Aqueous Solution-air Interface Research Articles

The adsorption of n-alkylammonium chlorides at the aqueous solution-air interface

Data on the surface tension of n-alkylammonium chloride solutions at various surfactant concentrations and at neutral and basic pH are given. By applying the Gibbs adsorption equation to the γ vs C curves, the adsorption isotherms of surfactants at the air-aqueous solution interface were obtained. These correspond to adsorption isotherms of the Langmuir type. Adsorbed monolayers obey the adsorption isotherm which is derived assuming immobility of the surfactants in the air-aqueous solution interface. This adsorption isotherm leads to consistent values for the standard free energy of adsorption. Finally, the hypothesis of the formation of stable complexes alkylamine-alkylammonium ion as responsible in determining the effect of pH on the interfacial density of these surface active substances is discussed.

Chemical structure and surface activity. 10. The effect of hydroxyl group configuration on the adsorption of 2-alkyl-4-(hydroxymethyl)-1,3-dioxolanes and 2-alkyl-5-hydroxy-1,3-dioxanes at the aqueous solution-air interface

Resultats de mesures des tensions superficielles des solutions aqueuses de cis- et trans-alkyl-2 (hydroxymethyl)-4 dioxolannes-1,3 avec alkyl=n-C 3 H 7 et n-C 5 H 11 et de trans-alkyl-2 hydroxy-5 dioxannes-1,3 avec alkyl=n-C 3 H 7 , n-C 5 H 11 et n-C 7 H 15 , a 293,2 K. Donnees sur l'influence de la structure chimique

Adsorption of Ionic Surfactants at the Aqueous Solution-Air Interface

Various factors (nature of surfactants, inorganic electrolyte addition, surfactant addition), determining the process of ionic surfactants adsorption at the aqueous solution-air interface are presented. Possibilities of application of the Butler-type isotherms of adsorption for describing these effects and predicting tbe surface properties of multicomponent solutions of ionic surfactants are also discussed.

On the adsorption of sodium alkylsulfonates at the air-aqueous solution interface

Data on the surface tension of sodium alkylsulfonate solutions at different surfactant concentrations and at 10, 20, and 30°C are presented. By applying the Gibbs adsorption equation to the γ vs C curves, the adsorption isotherms of alkylsulfonate ions at the air-aqueous solution interface were obtained. These correspond to adsorption isotherms of the Langmuir type. It is suggested that the adsorption of these surface active agents could take place by two different mechanisms, depending on the surfactant concentration range considered. The pressure vs area data for charged monolayers at the air-water interface have been examined in terms of limiting coarea and cohesional pressure. The Tajima equation derived for the dodecyl sulfate ion is moderately applicable to the alkylsulfonate ions, while the Davies equation does not fit the data well. The results indicate that the alkylsulfonate ions possess cohesional attraction for each other within the monolayer even at a very low concentrations. Adsorbed monolayers obey the adsorption isotherm which is derived assuming immobility of the ions in the air-aqueous solution interface. This adsorption isotherm leads to consistent values for the standard free energy of adsorption. Finally, a predominating role of the entropic effects in the process of adsorption of these surfactants at the air-water interface was found.

Chemical structure and surface activity: VIII. Statistical evaluation of the influence of alkyl monoethers of polyoxyethylene glycols structure on their adsorption at the aqueous solution-air interface

Surface tension isotherms of the individual alkyl monoethers of polyoxyethylene glycols C n H 2 n+1 (OCH 2CH 2) z OH ( n from 4 to 8; z from 1 to 5) at the aqueous solution-air interface have been determined. By using the appropriate multiple regression equations a quantitative correlation has been found between the change of standard free energy of adsorption, Δ G o, and the structure of the studied monoethers and of aliphatic alcohols as well. It has been found that within the studied range of surface tension decrease, π from 0 to 20 mN m −1, the change of standard free energy of adsorption, Δ G o, for the monoethers cannot be regarded as a sum of increments Δ G o[ X i ] corresponding to the definite fragments, X i , of monoether molecules. It has been shown, that not only methylene groups, -CH 2-, of the hydrocarbon chain, but the -OCH 2CH 2- groups of the polyoxyethylene chain have the hydrophobic character as well. The interaction of both these fragments is statistically significant and has an influence on the total value of Δ G o . However, the hydrophobic character of the -OCH 2CH 2- grouping is not constant. For the group of compounds studied it decreases with the increasing length of hydrocarbon chain and with an increase in π. For example, for π = 20 mN m −1, Δ G o[-OCH 2CH 2-] for the series of butyl and octyl derivatives is −0.32 and −0.13 RT, respectively. By assuming a simplified additive model which has been most often used to describe the relationships between Δ G o values and the chemical structure of surfactants at interfaces, we have calculated the Δ G π = 20 o[-CH 2-] and Δ G π = 20 o[-OCH 2CH 2-] values for the monoethers using multiple regression equations. These values are −1.07 and −0.25 RT, respectively. The Δ G π = 20 o[-CH 2-] value for aliphatic alcohols is −1.29 RT. By comparing the increments Δ G π = 20 o[-OH] for monoethers and alcohols (ΔΔ G π = 20 o[-OH] = −0.5 RT) it can be seen that the -OH group at the end of the polyoxyethylene chain seems to be less hydrated in the adsorption layer. This is probably caused by the participation of the mentioned hydroxyl group in inter- and intramolecular hydrogen bonds.

Relationship of structure to properties in surfactants. 11. surface and thermodynamic properties of N-dodecyl-pyridinium bromide and chloride

Surface and thermodynamic properties of well-purified N-dodecylpyridinium bromide and N-dodecylpyridinium chloride in aqueous solution and in solutions of the corresponding sodium halides of 0.1 M and 0.5 M total ionic strength have been measured at 10, 25 and 40°C. Properties measured are critical micelle concentration (cmc), maximum surface excess concentration and minimum area per molecule at the aqueous solution—air interface, efficiency and effectiveness of surface tension reduction, and standard thermodynamic parameters of micellization and of adsorption. N-Dodecylpyridinium bromide is somewhat more surface-active than the corresponding chloride. The difference appears to be due to the greater degree of hydration of the chloride ion compared to the bromide. The entropy factor is the major contributor to the free energy of both micellization and adsorption. Micellization appears to involve more dehydration of the counter-ion than adsorption at the aqueous solution-air interface.

Adsorption of alcohols at an air—solution interface: A pseudoregular monolayer model

Abstract A monolayer model of constant thickness has been utilized to explain the adsorption of n -propanol, t-butanol, s-butanol, and n -butanol at an air—aqueous solution interface. Two coefficients the one B σ , characterizing the interfacial properties and the other B σ those of the bulk solution have been correlated. Attention is drawn to the relation between B σ and the hydration of the alcohol molecules in solution.

ChemInform Abstract: RELATIONSHIP OF STRUCTURE TO PROPERTIES IN SURFACTANTS. 8. SYNTHESIS AND PROPERTIES OF SODIUM 3‐ALKYLTETRAHYDROPYRANYL 4‐SULFATES

A series of 3-alkyltetrahydropyranyl 4-sulfates, containing 9-15 carbon atoms in the alkyl group, has been synthesized, purified, and characterized. These materials have unusually high solubility in water. Surface tension measurements on aqueous solutions of these compounds have been used to calculate surface excess concentration, area/molecule at the liquid-air interface, critical micelle concentration, and efficiency and effectiveness of surface tension reduction. Values are compared with those for sodium n-alkyl sulfates. These data indicate that the tetrahydropyran group in these compounds is lying in the interface with the alkyl group oriented away from the aqueous phase. Using a new method for calculating standard free energies of adsorption and micellization, we calculated the standard free energy of adsorption of the tetrahydropyran group at the aqueous solution-air interface at 25/sup 0/C to be -1.7 kJ mol/sup -1/, somewhat less than that for a methylene group (-3.0/sub 3/ kJ mol/sup -1/) in the alkyl chain of the molecule, while the standard free energy of micellization of the tetrahydropyran group is shown to be -3.0 kJ mol/sup -1/, somewhat more than that for a methylene group (-2.5/sup 8/ kJ mol/sup -1/) in the alkyl chain. 4 tables, 2 figures.

Relationship of structure to properties in surfactants. 8. Synthesis and properties of sodium 3-alkyltetrahydropyranyl 4-sulfates

A series of 3-alkyltetrahydropyranyl 4-sulfates, containing 9-15 carbon atoms in the alkyl group, has been synthesized, purified, and characterized. These materials have unusually high solubility in water. Surface tension measurements on aqueous solutions of these compounds have been used to calculate surface excess concentration, area/molecule at the liquid-air interface, critical micelle concentration, and efficiency and effectiveness of surface tension reduction. Values are compared with those for sodium n-alkyl sulfates. These data indicate that the tetrahydropyran group in these compounds is lying in the interface with the alkyl group oriented away from the aqueous phase. Using a new method for calculating standard free energies of adsorption and micellization, we calculated the standard free energy of adsorption of the tetrahydropyran group at the aqueous solution-air interface at 25/sup 0/C to be -1.7 kJ mol/sup -1/, somewhat less than that for a methylene group (-3.0/sub 3/ kJ mol/sup -1/) in the alkyl chain of the molecule, while the standard free energy of micellization of the tetrahydropyran group is shown to be -3.0 kJ mol/sup -1/, somewhat more than that for a methylene group (-2.5/sup 8/ kJ mol/sup -1/) in the alkyl chain. 4 tables, 2 figures.

Kinetics and Mechanisms of Monolayer Interactions III: Models to Explain Time-Dependent Effects of Injected Cetrimonium Bromide

AbstractTwo kinetic models are derived to explain the time dependent effects of cetrimonium ions injected beneath an air aqueous solution interface without any previously adsorbed or spread monolayer at different ionic strengths. The data show excellent fit and consistency with a multicompartmental kinetic model which postulates a barrier or intermediate compartment between the ionic surfactant in the subphase and the sites on the surface. Such a barrier inhibits free diffusion of the surfactant from the bulk of the solution to these sites. The experimental data are not inconsistent with a model that postulates a time-dependent binding process and the absence of a diffusion-limiting subinterface since, within the limits of the error, the derived rate constants conform to the model prediction that they should be proportional to the surfactant-ion concentration.

Inductive effect of polar groups on CH and CF stretching vibrations of alkyl and perfluoroalkyl groups and its relation to adsorption

The trifluoromethyl-stretching vibrations for a series of perfluorocarboxylic acids and dihydroperfluoro alcohols were determined using an infrared spectrophotometer, and the results were compared with published information on the methyl-stretching vibrations of the corresponding hydrocarbon compounds. The frequency shifts of the CF 3-stretching vibrations are opposite in direction to those of the CH 3-stretching vibrations. This opposite shift may be attributed to the inductive effect of highly electronegative fluorine atoms. As a result, the alkyl groups are expected to become somewhat electropositive whereas the perfluoroalkyl groups electronegative. These induced polarities of the nonpolar groups were confirmed by the surface potential measurements at an air-aqueous solution interface and by the electrocapillary and differential capacity measurements at a mercury-aqueous solution interface.