Danuta Góralczyk

Thermodynamic characteristics and composition of anionic-cationic adsorption films

Abstract On the basis of surface tension measurements carried out at fixed ionic strength (0.1 M ) at different temperatures, the changes of standard thermodynamic functions ( ΔG o , ΔS o , and ΔH o ) have been calculated for the adsorption from solutions containing equimolar quantities of decylpyridinium chloride and sodium alkylsulfonates with different lengths of the hydrocarbon chain. Applying the Gibbs adsorption equation, the surface excess values have also been calculated for both types of surface-active ions which are adsorbed from solutions containing equimolar quantities of anionic and cationic detergents. It has been found that in the case of mixtures of detergents of different hydrocarbon chain lengths, the adsorption films are enriched in the more surfaceactive component, which is particularly marked at low surface coverage.

Effect of inorganic electrolyte type on anionic—cationic adsorption films

Abstract The effect of inorganic electrolyte type (NaCl, NaBr, NaI) on the composition of anionic—cationic films adsorbed from solutions containing alkylsulphonate (RmSO3−) and alkylpyridinium (RnPy+) ions has been investigated. The surface excess of each component has been determined by using a from of the Gibbs adsorption equation appropriate to the results of surface tension measurements. It has been found that the replacement of NaCl by NaBr has almost no effect on the mixed monolayer composition, whereas the replacement of NaCl by NaI gives a considerable effect — the largest one occurring for films having a resultant cationic character (n &>; m). On applying the integral adsorption isotherm based on Butlers equation to the results of surface tension measurements. ΔG values have been calculated for anionic—cationic surfactant adsorption. It has been found that, contrary to cationic monolayers investigated earlier, mixed adsorption films are actually insensitive to the inorganic electrolyte type, which indicates a substantial reduction of the resultant electric charge.

Application of the regular solution model to anionic-cationic adsorption films

Abstract The composition and mutual interactions of the components in anionic-cationic adsorption films have been calculated by using a regular solution model of the mixed monolayers. The components of the mixtures investigated were sodium alkylsulfonates and alkylpyridinium halides. It has been stated that the composition of monolayers adsorbed from equimolar solutions is close to that obtained on the basis of the Gibbs surface excesses and is dependent on the surface tension value (the degree of surface coverage), the difference in the surface activity of the components (except for the solutions in pure water) as well as the concentration and type of added inorganic electrolyte. The same factors influence the value of the interaction parameter β, for which negative values indicate a strong attraction between the components in the mixed monolayers.

Surface properties of the binary mixed systems of alkylpyridinium halides and sodium alkylsulfonates

Abstract Surface properties of the binary mixed systems of decyl- and dodecylpyridinium chloride or bromide and sodium pentyl- and heptylsulfonate have been investigated. The surface tension of solutions of equimolar mixtures of surfactants and individual surfactants was measured, and the composition of mixed monolayers and surface interaction parameter β were calculated with the regular solution theory. Our results indicate that the properties of mixed films depend on both ionic strength and the kind of added inorganic electrolyte. With the increase of inorganic electrolyte concentration, the content of more surface active ions in the adsorption films enhances and is the highest in the presence of NaI and the smallest when solutions contain NaCl. Mutual interactions in mixed adsorbed films were found to be attractive. However, the strength of interaction weakens with the increase of ionic strength and depends on the kind of inorganic ions in the order: Cl − >Br − >I − .

Thermodynamic characteristics of anionic—cationic adsorption films based on a butler-type equation

Abstract It was stated that the simplified form of an integral adsorption isotherm based on the Butlers equation and derived previously (D. Goralczyk and B. Waligora J. Colloid Interface Sci. 82, 1 (1981)), describes satisfactorily the surface behavior of the solutions containing equimolar amounts of anionic and cationic surfactants with various surface ativity only within the range of great surface pressures. On the other hand, in the case of a small degree of surface coverage, deviation appear due to the presence of excess of ions with longer alkyl chain in the mixed adsorption film. The values of ΔG of adsorption for anionic—cationic surfactants are within the limits of experimental error equal to the sum of the values characteristic for single ionic substances being components of the mixture. The presence of adsorption film influences on the water structure in the surface layer which causes nonzero values of ΔGH2O.

Properties of anionic–cationic adsorption films

Abstract The regular solution model for mixed monolayers was used to calculate the composition of the anionic–cationic adsorption films and parameters characterizing the mutual interactions between their components. The surfactants forming the mixed monolayers were decylpyridinium chloride and sodium hexylsulfonate. The monolayers under investigation were all adsorbed from equimolar solutions of surfactants. The results obtained show that the composition of the anionic–cationic adsorption films is dependent on the concentration and the kind of inorganic electrolyte present in the solution. The values of surface interaction parameter β , being all negative, show that the adsorbed components attract mutually. It has been observed that the strength of the attraction mentioned is also dependent on the factors given above for the composition of mixed adsorption films. It has also been established that the system examined here behaves, both qualitatively and quantitatively, in very similar manner to the previously investigated mixture of decylpyridinium chloride and sodium octylsulfonate, i.e. of surfactants with the same difference in length of the hydrocarbon chains as examined in this work.

Effect of the molar ratio of surfactants in the solution on the composition and mutual interactions in anionic-cationic adsorption films

Abstract The composition and mutual interactions of the components in anionic—cationic films adsorbed from solutions of composition varying over a wide range have been calculated by using a regular solution model of the mixed monolayer on the basis of surface tension measurements. Mixtures of surfactants of similar surface activity (sodium decylsulfonate and decylpyridinium chloride) as well as those differing markedly in their surface activity (dodecylpyridinium chloride and sodium octylsulfonate), containing a large excess of inorganic electrolyte (0.1 M NaCl), have been investigated. Both types of mixtures show negative deviations from ideal behavior. The attractive interaction between adsorbed components is strongest in the case of adsorption from solutions containing equimolar amounts of both surfactants. This interaction is stronger in the case of mixtures of surfactants containing hydrocarbon chains of the same length. Over a wide composition range these mixtures form mixed films of almost equimolar composition. However, in the case of mixtures of surfactants differing in their surface activity, mixed adsorption films are formed which consist predominantly of the component with the longer hydrocarbon chain even if its content in the solution is very small. The composition of mixed monolayers and the mutual interactions between their components are dependent on the surface tension in a significant way,