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

Abstract

Microelectrode voltammetry has been used to measure the long-time self-diffusion coefficients (D s) of AOT (AOT = sodium bis-2-ethylhexylsulfosuccinate) reverse micelles in isooctane using K3Fe(CN)6 as a micelle-immobilized electroactive probe. D s values were found to be a function of both reverse micellar volume fraction (φ mic) and probe concentration. The results show that increasing the probe concentration results in a decrease in D s, 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 for interacting micellar systems giving an attractive intermicellar interaction parameter of −2.33. Extrapolation to infinite dilution (i.e., φ mic → 0, the limit of zero interaction) reveals a reverse micellar long-time self-diffusion coefficient ( ) of 6.13 ± 0.07 × 10-7 cm-2 s-1, which gives a corresponding micellar hydrodynamic radius of 7.5 ± 0.02 nm. This value is approximately a factor of 2 greater than the know micellar size, and the behavior is interpreted in terms of adhesive “sticky” intermicellar interactions indicating the measurements of micellar cluster diffusion.

Ultrafast Chronoamperometry of Single Impact Events in Acoustically Agitated Solid Particulate Suspensions

“…[1][2][3][4][5][6][7][8][9][10] Most of the work conducted in this area has concentrated on adhesion events of colloidal particles on mercury electrodes. [1][2][3][4][5][6][7]10] The focus herein is the study of time-resolved chronoamperometric signals of single impact events of various solid particles on a polycrystalline platinum electrode under conditions of acoustic streaming. Several important advances are presented that have been made since this type of process was first studied in 2004 by Rees et al [8] Chief among these, are experiments that demonstrate the potential to determine the number and size of particles suspended in solution using this technique.…”

Physical chemical properties and kinetics of redox processes in water/soybean oil microemulsions

“…[1][2][3] However, the application of these techniques in nanoheterogeneous systems, including microemulsions (MEs), has been scarcely exploited. MEs are optically transparent, isotropic and thermodynamically stable systems.…”

Water in soybean oil microemulsions as medium for electrochemical measurements

“…These techniques can afford fruitful information about the core and surface monolayer structure, the particle size distribution, the polydispersity, the droplet clustering and diffusion dynamics, the inter-droplet exchange rate and the fluidity of the monolayer. 5,17,18 The rather classical methods of characterization through viscosity, interfacial tension, conductivity, turbidity and osmotic pressure measurements are still very reliable and informative. 14,[18][19][20][21] Particularly, the knowledge of the dynamic properties of the suspended droplets is very important in understanding the conductivity, chemical reactions and mass transfer processes occurring in these media.…”

“…Electroanalytical techniques may provide valuable information concerning the structural evolution, interparticle interaction and transport data, 17,23,24 yet there are very few studies employing electroanalytical methods in ME of water in vegetable oils. In this sense a Pt disk ultramicroelectrode (ume), allows to carry out linear voltammetric 25 measurements in resistive media 26 as is the case in this study.…”

“…The transparent to the turbid state can be brought about by variations of temperature, pressure or composition of the mixture and the transition point, the point of incipient phase separation, is the cloud point. 22 When the sample reaches the cloud point temperature, the sample gets turbid and ceases to show the transparency which characterizes a ME, a new phase starting to separate.Electroanalytical techniques may provide valuable information concerning the structural evolution, interparticle interaction and transport data, 17,23,24 yet there are very few studies employing electroanalytical methods in ME of water in vegetable oils. In this sense a Pt disk ultramicroelectrode (ume), allows to carry out linear voltammetric 25 measurements in resistive media 26 as is the case in this study.…”