One-pot in-situ surface modification of silica nanosphere by siloxane-coupled polycarboxylate with improved aqueous dispersion stability

Due to tendency of agglomeration in the nano-size scale, dispersion of silica nanosphere is of great importance for its application in aqueous phase system. In this paper, silica nanosphere was prepared by sol–gel method, followed by an immediate in-situ surface modification with siloxane-coupled polycarboxylate dispersants through a one-pot method. The particle size, surface topography, and chemical composition were analyzed by scanning electron microscopy, energy dispersive spectrometer, thermal gravimetry, and sedimentation test. For samples modified by siloxane-coupled polycarboxylate with concentration up to 3 wt%, the particle size decreased and monodispersity of the size increased, suggesting siloxane-coupled polycarboxylate have a size regulation effect on particle growth of silica nanosphere. Thermal gravimetry and energy dispersive spectrometer results confirmed that the dispersant strongly absorbed on the growing surface of silica nanosphere even after ultrasound cleaning and the absorbed amount increase with dispersant concentration for these samples. Compared with unmodified samples that completely precipitated after standing for 10 days, dispersion stability of modified samples in aqueous solution increased with dispersant solution content of up to 3 wt%. Interestingly, when siloxane-coupled polycarboxylate content increased to 5 wt%, particle size reverts back to larger size and the size dispersity increased which is due to decrease of dispersant absorption amount. The reverse behavior of higher dispersant concentration could be well explained by formation of dispersant micelles or oligomers, which indicates that there is an optimum modification concentration.