Surface modification of silica particles assisted by CO2

• The silane molecules are covalently bonded to the silica surface.
• The higher CO2 pressure lead to larger diameters of coated particles.
• The silica particles synthesized at 60 bar have a lower degree of agglomeration.
• Increasing CO2 pressure to 75 bar can lead to the contact angle value at 136 ± 3°.

This paper reports the synthesis of coating silica particles, in order to design hybrid materials with hydrophobic surface properties. The silica particles were prepared in basic conditions under atmosphere of carbon dioxide (CO2), using tetraethylorthosilicate (TEOS) as a precursor and octyltriethoxysilane (OTES) as a surface modifying agent. It was demonstrated that the contact angles of silica hybrid films could be changed by varying temperature and pressure of CO2. The investigation of the prepared hybrid materials by dynamic light scattering (DLS) and environmental scanning electron microscopy (ESEM), respectively, showed that they consisted mainly of particles with a diameter of 100–250 nm. Fourier transform infrared (FT-IR) spectra indicate that the interaction between the coupling reagents, at different conditions, is mainly through chemical bonding.

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