The catanionic system dodecyltrimethylammonium hydroxide- n -dodecanephosphonic acid-water. Triangular phase diagram

Surface and bulk properties of aqueous decyltrimethylammonium bromide–hexadecyltrimethylammonium bromide mixed system

“…At high bidimensional pressures (π > 30-33 mN m −1 ), which correspond to micellar solutions, the πA a/w value suddenly rises. Similar results were found in dodecyltrimethylammonium hydroxide solutions and n-dodecanephosphonic acid [19], and means that micelles have an energetic advantage when compared with the adsorbed state, as said above. All the above discussion is independent of the model adopted to study micelles.…”

“…The minimum area per surfactant molecule, A min a/w , was obtained below the cmc and the average value was A min a/w = (0.47 ± 0.04) nm 2 . As expected for soluble-surfactant monolayers, the minimum area per surfactant molecule is above A 0 = (0.439 ± 0.007) nm 2 similar to that found in the literature [19]. Above the cmc there is a strong desorption, as it can be seen in Figs.…”

“…To obtain the area of the hydrocarbon/water contact per micellized polar head group (A W/H ), the excluded head group area for a monolayer, A 0 , was subtracted to A ph . A 0 = (0.439 ± 0.007) nm 2 for -N(CH 3 ) + 3 [19], and its interpretation is similar to the excluded volume in van der Waals equation; i.e., A 0 is the area occupied by a trimethylammonium head group in a tightly packed monolayer at the air/water interface. Results are plotted in Fig.…”

“…Hence, using the activities of free ions obtained in the ion-selective electrode experiments, curves of σ vs ln(a i a j ) were made. Then the surface excess concentration, Γ , was computed for each [S] T using the Gibbs equation in the form [19] (1)…”

Are the mixtures of homologous surfactants ideal?

“…The main work in this sense was devoted to electrostatic interactions, while scarce attention has been put on the steric ones, mainly on the hydrophobic group geometry. Some work was devoted to the nature of molecular interactions in mixed micelles [1][2][3][4][5][6][7].…”