Hydrophobic coating based on tetraethoxysilane on graphite foil

In this work, a hydrophobic coating was obtained on the surface of graphite foil pressed from thermally exfoliated graphite. The original graphite foil contains residual oxygen groups on the surface, which are formed at the boundaries of crystallites during the production of expandable graphite and are preserved even after thermal shock. The uncoated material was characterized by a water wetting angle of 65$^\circ$, which indicates the hydrophilicity of the material. The coating was deposited from a solution of tetraethoxysilane in isopropyl alcohol with the addition of water and an aqueous solution of ammonia. Different tetraethoxysilane/water ratios were used for the hydrolysis-condensation process and the production of the coating. With a fixed amount of aqueous ammonia and with a decrease in the amount of added water, an increase in the static wetting angle of the material with water to 96$^\circ$ was observed. Using X-ray phase analysis, it was shown that the coating is an amorphous silicon oxide; using IR spectroscopy, the presence of residual ethoxy groups in the coating composition was confirmed, which lead to an increase in the hydrophobicity of the material.