College Park, Maryland      June 6 - 10 , 2004

MP25: Water Mobility in Small Aerosol-OT Reverse Micelles

M. R. Harpham, N. E. Levinger, B. M. Ladanyi (Colorado State University), K. W. Herwig (Oak Ridge National Laboratory)

Reverse micelles (RMs) are nanoscale droplets of polar solvent surrounded by a surfactant layer in nonpolar solvents. We have used quasielastic neutron scattering (QENS) to investigate the mobility of water molecules in small reverse micelles consisting of water/deuterated AOT/perdeuterated isooctane. Water/surfactant ratios of 1, 2.5, and 5 have been investigated using the QENS spectrometer at Argonne National Laboratory, IPNS division. This experimental data is reasonably well-fit by a jump-diffusion/isotropic rotation model, and gives diffusion constants that increase with w0 and rotational correlation times that decrease with w0. Computer simulations of reverse micelles of these water/surfactant ratios have been performed and used to predict QENS spectra to further investigate the dynamics of the water and make comparisons to experimental data. A Fourier transform of the simulation data convolved with the experimental instrument resolution function compares favorably to the experimental data. The simulations indicate that the dynamics of water is slower near the interface than at the core, and slower for small RMs than for large RM's. A mode coupling theory (MCT) analysis of the translational intermediate scattering function was performed. Results from this analysis indicate highly nonexponential behavior, and relaxation times that decrease as w0 increases.

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