Surface modification of hydrophilic pyrogenic silica and characterization studies

In this thesis, hydrophilic pyrogenic silica (FS) was modified with (3-aminopropyl)trimethoxysilane (APTMS), n-octyltriethoxysilane (OTES) and n-octadecyltrichlorosilane (OTS). Then, primary amine functionalized FS-APTMS was post-modified by using 1-bromobutane (BB), 1-bromodecane (BD) and 1-bromohexadecane (BHD). Fourier transform infrared spectrometer (FTIR), scanning electron microscope (SEM) and surface area and porosity instrument were used to determine some chemical and physical characteristics of silicas. Modification agent contents of silicas were calculated from elemental analysis results. The thermal stabilities of structures were investigated by thermogravimetric analysis (TGA). The hydrophobic/hydrophilic characteristics of the surfaces were evaluated by analysing wetting behaviors in water/toluene and contact angle measurements. The contact angle of FS was measured 12.63o and the highest contact angle values were observed for FS-OTS (134.22o) and FS-APTMS-BD (121.84o). The adsorption studies were carried out with Acid Orange 8 (AO8). Adsorption studies were carried out in the presence of hexadecyltrimethylammonium bromide (CTAB) for hydrophobic silicas. The highest adsorption capacity (approximately 435 mg g-1) was observed for FS-APTMS-BHD at 25oC. Color analyses were performed for hybrid pigments obtained by AO8 adsorption onto silicas. In particular, the solvent (with different polarities) resistance of hybrid pigments obtained by post-modification was higher compared to other hybrid pigments.