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 qua litatively with the known theoretical results of the viscoelastic mode l in an equilibrium system except in the vicinity of the gelation poin t. Near the sol-gel transition point of tungstic acid gel, we found in teresting features in the time variation of the velocities, namely, th e velocities of surface waves bad a maximum near the gelation point, d ecreased once rapidly, and again increased gradually as the,gelation p roceeded. On the other hand, the velocity of gelatin just decreased sl ightly near the gelation point. The reason for the velocity increase b efore the gelation point is possibly caused by the increase of the eff ective surface tension coupled with the elasticity of the networks. Ho wever, further investigation is necessary to clarify the mechanism of this particular property of tungstic acid gel.