LAUSR

Colloidal silica nanoparticles with average diameters less than 100 nm were made using a modified Stöber method involving tetraethylorthosilicate (TEOS) and octadecyl trimethoxysilane (OTMOS) as a surface modifier. We show that the hydrophobicity of the nanoparticles could be tuned in this one-step reaction by introducing methanol as a co-solvent with ethanol and optimizing the ammonium hydroxide concentration and time elapsed between TEOS and OTMOS addition. Using this approach, silica nanoparticles could be made directly with the proper surface hydrophobicity to stabilize invert (water-in-oil) emulsions with shear-thinning rheological behavior as needed in oil drilling applications. Particle characterization data from transmission and scanning electron microscopy (TEM and SEM), Fourier transform infrared (FTIR) spectroscopy, thermal gravimetric analysis (TGA), and contact angle measurements are presented.