Aerosol assisted deposition of melamine-formaldehyde resin: Hydrophobic thin films from a hydrophilic material

An intrinsically hydrophilic melamine-formaldehyde thin film (water contact angle of 34° for a cast flat surface) was deposited on a glass substrate using aerosol assisted chemical vapour deposition. The resultant resin films showed a highly developed microstructure consisting of spherical structures that were agglomerated into towers. The surface wetted via a Cassie–Baxter mechanism with air trapped underneath the water droplets and resultant water contact angles as high as 135°. Film thickness and coverage were crucial in determining the wetting properties. Films with limited deposition gave hydrophilic results, whereas thicker films greater than 4 μm were superhydrophilic. This behaviour could be explained by the ease of trapping air under the coating. It is shown that the water wetting properties of a single material can be altered from superhydrophilic to near superhydrophobic by controlling the surface microstructure in a single-step aerosol route.