Propagating property of surface waves and viscoelasticity near the gelation point

We studied the properties of surface waves during the gelation process of tungstic acid gel and gelatin. The experimental results agreed qualitatively with the known theoretical results of the viscoelastic model in an equilibrium system except in the vicinity of the gelation point. Near the sol-gel transition point of tungstic acid gel, we found interesting features in the time variation of the velocities, namely, the velocities of surface waves had a maximum near the gelation point, decreased once rapidly, and again increased gradually as the gelation proceeded. On the other hand, the velocity of gelatin just decreased slightly near the gelation point. The reason for the velocity increase before the gelation point is possibly caused by the increase of the effective surface tension coupled with the elasticity of the networks. However, further investigation is necessary to clarify the mechanism of this particular property of tungstic acid gel.