Effect of the macrobicyclic ligand Kryptofix 222 on AOT/water/cyclohexane microemulsions

Abstract

Aerosol OT (AOT) exhibits a pronounced tendency toward reverse curvature, forming water in oil (w/o) droplets in the L{sub 2} region of the phase diagram in the three-component AOT/water/cyclohexane system. AOT's sodium counterion can be complexed by the addition of the macrobicyclic ligand 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo(8.8.8)hexacosane (Kryptofix 222), which leads to significant changes in the phase behavior of the ternary microemulsion system. This contribution focuses on the structural changes occurring in the L{sub 2} phase upon addition of 25 mol % Kryptofix 222 with respect to AOT. The combination of static SANS, QELS, conductivity, viscosity, and PGSE FTNMR measurements lead to the following conclusions: (1) the droplet morphology is maintained; (2) a significant increase in the droplet-droplet attractions is observed; (3) the aggregates decrease in size at constant w{sub o}. The appearance of a critical point in the oil-rich corner of the pseudoternary phase diagram, where the surfactant system separated into dense and dilute microemulsion phases, confirmed the existence of strong interdroplet attractions. The AOT/25 mol % Kr222/water/cyclohexane microemulsion system resembles the AOT/water/decane droplet system in this respect.