STRUCTURE AND PHASE-BEHAVIOR OF LECITHIN-BASED MICROEMULSIONS - A STUDY OF THE CHAIN-LENGTH DEPENDENCE

We present a study of the structure and phase behavior of phospholipid-based water-in-oil microemulsions. The considerable influence of solvent (isooctane and cyclohexane) and cosolvent (short chain alcohol) structures and surfactant chain length on the phase behavior is shown, and an investigation of the aggregate size and structure by means of dynamic and static light scattering is reported. Synthetic short chain lecithin requires the use of a cosolvent and forms classical droplet-type microemulsion particles, whereby the droplet radius is largely determined by the water-to-surfactant molar ratio. Soybean lecithin as an example of a naturally occurring long-chain lecithin mixture requires no cosolvent, and we observe a water-induced transition from small spherical reverse micelles to giant flexible cylindrical particles. © 1993 Academic Press, Inc.