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Phase diagrams of alkyltrimethylammonium surfactants in some polar solvents

Abstract Phase diagrams of alkyltrimethylammonium surfactants and different polar solvents were determined or collected from the literature. Hexadecyltrimethylammonium bromide forms with water a solution phase L, a hexagonal liquid crystalline phase E, a cubic phase I, and a lamellar phase D, with increasing surfactant concentration. In glycerol, the same aggregation sequence was found. With ethylene glycol, the existence regions of the liquid crystalline phases were found to be considerably smaller. The alkyl chain length of the surfactant also influences the extensions of the liquid crystalline phases. With a shorter alkyl chain the size of the existence regions was found to decrease, in particular with ethylene glycol as solvent. The size of the existence regions for the liquid crystalline phases with hexadecyltrimethylammonium bromide and water, glycerol, formamide, ethylene glycol, and N-methylformamide, respectively, was correlated to the solvent/hydrocarbon interfacial tension. A high interfacial tension suggests a considerable solvophobic interaction which favors extensive surfactant aggregation. The interfacial tension decreases in the order water > formamide ≈ glycerol > ethylene glycol >N-methylformamide, the same sequence as for the size of the existence region of the hexagonal phase E.

Aggregation of tetradecyltrimethylammonium bromide in water, 1,2-ethanediol, and their mixtures

Abstract The formation of surfactant aggregates of tetradecyltrimethylammonium bromide in water, 1,2-ethanediol, and their mixtures was monitored by conductivity and density measurements. In addition, phase diagrams were determined for the systems. In water, the surfactant molality at the critical micellar concentration, CMC, is 4 mm, while, e.g., in a solvent mixture with a mass fraction of 0.40 of water and 0.60 of 1,2-ethanediol, the molality has risen to 20 mm. The phase diagrams reveal the formation of mesophases even in pure 1,2-ethanediol, showing that the surfactant aggregates in this solvent; however, no evidence for micelle formation in the solution phase was found. The decreasing sizes of the existence regions for the mesophases with increasing mass fraction of 1,2-ethanediol were found to correlate with the increasing molality at the CMC. The phenomenon is discussed in terms of the lowered solvophobic interaction; this has been directly monitored through measuring the interfacial tension between water-1,2-ethanediol mixtures and dodecane.

Hydrotropes - Performance Chemicals

Abstract The action of hydrotropes is reviewed emphasizing their influence in the formation of microemulsions, vesicle solutions, and other products involving surfactant association structures. It is demonstrated that the hydrotropes, the association structures of which, realistically, can only be described as trivial, actually, are powerful and sophisticated performance chemicals playing an essential role in complex applied formulations utilizing more composite amphiphilic association structures.

Temperature-dependent solubilization of hydrocarbon in a nonionic surfactant system with formamide

Abstract It has been demonstrated that systems containing a nonionic surfactant and formamide in certain cases display a lower consolute solution temperature, analogously to the corresponding aqueous systems. The solubilization of hydrocarbon in such solutions, containing tetraethylene glycol dodecyl ether as surfactant, has been investigated and is shown to be strongly temperature dependent. Three-phase regions in ternary systems formamide/hydrocarbon/tetraethylene glycol dodecyl ether exist in temperature intervals which, for a given surfactant, vary strongly depending on the hydrocarbon used. The trend for the intervals is similar to the trend for the aqueous systems: the larger the aliphatic hydrocarbon, the higher the temperature where the three-phase region occurs.

Surfactant aggregation in systems containing alkanolamines and fatty acids

Abstract The phase diagrams of six different alkanolammonium carboxylate-water systems have been determined. Their phase behavior differs from that of ordinary soaps, since there are large differences between the systems for varying alkyl chain lengths of the carboxylate. In addition, the chemical structure of the alkanolammonium counterion also effects the phase equilibria. For short alkyl chain carboxylates the liquid crystalline phases disappear (e.g., for the triethanolammonium octanoate) or decrease in extension (e.g., for monoethanolammonium octanoate), although the surfactant readily aggregates in solution. In contrast, long alkyl chain carboxylates behave like swelling amphiphiles with a low aqueous solubility and the immediate formation of a lamellar phase (e.g., for tri- and monoethanolammonium oleate). It is shown that the distribution between acid and soap causes these effects. The lower surface charge of the surfactant aggregates compared to that of ordinary soap micelles is also reflected in a lowering of the critical micellization concentration.

Interactions in phospholipid stabilized emulsion system

Abstract The interaction between a phospholipid stabilized triglyceride emulsion and a hydrophilic silica surface has been studied at varying pH and electrolyte content using ellipsometry. The adsorbed amount decreases with pH and increases with increasing electrolyte content in the emulsion, and this can be rationalized on the basis of the electrostatic interaction between the emulsion droplet and the surface. The layer thickness, however, is essentially independent of these parameters. In addition, the emulsion has been studied during turbulent shear conditions (applied mechanical stress), with the same variation of pH and electrolyte as in the adsorption experiments. A decrease in pH and an increase in electrolyte content, decreasing the repulsive interaction between the droplets, leads to a deterioration in emulsion stability with time.

The role of the solvent in sodium n-octanoate solutions studied by self-diffusion and nuclear magnetic relaxation measurements

Abstract Three-component systems containing water, sodium n-octanoate, and ethylene glycol, 1,2-butandiol, 1-butanol or ethylene glycol monobutyl ether have been investigated by means of 23Na and 2H NMR relaxation rate and chemical shift measurements as well as FT NMR pulsed gradient spin echo measurements of self-diffusion coefficients. All systems exhibit an increase in the 23Na relaxation rate at decreasing water content. The increase is most pronounced in the 1,2-butandiol system and least accentuated in the butanol system. 23Na chemical shifts indicate that the sodium ions remain fully solvated in ethylene glycol, i.e., no contact ion-pair formation occurs. The water self-diffusion coefficient is high in all systems and proportional to the water concentration. In the systems containing diols, the water and diol self-diffusion coefficients are approximately proportional to each other indicating that no partitioning of these components occur. For sodium n-octanoate dissolved in water/ethylene glycol mixtures, 23Na and 2H relaxation measurements have been performed at varying concentration of the surfactant and constant composition of the solvent. In a 80:20 (w/w) mixture of water and ethylene glycol only small differences could be seen in the 23Na relaxation compared with the pure water system indicating a similar aggregation behavior. In the pure ethylene glycol system, the increase in relaxation rate is discussed in terms of a more gradual and less cooperative aggregation process than in water.

Effect of cosurfactant structure on surfactant alkyl chain order in lamellar liquid crystals containing sodium n-octanoate

Abstract Phase diagrams have been determined for the ternary systems, water/sodium n -octanoate, and 2-pentanol or 3-pentanol, and compared with the corresponding phase diagram for the system containing 1-pentanol. The extension of the lamellar phase is correlated to the order parameters for the methylene segments in the surfactant alkyl chain, which have been obtained with 2 H NMR. The order parameters, as well as the extension of the lamellar phase, are found to decrease in the order 1-pentanol > 2-pentanol > 3-pentanol, i.e., a bulkier alkyl group of the cosurfactant gives a more flexible and disordered alkyl chain and a destabilization of the lamellar phase.

Aklyl Chain Order Parameters and Phase Diagrams for Systems Containing Sodium n-Octanoate, Water, and Different Alcohols

Abstract Lamellar liquid crystalline phases containing sodium n-octanoate, water, and an alcohol have been studied by means of 2H NMR. Order parameters have been determined for the octanoate alkyl chain in systems containing ethanol, 1-propanol, 1-butanol, 1-pentanol, benzyl alcohol or 1, 8-octandiol. The straight chain alcohols yield decreasing octanoate order parameters with decreasing chain length. With 1, 8-octandiol the octanoate order parameters are somewhat smaller than with 1-propanol, indicating quite flexible octanoate hydrocarbon chains. Using mono-deuteriated benzyl alcohol. C6H5CHDOH, the SCD as well as the SHD (= SHH ) order parameters were determined in the same measurement. A typical measurement yields |S HD|-|SCD | = 0.04 ± 0.04, where the error estimation includes the uncertainties in the quadrupole and the magnetic dipole-dipole coupling constants. It is stressed that in order to ascertain a significant difference between SHH and SCD , it is necessary to know the coupling constants with...

Preparation and characterization of surface active erucic acid derivatives

Nonionic, cationic and anionic surfactants, derivatives ofcis-13-docosenoic acid (erucic acid), have been prepared and characterized, and their performance has been evaluated and compared with the corresponding derivatives of fatty acids with shorter alkyl chain length.Nonionic erucic acid ethoxylates give a solution behavior anticipated from the hydrophilic-lipophilic balance of the molecule; however, the increased molecular size as compared to ordinary surfactants results, e.g., in higher temperature stability of the surfactant aggregates. Anomalous solution behavior was found and investigated for anionic surfactants, triethanolammonium salts of erucic acid, and some shorter homologues. The effects are discussed in terms of the acid-base equilibria of the alkanolammonium counterion and the acid, together with effects due to the molecular size of the counterion.