Scaling of small-angle neutron scattering intensities from gelling colloidal silica

Small-angle neutron scattering data, taken as a function of time from initi ation of gelation in colloidal silica suspensions, with silica mass fractio ns 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 aft er the gels have set, this peak stops growing, marking the end of the react ion. The data scale according to the relation, S(q, t) similar to q(m)(-df) (t) (S) over tilde(q/q(m) (t)), 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 frac tal dimension, and (S) over tilde is a characteristic structure function, T he exponent d(f) is insensitive to the silica mass Fraction but that the fo rm of (S) over tilde is mass fraction dependent.