Chemical and Structural Properties of Polyethyleneimine Film Coated on a SiO₂ Substrate in Different Concentrations

Abstract

Angle-resolved X-ray photoelectron spectroscopy (AR-XPS) and atomic force microscopy (AFM) were employed to investigate the detailed surface bonding structure and morphology of polyethyleneimine (PEI) layers coated on a SiO₂ substrate in concentrations of 0.5–10.0 mass%. With an increase in the PEI concentration, the C–N bonds corresponding to the imine group (–NH) became dominant in the PEI layers, implying a characteristic feature to verify the immobilization of PEI on the SiO₂ surface. The thickness of PEI layer calculated using AR-XPS gradually increased with increasing PEI concentration up to a maximum 5 mass%, above which it became saturated. AFM results showed that an increase in PEI concentration led to a decrease in the root mean square (RMS) roughness of PEI layers. Such a saturation tendency of PEI thickness combined with the strongly dependence of the surface morphology behavior of PEI layers on the PEI concentration indicated that SiO₂ surface was fully covered by monolayer PEI with a smooth surface morphology at PEI concentration in excess of 5 mass%.