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 microemul sion, CTAB/isooctane/n-hexanol/water, was achieved by the combined use of c hemical trapping and the time-resolved fluorescence quenching. Our estimate d values of R-w = 29.1 +/- 1.5 Angstrom compares reasonably well with the r eported size of the water pool core (32 Angstrom) of a structurally and com positionally similar CTAB/dodecane/n-hexanol/water cationic water-in-oil mi croemulsion (Atik, S. S.; Thomas, J. K. J. Am. Chem. Sec. 1981, 103, 4367), and our estimated interfacial thickness (6.3 Angstrom +/- 0.3) is consiste nt with the recently estimated thickness for the hydration layer (10 Angstr om) of the cationic CTAB/ n-hexane/n-pentanol/water water-in-oil microemuls ions (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 w ater pool core and interfacial thickness of a cationic water-in-oil microem ulsion using a chemical reaction.