Carbon-13 NMR investigations of Aerosol OT water/oil microemulsions

Abstract

The conformatiional and dynamic changes which occur when H/sub 2/O is added to Aerosol OT (AOT) inverted micelles have been studied by means of /sup 13/C NMR spin-lattice relaxation times (T/sub 1/) and chemical shifts (delta) in cyclohexane, benzene, and carbon tetrachloride. Chemical shift changes at T/sub 1/ gradients upon addition of H/sub 2/O indicate that gauche to trans conformational changes occur throughout the AOT molcule. Solvent penetration decreases in the order benzene > carbon tetrachloride > cyclohexane. Frequency-dependent T/sub 1/'s arise as the result of a distribution of correlation times affecting the relaxation of all the carbon nuclei in AOT inverted micelles in cyclohexane. Overall molecular reorientation is the primary contribution to the relaxation of carbons nearest the head group in all three solvents. There exist motional differences in the AOT alkyl chains when going from the inverted micelle region to the water-in-oil (w/o) microemulsions.