A method to prevent the irreversible agglomeration of silica nanoparticles prepared from sodium silicate, which occurs upon treatment with trialkoxy silanes, is presented. Electrostatic stabilisation is maintained by using mixtures of 3-aminopropyltrimethoxysilane and the cationic derivative N-trimethoxysilylpropyl-N,N,N-trimethylammoniumchloride (TMAPS), which gives rise to stable dispersions of aminofunctionalised particles with unusually high amine content. The particles can be isolated and redispersed without significant increase in particle size. However, an increase in the dispersed particle-size was observed on increasing the APS content in the reaction mixture. This was least pronounced for the 9 nm particles prepared from sodium silicate and more pronounced for the 30 nm particles, for which gel and/or precipitate formation occurred at high APS contents. (c) 2008 Elsevier Inc. All rights reserved.