Frequency Dependence of Viscoelastic Properties of Branched Polymers near Gelation Threshold

The frequency dependence of viscoelastic properties of a branched polymer sample near its gelation threshold has been studied in oscillatory measurements. The results are in agreement with De Gennes' analogy relating the critical behaviour of the elastic moduli G' and G'' to the electrical conductivity of percolation clusters. In particular the increase of both G' and G'' with frequency (0.1 to 10 Hz) can be described by power laws with a common exponent u = t/s + t, and the loss angle δ assumes near the gelation point the universal value δc = πu/2 (t and s denote, respectively, the exponents of elastic modulus and viscosity at zero frequency). The value of u determined in these experiments (u = 0.70 ± 0.02) is in very good agreement with percolation theory.