Rheological images of poly(vinyl chloride) gels. 3. Elasticity evolution and the scaling law beyond the sol-gel transition

The elasticity evolution of poly(vinyl chloride) (PVC)/bis(2-ethylhexyl) phthalate (DOP) gels beyond the gel point c(g) has been studied as a function of polymer concentration c and molecular weight. The gel elasticity G(e), which was defined as the frequency-independent dynamic storage modulus G' at low frequencies, developed as a function of polymer concentration. The scaling law for the elasticity evolution, G(e) = k epsilon(z), was found to hold well for all the PVC gels with different molecular weights. Here, epsilon [=(c - c(g))/c(g)] is defined as the relative distance, z the scaling exponent, and k the front constant. The z obtained was constant (z = 2.6 +/- 0.1), independent of the PVC molecular weight, being excellently consistent with the theoretical prediction (z = 8/3) using the percolation model. Furthermore, the analysis of the front constant k provided information about the dependence of the gel elasticity on molecular weight. As a result, the gel elasticity could be described as G(e) = 10(14) M(w)(-2.4)epsilon(8/3), allowing one to discuss separately the molecular weight contribution and the relative distance contribution. The ability of this relation to predict the elasticity evolution has also been examined.