Scaling of Small-Angle Neutron Scattering Intensities from Gelling Colloidal Silica

Abstract

Small-angle neutron scattering data, taken as a function of time from initiation of gelation in colloidal silica suspensions, with silica mass fractions ranging from 15 to 30%, are presented. Over a wide range of initial pH, the measured structure factor S(q) contains a low angle peak that, as time progresses, grows in height and moves to lower wave vectors q. Sometime after the gels have set, this peak stops growing, marking the end of the reaction. The data scale according to the relation, S(q,t)~$q_m^{-d_f}$ (t) (q/q _m (t)) $\tilde S$, where q _m(t) is the wave-vector location of the low angle peak as a function of time t from initiation, d _f is a fractal dimension, and $\tilde S$ is a characteristic structure function. The exponent d _f is insensitive to the silica mass fraction but that the form of $\tilde S$ is mass fraction dependent.