DYNAMICS OF ELECTRON-ATTACHMENT TO AOT/H2O REVERSED MICELLES

Values of the observed rate constant, k(obs), of excess electrons attaching to aerosol OT (AOT) reversed micelles encapsulating varying quantities of water were measured in isooctane and tetramethylsilane (TMS) at 21-degrees-C using a picosecond-pulse-conductivity technique. Dynamic light scattering was used to determine the micellar radii in TMS from which aggregation numbers of the micelles were determined. In the lower-mobility isooctane (mu(e) = 5.3 cm2/(V s)), values of k(obs) approach the diffusion-controlled attachment rate, k(d) at a molar H2O/AOT ratio of 18 and appear to exceed k(d) at larger values of H2O/AOT. In contrast, values of k(obs) in TMS (mu(e) = 100 cm2/(V s)) are 8-fold less than k(d) at the maximum ratio of H2O/AOT = 27 that was studied. Several factors that could contribute to k(obs) appearing to exceed k(d) in isooctane are discussed, and the less efficient attachment of electrons to the same reversed micelles in TMS compared to attachment in isooctane is interpreted in terms of the relative attachment time, tau(a), and the residence time of the electron within the electron-micelle encounter radius, tau(r). With this model, the tau(a) of electrons attaching to micelles at a diffusion-controlled rate is < 1 ps and may be identified with the solvation time of electrons in water.