Controlled formation of surface hydrophilicity enhanced chitosan film by layer-by-layer electro-assembly

Several surface hydrophilicity enhanced chitosan, CS, films were controllably formed by using the layer-by-layer electro-assembly, LBLEA, method with varied voltages. Experimentally, an employed electrostatic generator was employed by taking its anode and cathode electrodes alternatively linking to the CS solution or silicon plate to form two opposite cycles corresponding to the electrostatic force, EF, enhancement or reduction, respectively. Wetting results showed that the water contact angle, θW, on those CS film surfaces was gradually reduced with the applied voltage increase, especially by EF reduction, e.g. the θW on 0V sample at about 55° and on 4kV EF-reduction formed sample at about 20°. AFM images comparison showed that the LBLEA process can control the surface structure for CS film. ATR-FTIR spectra comparison showed that the EF reduction process would reveal the C-O groups on CS film surface to enhance the hydrophilicity.