Adsorption-Induced Surface Stresses of the Water/Quartz Interface: Ab Initio Molecular Dynamics Study

Adsorption-induced
deformation is expansion or contraction of a
solid due to adsorption on its surface. This phenomenon is important
for a wide range of applications, from chemomechanical sensors to
methane recovery from geological formations. The strain of the solid
is driven by the change of the surface stress due to adsorption. Using
ab initio molecular dynamics, we calculate the surface stresses for
the dry α-quartz surfaces, and investigate how these stresses
change when the surfaces are exposed to water. We find that the nonhydroxylated
surface shows small and approximately isotropic changes in stress,
while the hydroxylated surface, which interacts more strongly with
the polar water molecules, shows larger and qualitatively anisotropic
(opposite sign in xx and yy) surface
stress changes. All of these changes are several times larger than
the surface tension of water itself. The anisotropy and possibility
of positive surface stress change can explain experimentally
observed surface area contraction due to adsorption.