Einar Vikingstad

Partial molal volumes and isentropic partial molal compressibilities of surface-active agents in aqueous solution

Abstract The densities and the isentropic coefficients of compressibility of sodium-, potassium-, and tetramethylammonium laurate and of sodium dodecyl sulfate in aqueous solution have been measured. The apparent molal volumes and the isentropic apparent molal compressibilities have been evaluated at concentrations above and below the critical micelle concentration (CMC). The change in partial molal volumes and compressibilities in the formation of micelles has been evaluated from these measurements. These quantities have also been determined from conductance measurements. These two independent methods of measurements gave consistent values. The volume change and the compressibility change of micellization were positive and more positive the smaller the ionic radius of the counterion. The isentropic apparent molal compressibilities above the CMC are large and positive and indicate that the interior of the micelles resembles liquid hydrocarbons.

Partial molal volumes and compressibilities of the homologous series of sodium alkylcarboxylates, R6COONaR13COONa, in aqueous solution

Abstract The changes in partial molal volume (Δ V m ) and compressibility (Δ κ m ) in the formation of micelles have been determined at 25°C for the homologous series of sodium-alkylcarboxylates, R 6 COONaR 13 COONa. Δ V m has been determined by density measurements and by conductance measurements at different pressures. Δκ m has been evaluated from the conductance measurements and from ultrasound measurements. For each quantity the two independent methods of measurements gave consistent values. Δ V m and Δ κ m both increase with increasing chain length of the surfactant, but not in a linear manner. An analysis of the quantity Δ V m shows that the difference between successive values of Δ V m in the homologous series does not represent the group partial molal volume of the CH 2 group added to the micelle. The fraction of counterions associated with the micelles has been determined by EMF measurements, using a membrane electrode. This quantity was found to increase with increasing chain length.

Effect of pressure and temperature on the partial molal volume and compressibility of sodium decanoate micelles

Abstract Ultrasound measurements have been carried out under high pressure for solutions of sodium decanoate above and below the critical micelle concentration (CMC) at 25°C. From these measurements the partial molal volumes and compressibilities of sodium decanoate in singly dispersed state and in micellar state have been determined in the pressure range 1–1600 bar. It was found that the partial molal volume and compressibility in the micellar state both decreased with increasing pressure, but the corresponding quantities in the singly dispersed state increased with pressure. These results have been interpreted from changes in hydrophobic interactions and in electrostriction of water molecules with increasing pressure. From density measurements and ultrasound measurements in the temperature range 10–40°C the partial molal volumes and compressibilities of sodium decanoate above and below the CMC have been determined as a function of temperature. The partial molal volumes and compressibilities increase with temperature for sodium decanoate both in singly dispersed state and in micellar state.

The mean activity and the activities of the separate ions of sodium decanoate above and below the CMC determined by a surfactant selective silver/silver decanoate electrode

Abstract The mean activity a ± , and the mean concentration, m ± , of sodium decanoate have been determined at concentrations above and below the critical micelle concentration (CMC) at 25°C, using a surfactant selective silver/silver decanoate electrode and a cation exchange membrane electrode responsive to the sodium ions. It was found that both a ± and m ± increase somewhat above the CMC. The activity of the singly dispersed decanoate ions and the sodium ions were also determined separately above and below the CMC, using a calomel reference electrode. It was found that the activity of the free surfactant ions decreased above the CMC. The fraction of associated counterions was found to increase with increasing concentration of the surfactant.

Partial molal volumes and partial molal compressibilities of n-alkanes in sodium dodecanoate solutions

This work presents partial molal volumes and partial molal compressibilities for n-alkanes (C/sub 7/-C/sub 10/ in aqueous micellar solutions of sodium dodecanoate at 25/sup 0/C. The results are given in tabular form. It has been found that the partial molal volumes and compressibilities of n-alkanes in micelle solutions are higher than those in water. They resemble the partial molal quantities of liquid n-alkanes. These data tend to prove that the alkanes are dissolved in the interior of micelles and that the interior of the micelles themselves resemble liquid hydrocarbons. Separate contributions to the partial molal quantities from the different groups of the molecule are calculated. (27 refs.)

Partial molal volumes and compressibilities of n-alcohols in micellar solutions of sodium alkylcarboxylates

Abstract The partial molal volumes of n -alcohols (C 3 C 10 ) in micellar solutions of sodium dodecanoate, sodium decanoate, and sodium octanoate have been determined at 25°C by density measurements. From ultrasound measurements the partial molal compressibilities of the alcohols in the micellar solutions have been determined. The partial molal volumes and compressibilities of the alcohols in micellar solutions are higher than those in water and are similar to the partial molal quantities for the liquid alcohol. The partial molal volumes and compressibilities decrease with increasing chain length of the surfactant and with increasing surfactant concentration. The same trend has been found for the corresponding quantities for liquid alcohols, and the results have been interpreted by comparing the interior of the micelles to liquid alcohols.

The effect of alcohols on the change in partial molal volumes and compressibilities at micelle formation of sodium decanoate at 25°C

Abstract The effect of methanol, ethanol, 1-propanol, and 2-propanol on the change in partial molal volume, ΔV m , and compressibility, Δκ s m , during micelle formation of sodium decanoate has been determined at 25°C. Partial molal volumes were determined from density measurements, and partial molal compressibilities were determined from ultrasound measurements. It was found that both ΔV m and Δκ s m had a maximum in the concentration range 1–3 m alcohol, and then decreased rapidly on further addition of alcohol. These results have been interpreted from changes in the separate values of the partial molal quantities of the surfactant in the singly dispersed state and in the micellar state, respectively. The effect of the alcohols on the CMC at 25°C has been determined by conductivity measurements. It was found that the CMC decreases with increasing concentration and chain length of the alcohol. The fraction of associated counterions, β, has been determined by EMF measurements, and it was found that ,β decreases upon alcohol addition. This result has been interpreted from the reduced surface charge of the micelles caused by the alcohols.

Volume and compressibility changes of complex formation between 18-Crown-6 and NaCl, KCl, and CsCl in water

The apparent molal volumes and compressibilities of NaCl, KCl, and CsCl in mixtures of 18-Crown-6 and water have been calculated from density and speed-of-sound measurements at 25°C. The partial molal volumes and compressibilities of the salts when all cations have formed complexes with 18-Crown-6 molecules have been evaluated. The sign and magnitude of the volume and compressibility changes of complex formation strongly suggest that the charge of the cation becomes very effectively screened by the crown ether.

Isentropic apparent molal compressibilities and compressibilities of ionization of carboxylic acids in aqueous solution

Isentropic coefficients of compressibility of the homologous series of normal carboxylic acids and α-hydroxycarboxylic acids and their sodium salts have been determined from ultrasonic measurements. Isentropic apparent molal compressibilities at infinite dilution have been calculated.Compressibilities of ionization have been calculated from the isentropic apparent molal compressibilities and also from conductance measurements at high pressures. Values from the two independent methods of measurement do not agree in a satisfactory manner, but both show a lower limiting value for the higher homologues in each acid series.

Partial molal volumes and partial molal compressibilities of sodium-dodecanoate in NACl solutions

Abstract The changes in partial molal volume and partial molal compressibility in the formation of micelles have been determined for sodium-dodecanoate in aqueous NaCl solutions at 25°C. The volume change has been evaluated from density measurements and from conductance measurements at different pressures. The change in compressibility has been evaluated from the conductance measurements and from ultrasound measurements. The two independent methods of measurements gave consistent values for both quantities. The changes in partial molal volume and compressibility both seem to decrease with increasing concentration of NaCl.