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Abstract: This study examined the influence of different types of silane coupling agents on the dispersion of nanosilica particles with diameters of ca. 10nm and 25nm in two organic solvents, methylisobutylketone (MIBK) and cyclohexanone (CXN). The nanosilicas were prepared by the sol–gel process, and the following coupling agents were used: 3-glycidylpropyltrimethoxysilane (EpoSi), N-phenyl-3-aminopropyltrimethoxysilane (AmiSi), 3-mercaptopropyltrimethoxysilane (MerSi), and alkyltrimethoxysilane (AlkSi). While the 25-nm silica particles displayed dispersibility similar to that of submicron silica particles (ca. 150nm and 250nm), the dispersibility of the 10-nm silica particles proved to be dependent on the combinations of the agents and solvents; for example, EpoSi and MerSi were found to be suitable agents for MIBK and CXN, respectively. The slurries were also subjected to heating at 40°C for 24h, which resulted in a considerably higher stability of the dispersion state when CXN was employed as the solvent, regardless of which silica coupling agents were used. FTIR measurement revealed the presence of unreacted free Si–OH at 3740cm−1 for some nanosilicas. Combustion of the organic moieties introduced onto the silica surfaces also proved that the amount of organic groups present in a unit surface area of the nanosilicas were only 1/3 or 1/2 of that found on submicron silicas. From these observations, the low dispersibility of the nanosilicas was inferred to be due to the imperfect coverage of the silanol groups by the silane coupling agents. [Copyright &y& Elsevier]