev, and E. V. Ivanov Institute of Chemistry of Solutions, Russian Academy of Sciences, ul. Akademicheskaya 1, Ivanovo, 153045 Russia Received March 15, 2006 Abstract—The adsorption of unsaturated C 18:n fatty acids on magnetite and volume effects of their dissolution in n-hexane and carbon tetrachloride are studied. It is established that an increase in the values of limiting adsorption of a series of oleic, linolic, and linolenic acids corresponds to positive volume effects of their disso- lution in CCl 4 . Opposite picture of the adsorption behavior of studied acids in n-hexane corresponds to negative volume effects of the dissolution of the acids in this solvent. DOI: 10.1134/S1061933X06060135