Electrochemical investigation of acid-base properties of ordered liquid systems

Acid-base properties of ordered media were investigated via potentiometry, polarography and electrochemical probes. Electrochemical probes have a pH-dependent reduction potential and their oxidized and reduced forms have a different affinity for aqueous and organic phases. Solutions of anionic, cationic and nonionic surfactants were investigated. One anionic and one cationic surfactant stabilized emulsion were studied. A water-dodecane-pentanol-anionic surfactant microemulsion and a water-heptane-butanol-cationic surfactant were also investigated for several compositions. In micellar solutions and emulsions, it was possible to standardize and use the classical glass electrode for pH values in the range 1-12. The hydrogen electrode was required in the microemulsion systems. The reduction of electrochemical probes was studied by polarography. It is shown that in the ordered media studied, the aqueous phase played the most important role in micellar solutions and in O/W emulsions, as far as acid-base properties were concerned. In microemulsions, the acid-base properties of the aqueous phase were very different to those of water. The alizarin probe could be reduced at a "local" pH of about 12 when the aqueous phase pH was only 6.