This study investigates the one-step synthesis of functionalized silica nanoparticles using dichlorodimethylsilane (DDS), and examines the statistical effects of process variables on the synthesized silica particle size. This method simultaneously consisted base-catalyzed hydrolysis and condensation of tetraethyl orthosilicate (TEOS) in the presence of a DDS coupling agent. Fractional factorial design (FFD) is used to identify the most significant variables influencing the synthesis process, as well as the effects of different levels of each parameter on the mean silica particle size. The effects of five parameters (concentration of ammonium hydroxide, TEOS, DDS, ethanol, and reaction temperature) were investigated and the catalyst concentration was considered as the key factor influencing the process. Study of morphology and size of silica nanoparticles using particle size analysis (PSA) and transmission electron microscopy (TEM) showed successfully synthesis of mono dispersed silica nanoparticles with mean particle size of 65 nm. Fourier-transform infrared spectroscopy (FTIR) confirmed after the addition of DDS, SiCl(CH3)2 functional group took the place of H on the surface of silica nanoparticles, and the nanoparticles found hydrophobic properties.

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