Robust super-hydrophobic ceramic coating on alumina with water and dirt repelling properties

Artificial super-hydrophobic surfaces are required for various applications. The super-hydrophobic surfaces are usually made by applying a low surface-energy organic coating on a highly textured substrate. A major problem with the as-created surfaces is their poor durability. This problem is even severer for the surfaces created by applying the organic coating on inorganic substrates. The present study reports for the first time the all-inorganic super-hydrophobic surface created by modifying the inorganic substrates with polymer-derived inorganic coating. A polydimethylsiloxane (PDMS) film was applied to an alumina substrate having flower-like hierarchal micro-nano surface texture, and then subjected to pyrolysis at 400°C in a nonoxidizing atmosphere. As a result, a Si_xC_yO_z ceramic coating with low-surface energy methyl groups was formed on the alumina substrate. The as-modified alumina exhibited super-hydrophobicity with a water contact angle of 170° and a sliding angle of 5°. The super-hydrophobicity was well retained after abrasion with sandpaper and exposure to boiling water and acidic solution. The super-hydrophobic alumina demonstrated desired water repelling and self-cleaning function. The method explored in this study could also be used for super-hydrophobic surface modification of other inorganic materials such as glass and metals.