Synthesis and characterization of hydrophobic silica prepared by different acid catalysts

Silica particles tend to be aggregate and difficult to be dispersed homogeneously in organic coatings or polymer nanocomposites because of the large number of -OH groups in the surface, and this remains an obstacle to further applications. Surface modification was carried out to improve silica hydrophobic ability in order to afford materials with anticipated functional properties. Improving hydrophobic ability can be achieved by using silylation agent Dimethoxydimethylsilane (DMDMS). Synthesis of hydrophobic silica TEOS-DMDMS was conducted by sol-gel process. TEOS-DMDMS was dissolved into ethanol solution with molar ratio of TEOS:DMDMS:EtOH 1:0.5:50 by using magnetic stirrer. Various acid catalysts (CH3COOH, H2C2O4, HNO3, and H2SO4) were added to the ethanol solvent until they reached the same pHs of 3.5. The TEOS-DMDMS sols were used for the surface modification of the glass slide by dip-coating method and then were calcined at temperatures of 300°C, 500°C and 600°C. The hydrophobicity of thin silica thin layers was tested by measuring water contact angle (WCA) and silica xerogels were investigated by TGA and FTIR to determine the thermal properties and characteristics of each functional groups. The WCA values of the uncalcined silica, calcined at 300°C and calcined at 500°C were in the range of 85.4-89.6°, 90.5-92.6°, and 50.4-59.7° respectively. The results of the TGA analysis showed that the TEOS-DMDMS silica began to lose its hydrophobicity starting from temperature of 325°C. The FTIR spectra showed no significant difference in functional groups of the sample prepared from all acid catalysts.