Frequency Changes Observed with the EQCM Resulting from Hydrophilic/Hydrophobic Transitions

Abstract

The processes responsible for the altered frequency response of the EQCM when the electrode surface changes from a hydrophilic to a hydrophobic condition have been investigated using silver electrodes in ethyl xanthate solution. The frequency accurately tracks the voltammetric charge when silver ethyl xanthate is formed, but moves in the opposite direction when xanthate is chemisorbed; chemisorption is known to result in the surface becoming hydrophobic. The characteristics of the EQCM in a xanthate solution that had been completely degassed was the same as that in one deaerated with nitrogen. This is inconsistent with nanobubbles being formed at a hydrophobic surface, but is in agreement with slippage occurring as a result of a change in water structure. Similar voltammograms were observed for smooth silver surfaces to those for electrodeposited ones, but the alteration in frequency response during the change in wettability was much greater. This is also explained in terms of water structure.