ULTRASLOW RELAXATIONS IN NETWORKS - EVIDENCE FOR REMNANT FRACTAL STRUCTURES

An intriguing relationship has been found between the relaxation time spectra of a network at the gel point-the incipient gel-and in the fully cured state. Measurements of the dynamic shear moduli of several epoxy and siloxane networks, with equilibrium moduli varying by 4 orders of magnitude, show G" approximately omega-OMEGA at all extents of reaction past the gel point, where the viscoelastic exponent OMEGA remains at the incipient gel value of 0.5-0.8. This surprising correspondence suggests that chemical networks possess some remnant of the fractal structure of the incipient gel, so the implications of this are discussed. These viscoelastic results are compared to quasielastic light scattering studies on curing silica gels, where the power law decay S(q,t) approximately t-phi of the dynamic structure factor has been observed at and beyond the gel point, with phi unaltered by the extent of reaction.