Phase diagrams for cationic surfactants in polar solvent systems

• Phase diagrams are presented for cationic surfactants, and alkyltrimethyl ammonium bromide in polar solvent systems, such as ethylene glycol, formamide, glycerol, and their mixtures with water. Provided that the solvent is sufficiently lipophobic, and that the hydrocarbon moiety of the surfactant is sufficiently large, liquid crystalline phases form according to the normal association pattern for ionic surfactants. In, for example, ethylene glycol, liquid crystals are only formed with surfactants with a longer alkyl chain length than dodecyl.-The formation of didodecyldimethylammonium bromide microemulsions containing polar solvents- mainly formamide, water and their mixtures-and hydrocarbon has been studied. The extension of the solution phase region may decrease, although the mutual miscibility of polar solvent and the hydrocarbon increases. NMR self-diffusion measurements reveal that this is accompanied by a corresponding loss of structure, i.e., a smaller distinction between polar and apolar regions.

Nyckelord

Phase equilibria

polar solvents

alkyltrimethylammonium bromide

didodecyldimethylammonium bromide

non-aqueous microemulsions

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