SHEAR-WAVE DISPERSION IN MECHANICALLY SELF-SIMILAR GEL NETWORKS

A study of viscoelastic shear wave dispersion in a simulated gelation process involving mechanically self-similar nodal networks is reported . The network formed at the gel point (the infinite network cluster, o r 'critical gel') shares a common structural feature of smaller networ k clusters and the onset of a recognizably 'gel-like' feature is shown to occur when the characteristic wavelength of the network cluster be comes twice that of an individual node. It is shown that, during gelat ion, the dispersion of shear waves can be exploited to assess the prox imity of a system to an equivalent 'critical gel' state at any single frequency, thereby identifying the smallest length scale at which gel- like characteristics are established prior to the gel point. In this w ay, and for the first time, a rheometrical basis is established for ex amining the gel-like, self-similar characteristics of pre-gel point vi scoelastic liquid systems, in terms of the gel equation but in the abs ence of a frequency-independent loss tangent. Experiments are reported for a critical gel in which the high-frequency wave dispersion is in good agreement with theory.