Wetting Phenomena at the CO₂/Water/Glass Interface

Abstract

A novel high-pressure apparatus and technique were developed to measure CO2/water/solid contact angles (theta) in situ for pressures up to 204 bar. For two glass substrates with different hydrophilicities, theta increased significantly with CO2 pressure. As the pressure was increased, an increase in the cohesive energy density of CO2 caused the substrate/CO2 and water/CO2 interfacial tensions (gamma) to decrease, whereas the water/substrate gamma value increased. theta for the more hydrophobic substrate was predicted accurately from the experimental water/CO2 gamma value and an interfacial model that included only long-range forces. However, for the more hydrophilic substrate, short-range specific interactions due to capping of the silanol groups by physisorbed CO2 resulted in an unusually large increase in the water/substrate gamma value, which led to a much larger increase in theta than predicted by the model. A novel type of theta hysteresis was discovered in which larger theta values were observed during depressurization than during pressurization, even down to ambient pressure. Effective receding angles were observed upon pressurization, and effective advancing angles were observed upon depressurization on the basis of movement of the three-phase contact line. The greater degree of hysteresis for the more hydrophilic silica can be attributed in part to the capping of silanol groups with CO2. The large effects of CO2 on the various interfacial energies play a key role in the enhanced ability of CO2, relative to many organic solvents, to dry silica surfaces as reported previously on the basis of FTIR spectroscopy (Tripp, C. P.; Combes, J. R. Langmuir 1998, 14, 7348-7352).

Molecular dynamics simulation of wetting behavior at CO2/water/solid interfaces

“…This simulation result shows that the presence of CO 2 fluids decreases the wettability of the surface. This obtained phenomenon is qualitatively consistent with the experimental observations on the wetting behavior at the CO 2 /water/glass [9] and CO 2 /water/polystyrene [10] interfaces. Figure 4 illustrates the water wetting behavior on the hydrophobic surface.…”

“…Of particular interest is how the exposure to the CO 2 fluid modifies the wetting nature of a solid surface. Dickson et al [10] experimentally investigated the wetting behavior at CO 2 /water/glass interfaces. Li et al [11] examined the wetting of water on polystyrene thin films with different thicknesses in pressured CO 2 environments.…”

CO2 geological storage — Geotechnical implications

“…Furthermore, the contact angle formed by the CO 2 -water interface on mineral surfaces varies with fluid pressure in response to changes in CO 2 -water interfacial tension: as the fluid pressure increases, the contact angle increases on non-wetting surfaces such as oil-wet quartz and coal and slightly decreases in water-wet quartz and calcite surfaces (Chalbaud et al, 2009;Chi et al, 1988;Chiquet et al, 2007;Dickson et al, 2006;Espinoza and Santamarina, 2010).…”

A statistical analysis of the effects of pressure, temperature and salinity on contact angles in CO 2 –brine–quartz systems

“…These discrepancies are generally attributed to study-specific factors including surface contamination or the surface roughness of the quartz substrates Iglauer et al, 2014), repeated surface exposure (Bikkina, 2011), contact-angle direction (that is, stationary, advancing or receding; see, for example, Saraji et al, 2013Saraji et al, , 2014, droplet size (Mills et al, 2011), subtle differences in surface materials including the type of quartz used (Dickson et al, 2006;Mills et al, 2011;Sarmadivaleh et al, 2015) but not measurement methods such as sessile drop versus captive bubble (Fig. 2;Montes Ruiz-Cabello et al, 2011).…”