SYNTHESIS AND CHARACTERIZATION OF SELF-ASSEMBLED HYDROPHOBIC MONOLAYER COATINGS ON SILICA COLLOIDS

Monodispersed silica colloids of various diameters (0.25-1.4 mum) have been coated by the self-assembled technique with a monolayer of hydrophobic surfactants, such as SiCl3(CH2)nCH3, Si(OMe)3(CH2)nCH3, SiMe2Cl(CH2)nCH3 (n = 3,7,17), and HO(CH2)7CH3. Methods, such as elemental analysis, Fourier transform infrared spectroscopy, and thermogravimetric analysis have been used for quantitative characterization of these coatings. Other methods, such as advancing contact angle, complete spreading surface tension, and floatability measurements have been used for studying the wettability properties of these coatings. Conditions to obtain reproducible coatings have been established. The effect of heating of these particles on coating quality has been demonstrated. The range of critical surface tensions of these coatings has also been estimated. This research has demonstrated that the coatings prepared from the longer chain alkylsilane compounds are superior to coatings prepared from the short ones and that the superiority of the coatings is in the rank order Of SiCl3(CH2)nCH3 > HO(CH2)nCH3 > SiMe2Cl(CH2)nCH3 > Si(OMe)3-(CH2)nCH3. These studies have led to the synthesis of optimal hydrophobic monolayer coatings onto silica colloids.