Comments : Interaction of acoustic waves with thin films and interfaces
Résumé
commented: I would like to make some comments concerning the
interaction of acoustic waves with adsorption. For the two cases described below, the
adsorption of species on the electrode of the microbalance was followed by another
technique.
First, adsorption of albumin can be simultaneously followed by the QCM and by the
change of the double layer capacity of the electrode. Fig. 5 above shows the two plots
simultaneously obtained after addition of 0.5 g l~1 of albumin. The time constants
obtained through a Ðtting procedure with the sum of two exponentials are quite similar.
Fig. 6 shows the time variation of the double layer capacity for an oscillating and a
non-oscillating quartz crystal. It shows that the amplitude which indicates the amount
of albumin adsorbed is larger for a non-oscillating quartz.1
Secondly, a quite di†erent process was studied by means of a QCM: electrochemical
precipitation of calcium carbonate from hard waters. Fig. 7 shows the simultaneous plot
of the mass of scale obtained from the QCM and the change of current due to the
blocking of the active surface by the insulating scale (chronoamperometric curve). Fig. 8
shows chronoamperometric curves plotted on an oscillating (curve 2) and a nonoscillating (curve 1) quartz. Obviously the current decrease is faster for the nonoscillating quartz which demonstrates a faster scale precipitation.2
These two examples show that the vibration of the quartz crystal of the QCM
decreases the adsorption rate and then experiments carried out on QCM have to be
compared, at least quantitatively, with experiments carried out on a motionless electrode.
1 F. Lacour, R. Torresi, C. Gabrielli and A. Caprani, J. Electrochem. Soc., 1992, 139, 1619.
2 C. Gabrielli, M. Keddam, A. Khalil, G. Maurin, H. Perrot, R. Rosset and M. Zidoune, J. Electrochem.
Soc., to be published.