The behaviour of surfactants in concentrated acids 5. Micellization and interfacial activity of n-alkyltrimethylammonium bromides in methane sulphonic acid and concentrated sulphuric acid

Abstract

The adsorption isotherms of n-alkyltrimethylammonium bromides for the interfaces CH 3SO 3H/ n-hexane and conc.H 2SO 4/ n-hexane were determined by du Nouy's ring method. The measurement data were evaluated by approximation to the Von Szyskowski equation. The standard deviation was <3.5%. The CMC values of the homologous series were determined. They show a good correlation with the Klevens equation. The change in the energy of micelle formation —Δ M G and the energy of adsorption —Δ- G 0 as a function of the chain length was calculated as well as the plot of surface concentration against surfactant concentration, the maximum surface coverage and the percentage surface concentration at the CMC. The results obtained in the different solvents are compared with each other and also with the results at the conc.H 2SO 4/air interface obtained earlier. The chemical surfactant properties of n-C n H 2 n+1 N(CH 3) + 3 Br − are still less pronounced in methane sulphonic acid than in concentrated sulphuric acid. The surface tension decreases less strongly. The CMC values were found only for the C 14−, C 16− and C 18−homologues and occur at much higher concentrations. The energies of micelle formation and of adsorption are considerably less. The results obtained on the conc.H 2SO 4/ n-hexane interface differ considerably from those for conc.H 2SO 4/air. The adsorption tendency clearly predominates in the former.