A fluorescence and phosphorescence study of AOT/H2O/alkane systems in the L2 reversed micellar phase
Time-resolved fluorescence and phosphorescence quenching measurements were made to determine the size, n c , of possible micellar clusters and the aggregation number, Nagg, of micelles in oil-continuous microemulsions stabilized by aerosol OT (AOT). In particular, water/AOT/dodecane and water/AOT/isooctane systems were studied. The decay curves followed a “double Infelta”  decay: In(F)(t)/F(0))=A2t+A3(exp(A4t)-1)+A5(exp(A6t)-1), where the exponents A4 and A6 differ by a factor of 100; the A4 exponent is assumed to represent the intramicellar quenching rate, and A6 the intracluster quenching rate.
Cluster formation was found to occur in the L2 phase, even reasonably far from phase separation limits. ?The clusters showed polydispersity in size while the micelles did not. Cluster formation increased with the concentration of micelles [M], with the chain length of the alkane solvent, and with R=[H2O]/[AOT], the water to surfactant ratio. The micellar aggregation number appeared to be independent of the micelle concentration, but was higher in dodecane than in isooctane. It was not possible to determine whether the processes of exchange in the cluster were due to fusion fission or some other process. Exchange between different clusters, however, seemed to be very slow.
KeywordsChain Length Decay Curve Cluster Formation Aggregation Number Micellar Phase
- 1.Jóhannsson R, Almgren M (1991) J Phys Chem (in press)Google Scholar