Preparation and characterization of an ultrahydrophobic surface based on a stearic acid self-assembled monolayer over polyethyleneimine thin films

A novel ultrahydrophobic ultrathin film was prepared by stearic acid (STA) chemically adsorbed onto the polyethyleneimine (PEI) coated aluminum wafer. The formation and the structure of the films have been characterized by means of water contact angle measurement, ellipsometry, Fourier transformation infrared spectroscopy, and X-ray photoelectron spectroscopy. The static contact angle for water on the surface of this ultrathin organic film was measured to be as high as 166°. Apart from the hydrophobic STA monolayer, the needle-like surface nanostructures with enough roughness was found to be essential for the generation of ultrahydrophobicity. We suggest that a composite interface formed by the needle-like surface nanostructures, water droplet, and air trapped in the crevices is responsible for the superior water-repellent property.