MICELLAR SOLUTION SOLID-PHASE EQUILIBRIUM FOR TERNARY-SYSTEMS CONTAINING 2 N-ALKANOYL-N-METHYLGLUCAMINE HOMOLOGS

The equilibrium of mixed micellar solutions of N-alkanoyl-N-methylgluc amines (MEGA-n; n = 8,10,12) with solid phase was studied experimental ly at various concentrations of the surfactants and for their overall content from 5 to 45-50 wt%. The pure crystalline surfactant precipita tes in binary aqueous systems containing MEGA-12 or MEGA-10, the tempe rature of precipitation is nearly constant in the studied range of con centrations (ca. 321.7 and ca. 304.2 K respectively) The solid phase c rystallizing from micellar solutions of MEGA-8 is ice (temperature is close to 273.2 K). The temperature of the micellar solution-solid phas e equilibrium in systems containing two surfactants depends on relativ e content of the surfactants but not on their overall concentration. T wo branches are revealed in the solubility diagrams 'temperature vs. s urfactant-based molar fraction', one branch corresponds to crystalliza tion of the longer-tail surfactant, the other relates to crystallizati on of the second surfactant or ice (the latter is the case for systems with MEGA-8). A thermodynamic method is formulated for predicting the solubility diagram in the micellar system 'two homologous surfactants + water' on the basis of data for the aqueous binaries, The results o f prediction are in good agreement with experimental observations. The characteristics of critical micellization and the compositions of the micellar and monomer populations for concentrated surfactant solution s (above the CMC) have been estimated in accord with Nagarajan's molec ular-based model of mixed micelles. The results of the simulation supp ort the central assumptions of the phenomenological treatment: The ent ity of micelles can be considered as the macro-phase obeying the ideal behavior. (C) 1997 Elsevier Science B.V.