Electrical characterization of a new polymeric ion-exchanging membrane for the chemical detection of anions

PolyTHF terminated by a quaternary ammonium triflate group was used as an anion exchanging material. The polymer was deposited using a dip coating method on the surface of a silica/silicon heterostructure whose impedance characterization could be performed. Capacitance measurements of the silicon_insulator (silica and polymeric layer)_electrolyte heterostructure allowed the studying of the anion-exchange phenomena at the cationic groups in the functional polyTHF membrane. Both increases of the polymer layer thickness and dielectric permittivity were observed by impedance measurements due to swelling of the polymeric film when the electrode was immersed in a sodium triflate solution. In the first part, exchange phenomena of the triflate anion against anions—acetate, nitrate, methane sulfonate, Acid Blue 25 dye, and sulfate—in a sodium triflate background electrolyte solution was investigated. Specific ion exchange was observed according to the anion type. In the second part, ion-exchange phenomena have been studied in a sodium acetate background electrolyte solution after initial swelling and partial ion exchange of the triflate against acetate anion. The capacitance measurements (flat-band potential shift) were allowed to distinguish between triflate-anion and acetate-anion exchange phenomena.