Influence of polymer–surfactant interactions on the reactivity of the CoIII–FeII redox couple

In continuation of our recent study on the inner sphere electron transfer reduction of the cobalt(III) complex, [CoIII(NH3)5N3]Cl2 by Mohr’s salt (FeII), we have investigated the effect of neutral polymer (poly(ethylene glycol) with relative molecular mass 200, PEG 200)–surfactant (both cationic and non-ionic) mixture on the kinetics of the same reaction using spectrophotometric and conductometric techniques at 298 K. Both the cationic and non-ionic surfactants have undergone interaction with polymer. Experimental consequences reveal that the catalytic effect imposed by the polymer–surfactant complexes causes significant change of the kinetic activities of the reaction. The gradual enhancement and retardation of the rate have been found with gradual addition of PEG 200 and cationic surfactant respectively. An attempt has been taken to rationalize the experimental findings with proper correlation of the reported literature.

With gradual addition of surfactant molecules, the concentration of micelles increases and more and more polymer hydrophobic residues are incorporated into the micellar hydrophobic cores (I to II): A kinetic study.Figure optionsDownload high-quality image (86 K)Download as PowerPoint slideResearch highlights
► A polymer facilitates the micellization of the surfactant, leading to smaller size of micelles, a lower CMC value of surfactant and lower value of degree of ionization of micelles
► Both the cationic and non-ionic surfactant–polymer systems have catalytic effect on the reaction rate of the reduction of CoIII by FeII
► Effectively two forces, one for coulombic and other for hydrophobic interaction, contribute to the catalytic effect of the polymer–surfactant on the redox reaction
► Catalytic effect of the polymer–surfactant mixed systems on the redox reaction is related to the formation of a reverse micellar region with a decrease of dielectric constant of the water pool of the micelles at higher concentrations of polymer