Controlling surfactant self-assembly

Spontaneous self-assembly of surfactants in water to form vesicles has been reviewed, starting from the hypothesis that monomer solubility rather then packing parameters based on geometrical considerations could be utilized as the criterion to control this process. After a brief review of current theoretical considerations, several groups of surfactants have been evaluated. Surfactants were grouped based on criteria affecting monomer solubility: (i) changes in solution composition and temperature, (ii) enhanced attractive interactions between monomers, and (iii) changes in monomer structure. Main objectives were finding systems that result in stable, monodisperse, and small unilamellar vesicles with applicability in drug delivery, and identifying inexpensive processes to produce these systems. Several surfactant systems have been found that could meet these requirements, certain phospholipid surfactants, cationic/anionic mixtures, surfactants carrying sugar head groups, block copolymers, and mixtures between diblock copolymers and conventional surfactants. These examples clearly support above hypothesis that monomer solubility can be utilized as the criterion to control surfactant self-assembly. In addition, three approaches involving simple processing of surfactant systems have been discussed as potential drug carrier systems, utilizing (i) preformed vesicles as a matrix, (ii) inverted emulsions, and (iii) stabilized core-shell micelles. (C) 2004 Elsevier Ltd. All rights reserved.