octadecylsilane

Octadecylsilane is an organosilicon compound in which an octadecyl group (a C18 long-chain alkyl) is bonded to silicon via a carbon–silicon linkage. It is part of the family of long-chain alkylsilanes and is primarily used to modify surfaces to be hydrophobic. The molecule is nonpolar with low water solubility and high affinity for nonpolar solvents; it is typically a colorless solid or waxy material at room temperature, and like other silanes it can be reactive with moisture, undergoing hydrolysis to silanols and, over time, condensation to siloxanes.

In practical use, octadecylsilane serves as a precursor to surface-modifying agents and is encountered in more reactive derivatives such as octadecyltrichlorosilane and octadecyltrimethoxysilane. These derivatives are widely employed to form self-assembled monolayers on oxide surfaces (e.g., silica or glass), yielding robust hydrophobic coatings. Such monolayers find applications in microfabrication, sensors, chromatography (as hydrophobic stationary phases), and as coupling agents to tailor interfacial properties or to anchor organic molecules to inorganic substrates. The long, saturated hydrocarbon chain of octadecylsilane imparts low surface energy and reduced wettability to treated surfaces.

Safety and handling notes are similar to other alkylsilanes: materials are typically moisture-sensitive and are handled under dry or inert conditions to prevent premature hydrolysis and gelation. They are generally used by researchers with appropriate inert-atmosphere techniques and in compatible organic solvents.