Silicone oils aided fabrication of paraffin wax coated super-hydrophobic sand: A spectroscopic study

To address the global alarm of desertification and boost plant progress in arid and desert environments, super-hydrophobic sand has been suggested and fabricated in numerous researches. In the present work, sand was hydrophobized by coating with a mixture of paraffin wax and silicone oils. The contact angle (CA) of sand with 4.5 w% silicone oils increased from 143.2° to 154.2° with decreasing the chain size of silicone oil, and the further addition of 13.5 w% of paraffin wax produced a super hydrophobic sand with a CA value up to 160° comparing to 154.2° without added paraffin wax. The Fourier Transform Infrared spectra suggested the development of inter molecular forces between silicone oil and sand as well as between paraffin and silicone oil, the driving force of which was the variation in viscosity of silicone oils. The later was higher in the case of lower molecular weight silicone oil. In particular, analyzing the characteristic bands of -(CH₂)_n-in paraffin wax, i.e. the corresponding bands at 720, 730, 1460 and 1470 cm^-1 and the two bands at 1020 and 1095 cm^-1 of silicone oil revealed that two roles of paraffin were taking place. While paraffin was placed between sand and silicone oil, it coated the sand particles when lower molecular weight silicone oil was used in the first procedures, whereas it coated the higher molecular weight silicone oil in the second procedures. Molecular dynamic calculation has been performed and confirmed the previous reached conclusions and showed that paraffin molecules were encapsulated in a silicone oil shell. The average adsorption energy of paraffin and silicon oil molecules on sand particles were 29.5 and 38.9 kcal mol^-1 respectively.