Structure and dynamics of water-in-oil droplets stabilized by sodium bis(2-ethylhexyl)sulfosuccinate

Abstract

The structure and dynamical behavior of water-in-oil microemulsions, stabilized by sodium bis(2-ethylhexyl) sulfosuccinate (AOT), has been studied by means of time-resolved fluorescence probing. The surfactant aggregation number, N, and the second-order rate constant, ke, associated with the intermicellar exchange of reactants by collision and transient merging of the colliding micelles, increase as the temperature, the chain length of the oil used as solvent, the molar concentration ratio = [H20]/[AOT], and the volume fraction of the dispersed phase at constant increase. N and decrease upon increasing concentration of NaCl and CaCl2 added to the water pools. The results confirm the existence of water-in-oil droplets at high volume fraction of the dispersed phase up to 0.47. They show also that the surfactant aggregation number and, in effect, the size of droplets do not increase dramatically as the phase-separation boundary is approached by increasing either the temperature or the oil chain length. The increase of kt under these conditions reflects an increase of the intermicellar

Study of the Effect of Solubilized Gases on the Properties of Microemulsion Droplets

“…The data in Table 2 show an increase of the quenching rate constant with temperature, as previously reported for similar systems (12,20).…”

“…Lang et al (20) have also reported a small dependence of N on temperature in the range 15-35°C for the AOT/C 7 /W microemulsion. Large increases of N with T are observed with microemulsions only at the approach of a percolation threshold (20,21). All of the systems selected for the present investigation are not in this situation.…”

“…The fluorescent probequencher pairs used were the pyrene/dodecylpyridinium chloride for O/W systems and the ruthenium(II)(trisbipyridyl) chloride (rubipy) probe with the quenchers potassium ferricyanide for the anionic AOT/C 7 /W system (20) and methylviologen dichloride for the cationic (BHDC/Cl/W) system (21 droplet] molar concentration ratio in the five microemulsion systems was around 1. Pyrene was excited at 335 nm and the emission was recorded at 381 nm.…”

Molecular dynamics simulations of AOT-water/formamide reverse micelles: Structural and dynamical properties

“…The list includes fluorescence, 3,4 NMR, [5][6][7] neutron and x-ray scattering, [8][9][10][11] quasi-elastic light scattering, and infrared 12,13 and terahertz 14 spectroscopies, to cite a few relevant examples. On the other hand, and from a theoretical perspective, these systems have also been investigated, normally resorting on computer simulations incorporating different degrees of molecular detail to model the polar and non-polar phases and the surfactants as well.…”

Intermicellar material exchange in reverse micelles formed by ionic AOT and nonionic Igepal surfactants studied by means of pulse radiolysis. Influence of the temperature

“…There%re the activation parameters should be treated as apparent ones. The apparent activation energies of intermicellar exchange in AOT reverse micelles in n-heptane, i-octane and decane estimated from the kinetic data published by Lang et al [6] are 94, 88 and 66 kJ/mole, respectively. It means that they decrease with increasing viscosity of the solvent.…”