Microemulsions cyclic voltammetry

Chokshi et al. [24] described the use of two electrochemical techniques, cyclic voltammetry (CV) and rotating disk voltammetry (RDV), to characterize oil-in-water microemulsions containing a cationic surfactant CTAB, 1-butanol as cosurfactant, -octane, and water (in the range of 90-95%). NaBr was used as the electrolyte. Diffusion coefficients of microemulsions droplets were determined using ferrocene as a hydrophobic electroactive probe. Typical voltammograms and a corresponding plot of anodic peak current versus square root of scan rate are shown in Fig. 2 [24]. The diffusion coefficient is calculated from... 

Emulsion processes are of considerable importance and cyclic voltammetry allows these to be investigated. Texter et al. [23, 121] and Rusling et al. [122] voltammetrically studied processes in optically clear, stabilised microemulsions, in which the droplet size was smaller than 100 nm. Processes monitored were shown to be consistent with a CE-type reaction scheme in which reactant diffused from the organic emulsion droplet towards the electrode surface. 

Mass transport rates of electroactive solutes can be affected greatly by micelles and microemulsions. In cyclic voltammetry, for the reaction of a reversibly reduced or oxidized solute (O or R),... 

In bicontinuous DDAB microemulsions, Co L mediators reside in the water phase and DBCH in the oil phase, and the reaction (Eq. 21) probably occurs at the o/w interface. Cyclic voltammetry (Fig. 8) shows the reversible Co /Co reduction-oxidation peaks of the mediator and an increase in reduction current when DBCH is added. Direct reduction of DBCH occurs at a much more negative potential. 

Aqueous microemulsions with the IL as apolar phase are much more interesting than nonaqueous microemulsions. The reason is that both water and the IL are considered green solvents. The IL most commonly used in the preparation of aqueous IL microemulsions is l-butyl-3-methylimidazohum hexafluorophos-phate ([C mim][PF ]). The first aqueous IL microemulsion, water/TX-100/ [C mim][PFJ, was reported for Gao et al. showing water in [C mim][PFJ (w/IL), bicontinuous, and [C mim][PF ] in water (IL/w) subregions (see Fig. 13.1) [52]. These microregions were identified by cyclic voltammetry method using... 

Han and coworkers [38] determined the phase behavior of the ternary system consisting of [bmim][PFJ,TX-100, and water at 25 °C. By cyclic voltammetry method using potassium ferrocyanide, K Fe(CN)g, as the electroactive probe, the water-in-[bmim][PFJ, bicontinuous, and [bmim][PFJ-in-water microregions of the microemulsions were identified (Fig. 16.7). The hydrodynamic diameter of the [bmim] [PFJ-in-water microemulsions is nearly independent of the water content bnt increases with increasing [bmim] [PF ] content due to the swelling of the micelles by the IL. Sarkar and coworkers [39-41] reported the solvent and rotational relaxation studies in [bmim][PFJ-in-water microemulsions and water-in-[bmim][PFJ microemulsions using different types of probes, coumarin 153 (C-153), coumarin 151 (C-151), and coumarin 490 (C-490). The solvent relaxation time is retarded in the IL-in-water microemulsion compared to that of a neat solvent. The retardation of solvation time of water in the core of the water-in-IL microemulsion is several thousand times compared to pnre water. Nozaki and coworkers [42] reported a broadband dielectric spectroscopy study on a microemnlsion composed of water. 

Electropolymerization Zhang and coworkers [60] studied the electropolymerization behavior of pyrrole in water-in-[bmim][PFJ, bicontinuous, [bmim][PFJ-in-water microemulsions. It was shown that the water-in-[bmim][PFJ microemulsion was the optimal medium and its polymerization rate was the fastest. The resultant films electrodeposited in water-in-[bmim][PFJ microemulsion possessed excellent electrochemical activity and uniform morphology. He and coworkers [61] prepared PANI by cyclic voltammetry in [bmim][PFJ-in-water microemulsion. The specific capacitance of the PANI film obtained by 50-cycle electropolymerization in [bmim][PFJ-in-water microemulsion is 334 Fg" at the charge-discharge current density of 2mAcm . ... 

Zheng et al. reported a [bmim]BFyTX-100/toluene microemulsion system that was similar to the IL-based nonaqueous microemulsions mentioned earlier [10]. Cyclic voltammetry experiments were successfully introduced to verify the identification of microregions, in addition to conductivity measurements. 

As noted above, cyclic voltammetry is a powerful tool for the investigation of processes combining solution-phase reactions and heterogeneous charge transfer at the electrode surface. However, this technique can also be applied to systems with additional phase boundaries. For example, multi-phase processes in thin films covering an electrode surface (Fig. II. 1.24 a), particulate solids, bacteria, or microdroplets attached to the electrode surface (Fig. II.1.24b), or microemulsion systems (Fig. II. 1.24 c), can be studied. 

Unsupported Pt Microemulsion method with N2H4 as the reducing agent Pt nanoparticles with size 4.5 0.8 nm Cyclic voltammetry at room temperature in 0.1 MNH3 + O.2M NaOH Peak current density ca. 0.2 mA cm (v=10mVs ) 51... 

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