Motions of Water, Decane, and Bis(2-ethylhexyl)sulfosuccinate Sodium Salt in Reverse Micelle Solutions

Abstract

Reverse micellar solutions made from the surfactant bis(2-ethylhexyl)sulfosuccinate sodium salt (AOT), water, and decane have been studied using NMR inversion−recovery and pulsed-field gradient experiments. Spin-lattice relaxation times, T 1, and diffusion coefficients, D, were measured for the individual components of the reverse micellar phase of the water−AOT−decane microemulsion as a function of temperature, 277 < T < 313 K, and reverse micelle volume fraction, 0 < φ < 1. Activation energies for the decane rotational motions probed by the T 1 measurements and those for the translational motions probed by the D measurements are compared as a function of φ. Both types of activation energies increase by a factor of ∼2 as φ increases from zero (pure decane) to 0.8 (near the lamellar phase boundary), indicating the influence of the AOT tails on the decane motions. A T−φ phase diagram has been constructed showing an empirical boundary for the onset of percolation. This percolation characterization, together with the measured diffusion coefficients and relaxation times, is consistent with previous descriptions of the structure and dynamics of water−AOT−decane and similar microemulsions reported in the literature. This study also continues the evaluation of the water−AOT−decane microemulsion as the signal-bearing solution in a magnetic resonance imaging phantom. The T 1 of the water phase matches that of nonfatty tissues in the body; however, the hydrocarbon component will need to be adjusted to match its T 1 to that of adipose tissue. The percolation boundary in the T−φ phase diagram helps to define the T and φ values where the solution possesses the high dielectric constant needed to minimize a standing wave artifact in a magnetic resonance image of the phantom.

Pattern Formation in a Tunable Medium: The Belousov-Zhabotinsky Reaction in an Aerosol OT Microemulsion

“…Small molecules (e.g., Br 2 or BrO 2 ᭹ ) display very different diffusion coefficients D in the oil and dispersed phases. In the former, D is about the same as the diffusion coefficient of oil molecules, roughly 10 25 cm 2 ͞s [13]. For the latter, D is determined by the diffusion of droplets in the oil phase [13] and can be as small as 10 27 or 10 28 cm 2 ͞s.…”

Electric Field Effects in Chemical Patterns

“…The experiments are performed using the ferroin-or O , and V total are the volumes of AOT, H 2 O, and the total microemulsion, respectively) [27]. Both microemulsions are mixed with a ratio of 1:1.…”

Front velocity in models with quadratic autocatalysis

“…5 The very different diffusion coefficients of X and R, D X and D R , respectively, raise the question of how the velocity of reaction-diffusion waves in the BZ-AOT system depends on these parameters. For the Oregonator model ͑O1͒-͑O5͒, the wave velocity c is essentially determined by the rate of the autocatalytic step ͑O3͒ and is given by the Fisher-Kolmogorov equation 6,7 for the minimum velocity, c min , of a propagating front with quadratic autocatalysis ͑see also Ref.…”