Natalia A. Smirnova

Self-assembly in aqueous solutions of imidazolium ionic liquids and their mixtures with an anionic surfactant

Experimental data on micellization in aqueous solutions of 1-alkyl-3-methylimidazolium salts [C(n)mim]X and their mixtures with sodium dodecyl sulfate (NaDS) are reviewed. New results (the critical micelle concentration and enthalpy of micellization) are presented for mixtures of [C(4)mim]PF(6), [C(6)mim]BF(4), [C(6)mim]Br and [C(10)mim]Br with NaDS. Our data cover a wide range (from 0 to 0.9) of solvent-free based mole fractions of ionic liquid (IL). Even very small addition of ILs substantially decreases the cmc of NaDS due to the combined effect of electrostatic and hydrophobic interactions, and formation of mixed micelles. It is shown that the quasichemical aggregation model by Nagarajan and Ruckenstein may be successfully applied to aqueous solutions of long-chain ILs and their mixtures with NaDS. The local structure of micelles is obtained from all-atom MD simulations for [C(n)mim]Br and [C(n)mim]X+NaDS in aqueous medium.

Thermodynamic properties of pure fluids and solutions from the hole group-contribution model

The hole lattice model for pure fluids and fluid mixtures of molecules differing in size and shape is presented. Orientational effects are taken into account with the aid of the quasichemical approximation. The equation of state and relations for the wide range of thermodynamic quantities are deduced. The calculations are made for pure n-alkanes, n-alkanols, acetic acid, H2S, H2O, for binary mixtures of these substances with n-alkanes and for ternary hexaneheptaneoctane and hexanepropanoldecanol solutions. Systems under elevated pressures (up to 100 atm) are taken into consideration. The homologue series are treated in the group-contribution approach.

Ionic liquids as surfactants

Problems of self-assembling in systems containing ionic liquids (ILs) are discussed. Main attention is paid to micellization in aqueous solutions of dialkylimidazolium ILs and their mixtures with classical surfactants. Literature data are reviewed, the results obtained by the authors and co-workers are presented. Thermodynamic aspects of the studies and problems of molecular-thermodynamic modeling receive special emphasis. It is shown that the aggregation behavior of dialkylimidazolium ILs is close to that of alkyltrimethylammonium salts (cationic surfactants) though ILs have a higher ability to self-organize, especially as it concerns long-range ordering. Some aspects of ILs applications are outlined where their common features with classical surfactants and definite specificity are of value.

VLE modelling for aqueous systems containing methyldiethanolamine, carbon dioxide and hydrogen sulfide

Abstract A method is proposed for modelling vapor–liquid equilibria in ternary aqueous systems containing acid gas and alkanolamine with an equation of state describing both phases. A hole quasichemical model is modified with due regard for chemical reactions and electrostatic interactions in the liquid solution. The modelling was carried out for the carbon dioxide– N -methyldiethanolamine (MDEA)–water and hydrogen sulfide–MDEA–water systems in the temperature range from 313 to 413 K at pressures up to 5 MPa and amine concentrations up to 4 mol/kg of water. Satisfactory agreement with the experimental data was obtained.

Micellization in solutions of ionic liquids

This review is devoted to the problem of aggregation in solutions of ionic liquids (ILs) and the results of relevant studies published in recent years. To a great extent, this problem remains urgent, because the ability to self-organization extends the possibilities of the practical application of ILs. The fields of IL application in which their amphiphilicity is of importance in connection with widening the spectrum of objects under investigation are discussed. The results of studying the aggregation behavior of different systems are briefly considered, including IL solutions in water, water-organic, and organic solvents; aqueous solutions of IL-classical surfactant mixtures; and solutions in which one IL plays the role of a solvent, while another IL or a classical surfactant serves as an amphiphilic solute. Some experimental results are analyzed, and thermodynamic aspects of micellization and problems of molecular-thermodynamic simulation are discussed.

Fluid phase equilibria in water : natural gas component mixtures and their description by the hole group-contribution equation of state

Abstract Victorov A.I., Fredenslund Aa. and Smirnova N.A., 1991. Fluid phase equilibria in water:natural gas component mixtures and their description by the hole group-contribution equation of state. Fluid Phase Equilibria, 66: 187-210. Experimental data on fluid phase equilibria in binary mixtures of water with typical natural gas and oil components (light and heavy alkanes, nitrogen, hydrogen sulfide, carbon dioxide) have been examined and the phase behavior of these mixtures over wide ranges of temperature and pressure is reviewed. A quasi-chemical group-contribution hole model is used for calculating the phase equilibria in these systems. With few exceptions the model predicts correctly the basic types of phase behavior and, except for gas-gas equilibria, the accuracy for all the binaries and two multicomponent aqueous mixtures tested is satisfactory.

Description of asphaltene polydispersity and precipitation by means of thermodynamic model of self-assembly

A thermodynamic approach describing the precipitation of asphaltene materials from petroleum fluids as a consequence of aggregate break-up is presented. The aggregation equilibrium for asphaltenes and resins is considered along with the bulk-phase equation of state (EOS) to account for the effects of pressure and solvents on the thermodynamic behavior of asphaltene dispersions. Polydispersity of asphaltene aggregates is taken into account. The effect of the resin molecular shape on the size distribution is considered. Relation between the shape factors and elastic constants of the resin shell of the aggregates is given. Precipitation curves for several real crude oil mixtures are calculated and structural characteristics of the aggregates are estimated. Comparison with the experimental data shows that the results are reasonable.

Lattice model for the surface region of solutions consisting of different-sized molecules with orientation effects

Abstract Smirnova, N.A., 1978. Lattice model for the surface region of solutions consisting of different-sized molecules with orientation effects. Fluid Phase Equilibria , 2: 1–25. A multilayer lattice model for the surface region of solutions consisting of different-sized molecules with orientation effects is developed. The system is treated in the grand canonical ensemble on the basis of the quasi-chemical approximation. The results relate to the mixtures of monomers + flexible r -mers, where all r segments of r -mer may be different and the surface of monomer molecules and r -mer segments may be inhomogeneous (thus, the systems with polar components, associated solutions among them, are in the range of applicability of the model). The monomer + r -mer system is described based on the modified model for the multicomponent system formed by monomeric particles with strong directed interactions. Equations for the concentration profile and for the average molecular orientations, with respect to the surface, are derived; the formulae for the adsorption and surface tension are given. The surface properties calculated on the basis of the model for three monomer + dimer systems are in satisfactory agreement with the experimental data. The entropy contribution to the surface tension of pure r -mer composed of identical segments is reported for r = 2, 4, 6, 8, 12 and for different lattice parameters. The model can be generalized to mixtures of r -mers + l -mers.

Thermodynamic study of the micellar solution — Solid surfactant equilibrium

Abstract The temperature-composition dependence along the Krafft boundary in surfactant-water systems and the effect of the third component on the surfactant precipitation temperature are analyzed on the basis of strict thermodynamic relationships and using approximate models (the ideal monodispersed micellar solution approximation, the pseudo phase separation model). As it follows from the consideration a substantial decrease in the surfactant precipitation temperature (ΔT) may be observed on addition of light amphiphilic substances forming mixed micelles with the basic surfactant, the distribution coefficient between the micelles and the aqueous surroundings being an important characteristic of an additive. Regularities in the dependence of the ΔT-effects on the third component chemical nature and on the mixture composition are discussed. The model approaches are illustrated in application to the N-dodecanoyl-N-methylglycamine-water system and for the system containing n-butanol as the third component. For the ternary system the concentration dependence of the alcohol activity coefficient in the aqueous pseudo phase was taken into account with the help of the UNIFAC model, this dependence influencing seriously the calculated results. The estimated ΔT-effects are in a satisfactory agreement with the experimental data, an information on the mixed micelles composition is drawn from the calculations.

Phase equilibria modeling by the quasilattice equation of state for binary and ternary systems composed of carbon dioxide, water and some organic components

Abstract The hole lattice quasichemical group-contribution model (HM) has been applied to described liquid-liquid, liquid-liquid-vapour and vapour-liquid equilibria at elevated and high pressures in binary and ternary mixtures containing CO 2 , water, alkanols, paraffinic and aromatic hydrocarbons. An estimation of the concentration of alkanol monomers in the binaries with CO 2 has been performed. The results of modeling by the HM EOS and the Associated Perturbed Anisotropic Chain Theory (APACT) are compared. In most cases both EOS give satisfactory agreement with experimental data.