Adhesion energy between mica surfaces: Implications for the frictional coefficient under dry and wet conditions

Abstract

[1] The frictional strength of faults is a critical factor that contributes to continuous fault slip and earthquake occurrence. Frictional strength can be reduced by the presence of sheet-structured clay minerals. In this study, two important factors influencing the frictional coefficient of minerals were quantitatively analyzed by a newly developed computational method based on a combination of first-principles study and thermodynamics. One factor that helps reduce the frictional coefficient is the low adhesion energy between the layers under dry conditions. Potassium ions on mica surfaces are easily exchanged with sodium ions when brought into contact with highly concentrated sodium-halide solutions. We found that the surface ion exchange with sodium ions reduces the adhesion energy, indicating that the frictional coefficient can be reduced under dry conditions. Another factor is the lubrication caused by adsorbed water films on mineral surfaces under wet conditions. Potassium and sodium ions on mica surfaces have a strong affinity for water molecules. In order to remove the adsorbed water molecules confined between mica surfaces, a differential compressive stress of the order of tens of gigapascals was necessary at room temperature. These water molecules inhibit direct contact between mineral surfaces and reduce the frictional coefficient. Our results imply that the frictional coefficient can be modified through contact with fluids depending on their salt composition. The low adhesion energy between fault-forming minerals and the presence of an adsorbed water film is a possible reason for the low frictional coefficient observed at continuous fault slip zones.

Interlayer bonding energy of layered minerals: Implication for the relationship with friction coefficient

“…The experimentally determined E ILBE value was available only for muscovite (−150 to −200 mJ/m 2 ) [ Christenson , ]; this value is weaker than the calculated values obtained by using the DFT‐D2 method (−481 mJ/m 2 ). This result can be attributed to a combination of factors from both experiments and calculations, as discussed in previous research [ Sakuma , ]. These factors include the adsorption of contaminants on the mica surface, mismatched crystal axes among mica sheets, and the strong interaction in the underestimated interlayer distance (−2%) reflected by the DFT‐D2 calculations.…”

“…Herein, the ILBEs of sheet structure minerals were calculated by using the first‐principles density functional theory (DFT) method as previously applied to muscovite [ Sakuma , ]. DFT is rooted in quantum mechanics and has become a primary tool for calculating the electronic structures of minerals.…”

Frictional characteristics of single and polycrystalline muscovite and influence of fluid chemistry

“…The lubrication due to adsorbed water is mainly effective on the layered minerals [Moore and Lockner, 2004]. This seems to be curious since the adsorption energy of water on a quartz (À89.7 to À28.0 kJ/mol) [de Leeuw et al, 1999] and muscovite (001) surface (À49 kJ/mol) [Sakuma, 2013] is comparable, but the friction coefficient of quartz gauge remained to be constant under presence or absence of water at high normal stress (100 MPa) [Morrow et al, 2000]. One of a clue to understand the effect of adsorbed water on the friction coefficients of minerals may be the shape of minerals.…”

Frictional strength of wet and dry montmorillonite

“…These difficulties arise in part because montmorillonite is an expandable clay that typically takes on one to three layers of water in the interlayer spaces. In addition, it has a very high specific surface area, and each crystal surface can adsorb multiple layers of water (as many as six at saturation [ Hagymassy et al ., ; Ormerod and Newman , ; Sakuma , ]). Moreover, montmorillonite has extremely low permeability in the range of 10 −20 to 10 −22 m 2 at the pressures of interest (0 to 200 MPa) in crustal geophysical studies [ Morrow et al ., ].…”