In order to investigate the gelation process of tungstic acid, surface wave measurements at several frequencies (50–200 Hz) were carried out with a deflected-laser-light detection system using surface waves excited with a PZT bimorph vibrator. During the gelation process, marked changes were observed in the surface wave velocity and amplitude. From the relationship between the frequency and wave number of the surface wave in the sol and gel states, it was found that the surface wave in the sol state was mainly the surface tension wave, and that in the gel state, the Rayleigh wave. We also estimated surface tension in the sol state and shear elastic modulus in the gel state from the present experimental results. The results of the present investigations demonstrate the usefulness of the surface wave measurement for studying the gelation process beyond the transition point.
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