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Aggregation of tetradecyltrimethylammonium bromide, TTAB, in mixed solvent systems containing ethylene glycol, EG, 1,2-propylene glycol, 1,2-PROP, 1,3-propylene glycol, 1,3-PROP, and tetraethylene glycol, TEG, has been investigated by employing conductivity and fluorescence methods. Gibbs energies of micellization were determined in order to evaluate the effects of the co-solvent on the aggregation process. Information about the influence of the organic solvent on the surfactant adsorption at the air-solution interface, on the micellar size and on the polarity of the micellar interfacial region was obtained by means of surface tension and fluorescence measurements. The study of the reaction methyl naphthalene-2-sulfonate + Br - in the water–glycol TTAB micellar solutions provided information about the characteristics of TTAB micelles as microreactors in the water–solvent binary mixtures.

Effects of ethylene glycol (EG) addition on the micellization and on the micellar growth in two aqueous didodecyl dicationic dibromide surfactant, 12-s-12,2Br- (s=2, 6) solutions, with the weight percentage of EG up to 50%, have been investigated. An increment in the amount of EG makes the aggregation process less spontaneous due to the water-EG mixtures being better solvents for the cationic dimeric surfactant molecules than pure water (solvophobic effect). Results show that C*, the surfactant concentration where the sphere-to-rod transition occurs, increases when EG content in the bulk phase increases. The amount of the organic solvent influences C* principally through the decrease in the hydrocarbon/bulk phase interfacial tension (air/bulk phase surface tension) caused by its presence. Changes in the aggregation number, in the micropolarity, in the microviscosity, and in the rheological behavior accompanying micellar growth were studied in the water-EG micellar solutions. Kinetic studies provide information about the characteristics of the dimeric micelles as microreactors. Kinetic data also show that an increase in the surfactant concentration leads to micellar growth.

Micellization of cetyltrialkylammonium bromide (alkyl = methyl, ethyl, propyl, and butyl) surfactants has been studied in various water–ethylene glycol, EG, mixtures. This study provided the opportunity of investigating how, for a given hydrophobic tail length, the head group size determines the effect of the addition of EG on the micellization process. Conductivity, surface tension, spectroscopic and steady-state fluorescence measurements were carried out. The influence of additional methylenes in the headgroups on the Gibbs energy of micellization, Δ G M ° , was found to derive from changes in the solvophobic Gibbs energy contribution and from variations in the electrostatic headgroups interaction contribution.

The influence of the addition of various amounts of ethylene glycol, EG, up to a weight percent of 50%, on the micellization process in N-hexadecyl, N-tetradecyl, and N-dodecyltrimethylammonium chloride micellar solutions was investigated. Conductivity, fluorescence, and spectroscopic measurements give information about changes in the cmc, in the micellar ionization degree, in the aggregation number and in the polarity of the interfacial region upon changing the percentage by weight of the organic solvent. These changes were compared to those found when ethylene glycol was added to the analogous alkyltrimethylammonium bromide aqueous micellar solutions, results showing that the effects caused by the presence of the organic solvent were practically independent of the counterion nature. This conclusion was in agreement with the micellar kinetic effects observed on the spontaneous hydrolysis of phenyl chloroformate in both water-ethylene glycol alkyltrimethylammonium bromide and chloride micellar solutions.

Micellization in water-ethylene glycol (EG) N-dodecyl, N-tetradecyl, and N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (SB3-12, SB3-14, and SB3-16, respectively) micellar solutions, with the weight percent of EG changing within the range 0-40, was studied by means of surface tension measurements. Information about the influence of the added EG on the aggregation number of the sulfobetaine micelles and on the polarity of the interfacial region of micelles was obtained through fluorescence and spectroscopic measurements. Surface tension measurements also provide information about the dependence of the surface excess concentration, the minimum area per surfactant molecule, the surface pressure at the cmc, and the standard Gibbs energy of adsorption on the added weight percent of the organic solvent. The Gordon parameter of the water-EG mixtures was also estimated by means of surface tension measurements. The thermodynamic and structural changes originated by the presence of EG control the micellar kinetic effects observed in the reaction methyl 4-nitrobenzenesulfonate + Br(-) occurring in the water-EG sulfobetaine micellar solutions. Information about the distribution of bromide ions between the bulk and micellar pseudophases was obtained through conductivity measurements. The kinetic micellar effects were quantitatively explained by using the pseudophase kinetic model.

The spontaneous hydrolysis of phenyl chloroformate was studied in water-ethylene glycol, EG, cationic, zwitterionic, nonionic, and anionic micellar solutions, the surfactants being tetradecyltrimethylammonium bromide, tetradecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate, tricosaoxyethylene glycol ether, and sodium dodecyl sulfate. The dependence of the observed rate constant on surfactant concentration as well as on the percentage by weight of EG, varying from 0 to 50 wt %, was investigated. Information about changes in the critical micelle concentrations, in the micellar ionization degrees (for ionic surfactants), in the aggregation numbers, and in the polarity of the interfacial region of the micelles upon changing the weight percent of EG was obtained through conductivity, surface tension, spectroscopic, and fluorescence measurements. A simple pseudophase model was adequate to rationalize the kinetic data. Micellar medium effects were explained by considering charge-charge interactions and polarity, ionic strength, and water content in the micellar interfacial region. The acceleration of the reaction produced by an increase in the amount of EG present in the mixture was explained on the basis of the substantial decrease in the equilibrium binding constant of phenyl chloroformate molecules to the micelles, resulting in the contribution of the reaction taking place in the bulk water-EG phase being more important. The weight percent of EG did not substantially influence the rate constant in the micellar pseudophase.

The kinetics of the oxidation of iodide by hexacyanoferrate(III) have been studied in different H2O-methanol, t-butanol, ethylene glycol glycerol, glucose or sucrose mixtures. Specific solvent effects are found as shown by the different trends in activation parameters and in the variations of the initial state and transition state chemical potentials as observed in different media. From the results of a multiple linear correlation, it is concluded that the kinetics are controlled by the ionizing power of the solvents, their relaxation times and the outer sphere reorganization energies.

The micellization and micellar growth of cationic dimeric surfactant propanediyl-alpha-omega-bis(dodecyldimethylammonium) bromide, 12-3-12,2Br-, have been studied in several water-organic solvent mixtures. The organic solvents were ethylene glycol, glycerol, 1,2-propylene glycol, 1,3-propylene glycol, acetonitrile, dioxane, formamide, and N,N-dimethylformamide. Results showed that the aggregation process was less favored in the binary mixtures than in pure water, which was explained by considering the influence of the solvophobic effect on micellization. The addition of organic solvents was accompanied by a diminution in the average aggregation number, Nagg, of the dimeric micelles. This diminution was due to the decrease in the interfacial Gibbs energy contribution, Delta G0interfacial, to the Gibbs energy of micellization caused by the decrease in the hydrocarbon/bulk-phase interfacial tension. As a result of the micelle size diminution, the concentration at which the sphere-to-rod transition occurred, C*, was higher in the mixtures than in pure water. Micelle size reduction is accompanied by a decrease in the ionic interactions and in the extra packing contribution to the deformation of the surfactants tails, making the formation of cylindrical micelles less favorable.

Micellization of three didodecyl dicationic dibromide gemini surfactants with different methylene spacer lengths, 12-s-12,2Br- where s = 3-5 methylene groups, has been investigated in water-ethylene glycol, EG, mixtures with weight percentages of EG up to 50%. Subsequently, effects of the addition of the organic solvent on the micellar growth of these surfactants and on the surfactant concentration range where sphere-to-rod transitions occur were studied by means of steady-state and time-resolved fluorescence quenching and spectroscopic measurements. Results show that an increase in the weight percentage of ethylene glycol added to aqueous 12-s-12,2Br- (s = 3-5) micellar solutions causes the sphere-to-rod transition to occur at higher surfactant concentrations than in pure water. The diminution in the average aggregation number, N(agg), when wt % EG increases, provoked by the decrease in the interfacial Gibbs energy contribution to DeltaG degrees M, is the main factor responsible for this observation. The decrease in N(agg) is accompanied by a decrease in the ionic interactions and the extra packing contribution to the deformation of the surfactants tails, making formation of cylindrical micelles less favorable. Besides, an increase in the solvent content and polarity of the interfacial region does not favor formation of direct ion pairs, decreasing the tendency of micelles to grow.