Wettability of Fully Hydroxylated and Alkylated (001) α-Quartz Surface in Carbon Dioxide Atmosphere

Abstract

Wettability of alkylated quartz surfaces is of primary importance in several technological applications, including the development of oil and gas reservoirs and carbon geo-sequestration. It is intuitively understood and experimentally confirmed that hydroxylated quartz surfaces are hydrophilic. By gradually saturating a hydroxylated (001) α-quartz surface with pentyl groups, we show using molecular dynamics simulations that the surface can also exhibit extreme hydrophobicity. Within a range of surface pentyl group density from 0.29 to 3.18/nm2, the contact angle of a water droplet under 10 MPa pressure of carbon dioxide at 300 K changes from 10–20 to 180°. This study has shown that a complete description of wettability of alkylated quartz surfaces requires three contact angles—one at the tip level of pentyl groups and two at the level of the quartz surface. The latter two are the contact angle of the spherical droplet and the hidden contact angle of a water “skirt” formed between the tip level of pentyl g...