Hydrophobic Modification of Silica Surfaces via Grafting Alkoxy Groups

The surface modification of hydrophobicity on silica is important in industrial applications. Silane adhesives, such as chlorosilane, hexamethyldisilazane, and polydimethylsiloxane, are widely used in surface hydrophobicity modification, but most silane reagents are toxic and expensive. In addition, this approach suffers from the complexity and duration of preparative methods. Here, an operable, feasible, and environmental friendly method for the hydrophobic modification on silica surfaces has been realized by grafting alkoxy groups on the surfaces via the alkoxylation reaction of alcohol molecules, for which no additional solvents are needed except alcohols. The hydrophobicity of the modified silica surface was characterized by measuring the water contact angle, larger than 90°. The origin of hydrophobicity was investigated by probing the vibrational spectra of alkoxy species on silica with surface-sensitive sum-frequency vibrational spectroscopy. Our work not only provides guidelines for efficiently designing surface structures to improve the hydrophobic performance but also is expected to replace the traditional surface modification processes using silane adhesives in industry.