Electrochemical Studies of a Redox-Active Surfactant. Correlation between Electrochemical Responses and Dissolved States

Abstract

Electrochemical studies of a nonionic surfactant, R-(ferrocenylundecyl)-ω-hydroxy-oligo(ethylene oxide) (FPEG), have been conducted in 0.16 M NaCl aqueous solution at a glassy carbon electrode. The correlation between electrochemical responses and dissolved states has been examined in detail. Cyclic voltammograms (v ) 10 mV/s) of the FPEG solutions change with the concentration; below the critical micelle concentration (cmc), the voltammetric shape is of a typical surface-confined species, while above the cmc the diffusioncontrolled waves are superimposed at the cathodic side of the surface waves, and far above the cmc the voltammetric shape is of a typical diffusion-controlled species. FPEG in the aqueous solutions adsorbs onto the glassy carbon electrode surface to form a monolayer because of its surface activity. The adsorption isotherm has been represented by the Frumkin isotherm, which includes the repulsive interaction between the adsorbed FPEG molecules. Above the cmc, FPEG forms micelles. Chronoamperometrically determined apparent diffusion coefficients of the micellar solutions decrease with increasing concentrations. This has been interpreted in terms of the change in the diffusion species by disruption of the micelles into monomers at the cmc in the concentration gradient in diffusion layers. Cyclic voltammetric peak potentials of the micellar solutions shift toward the anodic side with the concentration. This behavior has been explained as the electrochemical reaction coupled with a preceding disassembled reaction of the micelles.

Voltammetry as a Tool to Monitor the Aggregation Behavior of a Zwitterionic Ferrocene Surfactant

“…Similar immobilization of micellar aggregates of ferrocene-containing amphiphiles on an electrode surface was observed on previous occasions. 28,46,47 The average size of the micellar aggregates of ca. 4 nm (see the cryo-TEM (transmission electron microscopy) image in Figure 5a; surface area ≈ 50.5 nm 2 ) and the headgroup size of ca.…”

Role of the thermoresponsive segment in determining the redox properties of phenothiazine-labeled poly(ethoxyethyl glycidyl ether)-block-poly(ethylene oxide)

“…The above results indicate that the PEE-GE segment is essential for the reduction in i pa v À1/2 at low v 1/2 values. One reason for this reduction in i pa v À1/2 value, could be the occurrence of a preceding disassembly reaction of micelles or other types of aggregates coupled with the electrochemical reaction of PT, as observed in the case of redox-active surfactant systems [33,34], although the origin of the downward i pa v À1/2 vs. v 1/2 plot has not been fully understood at present. The disassembly reaction of aggregates in the diffusion layer at the electrode surface will easily proceed in the case of less stable aggregates.…”

Electrochemical Behavior of Malachite Green in Aqueous Solutions of Ionic Surfactants

“…The difference in the technique of measurements gives rise to difference in CMC. Takeoka et al [22] reported the CMC value of a ferrocenyl surfactant from the surface tension measurements to be 0.012 mM, which is estimated as 0.089 mM from electrochemical measurements. Similar observations are also reported for an anthraquinonyl surfactant [25].…”

“…There are numerous reports on the study of the electrochemical behavior of electroactive species in surfactant-based organized media in literature. The electrochemical behavior of redox-active surfactants containing different electroactive groups has been found to be controllable by changing the concentration of surfactants [21,22]. Susan and coworkers [23][24][25] reported the solution behaviors of redox-active amphiphiles linked with an anthraquinone group and correlated the electrochemical behavior of anthraquinone with the dissolved states of the nonionic surfactant.…”