**3.1. Fluids**

preventing droplet evaporation due to leakage of fluids and/or using unsaturated fluids [31]; and using same type of substrates with similar surface chemistry and morphology [32, 33].

Wettability of an inert solid surface is its relative affinity towards a fluid in the presence of another immiscible or sparingly soluble fluid. CA measurement is a widely used and accepted method for quantifying wettability of a surface. Direct and indirect measurement methods have been used for the published CA data [12, 16, 23, 31–38]. Direct methods include static

**2.2. Contact angle**

168 Carbon Capture, Utilization and Sequestration

**Figure 4.** (a) Sessile aqueous fluid droplet on substrate in CO<sup>2</sup>

. Notation: θ—static CA; θ<sup>a</sup>

substrate in CO<sup>2</sup>

fluid; (c) sessile aqueous fluid droplet on inclined substrate in CO<sup>2</sup>

in aqueous fluid; (e) advancing aqueous fluid droplet on substrate in CO<sup>2</sup>

; (b) captive CO<sup>2</sup>

—aqueous fluid advancing CA; and θ<sup>r</sup>

; (d) captive CO<sup>2</sup>

bubble/droplet on substrate in aqueous

; and (f) receding aqueous fluid droplet on

—aqueous fluid receding CA.

bubble/droplet on inclined substrate

Various compositions of aqueous-rich phase and CO<sup>2</sup> -rich phase fluids, ranging from pure water and CO<sup>2</sup> to brines containing different types of salts and salinities, and CO<sup>2</sup> streams with impurities such as H<sup>2</sup> S, SO<sup>2</sup> , N<sup>2</sup> , and Ar have been used for both the published IFT and CA data. The details of the compositions of the fluid phases, ranges of pressure and temperature, whether the fluids had been mutually saturated before the IFT and CA measurements, whether the saturated fluid phase densities were used for the IFT measurement, and how the phase densities were obtained are provided in **Table 1**.

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

Chun et al. (1995) [29]

Chiquet et al. (2007) [18]

Chiquet et al. (2007) [55]

Bachu et al. (2008) [20]

Shah et al. (2008) [21]

Chalbaud et al. (2009) [13]

Espinoza et al. (2010) [23]

Georgiadis et al. (2010) [24]

Aggelopoulos et al. (2011) [22]

Bikkina et al. (2011) [15]

Bikkina (2011) [31]

Broseta et al. (2012) [40]

Jung et al. (2012) [41]

Shariat et al. (2012) [25]

Saraji et al. (2013) [16]

Farokhpoor et al. (2013) [35]

**CO2**

:H<sup>2</sup> S, 70:30 mol%

Water CO<sup>2</sup>

0.045–1.5 M NaCl: CaCl<sup>2</sup>

50:50 mol%

,

DIW CO<sup>2</sup> 1.48–

DIW CO<sup>2</sup> 1.48–

DIW CO<sup>2</sup> 6.89–

DIW CO<sup>2</sup> 3.45–

**-rich phase P** 

**(MPa)**

0.45– 15.6

0–2.75 M NaCl CO<sup>2</sup> 4.5–25.5 300–373 Yes Brine:

0–3.42 m NaCl CO<sup>2</sup> 0.1–20 296.5 ± 1.5 No Brine:

20.76

20.76

124.1

11.72

0.08–6 M NaCl CO<sup>2</sup> 0.5–15.5 282–413 Yes NA NM

0–5 M NaCl CO<sup>2</sup> 0.1–25 318 Yes NA C: DIW,

0–0.8 M NaCl CO<sup>2</sup> 0.1–40 309–339 No NA S: DDN

DIW CO<sup>2</sup> 1–60 298–374 No NIST C: HITC

CO<sup>2</sup> 5–25 300–373 Yes Brine:

DIW CO<sup>2</sup> 0.1–18.6 278–344 No Water:

0–0.34 M NaCl CO<sup>2</sup> 5–48 308–383 Yes DM C: NM

0.01–1 M NaCl CO<sup>2</sup> 1–11 NM No NA S: TND

0–5.72 M NaCl CO<sup>2</sup> 2–27 293–398 Yes DM NM

**T (K) Pre-**

**equilibrated?**

Interfacial Tension and Contact Angle Data Relevant to Carbon Sequestration

313–393 Yes Water:

298–333 Yes Water:

298–323 Yes NA C: AD,

323–478 No BM NM

308–333 Yes DM S: IHND

**Densities for IFT**

NM, CO<sup>2</sup> : Pure

http://dx.doi.org/10.5772/intechopen.79414

PRSW, CO<sup>2</sup> : PRSW

SWRC, CO<sup>2</sup> : Pure

PGM, CO<sup>2</sup> : DS

SWRC, CO<sup>2</sup> : Pure

HB, CO<sup>2</sup> : MS **Cleaning chemicals** 171

NM

NM

C: DIW

NM

C: EDC

C: ADC

Quartz: AD, Calcite: DIW

S: Ethanol

C: WMC

### **3.2. Substrates**

Quartz is one of the polymorphs of silica (SiO<sup>2</sup> ). The other polymorphs include tridymite, cristobalite, coesite, stishovite, etc. There are two types of quartz based on the geometrical positions of the atoms: α-quartz and β-quartz [51]. The published CA data were collected on α-quartz as it is related to typical pressure and temperature ranges of CO<sup>2</sup> sequestration. Calcite and aragonite are the two polymorphous groups of carbonate minerals. Calcite (CaCO3 ) is a mineral in calcite group. Generally, these minerals are impure, but majority of the CA data were collected on Iceland Spar calcite crystals which are pure CaCO3 [33, 34, 52]. Mica group is a subdivision of phyllosilicates. Muscovite (KAl3 Si3 O10(OH)<sup>2</sup> ), also known as common mica or potash mica, is the most common form of mica. Phlogopite (KMg3 (AlSi3 O10(OH,F)<sup>2</sup> ), called as Mg-Mica, is another form of mica. Mica is usually soft and has perfect basal cleavage [53]. Both muscovite [27, 35, 40, 54, 55] and phlogopite [34] micas have been used for CA data related to carbon sequestration.

In a short communication, Iglauer et al. attempted to identify possible reasons for the observed scatter in the reported CA data of quartz/glass-CO<sup>2</sup> -water/brine systems [30]. Different cleaning procedures such as acetone washing followed by DI water rinsing, piranha solution (5:1 v/v H<sup>2</sup> SO<sup>4</sup> and H<sup>2</sup> O2 ) cleaning (etching), and air plasma cleaning were evaluated. Approximately 0° CAs on the surfaces cleaned using piranha solution and air plasma were reported. It was also reported that the CA of piranha solution cleaned substrate increased to about 25° when a clean paper towel was used to wipe the substrate and to 70° when the substrate was kept in the laboratory atmosphere for several weeks. Even though both the piranha solution and plasma cleaning could give near 0° CA, plasma cleaning was suggested based on its relative merits in terms of health and environmental hazards. However, there is a significant scatter in the CA data of plasma cleaned quartz/silica surfaces. For example, water advancing CAs reported for Ar plasma and 20% O<sup>2</sup> –80% Ar plasma cleaned quartz surfaces were 40 and 16°, respectively [56]. The publication also reported advancing and receding CAs of about 39 and 23° for piranha solution cleaned quartz surface. Another study reported an air-water CA of about 45° on silica that had been cleaned using reactive ion etching oxygen plasma [57].

As Iglauer et al. [30] pointed out, surface contamination is one of the critical factors that affects wettability of a substrate; however, severe surface cleaning methods such as plasma or piranha etching could also alter the surface chemistry and/or morphology both of which are known to modify the wettability of a substrate [58, 59]. Quartz/silica surface cleaning has been done using degreasing chemicals such as acetone, methanol, and trichloroethylene and strong oxidizing agents such as hot nitric acid, hydrogen peroxide, and hydrofluoric acid that may remove surface layer [56].


CA data. The details of the compositions of the fluid phases, ranges of pressure and temperature, whether the fluids had been mutually saturated before the IFT and CA measurements, whether the saturated fluid phase densities were used for the IFT measurement, and how the

cristobalite, coesite, stishovite, etc. There are two types of quartz based on the geometrical positions of the atoms: α-quartz and β-quartz [51]. The published CA data were collected on

mineral in calcite group. Generally, these minerals are impure, but majority of the CA data

as Mg-Mica, is another form of mica. Mica is usually soft and has perfect basal cleavage [53]. Both muscovite [27, 35, 40, 54, 55] and phlogopite [34] micas have been used for CA data

In a short communication, Iglauer et al. attempted to identify possible reasons for the

Different cleaning procedures such as acetone washing followed by DI water rinsing, piranha

Approximately 0° CAs on the surfaces cleaned using piranha solution and air plasma were reported. It was also reported that the CA of piranha solution cleaned substrate increased to about 25° when a clean paper towel was used to wipe the substrate and to 70° when the substrate was kept in the laboratory atmosphere for several weeks. Even though both the piranha solution and plasma cleaning could give near 0° CA, plasma cleaning was suggested based on its relative merits in terms of health and environmental hazards. However, there is a significant scatter in the CA data of plasma cleaned quartz/silica surfaces. For example, water

were 40 and 16°, respectively [56]. The publication also reported advancing and receding CAs of about 39 and 23° for piranha solution cleaned quartz surface. Another study reported an air-water CA of about 45° on silica that had been cleaned using reactive ion etching oxygen

As Iglauer et al. [30] pointed out, surface contamination is one of the critical factors that affects wettability of a substrate; however, severe surface cleaning methods such as plasma or piranha etching could also alter the surface chemistry and/or morphology both of which are known to modify the wettability of a substrate [58, 59]. Quartz/silica surface cleaning has been done using degreasing chemicals such as acetone, methanol, and trichloroethylene and strong oxidizing agents such as hot nitric acid, hydrogen peroxide, and hydrofluoric acid that

Si3

O10(OH)<sup>2</sup>

) cleaning (etching), and air plasma cleaning were evaluated.

and aragonite are the two polymorphous groups of carbonate minerals. Calcite (CaCO3

α-quartz as it is related to typical pressure and temperature ranges of CO<sup>2</sup>

were collected on Iceland Spar calcite crystals which are pure CaCO3

or potash mica, is the most common form of mica. Phlogopite (KMg3

observed scatter in the reported CA data of quartz/glass-CO<sup>2</sup>

O2

). The other polymorphs include tridymite,

(AlSi3

–80% Ar plasma cleaned quartz surfaces

sequestration. Calcite

[33, 34, 52]. Mica group

), also known as common mica

O10(OH,F)<sup>2</sup>


) is a

), called

phase densities were obtained are provided in **Table 1**.

Quartz is one of the polymorphs of silica (SiO<sup>2</sup>

is a subdivision of phyllosilicates. Muscovite (KAl3

related to carbon sequestration.

170 Carbon Capture, Utilization and Sequestration

SO<sup>4</sup>

and H<sup>2</sup>

advancing CAs reported for Ar plasma and 20% O<sup>2</sup>

solution (5:1 v/v H<sup>2</sup>

plasma [57].

may remove surface layer [56].

**3.2. Substrates**


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

various research groups for systems pertaining to CO<sup>2</sup>

experimental values. The models evaluated were CO<sup>2</sup>

The predictions on the effect of temperature and pressure on IFT for CO<sup>2</sup>

DRVH [19, 63, 64, 66, 68].

300 K and ~4 MPa.

Molecular dynamics simulations for the prediction of IFT and CA data were performed by

tion 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

TraPPE; Water—SPC, SPC/E, TIP4P2005, F3C, and flexible F3C; and NaCl brine—SD and

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].

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

the low-pressure region (0–6.7 MPa) and a nearly constant CA above 6.7 MPa. Simulations

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

Liu et al., McCaughan et al., and Chen et al. considered hydroxylated quartz surfaces with different

[70] modeled a pristine silica plane having silicon atoms on the surface as hydrophobic surface

increased from 0 to 1 g/cc. In the case of hydrophobic surface, water droplet with a CA of 115° at

They reported that CA on the hydrophilic surface increased from ~60 to ~90° when the CO<sup>2</sup>

brine-CO<sup>2</sup>

Various research groups performed CA predictions for water/brine–CO<sup>2</sup>

et al. [64] reported an abrupt increase in CA (0–80°) for water-CO<sup>2</sup>

and its partially hydroxylated variant with a silanol density of 1.6 OH/nm<sup>2</sup>

performed by McCaughan et al. [67] for 1 M CaCl<sup>2</sup>

silanol group densities ranging from 1.6 to 9.4 OH/nm<sup>2</sup>

sequestration [19, 63–70]. The simula-

http://dx.doi.org/10.5772/intechopen.79414

173

Interfacial Tension and Contact Angle Data Relevant to Carbon Sequestration

—DZ, EPM2, flexible EPM2, PPL and


–quartz/silica systems


as hydrophilic surface.

density


for CA measurements [67, 69, 70]. Liu et al.

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, isopropanol, and/or toluene, CO<sup>2</sup> flush; KID: KOH-isopropanol solution and DI water; CNE: cyclohexane, nitrogen, and ethanol; EDC: ethanol, DI water, and CO<sup>2</sup> ; ADC: acetone, DI water, and CO<sup>2</sup> ; DA: DI water and acetone; DDN: DI water, Deconex, and 6% nitric acid solution; WMC: water, methanol, and dry CO<sup>2</sup> ; IHND: IPA, H<sup>2</sup> SO<sup>4</sup> with 10% Nochromix, DI water [43–50].\*(10.88 g/L KCl, 6.68 g/L NaHCO3 , 3.14 g/L NaCl, and 2.38 g/L K<sup>2</sup> CO3 ).

**Table 1.** Details of fluids, process conditions, and cleaning chemicals used for published IFT and CA 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 44° and a receding CA of 39° [60].

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 data comparison section.
