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.

吸附诱导形变是指固体因表面吸附而引起的膨胀或收缩现象。此现象在众多应用中具有重要意义，涵盖从化学机械传感器至从地质构造中提取甲烷等多个领域。固体的应变是由吸附引起的表面应力变化所驱动的。通过使用从头算分子动力学方法，我们计算了干燥α-石英表面的表面应力，并探讨了当表面暴露于水时，这些应力如何变化。我们发现，非羟基化表面在应力上的变化微小且近似各向同性，而羟基化表面，由于与极性水分子相互作用更强，其表面应力变化较大且质向异性明显（xx和yy方向上的符号相反）。所有这些变化均远大于水的表面张力。这种各向异性和表面应力变化为正的可能性可以解释实验中观察到的由于吸附引起的表面积收缩现象。