Surface properties of poly(dimethylsiloxane)-based inorganic/organic hybrid materials

Poly(dimethylsiloxane) (PDMS)-based hybrid materials were prepared by the sol–gel method on Si wafers, Al and polystyrene (PS) substrates. The reaction was monitored by attenuated total reflectance-infrared (ATR-IR) spectroscopy. The hybrid materials have always one surface made in contact with air and one with a substrate. These surfaces were investigated by using tapping mode atomic force microscopy (AFM), X-ray photo-electron spectroscopy (XPS), low-energy ion scattering (LEIS) and dynamic contact angle (DCA) analysis. The hybrid sample surfaces made in contact with air and substrates appeared to have different structures. The former have a silica-free PDMS top layer of ∼2 nm thick; while in the latter cases, SiO 2 are located at or just beneath the outermost atomic layer. In air and at room temperature, SiO 2 are likely beneath the outermost atomic layer. In contact with water, polar –OH groups at the surface of SiO 2 can easily stretch out to the outermost atomic layer. No correlation was found between the roughness of the surfaces and the amount of in situ formed SiO 2 present in the materials.