**4. Theoretical studies on IFT and contact angle data**

Iglauer et al. concluded that a clean quartz/silica surface should have a 0° air-water CA; however, since the wettability of quartz/silica is primarily determined by surface silanol (Si-OH) group density that could vary from a sample to sample, the CA does not necessarily be 0° [30, 60, 61]. For example, as reported in [58], even a freshly prepared silica surface has an air-water CA of about 45°. The publication also mentions that cleaning methods such as acid washing would hydroxylate the surface and correspondingly reduce the CA (or make it hydrophilic). Suni et al. mentioned that plasma treatment induces a highly disordered surface structure and significantly increases the surface silanol group density [59]. Lamb and Furlong reported that when the surface silanols on a quartz substrate are changed to siloxane (Si-O-Si) bridges, the substrate becomes less water-wet with an advancing CA of

DIW: DI water; C: cell; S: substrate; NM: not mentioned; NA: not applicable; DM: Anton Paar DMA density meter; PRSW: Peng and Robinson [43] and Søreide and Whitson [44]; SWRC: Søreide and Whitson [44] and Rowe and Chou [45]; PGM: Perry and Green [46] and McCutcheon et al. [47]; DS: Duan and Sun [48]; NIST: National Institute of Standards and Technology Chemistry Webbook; BM: Blue M Model CSP-400A; HB: Hebach et al. [49]; MS: modified Spycher et al. [50]; GS: from Georgiadis et al. [24]; TND: tensioactive solution, 10% nitric acid solution and DI water; HITC: hexane,

; ADC: acetone, DI water, and CO<sup>2</sup>

**Table 1.** Details of fluids, process conditions, and cleaning chemicals used for published IFT and CA data.

, 3.14 g/L NaCl, and 2.38 g/L K<sup>2</sup>

Quartz, calcite, and mica substrates used for published CA data have many orders of magnitude difference in their surface roughness values. For example, quartz and calcite substrates with surface roughness values ranging from 0.5 to 1300 nm [16, 32, 34, 38] and 7.5 to 250 nm [33, 34], respectively, were used for the CA measurements. CA values are known to be affected by the surface roughness values and cleaning methods [32, 33, 56, 62]. The trends of the effect of surface roughness on CAs measured on quartz and calcite substrates are discussed in CA

44° and a receding CA of 39° [60].

**Author (Year) Aqueous-rich phase**

172 Carbon Capture, Utilization and Sequestration

0–0.342 M NaCl & 1 M NaHCO3

Iglauer et al. (2014) [30]

Saraji et al. (2014) [42]

Arif et al. (2016) [27]

Al-Yaseri et al. (2015) [26]

Kravanja et al. (2018) [28]

isopropanol, and/or toluene, CO<sup>2</sup>

ethanol; EDC: ethanol, DI water, and CO<sup>2</sup>

water [43–50].\*(10.88 g/L KCl, 6.68 g/L NaHCO3

**CO2**

(0–6 wt%)

(0–50 mol%)

(0–100 vol%)

0.2–5 M NaCl CO<sup>2</sup> + SO<sup>2</sup>

0.084 M NaCl CO<sup>2</sup> + N<sup>2</sup>

0.3 M Brine\* CO<sup>2</sup> + Ar

Deconex, and 6% nitric acid solution; WMC: water, methanol, and dry CO<sup>2</sup>

**-rich phase P** 

CO<sup>2</sup> 0.1–

**(MPa)**

13.89

13.89– 27.68

**T (K) Pre-**

0–5.13 M NaCl CO<sup>2</sup> 0.1–20 308–343 No NM S: Air plasma

**equilibrated?**

296–323 No NA Piranha

323–373 Yes DM S: IHND

13 333 No GS S: Acetone

0.1–40 313–363 Yes DM NM

; IHND: IPA, H<sup>2</sup>

CO3 ).

flush; KID: KOH-isopropanol solution and DI water; CNE: cyclohexane, nitrogen, and

**Densities for IFT**

; DA: DI water and acetone; DDN: DI water,

with 10% Nochromix, DI

SO<sup>4</sup>

**Cleaning chemicals**

solution or air plasma

and air plasma

for 45 min

data comparison section.

Molecular dynamics simulations for the prediction of IFT and CA data were performed by various research groups for systems pertaining to CO<sup>2</sup> sequestration [19, 63–70]. The simulation procedure consists of choosing potential models for molecules, intermolecular interaction models for short-range and/or long-range interactions, initial and boundary conditions, and the ensemble (NVE, NVT, NPT, etc.), followed by simulation until equilibration criteria is satisfied. After simulation, the results (IFT/CA data) are analyzed and compared with experimental values. The models evaluated were CO<sup>2</sup> —DZ, EPM2, flexible EPM2, PPL and TraPPE; Water—SPC, SPC/E, TIP4P2005, F3C, and flexible F3C; and NaCl brine—SD and DRVH [19, 63, 64, 66, 68].

The predictions on the effect of temperature and pressure on IFT for CO<sup>2</sup> -water system were found to be in good agreement with experimental data for the models used by Nielsen et al. (PPL-TIP4P2005 and renormalized PPL-SPC/E) and Liu et al. (TraPPE-TIP4P2005 (and SD model for NaCl) below 250°C except at 150°C and EPM2-SPC at 150°C), whereas EPM2- TIP4P2005 model combination used by Iglauer et al. and Liu et al. resulted in overprediction of IFT [64–66]. EPM-SPC/E model combination used by Kvamme et al. and Nielsen et al. underpredicted IFT data in the low-pressure region (<4 MPa) and overpredicted in the highpressure region (>10 MPa) [19, 65]. Nielsen et al. [65] observed the similar trend for DZ-SPC/E model combination, and they also observed that PPL-SPC/E model combination underpredicted IFT throughout 0–40 MPa. In agreement with experimental data [20, 22, 41, 42], IFT was found to increase with salinity by Zhao et al., Iglauer et al., and Liu et al. [63, 64, 66].

Various research groups performed CA predictions for water/brine–CO<sup>2</sup> –quartz/silica systems using molecular dynamics simulations [64, 67, 69, 70]. Iglauer et al. and McCaughan et al. considered fully coordinated quartz (i.e., siloxane bridges (Si-O-Si) and no silanol groups) surface structure and they only used short-range force field parameters Si-O (bonded) and O-O (non-bonded) retrieved from Beest and Kramer [64, 67, 71] in their simulations. Iglauer et al. [64] reported an abrupt increase in CA (0–80°) for water-CO<sup>2</sup> -quartz system at 300 K in the low-pressure region (0–6.7 MPa) and a nearly constant CA above 6.7 MPa. Simulations performed by McCaughan et al. [67] for 1 M CaCl<sup>2</sup> brine-CO<sup>2</sup> -quartz system at 300 K yielded similar CA values with pressure showing negligible effect of the divalent ions. At 350 K, significantly smaller CA values near both sides of the phase changing pressure were reported by Iglauer et al. [64] and the CA values at pressures above 17 MPa were found to be identical for 300 and 350 K. They also reported no significant effect of salinity (1 and 4 m NaCl) on CA at 300 K and ~4 MPa.

Liu et al., McCaughan et al., and Chen et al. considered hydroxylated quartz surfaces with different silanol group densities ranging from 1.6 to 9.4 OH/nm<sup>2</sup> for CA measurements [67, 69, 70]. Liu et al. [70] modeled a pristine silica plane having silicon atoms on the surface as hydrophobic surface and its partially hydroxylated variant with a silanol density of 1.6 OH/nm<sup>2</sup> as hydrophilic surface. They reported that CA on the hydrophilic surface increased from ~60 to ~90° when the CO<sup>2</sup> density increased from 0 to 1 g/cc. In the case of hydrophobic surface, water droplet with a CA of 115° at 0.2 g/cc CO<sup>2</sup> density lost its contact from the surface upon further increase in CO<sup>2</sup> density. At 300 K and 10 MPa, McCaughan et al. [67] reported that the CA reduced with increasing silanol group density (42° at 1.7 OH/nm<sup>2</sup> to 35° at 3.7–4.5 OH/nm<sup>2</sup> ). Chen et al. [69] performed molecular simulations, on fully hydroxylated silica surface with 9.4 OH/nm<sup>2</sup> silanol group density, using force field parameters for Si-O, O-H, O-Si-O, Si-O-Si, and Si-O-H groups to predict CAs for brine-CO<sup>2</sup> -quartz systems. 0–3 M NaCl and CaCl<sup>2</sup> brines were used in the study. The predicted static CAs (e.g., 22.6° for water) agreed well with their experimental results (20–21°). Their results indicate that CA slightly increases (about 7–13°) with ionic strength (0–3 M), and the trend is similar for both monovalent and divalent ions. They also reported that CA dependence on pressure and temperature is insignificant within the conditions tested (7 and 9.6 MPa at 318 K and 10.9 MPa at 333 K).

Tenney and Cygan performed molecular dynamics simulations for brine-CO<sup>2</sup> -clay system at 330 K and 20 MPa and reported CO<sup>2</sup> CAs for hydrophilic gibbsite and hydrophobic siloxane surfaces in the presence of water, NaCl, and CaCl<sup>2</sup> brine solutions. The reported CO<sup>2</sup> CAs were 169° in water and 180° in both brines on the hydrophilic surface, whereas on the hydrophobic surface, the reported CO<sup>2</sup> CAs were 145° in water, 141° in 0.78 M NaCl brine, and 145° in 0.26 M CaCl<sup>2</sup> brine [68].
