Surface modification of Si/SiO 2 by polymeric anion-exchanging membrane: Effect on interfacial morphology and electrochemical properties

Abstract

PolyTHF as anion exchanger membrane was deposited by dip-coating on SiO 2/Si samples. Wettability measurements allowed monitoring hydrophobicity and conformation of polymeric chains on the silicon-based electrode, during swelling of PolyTHF polymer in water. The reduction of the contact angle after immersion in de-ionized water has shown the possibility for a conformational reorganization of the layer characterized by a reversal of the ionic extremities of the polymeric chains toward the outer surface as the polymer equilibrated with the aqueous medium. Impedance spectroscopy allowed to model the PolyTHF coating by equivalent electrical circuits, and led to a better understanding of the different processes: swelling of the membrane, morphology of the surface and ionic charge transfer during ionic exchanging. Variation of R tc toward ionic potential of NO 3 − and AB25 reflect clearly ionic charge transfer and presents a sigmoid shape. The observed dynamic range are 10 − 5 M to 10 − 3.2 M for NO 3 − and 10 − 4.8 M to 10 − 3.8 M for AB25. A narrower dynamic range and a weaker sensitivity (10 times) are observed for AB25 detection compared to NO 3 − detection.