Effect of a Biosurfactant on Micellar Behavior of Cationic Surfactants in Aqueous Solution

Binary Mixed Micelles of Hexadecyltrimethylammonium Bromide–Sodium Deoxycholate and Dodecyltrimethylammonium Bromide–Sodium Deoxycholate: Thermodynamic Stabilization and Mixed Micelle Solubilization Capacity of Daidzein (Isoflavonoid)

“…In aqueous solutions, binary mixtures of surfactants form micelles at a specific concentration (the critical micelle concentration, cmc), similar to monocomponent surfactants, i.e., binary mixed micelles. − An ideal binary mixed micelle is formally created by mixing monocomponent micellar pseudophases so that different particles of surfactants in the quasi-crystalline mixed micellar pseudophase are randomly distributed; the entropic driving force of mixed micelle formation is without enthalpy contribution. − A real binary mixed micelle can be thermodynamically more stable (synergistic interactions between structurally different surfactants) or thermodynamically less stable (antagonistic interactions between structurally different surfactants) than an ideal mixed micelle. − The thermodynamic stabilization of binary mixed micelles is expressed with the molar excess Gibbs free energy ( g E ). , Rubingh and Holland applied Guggenheim’s theory of regular mixtures (RST) to obtain g E for binary mixed micelles, according to which the surfactants are randomly arranged in the hypothetical crystal lattice of the micellar pseudophase. Unlike the ideal state, the energies of intermolecular interactions between different types of surfactants are not equal to the energies of intermolecular interactions between the same surfactant particles, i.e., during the formation of the real binary mixed micellar pseudophase, there is a change in enthalpy (excess molar enthalpy). − According to RST, conformations of surfactants in the binary mixed micellar pseudophase and in the monocomponent micellar states are identical. , In regular solution theory (applied to micellar pseudophases), the molar excess Gibbs energy is expressed by the first-order Margules function (at constant pressure p and constant temperature T ): normalRST | : g E = h E = R T β x i x j , s E = 0 where R is the universal gas constant, β r...…”