Terminal silanization of perfluoropolyether, polydimethylsiloxane, their block polymer and the self-assembled films on plasma-treated silicon surfaces

Abstract

In this paper, terminal silanization of perfluoropolyether, polydimethylsiloxane and their block polymer was studied and N-(Triethoxysilylpropyl) urethano-perfluoropolyether (silanized-PFPE), N-(triethoxysilylpropyl) urethano-polydimethylsiloxane (silanized-PDMS), N-(Triethoxysilylpropyl) urethano-polydimethylsiloxane -block-perfluoropolyether (silanized-PSPF) were obtained, respectively. The self-assembled films of terminal silanized polymers were prepared on plasma-treated silicon surfaces via the liquid phase deposition method (LPD), and the surface structures and properties were investigated by contact angle (CA) measurements, X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS) and atomic force microscopy (AFM). It was discovered that the hydrophilic plasma-treated silicon surfaces became hydrophobic and possessed lower surface-free energies after treating by all three silanized polymers. Among them, the self-assembled film of silanized-PFPE provided the lowest surface-free energy of 12.77 mN/m with the water contact angle being 118.2°. Self-assembled films with different deposition concentrations were prepared. Results showed that the higher the treating concentration, the higher water contact angle (WCA) obtained. The terminal silanized polymers were coated on the silicon substrates uniformly. This was identified by XPS and EDS measurements of chemical compositions on the surface of the films. AFM was used to analyze the surface morphologies of silanized PFPE-deposited films, which was found to be rough at all the different concentrations of treatment solution. A concentration of 5% could provide the completely covered film with the roughest surface and thus develop the surface with excellent hydrophobicity.