Rheological images of poly(vinyl chloride) gels. 2. Divergence of viscosity and the scaling law before the sol-gel transition

The zero sheaf viscosity eta(0) of poly(vinyl chloride) (PVC)/bis(2-etylhexyl) phthalate (DOP) pregels has been measured as a function of polymer concentration c as well as molecular weight. It was observed that the zero shear viscosity diverged as the gelling system approached the gel point. The establishment of the scaling law, eta(0) proportional to epsilon(-gamma) was examined where gamma is the scaling exponent and epsilon the relative distance defined as (c(g) - c)/c(g). Here c(g) is the critical concentration for the sol-gel transition. Two methods were used to determine the scaling exponent gamma. One is the direct determination of gamma using the c(g) obtained by means of the frequency independence of loss tengent, The other is called the Takigawa method that determines simultaneously gamma and c(g) by mathematically transforming the scaling law into -eta(0)(-1) (d eta(0)(-1)/dc)(-1) = (c(g) - c)/gamma. Good agreement was obtained between the two methods. The scaling law, eta(0) proportional to epsilon(-gamma), was found to hold well for the PVC pregels, and the scaling exponent gamma eta was a constant (= 1.5 +/- 0.1) and was independent of the PVC molecular weight. The results suggest that the gelation rate defined as -d eta(0)/d epsilon(=gamma eta(0)/epsilon) is related to PVC molecular weight, and at the same epsilon increases with decreasing molecular weight. The errors in determining the scaling exponent gamma were also discussed.