Molecular Dynamics Simulation of Hydration and Swelling of Mixed

Subscriber access provided by MT SINAI SCH OF MED

C: Surfaces, Interfaces, Porous Materials, and Catalysis

Molecular Dynamics Simulation of Hydration and Swelling of Mixed- Layer Clays in the Presence of Carbon Dioxide Mahsa Rahromostaqim, and Muhammad Sahimi J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b11589 • Publication Date (Web): 29 Jan 2019 Downloaded from http://pubs.acs.org on February 3, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

Molecular Dynamics Simulation of Hydration and Swelling of MixedLayer Clays in the Presence of Carbon Dioxide Mahsa Rahromostaqim and Muhammad Sahimi∗ Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-1211, United States ABSTRACT: Swelling of clay minerals is an important phenomenon that is relevant to a many problems in geoscience, oil and gas reservoirs, geophysics and engineering. The phenomenon is even more complex when carbon dioxide is also present. Since sequestration of CO2 in sedimentary rock has been under active consideration as a way of alleviating the increasing concerns over climate change for which CO2 is a prime culprit, studying swelling of clays minerals in the presence of CO2 has taken on added urgency. The swelling changes the permeability and porosity of porous formations, which in turn may lead to reactivation of dormant fractures, triggering seismic activities, and opening up new pathways for CO2 to return to the porous formations’ surface. Although the large majority of sedimentary rocks contain various types of mixed-layer clays (MLCs) with intermixed stacking sequences of several types of distinct layers within a single crystal, the vast majority of the past experimental and computational studies of the swelling was focused on pure clays. We present the results of extensive molecular dynamics simulation of hydration and swelling of illite-montmorillonite (I-MMT) MLCs, the most common type of mixed clays, in the presence of both water and CO2 and various combinations of interlayer cations, Na+ and K.+ To understand the differences with pure clays, we also report on the same phenomenon in the MMT only. At low CO2 concentrations in Na-MMT, which has its layers’ charg concentrated in its octahedral sheet, weak ion-surface interactions result in fully hydrated ions and, therefore, more extensive swelling than in I-MMT. Without CO2 , adsorption of the cations at the illite surface increases the hydrophobicity of its surface. Thus, in the asymmetric interlayer of I-MMT, illite with stronger surface-ion interactions causes accumulation of cations near its surface, which limits their hydration and, therefore, controls swelling of the MLCs. Further inhibition of swelling of Na-MLC can be achieved by increasing the concentration of K+ in the interlayer. At higher CO2 concentrations, however, intercalation of water and CO2 results in a completely different behavior, since in the 2W and 3W hydration states the hydrophobicity of the MMT surface is stronger than that of illite. Therefore, the ACS Paragon Plus Environment

1

The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 47

density distributions of the intercalated molecules are considerably different from that with water only, which, together with disruption of the water network by CO2 , reduces the difference between the extent of swelling of the MLC and pure MMT.

ACS Paragon Plus Environment

2

Page 3 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1. INTRODUCTION The dramatic increase in the amount of CO2 , produced by consumption of fossil energy over the past several decades, and its role in the drastic global changes in the climate have become sources of serious concern. To alleviate the problem, several approaches have been proposed, one of which is injecting and storing CO2 in geological formations. According to a study by the European Technology Platform for Zero Emission Fossil Fuel Power Plants,1 deep saline aquifers represent 90 percent of potential storage opportunities for CO2 in the world. But, although the proposed solution is even being tested, many aspects of the behavior of CO2 buried deep in geological formations are still not well understood. For example, the pressure of the injected CO2 , as well as swelling of rock caused by CO2 , may change the permeability and porosity of the caprock, leading to reactivation of dormant fractures and triggering of seismic activities.2,3 The seismic events can not only open up new paths for the CO2 to reach the porous formations’ surface again, but can also lead to earthquakes. Caprocks include various types of clays, including pure and mixed-layer clays (MLCs). The pure clays are typically composed of illites, kaolinites, chlorites, or smectites.4 Although pure clays and their properties in the presence of water and/or CO2 have been studied extensively, MLCs do exist in abundance in caprocks, to the extent that it is more likely5 to find mixed-layer illite-montmorillonite (I-MMT) and chlorite-MMT than the pure illite or chlorite in geological formations. There has, however, been limited research focused on the swelling behavior of MLCs. Both illite and MMT are formed in a 2:1 or tetrahedral-octahedral-tetrahedral pattern. Their surfaces are composed of tetrahedral silicate sheets that surround the central octahedral sheet. Due to the metal substitution, the overall charge in both types of clays is negative. In the MMT, for example, most of the substitutions occur in the octahedral sheet where Al3+ is substituted by Mg2+ or by Fe,2+ whereas in illites substitution of Si4+ by Al3+ ions is dominant. Therefore, the charge densities of illite and MMT clays are concentrated, respectively, more on their surface and center of their clay structure. In addition to such major substitutions, minor substitutions also occur in the tetrahedral sites of the MMTs and the octahedral sites of illites. The negative charge of the clay layers is balanced by the interlayer cations, hence generating an electrically-neutral material. The common cations for the MMTs are6 Na,+ K,+ ACS Paragon Plus Environment

3


Page 4 of 47

Li,+ Cs,+ and Ca,2+ whereas it is K+ that usually neutralizes the illite clay layers. McGoldrick et al.7 compared swelling of pure MMT and pure beidellite at various water concentrations in the interlayer, noting that the beidellite structure is very similar to that of illite. They also reported that the behavior of the two types of the clays is very different and sensitive to the interlayer water content, due to the differences in the layer charge location. Paez et al. reported8 that, depending on the location of the substitutions, the interaction between the clay surface and the interlayer species may vary. The size and charge of the interlayer cations may also play important roles in the swelling.9,10 Depending on the hydration enthalpy of the cation and the strength of its interaction with the clay surface, extent of swelling varies. There have been studies that focused on the relationship between the interlayer K+ and swelling of clay,11−14 reporting that K+ could break the water network and, therefore, was able to control swelling of the clay. We recently reported15 on the results of extensive molecular dynamics (MD) simulations of swelling of I-MMT in the presence of water and interlayer cations. The MLC that we studied is the most abundant type of mixed clays, representing more than 60 percent of MLCs in the United States.5 We studied the effect of the layer charge and the interlayer cations on the swelling of I-MMT, and showed that, as the water concentration is varied, the swelling behavior of pure clays is quite different from that of the MLCs that we studied. In particular, at all water concentrations that we studied, the I-MMT swelled less than pure MMT-MMT clay. In addition, the presence of K+ in the interlayer of the MLC contributed to inhibiting the swelling.15,16 CO2 is in supercritical (SC) state when it is stored in geological formations and, therefore, understanding the interactions between SC CO2 and clays, particularly in the presence of water, is essential to understanding the long-term potential problems that may be caused by CO2 sequestration in the formations. The interaction between clay minerals, water and CO2 is, however, complex. A few studies with pure clays have shed some light on the phenomenon. For example, using NMR, Loring et al.17 found that there is no reaction between the interlayer CO2 and water that would produce bicarbonate or carbonic acid. Giesting et al.18 reported that the expansion of clay minerals due to CO2 adsorption is greatly affected by the initial water concentration in the clays. Ilton et al.19 showed that the stepwise hydration of Na-MMT to one-water, two-water and three-water (1W, 2W, 3W, respectively) and higher hydration states ACS Paragon Plus Environment

4

Page 5 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


with added SC CO2 is a function of the water saturation in the clay interlayer. Other studies,20−25 both experimental and computational, have also demonstrated that the initial water content plays a significant role in the extent of MMT swelling, when exposed to SC CO2 . For example, Rao et al.25 studied intercalation of water and CO2 in the MMT under geological conditions. They reported that CO2 molecules were highly mobile in the interlayer, but that they could hardly penetrate the hydration shell of Na,+ which indicated low probability of direct interaction between intercalated CO2 and Na.+ Bowers et al.26 also investigated the relationship between the interlayer cations, hydration and adsorption of CO2 in smectite clays. They reported that cations with small radii and higher hydration enthalpies prevent CO2 intercalation and maintain the water molecules in their hydration shell and, thus, rapidly swell the clay to higher hydration states. In contrast, counterions with large radii and lower hydration enthalpies interact with both water and CO2 , and allow their coexistence in a wide range of wetted SC CO2 concentrations. There have also been a few computational studies27−31 of the relationship between intercalated CO2 in smectite clays and swelling. Because the hydration enthalpy of the counterions can strongly influence swelling of smectite clays,32−35 the interactions between SC CO2 and hydrated clay are also expected to depend on the type of the counterion. In experiments in a quartz crystal microbalance Schaef et al.21 observed that at constant pressure, Ca-MMT adsorbed more CO2 than Na-MMT. This could be related to the number of cations needed to neutralize the clay negative charge, which is fewer in the case of Ca-MMTs that accommodate fewer hydration sites. There have been very limited studies on the interactions of K-smectites and intercalated CO2 . Giestign et al.,18 in particular, reported that in K-MMT bulk SC CO2 reached equilibrium with the clay structure, which resulted in the removal of water from the interlayer. Therefore, similar to Ca-MMT, swelling decreased. To our knowledge, there has never been any study focused on the interactions between hydrated MLCs and SC CO2 . The purpose of the present paper is, therefore, to report the results of such a study. We have carried out extensive MD simulation of swelling of I-MMT MLCs in the presence of interlayer water and SC CO2 . In addition, we present the results of MD simulations pertaining to the role of the interlayer Na+ and K+ in the MLC hydration, and compare the swelling behavior of various hydration states. The organization of the rest of this paper is as follows. In the next section we describe ACS Paragon Plus Environment

5


Page 6 of 47

the molecular models, the force fields, and the details of the MD simulations. The results are presented and discussed extensively in Section 3. The paper is summarized in Section 4. 2. THE FORCE FIELD AND DETAILS OF SIMULATION PROCEDURE The I-MMT mixed-layer representation is described comprehensively by Altaner and Ylagan.36 We constructed molecular models for the I-MMT. The chemical composition of the illite is K0.9 [(Al0.9 Mg0.1 )(Si3.2 Al0.8 )O10 (OH)2 ], while that of the sodium-saturated montmorillonite, NaMMT, is, Na0.75 [Si7.75 Al0.25 ](Al3.5 Mg0.5 )O20 (OH)4 . Each MMT layer has a net negative charge of -0.75—e— per unit cell, while the corresponding net charge for illite is -1.8—e—. The substitutions were inserted symmetrically in the clays’sheets. Figure 1 presents the side view of the clay layers, water, CO2 , and the counterions in the supercell structure of the MLC, which contains three distinct interlayers. The top and bottom layers are illite, whereas the two central ones are made of MMT. Therefore, the structure of the MLC is symmetric with respect to the central line located between the MMT sheets. The I-I and MMT-MMT interlayers contain, respectively, K+ and Na+ in order to balance the pure layers’ charge. The supercell structure contained a total of 80 unit cells. Each layer was constructed with 20 unit cells, organized as 5 × 4 unit cells along the x and y directions; see Fig. 1. The dimensions ˚2 and 5 × 8.8 A ˚2 . The equilibrium of the illite and MMT layers were, respectively, 5 × 9 A dimensions of the individual sheets in the illites and MMTs were, respectively, 26 × 35 ˚ A2 and 26 × 36 ˚ A2 . Periodic boundary conditions were imposed on the molecular structures. We used the force field CLAYFF37 and the LAMMPS package in order to generate molecular models of the MLCs, as well as Na-MMT that is used as a reference in order to understand the differences between MLCs and pure clays, and carried out the MD simulations. The flexible SPC model and the CLAYFF parameters for the hydroxyl group in the octahedral sheets were used to model water and the O-H groups in the supercell structure, respectively. The associated parameters, as well as those for the optimized force field parameters for CO2 were estimated by Cygan et al.29 The fully flexible model for CO2 that we utilized in the simulations produce predictions that agree with the experimental data,38 whereas the rigid models could not capture39 the deformation of the molecules due to vibration. According to CLAYFF the


6

Page 7 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


total interaction energy E of the material is given by, 

E=

X bonds

2

X

k1 (rij − r0 ) +

2

k2 (θijk − θ0 ) +

angle

X ij

σij ij  rij

!12

σij −2 rij

!6  +

e2 X qi qj . (1) 4πε0 i,j rij

Here, k1 and k2 are force constants, θijk is the angle between bonds ij and jk, e is the electron’s charge, qi is the partial charge of atom i, ε0 is the dielectric permittivity of vacuum, and r0 and θ0 are the equilibrium values of the corresponding quantities. i and σi are the usual Lennard-Jones (LJ) energy and size parameters, and the Lorentz-Berthelot mixing rules were used for the pairs ij. Table 1 presents the optimized parameters of CO2 for both the bond and non-bond interactions that we utilized in the simulations. Table 1. The CO2 parameters used in the MD calculations.29 Non-bond Parameters qC

0.6512 e

qO

-0.3245 e

εC

0.234 kJ/mol

εO

0.6683 kJ/mol

σC

2.80 ˚ A

σO

3.028 ˚ A Bond Parameters

k1 (C-O)

8433 kJ/mol-˚ A2

r0 (C-O)

1.162 ˚ A

k2 (O-C-O)

451.9 kJ/mol-rad2

θ0 (O-C-O)

180◦

Before carrying out any simulation involving water and CO2 , the molecular model of dry clay was generated in the N P T ensemble, which took 3 ns to reach equilibrium, after which the simulations involving water and CO2 began for each case that we studied at T = 348 K and P = 130 bar. The Nosé-Hoover thermostat and barostat were employed to control T and P with the coupling constants of 1000 and 100, respectively. After some preliminary simulations, the cut-off distance for computing the non-bonded interactions was set at 13 ˚ A. Therefore, long-range dispersion correction of the pressure and energy was enforced, and the long-range electrostatic interactions were computed with an accuracy of 10−4 using the Ewald ACS Paragon Plus Environment

7


Page 8 of 47

summation technique. Simulations with a time step of 0.01 fs for 1000 ps were followed by longer simulations with a time step of 1 fs. The duration of the simulations in the N P T ensemble in the presence of both water and CO2 varied between 25 and 40 ns, considerably longer than those used in our previous work15 involving only water. Next, the simulation continued in the N V T ensemble in order to calculate the density profiles, the radial distribution functions, and the diffusion coefficients (see below). After equilibrium was reached, the results were computed and averaged over the last 10 ns of the simulations. In all the simulations, the counterions were initially distributed at the midplane of each interlayer, whereas the initial spatial distributions of water and CO2 molecules were random. For each case involving the I-MMT interlayers, three series of simulations were carried out. One was with Na+ only; the second case was with K+ only, while the third involved a combination of two cations with 72% of the total being K+ and the remaining 28% being Na.+ To better understand the role of cations in the MLCs swelling and to have a basis for comparison with pure clays, two other sets of simulations were carried out in which either pure K+ or Na+ was present in the I-MMT interlayer, in order to neutralize the net negative charge of the MLCs. The CO2 content was varied from 0.5 to 4 molecules per unit cells, while the water content varied between one to nine molecules per unit cell. Note that since pure illite does not swell, there is only K+ in the I-I interlayer, which locks the two adjacent illite layers together. Therefore, the water-CO2 mixture is only added to the MMT-MMT and I-MMT interlayers. The main purpose of our study is to understand the effect of mixtures of water and CO2 , as well as the effects of the initial water concentration, the interlayer cations and the surface charges on the swelling of I-MMT MLCs and its differences with swelling of pure Na-MMT. As we describe below, since the combined number of water and CO2 molecules in the interlayer is large (up to 780 atoms of water and CO2 in each interlayer region), the 3W hydration state, in addition to the 1W and 2W states, also develops in some of the MLCs with high concentrations of water. 3. RESULTS AND DISCUSSION We computed several important and characteristic properties of the MLCs in the presence of water and CO2 . In what follows we present and describe the results and discuss their ACS Paragon Plus Environment

8

Page 9 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


implications. 3.1 Swelling and Basal Spacing. We define basal spacing d as the sum of the clay sheet’s thickness and the interlayer distance between that sheet and its neighboring ones. In the case of I-MMT all the basal spacings were calculated based on MMT’s thickness. AS already pointed out, in the case of the I-I interlayer the basal spacing d of pure illite remains constant about 10 ˚ A in all the simulations that we carried out. Figure 2(a) presents the computed basal spacing d of pure MMT interlayer as a function of the number of intercalated water and CO2 molecules. Also shown are the results without any CO2 , which were described in our previous study15 and are included here as a reference for comparison. The computed basal spacings are very close to the experimental and computational results reported previously.23,30 The small differences between the computed results and some of the experimental data may be due to slightly different original structure of the MMTs as a result of a slight difference in the chemical compositions. In addition, given that no force field is exact, some of the minor differences may be attributed to the CLAYFF. Water is adsorbed by clays in two steps. First, some water is adsorbed and forms the hydration shell for the counterions. This results in the expansion of the layer. In the second step, as the water content increases, it fills up the remaining volume of the interlayer without much swelling. As Figures 2(b) - 2(d) demonstrate, in almost all cases the more CO2 is added to the interlayer, the larger is the extent of swelling and the expansion of the interlayer region, when they are compared with the reference cases with water only. Figure 2 also indicates that the rate of the increase in the basal spacing is larger at the beginning of the transition between the hydration states. The rate reduces, however, at the end of the transition when the expanded volume is filled with more water and CO2 . Various combinations of water and CO2 give rise to three hydration states, namely, the aforementioned 1W, 2W and 3W states. In absence of CO2 , the 1W-to-2W transition in the MMT-MMT interlayer begins with 80 water molecules, with the 2W state becoming fully saturated when there are 160 water molecules in the interlayer region. As shown in Figure 2(a), as more CO2 was inserted into the interlayer region, the steep step signifying the transition was shifted to lower water contents. For example, with 40 CO2 molecules the transition begins with 40 water molecules also. Since the molecular size of CO2 is larger than water’s, swelling in some of the cases with similar extents happens at lower CO2 content. It should also be ACS Paragon Plus Environment

9


Page 10 of 47

noted that the transition between the hydration states happens more smoothly at higher CO2 concentrations; see the discussion of Figure 3 below. In general, however, and independent of the CO2 concentration, the transition between the 1W and 2W hydration states is sharper than that between 2W to 3W state at a constant CO2 concentration. This may be due to the small changes in the interactions between the interlayer species and the surface during the transition between 2W and 3W states, which also result in the 1W and 2W states being more stable states than the 3W. The computed basal spacings of MMT-MMT in the 1W, 2W, and 3W hydration states, when both water and CO2 are present are, respectively, in the ranges 11.5 − 12.5 ˚ A, 14 − 15 ˚ A, and 17.5 − 19 ˚ A. These are completely consistent with the experimental data.24,40 . As Figure 2 indicates, for I-MMT the transition between the first two hydration states is delayed to higher water and CO2 contents, especially in the presence of K+ as the counterion. The delay in the transition is caused by the asymmetry in the interlayer charges, as well as the effect of the hydration enthalpy of K+ on swelling, which was alluded to earlier. To gain a deeper understanding of the differences between the basal spacing of the four types of clays, both pure and mixed that we have studied, Figure 3 compares the relative basal spacings d as a function of the water and CO2 content. The relative basal spacings were computed by subtracting their absolute values shown in Figure 2 from those of their dry states. At low CO2 content the order of the relative swelling is MMT-MMT > Na-I-MMT > K-I-MMT and (K+Na)-I-MMT. The relative basal spacings at high CO2 contents, shown in Figures 3(d) and 3(e), indicate that the interlayers expand similarly, with little difference between their relative d values. Figure 3 also demonstrates the disruption of the hydration shells by CO2 . The distinguishable sharp transition between the 1W and 2W states in Figure 3(a) is gradually shifted to the more similar and continuous expansion for all the cases in Figure 3(e). The reason for the difference is that high concentrations of CO2 disrupt the hydration shells. In addition, the reduced hydrogen bonding, as well as the hydrophobicity of the clay surfaces, results in similar trends in the swellings. In fact, as CO2 is added, it escapes the more charged surface and disrupts the water hydration shells, which results in comparable basal spacing for all the cases that was pointed out earlier. We will return to this important point when we describe the results for the density profiles of the hydration states of the various cases in the next section. ACS Paragon Plus Environment

10

Page 11 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


3.2 Density Profiles. The density profiles were calculated for all the cases that we studied in order to understand the spatial distribution of the species in the interlayer region. The results represent averages along the direction perpendicular to the clay surfaces. As mentioned earlier, each of the hydration states develops in a range of water and CO2 composition. The monolayer was developed by 2H2 O + CO2 , 3H2 O + CO2 , 4H2 O + CO2 , etc. However, the density profiles and the extent of the saturation were slightly different for various combinations of the number of water and carbon dioxide. The bilayer was developed for a wider range of water plus CO2 , beginning from 2H2 O + 3 CO2 and 3H2 O + 3CO2 , up to the fully-saturated 2W state with 8H2 O + CO2 and 9H2 O + 0.5CO2 (per unit cell). The trilayer emerged at high water and CO2 concentrations, and is expected to still exist at concentrations larger than what we have considered in this study. It was first developed with 5H2 O + 4CO2 , until it was fully saturated with 7H2 O + 3CO2 and 9H2 O+4CO2 . The results are presented in Figure 4. The results for MMT-MMT, shown in Figures 4(a) - 4(c), should be compared with those reported by Myshakin et al.,30 who reported the 3W state with 3 peaks for CO2 and 2 peaks for water, which does not, however, represent the fully-saturated 3W state. Nevertheless, as mentioned earlier, in our simulations the 3W state emerged at low water and CO2 concentrations with 5H2 O + 4CO2 , with the fully-saturated 3W state at higher contents. The reason is that clays need to be wetted to intercalate CO2 . In the work of Myshakin et al.30 the CO2 concentration was high in the density profiles that they reported, which explains why more water was needed in order for the clay to expand to the fully-saturated 3W state. In our study, however, water concentration is up to 2.5 times that of CO2 in the fully-saturated 3W state. The extent of the swelling is, however, similar in both studies, if we compare the basal spacings. Our results for the density profiles for the 1W and 2W states in MMT-MMT clays agree with the previous results.23−25,30 According to the density profiles in MMT-MMT and Na+I-MMT that are presented in Figure 4, the distributions of water and CO2 in the case of monolayers are very similar. Due to the stronger negative charge on the illite surface, the Na+ cations are distributed close to the surface in I-MMT where they form inner sphere surface complexes (ISSCs), and where the basal oxygens also contribute to their first hydration shell. In MMT-MMT, however, Na+ is distributed predominantly in the outer-sphere surface complexes (OSSCs) with water. The 1W hydration state for the two interlayers is very similar to that of pure water.15 ACS Paragon Plus Environment

11


Page 12 of 47

Although when both water and CO2 are present, the density profiles in the bilayer region of MMT-MMT are analogous to the same in MMT-MMT but with only water,15 the same profiles for Na+I-MMT depend strongly on whether CO2 is present. When CO2 intercalates in the interlayer region, it prefers to migrate away from the clay surface substitutions. Therefore, in the MLC CO2 is at the farthest point from the more charged surface, namely, illite’s surface, and is distributed near the MMT surface. This results in more pronounced peaks in the density profiles of CO2 and water near the MMT and illite surface, respectively, with a weaker CO2 peak near the illite surface. For Na+ the distribution near the illite surface is similar to the case with only water. Close to the MMT surface, however, inserting CO2 in the MLCs splits the Na+ density profile into two peaks of the ISSC adsorption, including one deep into the hexagonal cavities41 of the clay and above the hexagonal ring of the tetrahedral sheet. Similar behavior occurs in the trilayer region with much stronger CO2 peaks near the MMT surface. Figure 5 compares the density distribution of oxygen in water, CO2 and the interlayer cations in the three hydration states of (Na+K)+I-MMT and K+I-MMT. We first note that, with the exception of the presence of Na+ in the former case with a notable peaks near the illite surface, the density profiles in the two clays are quite similar. Moreover, the distributions of Na+ and K+ are nearly independent of the amount of intercalated water and, therefore, the hydration states. A comparison of the density profiles for the two cases that contain both water and CO2 with those that contain only intercalated water in the 2W state indicates clear differences. In the bilayer states in the former cases the sharper water density peaks are near the MMT surface, whereas in the latter case they are near the illite surface. There are at least two reasons for the hydrophobicity of the surfaces in the cases with and without CO2 . In the absence of CO2 the cations make the illite surface hydrophobic and contribute to the migration of water molecules to the MMT surface, where they form hydrogen bonds with the basal oxygen atoms. On the other hand, in the presence of CO2 and due to its accumulation near the MMT surface, the extent of hydrophobicity of the MMT surface is stronger than that of the illite surface. Therefore, water molecules are inclined to distribute themselves on the opposite side of the MLC interlayer. This behavior, together with the disruption of the water network by CO2 , also explains the trends in the basal spacing d with no sharp jump between the states at high CO2 concentration (40 molecules and larger) in all the interlayers.


12

Page 13 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


3.3 Radial Distribution Functions. More insight into the distribution of the species in the interlayer region is gained by the radial distribution functions (RDFs) g(r) of a few pairs of the atoms. Figure 6 presents the results for the Na-OW (water oxygen) and Na-OS (surface oxygen) in the three interlayers containing the Na cations. In each case the water concentration was increased from 3 to 8 molecules per unit cell at constant CO2 concentration, which included the transition from the monolayer to the fully-saturated bilayer in each interlayer According to Figure 6(a), as the water content increases, the height of the peaks decreases. Note, however, that the peaks remain identical if we increase the water content of the clays with 80 and 100 water molecules. This may be understood if we consider Figures 6(a) 6(b), together with the results for the basal spacings presented earlier. The largest increase in the basal spacings in Figure 2(a) occurs when the water content increases from 80 to 100 molecules per unit cell. As explained earlier, the first step of hydration takes place when counterions are hydrated and transition from the ISSC- to the OSSC-dominated adsorption. Figures 6(a) and 6(b) demonstrate this clearly. As Figure 6(b) indicates, the RDF peak with between 80 and 100 water molecules decreases significantly, hence indicating migration of more Na+ from the surface toward the added water. At the same time, the equal heights of the two cases in Figure 6(a) confirm that the extra water has formed a hydration shell around the Na+ cations. Figures 6(c) - 6(f) indicate, however, that the transition between the 1W and 2W states occurs more smoothly for I-MMT than for MMT-MMT. In addition, although as Figures 6(c) and 6(e) indicate, the height of the Na-OW peak reduces during the transition from fully-saturated 1W to fully saturated 2W, the RDF of Na-OS contains several peaks near the MMT surface, and indicate a small decrease in the height of the peak due to the strong adsorption of the cations onto the clay surface. In addition, the peak of the RDFs of Na-OS in I-MMT does not continuously decrease as water concentration increases. This may be due to the instability of the Na hydration shells during their transitions when CO2 is present in the interlayer. Figure 7 compares the RDFs of K-OS and K-OW in K+I-MMT and (Na+K)+I-MMT. Figures 7(a) and 7(c) confirm the reluctance of K+ to hydrate relative to Na.+ As water is added to the interlayer region, the height of the peak in the RDF of K-OW decreases, whereas it increases for K-OS . This is similar to the case with only water in the interlayer space that manifested a jump from the 1W to 2W hydration state. It should also be noted that, compared with Na,+ the RDFs have sharper peaks with OS as one of the atoms in the pair and weaker ACS Paragon Plus Environment

13


Page 14 of 47

ones with OW , which is due15 to the low hydration enthalpy of K.+ In Figures 8 and 9 we compare the RDFs of K+ and Na+ for a constant water concentration as a function of CO2 concentration, varying from 0.5 to 4 molecules per unit cell. As Figures 8(a) - 8(c) indicate, the RDFs of Na-OW in I-MMT are independent of CO2 concentration, whereas the height of the RDF peak for pure MMT-MMT reduces at higher CO2 concentrations. Such similarities and differences are due to the difference in the spatial distributions of the interlayer species in pure MMT and I-MMT, which were presented in Figures 4 and 5. In the case of pure MMT, the locations of the peaks of density profiles of water and CO2 are at similar distances from the clay surface. Therefore, as CO2 is added, they disrupt the hydration shell of the counterions, which results in reduced stable interaction of water and Na.+ As discussed earlier, however, the density distribution of CO2 has a sharper peak close to the MMT surface. Recall that in the MLC interlayer most of the interlayer cations, as well as water molecules, are adsorbed onto the illite surface. Therefore, only a small portion of the total number of cations are adsorbed onto the MMT surface, where CO2 migrates and its density distribution has a sharp peak. Thus, the added CO2 mostly increases the density peak near the MMT surface, which does not considerably affect the interaction between water and Na+ with the higher density peaks near the illite surface. Figures 8(e) and 8(f) show that, contrary to the cases with constant CO2 concentration, the heights of the MLC’s RDFs increase as the amount of CO2 increases at constant water concentration. In the case of pure MMT, shown in Figure 8(d), there is a difference between its RDF with those of the MLCs in Figures 8(e) and 8(f). In pure MMT with lower CO2 concentrations, where fully-saturated 1W state begins transitioning to the 2W state (with 10 and 20 CO2 per unit cell, respectively), the ISSC adsorption is dominant. In fully-saturated 2W state (with 40 and 60 CO2 molecules per unit cell) the strongest Na peak belongs to the OSSCs. Finally, with 80 CO2 molecules per unit cell the transition from the 2W to 3W state is initiated in which the ISSCs are again more dominant than the OSSCs. The three different behaviors are better understood based on their associated density profiles, hence confirming the sensitivity of counterions in pure MMT to the intercalated species. In the case of pure MMT shown in Figure 8(d), however, if we consider the RDF for Na-OW shown in Figure 8(a), we recognize that as the interactions between Na+ and water decrease, the tendency of Na+ for surface adsorption increases. In the case of I-MMT with constant ACS Paragon Plus Environment

14

Page 15 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


water concentration, as CO2 content increases, the peaks in the density profiles of the ISSCs of the counterions become consistently sharper near the illite surface, resulting in a larger height for the first peak of the ISSC larger than that the second peak at the illite clay surface. In addition, the OSSCs in Na+ +I-MMT, shown in Figure 4(e), transition to the ISSCs at higher CO2 amounts, which also plays a role in giving rise to the sharper peaks of the density distribution of the counterions near the clay surface. Therefore, the height of the RDF for Na-OS increases considerably with the added CO2 , as indicated by Figures 8(e) and 8(f). K+ reacts to a change in the CO2 concentration in a manner similar to its reaction to increasing water concentration in the clays. Due to the low hydration enthalpy of K,+ adding water results in stronger adsorption of the cations onto the surface. Thus, as CO2 is added, the aforementioned disruption of the water network and the low hydration energy of K+ conspire together to increase the chances of migration of K+ to the clay surface, but this also decreases the chances of allocation of K+ near water molecules. The results are shown in Figure 9. The RDFs for the pairs CCO2 (carbon in CO2 ) and HW (hydrogen in water), as well as between OS and OCO2 are presented in Figure 10. In the case of CCO2 - HW there is a shoulder near r ≈ 2.3 ˚ A for both monolayer and bilayer states, which represents a hydrogen bond between water and CO2 . The life time of the hydrogen bond decreases as water concentration increases from the 1W to 2W state, which is also consistent30 with the average life times of OCO2 and HW . For the bilayer the RDF is similar for all the interlayer regions. In the monolayer, however, the MMT-MMT interlayer and Na+I-MMT manifest more pronounced shoulders that drop sharply when the 2W state forms. The difference between the life times of the hydrogen bonding in the monolayer of the MLCs with only Na+ and those containing K+ is linked with the distributions of water and CO2 in the latter cases. In fact, a perfect single density peak for water is not observed in the 1W state when K+ is present in the interlayer region that could result in a smoother changes in the lifetime of the hydration states of such cases. The RDFs for the OCO2 - OS , which are also shown in Figure 10, are very similar in all the cases at the beginning and the end of the transition from the monolayer to the bilayer states. However, similar to the transition of Na+ - OS , the transition in the shape of the RDF is smoother for the cases with K,+ and decays more rapidly in the cases of MMT-MMT and Na+I-MMT. The reason is that in the latter cases the emergence of the 2W state is delayed, as it is not formed until water concentrations are high. ACS Paragon Plus Environment

15


Page 16 of 47

3.4 Diffusion Coefficients. We also computed the diffusion coefficients of water, CO2 , Na+ and K+ in the interlayer regions by calculating the time-dependence of their mean-square displacements (MSDs) hR2 (t)i and using the Einstein’s relation. In the case of water and CO2 the MSDs were computed for their centers of mass. Typical plots of time-dependence of hR2 (t)i are shown in Figure 11. The computed diffusion coefficients are presented in Table 2. 3H2 O + CO2 refers to the monolayer state, while the other two cases in Table 2 represent bilayer hydration states. Generally speaking, the diffusion coefficients of water, CO2 and Na+ increase as the transition from the 1W to 2W state takes place. K+ has the lowest extent of mobility, which increases only slightly in the bilayer. This is explained by recalling the strong adsorption of K+ onto the illite surface. The mobility of Na+ is higher in pure MMT interlayer than in the MLCs, which is expected. In fact, the strong surface-counterion attraction in the MLCs reduces the mobility of the cations. In addition, in the two bilayer cases that we studied with a total of 8 and 9 water molecules per unit cells, the diffusivities of water and CO2 are considerably larger with a higher water-to-CO2 concentration ratio. Moreover, comparing the diffusivities in the 1W and 2W hydration states indicates that the change in them due to transition from the 1W to 2W state is more pronounced for CO2 than for water, which is due to the tendency of CO2 molecules to distribute themselves parallel to the clay surface. Table 2. The computed diffusion coefficients (×10−5 ) in the mixed-layers clays (in cm2 /s).


16

Page 17 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


3H2 O + CO2 H2 O 0.17

0.11

0.09

0.16

CO2

0.15

0.04

0.02

0.02

Na+

0.04

0.03

0.007

-

K+

-

-

0.002 0.001

4H2 O + 4CO2 H2 O 0.23

0.18

0.31

0.29

CO2

0.65

0.40

0.42

0.35

Na+

0.06

0.04

0.01

-

K+

-

-

0.01

0.002

8H2 O + CO2 H2 O 1.72

1.19

1.94

2.03

CO2

0.98

1.17

1.82

1.76

Na+

0.51

0.04

0.02

-

K+

-

-

0.01

0.001

The computed diffusivities in the 3H2 O + CO2 in the MMT are in good agreement with those reported previously.23,27 The species’ concentrations in the bilayers that we simulated are not the same as those in the previous works and, thus, no direct comparison is possible. We are also not aware of any experimental data to compare with the computed diffusivities. 4. SUMMARY This paper reported on the results of extensive molecular dynamics simulation of hydration and swelling of mixed-layer clays (MLCs) consisting of intermixed stacking of illite-montmorillonite (I-MMT), the most common type of mixed clays, in the presence of water and CO2 . Various combinations of the MLCs with interlayer cations Na+ and K+ were simulated, and their swelling was studied as a function of the water and CO2 contents. In order to have a basis for comparison and understand the differences between swelling of pure and mixed clays, we also reported on the same phenomenon in the MMT only. We found that at low CO2 concentrations in Na-MMT, which has its layer charge concentrated in its octahedral sheet, weak ion-surface interactions result in fully hydrated ions and, therefore, more extensive swelling than in I-MMT ACS Paragon Plus Environment

17


Page 18 of 47

under the same conditions. In the asymmetric interlayer region of I-MMT, however, the illite that has stronger surface-ion interactions gives rise to considerable cation concentration near its surface, which limits their hydration and, therefore, controls swelling of the MLCs. Further inhibition of swelling of Na-MLC may be achieved by increasing the concentration of K+ in the interlayer region. At higher CO2 concentrations, however, intercalation of a mixture of water and CO2 produces a completely different behavior. In the 2W and 3W hydration states the hydrophobicity of the MMT surface is stronger than that of the illite. Therefore, the density distributions of the intercalated molecules are considerably different from those with water only. This behavior, together with the disruption of water network by CO2 , reduces the difference in the extent of swelling of the MLC relative to pure MMT.

AUTHOR INFORMATION Corresponding Author ∗

E-mail: [email protected]. Phone: (213) 740-2064.

ORCID Muhammad Sahimi: 0000-0002-8009-542X Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS This work was supported as part of the Center for Geologic Storage of CO2 , an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Award DE-SC0C12504. The calculations were carried out using 12 nodes (each with 16 processors) of the computer network at the University of Southern California HighPerformance Computing Center.


18

Page 19 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


REFERENCES (1) The European Technology Platform for Zero Emission Fossil Fuel Power Plants, 2017, http://www.zeroemissionsplatform.eu/, accessed 28 November 2018. (2) Juanes, R.; Spiteri, E.J.; Orr Jr., F.M.; Blunt, M.J. Impact of Relative Permeability Hysteresis on Geological CO2 Storage. Water Resour. Res. 2006, 42, 2005WR004806. (3) Busch, A.; Bertier, P.; Gensterblum, Y.; Rother, G.; Spiers, C.J.; Zhang, M.; Wentinck, H.M. On Sorption and Swelling of CO2 in Clays. Geomech. Geophys. Geo-Energy GeoResour. 2016, 2, 111-130. (4) Brigatti, M.F.; Galan, E.; Theng, B. Structure and Mineralogy of Clay Minerals. In Developments in Clay Science., edited by Bergaya, F.; Theng, B.K.G.; Lagaly, G., Elsevier (2013), pp. 21-81. (5) Weaver, C.E. The Distribution and Identification of Mixed-Layer Clays in Sedimentary Rocks. Clays Clay Miner. 1955, 4, 385-386. (6) Norrish, K. The Swelling of Montmorillonite. Discussions of the Faraday Society 1954, 18, 120-134. (7) Teich-McGoldrick, S.L.; Greathouse, J.A.; Jové-Colón, C.F.; Cygan, R.T. Swelling Properties of Montmorillonite and Beidellite Clay Minerals from Molecular Simulation: Comparison of Temperature, Interlayer Cation, and Charge Location Effects. J. Phys. Chem. C 2015, 119, 20880-20891. (8) Chávez-Páez, M.; de Pablo, L.; de Pablo, J. Monte Carlo Simulations of Ca-Montmorillonite Hydrates. J. Chem. Phys. 2001, 114, 10948-10953. (9) Bérend, I.; Cases, J.-M.; Francois, M.; Uriot, J.-P.; Michot, L.; Masion, A.; Thomas, F. Mechanism of Adsorption and Desorption of Water Vapor by Homoionic Montmorillonites: 2. The Li+ , Na+ , K+ , Rb+ and Cs+ -Exchanged forms. Clays Clay Miner. 1995, 43, 324-336. (10) Young, D.A.; Smith, D.E. Simulations of Clay Mineral Swelling and Hydration: Dependence upon Interlayer Ion Size and Charge. J. Phys. Chem. B 2000, 104, 9163-9170. ACS Paragon Plus Environment

19


Page 20 of 47

(11) Degrév, L.; Vechi, S.M.; Junior, C.Q. The Hydration Structure of the Na+ and K+ Ions and the Selectivity of Their Ionic Channels. Biochimica Biophysica Acta - Bioenergetics 1996, 1274, 149-156. (12) Hensen, E.J.M.; Tambach, T.J.; Bliek, A.; Smit, B. Adsorption Isotherms of Water in Li-, Na- and K-Montmorillonite by Molecular Simulation. J. Chem. Phys. 2001, 115, 3322-3329. (13) Ferrage, E.; Sakharov, B.; Michot, L.J.; Delville, L.; Bauer, A.; Lanson, B.; Grangeon, S.; Frapper, G.; Jiménez-Ruiz, M.; Cuello, G.J. Hydration Properties and Interlayer Organization of Water and Ions in Synthetic Na-Smectite with Tetrahedral Layer Charge. Part 2. Toward a Precise Coupling Between Molecular Simulations and Diffraction Data. J. Phys. Chem. C 2011, 115, 1867-1881. (14) Denis, J.H.; Keall, M.J.; Hall, P.L.; Meeten, G.H. Influence of Potassium Concentration on the Swelling and Compaction of Mixed (Na, K) Ion-Exchanged Montmorillonite. Clay Miner. 1991, 26, 255-268. (15) Rahromostaqim, M.; Sahimi, M. Molecular Dynamics Simulation of Hydration and Swelling of Mixed-Layer Clays. J. Phys. Chem. C 2018, 122, 14631-14639. (16) Liu, X.D.; Lu, X.C. A Thermodynamic Understanding of Clay-Swelling Inhibition by Potassium Ions. Angew. Chemie Int. Edition 2006, 45, 6300-6303. (17) Loring, J.S.; Ilton, E.S.; Chen, J.; Thompson, C.J.; Martin, P.F.; Bénézeth, P.; Rosso, K.M.; Felmy, A.R.; Schaef, H.T. In Situ Study of CO2 and H2 O Partitioning between Na-Montmorillonite and Variably Wet Supercritical Carbon Dioxide. Langmuir 2014, 30, 6120-6128. (18) Giesting, P.; Guggenheim, S.; Koster van Groos, A.F.; Busch, A. Interaction of Carbon Dioxide with Na-Exchanged Montmorillonite at Pressures to 640 Bars: Implications for CO2 Sequestration. Int. J. Greenhouse Gas Control 2012, 8, 73-81. (19) Ilton, E.S.; Schaeff, H.T.; Qafoku, O.; Rosso, K.M.; Felmy, A.R. In Situ X-Ray Diffraction Study of Na+ Saturated Montmorillonite Exposed to Variably Wet Super Critical CO2 . Environ. Sci. Technol. 2012, 46, 4241-4248. ACS Paragon Plus Environment

20

Page 21 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(20) Loring, J.S., et al. In Situ Molecular Spectroscopic Evidence for CO2 Intercalation into Montmorillonite in Supercritical Carbon Dioxide. Langmuir 2012, 28, 7125-7128. (21) Schaef, H.T., et al. Competitive Sorption of CO2 and H2 O in 2:1 Layer Phyllosilicates. Geochimica Cosmochimica Acta 2015, 161, 248-257. (22) Loring, J.S., et al. Clay Hydration/Dehydration in Dry to Water-Saturated Supercritical CO2 : Implications for Caprock Integrity. Energy Procedia 2013, 37, 5443-5448. (23) Makaremi, M.; Jordan, K.D., Guthrie, G.D., Myshakin, E.M. Multiphase Monte Carlo and Molecular Dynamics Simulations of Water and CO2 Intercalation in Montmorillonite and Beidellite. J. Phys. Chem. C 2015, 119, 15112-15124. (24) Kadoura, A.; Narayanan Nair, A.K.; Sun, S. Molecular Dynamics Simulations of Carbon Dioxide, Methane, and Their Mixture in Montmorillonite Clay Hydrates. J. Phys. Chem. C 2016, 120, 12517-12529. (25) Rao, Q.; Leng, Y. Molecular Understanding of CO2 and H2 O in a Montmorillonite Clay Interlayer under CO2 Geological Sequestration Conditions. J. Phys. Chem. C 2016, 120, 2642-2654. (26) Bowers, G.M.; Schaef, H.T.; Loring, J.S.; Hoyt, D.W.; Burton, S.D.; Walter, E.D.; Kirkpatrick, R.J. Role of Cations in CO2 Adsorption, Dynamics, and Hydration in Smectite Clays Under in Situ Supercritical CO2 Conditions. J. Phys. Chem. C 2017, 121, 577-592. (27) Botan, A.; Rotenberg, B.; Marry, V.; Turq, P.; Noetinger, B. Carbon Dioxide in Montmorillonite Clay Hydrates: Thermodynamics, Structure, and Transport from Molecular Simulation. J. Phys. Chem. C 2010, 114, 14962-14969. (28) Sena, M.M.; Morrow, C.P.; Kirkpatrick, R.J.; Krishnan, M. Supercritical Carbon Dioxide at Smectite Mineral-Water Interfaces: Molecular Dynamics and Adaptive Biasing Force Investigation of CO2 /H2 O Mixtures Nanoconfined in Na-Montmorillonite. Chem. Mater. 2015, 27, 6946-6959. (29) Cygan, R.T.; Romanov, V.N.; Myshakin, E.M. Molecular Simulation of Carbon Dioxide Capture by Montmorillonite Using an Accurate and Flexible Force Field. J. Phys. Chem. ACS Paragon Plus Environment

21


Page 22 of 47

C 2012, 116, 13079-13091. (30) Myshakin, E.M.; Saidi, V.; Romanov, V.N.; Cygan, R.T.; Jordan, K.D. Molecular Dynamics Simulations of Carbon Dioxide Intercalation in Hydrated Na-Montmorillonite. J. Phys. Chem. C 2013, 117, 11028-11039. (31) Krishnan, M.; Saharay, M.; Kirkpatrick, R.J. Molecular Dynamics Modeling of CO2 and poly (ethyleneglycol) in Montmorillonite: The Structure of Clay-Polymer Composites and the Incorporation of CO2 . J. Phys. Chem. C 2013, 117 20592-20609. (32) Reddy, U.V.; Bowers, G.M.; Loganathan, N.; Bowden, M.; Yazatdin, A.O.; Kirkpatrick, R.J. Water Structure and Dynamics in Smectites: X-Ray Diffraction and 2H NMR Spectroscopy of Mg-, Ca-, Sr-, Na-, Cs-, and Pb-Hectorite. J. Phys. Chem. C 2016, 120, 8863-8876. (33) Bowers, G.M.; Bish, D.L.; Kirkpatrick, R.J. H2 O and Cation Structure and Dynamics in Expandable Clays: 2 H and

39

K NMR Investigations of Hectorite. J. Phys. Chem. C

2008, 112, 6430-6438. (34) Baalousha, M.; Motelica-Heino, M.; Le Coustumer, P. Conformation and Size of Humic Substances: Effects of Major Cation Concentration and Type, pH, Salinity, and Residence Time. Colloid Surfaces A: Physicochem. Eng. Aspects 2006, 272, 48-55. (35) Weiss Jr., C.A.; Kirkpatrick, R.J.; Altaner, S.P. The Structural Environments of Cations Adsorbed onto Clays:

133

Cs Variable-Temperature MAS NMR Spectroscopic Study of

Hectorite. Geochimica Cosmochimica Acta 1990 54, 1655-1669. (36) Altaner, S.P.; Ylagan, R.F. Comparison of Structural Models of Mixed-Layer Illite/Smectite and Reaction Mechanisms of Smectite Illitization. Clays Clay Miner 1997, 45, 517-533. (37) Cygan, R.T.; Liang, J.-J.; Kalinichev, A.G. Molecular Models of Hydroxide, Oxyhydroxide, and Clay Phases and the Development of a General Force Field. J. Phys. Chem. B 2004, 108, 1255-1266. (38) Yagi, Y.; Tsugani, H.; Inomata, H.; Saitp, S. Density Dependence of Fermi Resonance of Supercritical Carbon Dioxide. J. Supercrit. Fluids 1993, 6, 139-142. ACS Paragon Plus Environment

22

Page 23 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(39) Qin, Y.; Yang, Y.; Zhu, Y.; Ping, J. Molecular Dynamics Simulation of Interaction Between Supercritical CO2 Fluid and Modified Silica Surfaces. J. Phys. Chem. C 2008, 112, 12815-12824. (40) Whitley, H.D.; Smith, D.E. Free Energy, Energy, and Entropy of Swelling in Cs-, Na-, and Sr-Montmorillonite Clays. J. Chem. Phys. 2004, 120, 5387-5395. (41) Lammers, L.N.; Bourg, I.C., Okumura, M.; Kolluri, K.; Sposito, G.; Machida, M. Molecular Dynamics Simulations of Cesium Adsorption on Illite Nanoparticles. J. Colloid interface Sci. 2017, 490, 608-620.


23


total atom count

MMT

MMT

Illite

3

water O CO2 O CO2 C Na+ K+

2.5 2 1.5 1 0.5 0

Illite

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 47

0

1

2

3 4 5 6 7 8 interlayer distance (Å)

Figure 1: Table of contents graphic


24

9

10 11

Page 25 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2: Side view of the simulation cell for I-MMT. The top and bottom layers are illite, while the two middle layers are the MMT.


25


20

16

d (Å) spacing

d (Å) spacing

20

0 10 20 40 60 80

18

14

0 10 20 40 60 80

18 16 14 12

12

(b)

(a)

10

10 0

20

40

60

80

0

100 120 140 160 180 200

20

40

60

80

100 120 140 160 180 200

number of water molecules

number of water molecules 20

20 0 10 20 40 60 80

18

16

0 10 20 40 60 80

18

d (Å) spacing

d (Å) spacing

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 47

14 12

16

14 12

(c)

(d)

10

10

0

20

40

60

80

100 120 140 160 180 200

0

20


40

60

80

100 120 140 160 180 200


Figure 3: Absolute basal spacings d of (a) MMT-MMT; (b) I-MMT with Na;+ (c) I-MMT with 72% K+ and 28% Na,+ and (d) I-MMT with K.+ The number of CO2 molecules is per unit cell. ACS Paragon Plus Environment

26

Page 27 of 47

8

8

MMT-MMT

MMT-MMT Na+I-MMT (K+Na)-I-MMT

4

Na+I-MMT

6

K+I-MMT

d (Å)

d (Å)

6

K+I-MMT (K+Na)-I-MMT

4

2

2

(b)

(a)

0

0 0

0

20 40 60 80 100 120 140 160 180 200

20 40 60 80 100 120 140 160 180 200

Number of water molecules


10

8

MMT-MMT

MMT-MMT Na+I-MMT

Na+I-MMT

8 d (Å)


6 d (Å)

4


6 4

(d)

(c)

2

2 0

20 40 60 80 100 120 140 160 180 200

0

20 40 60 80 100 120 140 160 180 200


Number of water molecules 10 MMT-MMT Na+I-MMT

8

K+I-MMT

d (Å)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(K+Na)-I-MMT

6 (e)

4 0

20 40 60 80 100 120 140 160 180 200


Figure 4: Dependence of the relative basal spacings on the water content at a fixed number of CO2 molecules per unit cell. (a) 10 CO2 ; (b) 20CO2 ; (c) 40CO2 ; (d) 60CO2 , and (e) 80 CO2 molecules. ACS Paragon Plus Environment

27


(a) total atom count

total atom count

4.5 4 3.5 3 2.5 2 1.5 1 0.5 0

0

1

2 3 4 interlayer distance (Å)

total atom count

total atom count

2

1.5 1 0.5 0 0

1

2

3

4

5

6

7

(d)

0

(b)

2.5

4 3.5 3 2.5 2 1.5 1 0.5 0

5

3

3.5 3 2.5 2 1.5 1 0.5 0

8

1

1

interlayer distance (Å)

total atom count

1.5 1

0.5 0

0

1

2 3 4 5 6 7 8 interlayer distance (Å)

5

2

7

3

4

5

6

8


(c)

2


(e)

0

2.5 total atom count

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 47

9 10 11

3.5 3 2.5 2 1.5 1 0.5 0

(f)

0

1

2

3 4 5 6 7 8 9 10 interlayer distance (Å)

Figure 5: Density profiles of the 1W, 2W, and 3W hydration states, perpendicular to the clay surfaces of MMT-MMT, shown in (a), (b), and (c), and in Na+I-MMT shown in (d), (e), and (f). The results for water oxygen are represented by red, CO2 oxygen and carbon by black and blue, and Na+ in green. In the I-MMT interlayer the left layer is illite and the right layer is MMT. ACS Paragon Plus Environment

28

Page 29 of 47

total atom count

3 2.5

(d)


2

total atom count

total atom count

total atom count

total atom count

totalatom atomcount count total total atom count

total atom count


1.5 1 2 1 3 0.5 4 0 5 3 6 4 5 0 1 2 3 4 5 tance (Å) interlayer distance (Å) 7 3 3 3 8 2.5 (a) (d) (d) 2.5 (e) 9 2.5 2.5 2 10 2 22 11 1.5 1.5 1.5 1.5 12 1 13 11 1 14 0.5 0.5 0.5 0.5 15 0 00 0 16 0 1 2 2 3 3 4 4 5 5 0 1 2 3 4 5 4 5 0 1 0 1 2 3 4 5 6 7 8 9 517 6 7 8 interlayer distance (Å) interlayer distance (Å) ance interlayer 18 (Å) tance(Å) interlayer distance distance (Å) (Å) 3 19 2.5 2.53 (b) (e) (e) 20 2.5 (f) 2 2.5 2 21 2 22 1.5 1.52 23 1.5 1.5 1 24 1 11 25 0.5 0.5 0.5 26 0.5 27 0 000 28 0 1 2 3 4 5 6 7 8 9 00 0 11 12 2 32 34 345 465 756 8 769 10 87 11 98 6 5 7 68 97 108 11 29 interlayerdistance distance(Å) interlayer distance (Å) ance(Å) interlayer (Å) interlayer distance (Å) ance(Å) 30 3 33 31 (c) (f) (f) 2.5 2.5 2.5 32 33 2 22 34 1.5 1.5 1.5 35 1 11 36 37 0.5 0.5 0.5 38 0 00 39 0 1 2 3 4 5 6 7 8 9 10 11 0 1 2 3 4 5 6 7 8 9 10 11 0 1 2 3 4 5 6 7 8 9 10 11 6 7 8 9 10 11 40 interlayer distance (Å) interlayer (Å) interlayer distance distance(Å) ance(Å) 41 42 43 44 45 46 47 48 49 50 51 Figure 6: Density profiles of 1W, 2W and 3W states perpendicular to the clay surfaces of 52 53 I-MMT with 72% K+ and 28% Na+ , shown in (a), (b), and (c), and K+I-MMT, shown in (d), 54 (e), and (f). The results for water oxygen are represented by red, CO2 oxygen and carbon by 55 56 black and blue, Na+ by green, and K+ by purple. In the I-MMT interlayer the left layer is illite 57 58 and the right layer is MMT. 59 ACS Paragon Plus Environment 60

29


1.6

32.0

(a)

60-20 80-20 100-20 120-20 160-20

16.0

60-20 80-20 100-20 120-20 160-20

1.2

g(r)

g(r)

24.0

0.8

8.0

0.4

0.0

0

(b)

0

1

2

3

4

5

6

7

0

1

2

3

4

5

6

7

4

5

6

7

3 r (Å)4

5

6

7

r (Å)

r (Å)

20.0

1.6 (c) 60-20 80-20 100-20 120-20 160-20

12.0

8.0

60-20 80-20 100-20 120-20 160-20

1.2

g(r)

g(r)

16.0

0.8 0.4

4.0

(d)

0.0

0

0

1

2

3

4

5

6

7

0

1

2

3 r (Å)

r (Å) 20.0

1.6

(e) 60-20 80-20 100-20 120-20 160-20

12.0 8.0

60-20 80-20 100-20 120-20 160-20

1.2

g(r)

16.0

g(r)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 47

0.8

0.4

4.0

(f)

0.0

0

0

1

2

3

4

5

6

7

0

r (Å)

1

2

Figure 7: Radial distribution functions for Na-OW (left) and Na-OS (right) at constant CO2 concentrations in (a) and (b) MMT-MMT; (c) and (d) I-MMT with Na,+ and (e) and (f) I-MMT with 72% K+ and 28% Na.+ ACS Paragon Plus Environment

30

Page 31 of 47

3.0

10.0

(a) 8.0

2.0

g(r)

g(r)

60-20 80-20 100-20 120-20 160-20

2.5

60-20 80-20 100-20 120-20 160-20

6.0

4.0

1.5

1.0

2.0

0.5

0.0

0.0

0

1

2

3 r (Å)4

5

6

(b)

0

7

1

2

3 4 r (Å)

5

6

7

3 4 r (Å)

5

6

7

3.0

10.0 (c)

2.5

60-20 80-20 100-20 120-20 160-20

6.0

4.0

60-20 80-20 100-20 120-20 160-20

2.0

g(r)

8.0

g(r)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1.5 1.0

2.0

0.5

0.0

0.0

0

1

2

3

4 r (Å)

5

6

7

(d)

0

1

2

Figure 8: Radial distribution functions of K-OW (left) and K-OS (right) at constant CO2 concentrations in (a) and (b) I-MMT with 72% K+ and 28% Na,+ and (c) and (d) I-MMT with K+ only. ACS Paragon Plus Environment

31


1.2

35.0 80-10 80-20 80-40 80-60 80-80

21.0

80-10 80-20 80-40 80-60 80-80

0.8

g(r)

g(r)

28.0

14.0

0.4

7.0

(a)

(d) 0.0

0.0

0

1

2

3 r (Å)

4

5

0

6

20.0 80-10 80-20 80-40 80-60 80-80

2

3 r (Å)

4

5

6

12.0 8.0

4

5

6

4

5

6

80-10 80-20 80-40 80-60 80-80

1.2

g(r)

g(r)

1

1.6

16.0

0.8 0.4

4.0

(b)

(e)

0.0

0.0

0

1

2

3 r (Å)

4

5

6

0

20.0

1

2

3 r (Å)

1.6 80-10 80-20 80-40 80-60 80-80

12.0 8.0

80-10 80-20 80-40 80-60 80-80

1.2

g(r)

16.0

g(r)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 47

0.8 0.4

4.0

(e)

(f)

0.0

0.0

0

1

2

3 r (Å)

4

5

6

0

1

2

3 r (Å)

Figure 9: Radial distribution functions for Na-OW (left) and Na-OS (right) at constant water concentrations in (a) and (d) MMT-MMT; (b) and (e) I-MMT with Na,+ and (c) and (f) I-MMT with 72% K+ and 28% Na.+ ACS Paragon Plus Environment

32

Page 33 of 47

10.0

3.0 80-10 80-20 80-40 80-60 80-80

6.0

80-10 80-20 80-40 80-60 80-80

2.0

g(r)

g(r)

8.0

4.0

1.0

2.0

(c)

(a) 0.0

0.0

0

1

2

3 r (Å)

4

5

0

6

10.0

1

2

3 r (Å)

4

5

6

4

5

6

3.0 80-10 80-20 80-40 80-60 80-80

6.0

80-10 80-20 80-40 80-60 80-80

2.0

g(r)

8.0

g(r)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


4.0

1.0

2.0

(d)

(b) 0.0

0.0

0

1

2

3 r (Å)

4

5

6

0

1

2

3 r (Å)

Figure 10: Radial distribution functions of K-OW (left) and K-OS (right) at constant CO2 concentrations in (a) and (b) I-MMT with 72% K+ and 28% Na,+ and (c) and (d) I-MMT with K+ only. ACS Paragon Plus Environment

33


1.5

2.0 60-20 80-20 100-20 120-20 160-20

1.0

60-20 80-20 100-20 120-20 160-20

1

g(r)

g(r)

1.5

0.5 0.5

(b)

(a)

0

0.0

0

1

2

3 4 r (Å)

5

6

7

0

8

0.8

1.5

g(r)

1.2

g(r)

2

3 r (Å)

4

5

6

2

3 r (Å)

4

5

6

3

4

5

6

2 3 r (Å)

4

5

6

60-20 80-20 100-20 120-20 160-20

2

60-20 80-20 100-20 120-20 160-20

1.6

1 0.5

0.4 (c)

(d)

0

0.0

0

1

2

3 4 r (Å)

5

6

7

0

8

1

2.5

1.6

1.5

g(r)

0.8

60-20 80-20 100-20 120-20 160-60

2.0

60-20 80-20 100-20 120-20 160-20

1.2

g(r)

1

2.5

2.0

0.4

1.0 0.5

(f)

(e)

0

0.0

0

1

2

3 4 r (Å)

5

6

7

8

0

1

2 r (Å)

2.5

1.6 60-20 80-20 100-20 120-20 160-20

0.8

2.0

60-20 80-20 100-20 120-20 160-20

1.5

g(r)

1.2

g(r)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 47

0.4

1.0 0.5

(h)

(g)

0.0

0.0

0

1

2

3 4 r (Å)

5

6

7

8

0

1

Figure 11: Radial distribution functions for OCO2 -OS (left) and CCO2 -HW (right) in (a) and (b) MMT-MMT; (c) and (d) Na+I-MMT; (e) and (f) I-MMT with 72% K+ and 28% Na,+ and (g) and (h) K+I-MMT. ACS Paragon Plus Environment

34

Page 35 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 12: Mean-square displacements (MSD) of water (a) and Na+ (b).


35


3

Illite

total atom count

MMT

MMT

Illite

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 36 of 47

water O CO2 O CO2 C Na+ K+

2.5 2 1.5 1 0.5 0 0

1

2

3 4 5 6 7 8 interlayer distance (Å)


9

10 11

Page 37 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41




20

20

18 16

d (Å) spacing

0 10 20 40 60 80

14

0 10 20 40 60 80

18 16 14 12

12

(b)

(a)

10

10 0

20

40

60

80

0

100 120 140 160 180 200

20

40

60

80

100 120 140 160 180 200


number of water molecules 20

20 0 10 20 40 60 80

18

16

0 10 20 40 60 80

18

d (Å) spacing

d (Å) spacing

d (Å) spacing

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 38 of 47

14 12

16

14 12

(c) 10

(d) 10

0

20

40

60

80

100 120 140 160 180 200

0

20


40

60

80

100 120 140 160 180 200



Page 39 of 47

8

8

MMT-MMT

MMT-MMT Na+I-MMT

6

d (Å)

(K+Na)-I-MMT

4

Na+I-MMT

6

K+I-MMT


4

2

2

(b)

(a)

0

0 0

0

20 40 60 80 100 120 140 160 180 200

20 40 60 80 100 120 140 160 180 200



10

8

MMT-MMT

MMT-MMT Na+I-MMT

Na+I-MMT

8 d (Å)


6

d (Å)

4


6 4

(d)

(c)

2

2 0

20 40 60 80 100 120 140 160 180 200

0

20 40 60 80 100 120 140 160 180 200



10 MMT-MMT Na+I-MMT

8

K+I-MMT

d (Å)

d (Å)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(K+Na)-I-MMT

6 (e)

4 0

20 40 60 80 100 120 140 160 180 200




4.5 4 3.5 3 2.5 2 1.5 1 0.5 0

total atom count

(a)

0

1


total atom count

2

1.5 1 0.5 0 0

1

2

3

4

5

6

7

(d)

0

(b)

2.5

4 3.5 3 2.5 2 1.5 1 0.5 0

5

3

3.5 3 2.5 2 1.5 1 0.5 0

8

1

0

(c) total atom count

1.5 1

0.5 0

0

1

2 3 4 5 6 7 8 interlayer distance (Å)

5

1

2

7

3

4

5

6


2.5 2


(e)


total atom count

total atom count

total atom count

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 40 of 47

9 10 11

3.5 3 2.5 2 1.5 1 0.5 0

(f)

0


1

2

3 4 5 6 7 8 9 10 interlayer distance (Å)

8

tot

0.541 of 47 Page


0

5 3 2 1.5 1 0.5 0

58 5 9

0

1

total atom count


2.5


5

(e)

2

1.5 1

0.5 0 0

87 11 98 10

1

2

3 4 5 6 7 interlayer distance (Å)

8

9

3

total atom count

total atom count

total atom count

(d)

2.5

total atom count


0 1 2 3 4 1 2 interlayer distance (Å) 3 3 4 3 2.5 (a) 5 2.5 (d) (e) 62.5 7 22 8 2 9 1.5 1.5 1.5 10 11 1 1 12 1 13 0.5 0.5 0.5 14 15 0 0 16 0 00 0 1 1 12 32 2 4 3 53 64 47 17 18 interlayer distance(Å) (Å) interlayer interlayer distance distance (Å) 19 20 2.5 3 21 3 (b) (e) 22 2.5 (f) 2 232.5 24 2 1.52 25 1.5 261.5 27 1 28 11 29 0.5 0.5 300.5 31 32 000 33 00 0 11 12 2 32 34 345 465 756 8 769 34 interlayerdistance distance(Å) interlayer (Å) interlayer distance (Å) 35 36 3 37 3 (c) 38 2.5 (f) 2.5 39 40 2 2 41 42 1.5 1.5 43 44 1 1 45 0.5 0.5 46 47 48 0 0 49 0 0 1 1 2 23 34 45 56 67 78 98 50 interlayer (Å) interlayer distance distance(Å) 51 52 53 54 55 56 57 58 59 60

2.5

(f)

2 1.5

1 0.5 0

10 9 11 10 11

0 1 2 3 4 5 6 7 8 9 10 11 interlayer distance (Å)



1.6 60-20 80-20 100-20 120-20 160-20

60-20 80-20 100-20 120-20 160-20

1.2

g(r)

g(r)

0.8 0.4

(b) 0

2

3

4

5

6

7

0

1

2

3

4

5

6

7

4

5

6

7

3 r (Å)4

5

6

7

r (Å)

r (Å) 1.6 60-20 80-20 100-20 120-20 160-20

1.2

g(r)

g(r)

60-20 80-20 100-20 120-20 160-20

0.8 0.4

(d)

0

2

3

4

5

6

7

0

1

2

3 r (Å)

r (Å)

1.6

g(r)

60-20 80-20 100-20 120-20 160-20

60-20 80-20 100-20 120-20 160-20

1.2

g(r)

1 2 3 32.0 4 (a) 5 6 24.0 7 8 9 16.0 10 11 12 8.0 13 14 15 0.0 16 0 1 17 18 19 20.0 20 (c) 21 16.0 22 23 24 12.0 25 26 8.0 27 28 29 4.0 30 31 0.0 32 0 1 33 34 35 20.0 36 (e) 37 38 16.0 39 40 12.0 41 42 43 8.0 44 45 4.0 46 47 0.0 48 0 1 49 50 51 52 53 54 55 56 57 58 59 60

Page 42 of 47

0.8

0.4 (f)

0

2

3

4

5

6

7

0

r (Å)


1

2

Page 43 of 47

3.0 (a)

60-20 80-20 100-20 120-20 160-20

2.5

60-20 80-20 100-20 120-20 160-20

2.0

g(r)

g(r)

1.5

1.0 0.5

(b)

0.0

0

1

2

3 r (Å)4

5

6

0

7

1

2

3 4 r (Å)

5

6

7

3 4 r (Å)

5

6

7

3.0 (c)

2.5

g(r)

60-20 80-20 100-20 120-20 160-20

60-20 80-20 100-20 120-20 160-20

2.0

g(r)

1 2 3 4 10.0 5 6 8.0 7 8 9 6.0 10 11 4.0 12 13 14 2.0 15 16 0.0 17 18 19 20 10.0 21 22 8.0 23 24 25 6.0 26 27 4.0 28 29 30 2.0 31 32 0.0 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1.5 1.0 0.5

(d)

0.0

0

1

2

3

4 r (Å)

5

6

7

0


1

2


1.2

35.0 80-10 80-20 80-40 80-60 80-80

21.0

80-10 80-20 80-40 80-60 80-80

0.8

g(r)

28.0

14.0

0.4

7.0

(a)

(d) 0.0

0.0

0

1

2

3 r (Å)

4

5

0

6

20.0

1

2

3 r (Å)

4

5

6

4

5

6

4

5

6

1.6 80-10 80-20 80-40 80-60 80-80

12.0 8.0

80-10 80-20 80-40 80-60 80-80

1.2

g(r)

16.0

0.8 0.4

4.0

(b)

(e)

0.0

0.0

0

1

2

3 r (Å)

4

5

6

0

20.0

1

2

3 r (Å)

1.6 80-10 80-20 80-40 80-60 80-80

16.0 12.0 8.0

80-10 80-20 80-40 80-60 80-80

1.2

g(r)

g(r)

g(r)

g(r)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 44 of 47

0.8 0.4

4.0

(e)

(f)

0.0

0.0

0

1

2

3 r (Å)

4

5

6

0


1

2

3 r (Å)

Page 45 of 47

10.0

3.0 80-10 80-20 80-40 80-60 80-80

6.0

80-10 80-20 80-40 80-60 80-80

2.0

g(r)

8.0

4.0

1.0

2.0

(c)

(a) 0.0

0.0

0

1

2

3 r (Å)

4

5

0

6

10.0

1

2

3 r (Å)

4

5

6

4

5

6

3.0 80-10 80-20 80-40 80-60 80-80

8.0 6.0

80-10 80-20 80-40 80-60 80-80

2.0

g(r)

g(r)

g(r)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


4.0

1.0

2.0

(d)

(b) 0.0

0.0

0

1

2

3 r (Å)

4

5

6

0


1

2

3 r (Å)


1.5

2.0 60-20 80-20 100-20 120-20 160-20

1.0

60-20 80-20 100-20 120-20 160-20

1

g(r)

g(r)

1.5

0.5 0.5

(b)

(a)

0

0.0

0

1

2

3 4 r (Å)

5

6

7

0

8

0.8

1.5

g(r)

1.2

g(r)

2

3 r (Å)

4

5

6

2

3 r (Å)

4

5

6

3

4

5

6

2 3 r (Å)

4

5

6

60-20 80-20 100-20 120-20 160-20

2

60-20 80-20 100-20 120-20 160-20

1.6

1 0.5

0.4 (c)

(d)

0

0.0

0

1

2

3 4 r (Å)

5

6

7

0

8

1

2.5

1.6

1.5

g(r)

0.8

60-20 80-20 100-20 120-20 160-60

2.0

60-20 80-20 100-20 120-20 160-20

1.2

g(r)

1

2.5

2.0

0.4

1.0 0.5

(f)

(e)

0

0.0

0

1

2

3 4 r (Å)

5

6

7

8

0

1

2 r (Å)

2.5

1.6 60-20 80-20 100-20 120-20 160-20

0.8

2.0

60-20 80-20 100-20 120-20 160-20

1.5

g(r)

1.2

g(r)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 46 of 47

0.4

1.0 0.5

(h)

(g)

0.0

0.0

0

1

2

3 4 r (Å)

5

6

7

8

0


1

Page 47 of 47 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41



Molecular Dynamics Simulation of Hydration and Swelling of Mixed

Recommend Documents