Abstract:

The effect of pH on the particle distribution and zeta potential of the fumed silica(SiO2) suspended in H2SO4 or NaOH aqueous solution and their relationship were investigated with laser dynamic light scattering(DSL). The experiment showed that the isoelectric point(IEP) and titration end(TE) of silanol were at pH(IEP)=2.09 and pH(TE)=7.47, respectively, and a simple method was given for the determination of Si-OH concentration on SiO2 particle surface based on pH(TE). The dispersed phase particle size measurement showed that between IEP and TE, the hydration radius of SiO2 was stabilized near 230 nm; in H2SO4 medium, when pH＜pH(IEP), the apparent hydration radius of SiO2 increased with the increased H2SO4 concentration due to the coalescence of dispersed SiO2 aggregates; in NaOH medium, when pH＞pH(TE), the SiO2 aggregates decomposed and the apparent size of the dispersed phase decreased with increasing the NaOH concentration, which showed that NaOH can promote the dispersion stability of fumed silica in aqueous.

Key words: Fumed silica, Laser dynamic light scattering, Zeta potential, Si-OH concentration