First simultaneous estimates of the water pool core size and the interfacial thickness of a cationic water-in-oil microemulsion by combined use of chemical trapping and time-resolved fluorescence quenching

The first simultaneous experimental estimates of the water pool core size (R-w) and the interfacial thickness (d) of a cationic water-in-oil microemulsion, CTAB/isooctane/n-hexanol/water, was achieved by the combined use of chemical trapping and the time-resolved fluorescence quenching. Our estimated values of R-w = 29.1 +/- 1.5 Angstrom compares reasonably well with the reported size of the water pool core (32 Angstrom) of a structurally and compositionally similar CTAB/dodecane/n-hexanol/water cationic water-in-oil microemulsion (Atik, S. S.; Thomas, J. K. J. Am. Chem. Sec. 1981, 103, 4367), and our estimated interfacial thickness (6.3 Angstrom +/- 0.3) is consistent with the recently estimated thickness for the hydration layer (10 Angstrom) of the cationic CTAB/ n-hexane/n-pentanol/water water-in-oil microemulsions (Giustini, M. et al. J. Phys. Chem. 1996, 100, 3190). To our knowledge, this is the first simultaneous experimental estimate of the size of the water pool core and interfacial thickness of a cationic water-in-oil microemulsion using a chemical reaction.