Dynamic structure factor scaling in dense gelling silica suspensions

Small-angle neutron scattering data from dense (30% by mass) gelling 7 nm colloidal silica spheres are presented. The coarsening process that occurs during gelation exhibits temporal self-similarity, and the time-dependent structure factor obeys the dynamic scaling relation S(q, t) similar to q(m)(-df) (t)(S) over bar(q/q(m)(t)). Here, q is the scattered wavevector, q(m)(t) is the location of the low-angle peak in S(q, t), (S) over bar(x) is a time-independent characteristic structure function which has a maximum at x = 1, and d(f) is the fractal dimension. Connections between the silica gelation and spinodal decomposition in a simple fluid are reviewed.