Adsorption of octadecyltrichlorosilane on Si(1 0 0)/SiO2 and SBA-15

Adsorption of octadecyltrichlorosilane (OTS) on Si(1 0 0)/SiO2 substrate and mesoporous SBA-15 has been studied by energy dispersive X-ray analysis (EDAX), Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). Contact angle technique is used to study the adsorption kinetics of OTS on Si(1 0 0)/SiO2 and thermal stability of adsorbed OTS layer. Thermogravimetric (TGA) technique is employed to understand the thermal behavior of OTS adlayer on SBA-15. Langmuir isotherms fit very well with OTS adsorption kinetics data on Si(1 0 0)/SiO2 and furnish adsorption rate constant, ka = 236 M−1 s−1, desorption rate constant, kd = 0.0082 s−1 and Gibbs free energy of adsorption, ΔGads = −6.28 kcal mol−1. EDAX and XPS results both show increased carbon content due to OTS adsorption and decreased oxygen and silicon content due to screening of these elements by OTS adlayer. FTIR data shows methylene (–CH2) and methyl (–CH3) stretching bands, in close agreement with reported data. The OTS layers are found to be thermally stable up to a temperature of ≈260 °C on both Si(1 0 0)/SiO2 and SBA-15.