Evgenia A. Safonova

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.

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.

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.

Flow method based on cloud point extraction for fluorometric determination of epinephrine in human urine

A novel stepwise injection fluorometric method for the determination of epinephrine in human urine has been developed. In the current study, the stepwise injection analysis (SWIA) was successfully combined with on-line in-syringe cloud point extraction (CPE) and fluorometric detection. The procedure was based on the epinephrine derivatization in the presence of o-phenylenediamine followed by the preconcentration stage based on the CPE with the nonionic surfactant Triton X-114. After the phase separation into a syringe of the flow system, the micellar phase containing the epinephrine derivative was transported to a fluorometric detector. The excitation and emission wavelengths were set at 447xa0nm and 550xa0nm, respectively. The conditions of epinephrine derivatization and CPE have been studied. The calibration plot constructed using the developed procedure was linear in the range of 1·10(-11)-5·10(-7)xa0molxa0L(-1). The limit of detection, calculated as 3 σ of a blank test (nxa0=xa010), was found to be 3·10(-12)xa0molxa0L(-1). The proposed method was successfully applied for the determination of epinephrine in human urine samples.

Spatial networks in solutions of wormlike aggregates: universal behaviour and molecular portraits

The structures, phase behaviours and viscoelastic properties of solutions in which the growth of wormlike aggregates results in the reversible formation of a spatial network are considered. The general (independent of the molecular nature) regularities of equilibrium and dynamic characteristics of these solutions are considered and the mechanisms of manifestation of individual chemical portraits of particles are discussed. For solutions of wormlike micelles, the achievements of molecular thermodynamic theory are summarized. The potential applications of systems with controllable viscoelasticity are discussed. The bibliography includes 146 references.

The effect of acidity on micellization in dodecyldimethylamine oxide-sodium dodecyl sulfate aqueous mixtures

The effect of acidity on micellization in aqueous solutions of dodecyldimethylamine oxide-sodium dodecyl sulfate mixtures is studied. The CMC values are determined for acidic and nonacidified solutions at 50 °C and different ratios of two surfactants. The measurements are taken using potentiometry, conductometry, and tensiometry techniques. The CMC values are calculated within the framework of a quasi-chemical model of micellization modified with regard to the specific features of the system under consideration. Nonacidified solutions are modeled as a mixture of anionic and nonionic surfactants, whereas acidic solutions are treated as a mixture of anionic and cationic surfactants. The results of model calculations are in satisfactory agreement with the experimental data.

The structure and rheology of mixed micellar solutions of sodium dodecyl sulfate and dodecyldimethylamine oxide

The paper presents the results of viscosity measurements by capillary and rotational viscometry for aqueous solutions of sodium dodecyl sulfate and dodecyldimethylamine oxide and data on the hydrodynamic radii of aggregates obtained from dynamic light scattering measurements. A wide range of solution compositions predominantly containing dodecyldimethylamine oxide was studied at 308.15 K; the total content of surfactants was from 1 to 15 wt %, pH ∼ 8. Solution viscosities were found to change by several orders of magnitude when the composition of the system was varied; the dependence of viscosity on the ratio of surfactants passes through maximum and inflections. The dependences of viscosity and hydrodynamic radii on the ratio between two surfactants were similar in character. The conclusion was drawn that various nanostructural rearrangements occurred in the solutions studied and synergistic effects were observed.