Simultaneous Observation of Attractive Interaction, Depletion Forces, and “Sticky” Encounters between AOT Reverse Micelles in Isooctane Using Microelectrode Voltammetry

Microelectrode voltammetry has been used to measure the long-time self-diffusion coefficients (Ds) of AOT (AOT = sodium bis-2-ethylhexylsulfosuccinate) reverse micelles in isooctane using K3Fe(CN)6 as a micelle-immobilized electroactive probe. Ds values were found to be a function of both reverse micellar volume fraction (φmic) and probe concentration. The results show that increasing the probe concentration results in a decrease in Ds, suggesting an increase in attractive intermicellar interaction upon addition of probe. This has been interpreted in terms of attenuated surfactant tail-group reorganization facilitating interpenetrating of the surfactant tails. Increasing the micellar volume fraction is seen to diminish attractive interaction which indicates the presence of entropy-driven solvent mediated depletion forces. Self-diffusion coefficients at the limit of zero probe concentration ( ) were found to be micellar volume fraction dependent, and the behavior conformed to the linear interaction theory ...