Effect of Thickness on the Water-Barrier Properties of Silane Films

Although it is known that certain silane coupling agents can dramatically improve corrosion resistance when deposited on metals, the origin of this effect and its dependence on film characteristics are not understood. To elucidate these issues, neutron reflectivity is used to investigate the morphology and structure of the silane films as well as their response to water exposure. Films with thicknesses approaching practical levels (0.2 μm) are investigated. This study complements previous work on thinner films. Although some characteristics of thick films are similar to thin films regarding water-barrier properties, there are notable exceptions. Bis-sulfur silane film, for example, provides an adequate water barrier only for films cured at 180 °C with thicknesses exceeding 1200 Å. For bis-sulfur silane films, therefore, both larger thicknesses and higher cure temperatures are expected to improve anticorrosion performance.