Average packing factor approach for designing micelles, vesicles and gel phases in mixed surfactant systems

The concept of average packing parameter is combined with the complex formation in mixed surfactant systems resulting in a common simple approach to apparently diverse systems. The systems considered are: lipid–detergent system in which vesicle-to-micelle transition occurs and which is of interest to membrane reconstitution in Biochemistry; cationic–anionic surfactant mixture which shows natural emergence of pairs of vesicle and wormlike micellar phases of opposite charges which are observed in experiments; and the less studied surfactant–multivalent ion mixture in which the formation of gels and vesicles is predicted which are of interest in industry. Results are obtained for chain length dependence for sequence of transitions and appearance of vesicle and wormlike phases in cationic–anionic surfactant mixture. A method of assigning packing parameter to a surfactant, similar to the concept of hydrophilic lipophilic balance (HLB) is proposed. This method can be generalized along similar lines to mixtures of more than two surfactants.