Correlation of Oil−Water and Air−Water Contact Angles of Diverse Silanized Surfaces and Relationship to Fluid Interfacial Tensions

摘要

The use of air−water, θwa, or air−liquid contact angles isncustomary in surface science, while oil−water contact angles, θow, are ofnparamount importance in subsurface multiphase flow phenomena includingnpetroleum recovery, nonaqueous phase liquid fate and transport, andngeological carbon sequestration. In this paper we determine both the air−nwater and oil−water contact angles of silica surfaces modified with a diversenselection of silanes, using hexadecane as the oil. The silanes includednalkylsilanes, alkylarylsilanes, and silanes with alkyl or aryl groups that arenfunctionalized with heteroatoms such as N, O, and S. These silanes yieldednsurfaces with wettabilities from water wet to oil wet, including specific silanized surfaces functionalized with heteroatoms thatnyield intermediate wet surfaces. The oil−water contact angles for clean and silanized surfaces, excluding one partially fluorinatednsurface, correlate linearly with air−water contact angles with a slope of 1.41 (R = 0.981, n = 13). These data were used to examinena previously untested theoretical treatment relating air−water and oil−water contact angles in terms of fluid interfacial energies.nPlotting the cosines of these contact angles against one another, we obtain the relationship cos θwa = 0.667 cos θow + 0.384n(R = 0.981, n = 13), intercepting cos θow = −1 at −0.284, which is in excellent agreement with the linear assumption of thentheory. The theoretical slope, based on the fluid interfacial tensions σwa, σow, and σoa, is 0.67. We also demonstrate how silanesncan be used to alter the wettability of the interior of a pore network micromodel device constructed in silicon/silica with a glassncover plate. Such micromodels are used to study multiphase flow phenomena. The contact angle of the resulting interior wasndetermined in situ. An intermediate wet micromodel gave a contact angle in excellent agreement with that obtained on an opennplanar silica surface using the same silane.