Noncontact AFM First-Principles Simulations of Functionalized Silicon

Article pubs.acs.org/JPCC

Noncontact AFM First-Principles Simulations of Functionalized Silicon Tips on the Montmorillonite (001) Surface Raphael da Silva Alvim† and Caetano R. Miranda*,†,‡ †

Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, Santo André, São Paulo 09210-580, Brazil Departamento de Física dos Materiais e Mecânica, Universidade de São Paulo, São Paulo, São Paulo 05508-090, Brazil

‡

ABSTRACT: The interaction between functionalized silicon probe tips and the montmorillonite (MMT) surface was studied through density-functional theory (DFT) with the van der Waals DF (vdW-DF) to include the contribution of the vdW forces in the interaction energy of the tip/MMT interface. On the basis of the noncontact AFM (NC-AFM) technique, we modeled an explicit Si probe tip that was functionalized with sulfonic acid (SA) and ethylene glycol (EG) groups present in polymeric surfactants. Accordingly, we obtained the short-range microscopic forces to investigate the hysteresis mechanism due to the approach and retraction processes of the tips as well as tip tilt, usually leading to the topographic and dissipation image contrasts. Furthermore, it was possible assert the influence of different hydrophilicity degrees toward the oxygen sites at the silicate sheet of the MMT (001) surface, which is related to important processes of surface interaction. Our results showed both SA and EG hydrophilic functional groups are selective onto the two basal oxygen sites, which also take place in the interaction on the siloxane cavity in the MMT surface. In particular, on the basal oxygen site that interacts with the intralayer hydroxyl group, the EG tip leads to an energy dissipation due to different force pathways mainly in the repulsion region, while possible energy barriers can be overcome by approaching a larger tip tilt on the other basal oxygen site in the attraction region. This tip could then display less frequency shift on the basal oxygen sites of MMT. Therefore, our results can clarify important questions about the complexity of the interaction forces between functionalized silicon probe tips and MMT in the NC-AFM experiments. Moreover, this work provides a first-principles model to describe the hydrophilic selectivity of polymeric surfactants from the interaction between nonionic −OH groups and aluminosilicate surfaces in the absence of hydrophilic ions at the interlayer region.

1. INTRODUCTION

Knowledge of the oil/clay interactions is essential to obtain a more effective enhanced oil recovery (EOR). In particular, in the industrial point of view, although water flooding gives a poor sweep efficiency,12 an important low-cost EOR process that does not require the addition of chemical additives is called low-salinity EOR.13,14 However, it remains yet unanswered the role of salinity toward the main interaction mechanisms of organic molecules in the MMT interlayer region. In a recent study by classical molecular dynamics simulations, Underwood et al.14 concluded that multicomponent ionic exchange in MMT is independent of the salt concentration. On the other hand, the interaction between the MMT silicate surface and organic functional groups present in the oil molecules is directly influenced by chemical additives. In general, these high-cost surfactants release the oil trapped in the clay by the respective increase and decrease of viscosity and permeability of water molecules mainly in light oil reservoirs.12,15,16 Consequently,

One of the main layered aluminosilicate clays that coats pores of sandstone natural reservoirs is classified as the smectite group, such as montmorillonite (MMT). MMT is also the main component in bentonite that is used as a buffer in radioactivewaste management.1 MMT displays perfect cleavage parallel to the plane (001) to form silicate layers with hexagonal siloxane cavities, besides other possible faces with smaller surface area.2 The MMT phyllosilicate structure has its own variations in the intra- and interlayer chemical composition with the natural attraction of positively charged ions, which leads to important hydrophilic properties.3−6 Moreover, based on pyrophyllite, MMT (001) surface also displays an adsorptive region in the absence of the ionic influence on the siloxane cavity, consisting of basal oxygen sites in the edge and inner hydroxyl groups. The silicate surface can be influenced by the inner chemical environment in the layered sheet due to the hydroxyl groups7 and the ionic substitutions. 8 Although the MMT is preferentially water wet in reservoir regions of mixed wet, the oil wettability of the rock is also determined by the clay surface.9−11 © XXXX American Chemical Society

Received: February 6, 2016 Revised: June 1, 2016

A

DOI: 10.1021/acs.jpcc.6b01319 J. Phys. Chem. C XXXX, XXX, XXX−XXX

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The Journal of Physical Chemistry C

works have modeled the complex interaction processes between explicit probe tips and surfaces by first-principles calculations.36,46−55 Accordingly, it is important to take account that the chemical complexity of the probe tips is the biggest challenge for its modeling in the NC-AFM simulations, even for the standard silicon usually used in the experiments. On the other hand, according to Si probe tip models proposed in Caciuc et al.,35,36 Oyabu et al.,48 Kantorovich et al.,49 and Bamidele et al.,50 just the terminal probe tips indeed dominate the short-range forces for each surface atomic site. Our aim was to investigate, via first-principles and including vdW forces, the short-range microscopic force Fsr in the interactions between a hydrophobic model of explicit hydrogenated Si probe tip (tH) and the MMT (001) surface. Furthermore, the Si tip was functionalized from the SA and EG hydrophilic groups to produce the probe tips tSA and tEG with different sizes, respectively. Then we asserted the tip/surface interactions through functionalized silicon tips on the oxygen sites present at the siloxane cavities of aluminosilicate clay surfaces like MMT. In particular, we obtained the energy dissipation related to the presence of hysteresis and tip tilt during the approach and retraction pathways of the tip, displaying the complexity in interpreting the origin of Fsr. From the complete force Fts with the inclusion of the vdW macroscopic force FvdW, our work makes calculation of the frequency shift from the microscopic and macroscopic parts of an experimental tip more accurate. In addition, it was possible to probe the hydrophilicity effects of these functional groups present in polymeric surfactants toward the MMT surface.

there is reduction in the oil/water interfacial tension, allowing stronger interaction between water/clay. Accordingly, several works have studied different types of surfactants.12,15−21 In particular, polymeric surfactants are amphiphilic macromolecules often used in chemical methods for EOR,22 as well as mineral nanoparticles (NP) covered by polymeric additives.23−25 These polymer/mineral nanocomposites (NCs) are a class of materials in which the mineral NP is dispersed within polymeric matrices. Depending on the type and content of the NP, the NCs show markedly improved wettability property with greater interaction on the hydrophilic reservoir surface, which is key for EOR processes from natural reservoirs. Furthermore, the nanostructured mineral must be economically of low cost and drive to achieve high-value-added products. MMT itself takes place in polymer/clay NCs.26,27 Specific hydrophilic functional groups in polymeric surfactants can increase the hydrophilicity in polymer/mineral NCs. Commonly, the nonionic head groups of polymeric molecules are represented as sulfonic acid (SA) and ethylene glycol (EG), which are present in sulfonated polyacrylamide28 and polyethylene glycol29,30 surfactants, respectively. The nonionic surfactant molecules act mainly on the pores of natural reservoirs. This interaction is affected by the composition of the mineral surface.31 The microtopography characterization of the aluminosilicate surfaces from the modification effects of the organic9−11 and surfactant 11,26 molecules is observed by atomic force microscopy (AFM). The tiny particles of MMT make it difficult to experimentally analyze the AFM images at atomicscale resolution,26 i.e. the interatomic force Fts between a sharp probe tip (t) attached to a oscillating cantilever and the sample surface (s) is not easily obtained. The noncontact AFM (NCAFM) technique is able to generate topographic and dissipation images of surface structures.32−37 In each probed surface site, the variation of resonance oscillation frequency of the cantilever is kept constant. Accordingly, NC-AFM uses the same amount of energy to one dissipated in the tip/surface interaction from extra energy supplied experimentally for driving the cantilever at resonance. Therefore, the NC-AFM image is displayed through both maps of constant frequency shift and dissipation, which can be calculated by the interaction forces.33,36 In addition to the long-range vdW forces always present in ultrahigh vacuum (UHV) NC-AFM, short-range forces determine the map of constant frequency shift. Besides, the latter are often responsible for the atomic-scale contrast observed in the topographic and dissipation images due to the nature and structure of the probe tip termination. Although there is significant recent progress in developing NC-AFM with single-bond resolution in experimental topographic and dissipation images, such as the CO front atom identification method (COFI),38−44 energy dissipation, tip tilt, and the nature of the short-range forces must be better understood.33,43 Recently, f irst-principles calculations become an effective and powerful tool to determine the origin of the fundamental distance-dependent measurement of tip/sample forces, as it is done in NC-AFM experiments. This information is related to the chemical activity at the surface sites due to interaction with the probe tips.33,41 Chan et al.45 used f ictitious probe tips to obtain a correlation between the bright spots in the NC-AFM image and the first-principles potential calculated for the surface of the system. This approach has been an interesting approach to simulate AFM images,7,45 but this does not fully capture the nature of the tip/sample forces. For this reason, many other

2. COMPUTATIONAL PROCEDURE The montmorillonite (MMT) structure and the probe tip models were investigated at the density-functional theory (DFT)56 level with the generalized gradient approximation (GGA)57,58 implemented in the Quantum Espresso59−61 package. We used a plane wave basis set under periodic boundary conditions62 and Vanderbilt ultrasoft pseudopotentials.63 We used here the exchange-correlation functional of revised Perdew, Burke, and Ernzerhof (revPBE).64−66 The revPBE is allowed to properly apply vdW density functional (vdWDF),67−69 displaying the dispersion interaction with nonlocal functional of the correlation energy for the vdW force inclusion, and then it contributes indeed in the interaction energy of the tip/MMT interface. Furthermore, vdW-DF is necessary to better describe the layered structure of the montmorillonite (MMT).7 On the basis of our surface characterization work,7 we showed the presence of two types of basal oxygen sites (O1 and O2 in Figure 1A) that may be differently affected by vdW forces and/or the chemical environment of the hydroxyl groups (O3 in Figure 1A). Although the structural hydroxyl groups O3 are in the siloxane cavity, surface characterization also brings out that the oxygen sites O1 and O2 are affected by those sites in a hydrophilic way. For this reason, the hydrophobic and hydrophilic interactions on the three surface sites O1, O2, and O3 should be probed. The MMT structure was built from an orthorhombic unit cell with lattice parameters calculated in a = 5.25 Å, b = 9.17 Å, c = 15.09 Å, α = γ = 90.00°, and β = 90.71° and basal d spacing of about 8.00 Å. Whereas our aim is to probe the possible selectively hydrophilic between each surface site and the proposed tip models, we simulated MMT in the absence of the ionic influence from a pyrophyllite-like structure with a bulk B


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allowed to relax, i.e., all surface sites displayed in Figure 1A. Thus, the bottom silicate sheet and the sites in its respective octahedral sheet are fixed in the bulk positions. Regarding the probe tips, the three sites of the silicon bulk passivated by hydrogen are kept fixed, while the other site Si and the H, SA, and EG groups bounded to it are allowed to relax at different distances from MMT surface sites onto tip’s approach and retraction. To obtain the approach and retraction processes of the tip (t) models on the MMT surface sites (s), the calculations were started from the point whereupon the tip is release with the short-range force Fsr close to zero. Then each subsequent point concerning the tip/MMT interaction was optimized from the optimized positions of the system in the previous point. Thereby, the decrease and increase in the distance Z were calculated for the downward and upward tip movement upon the approach and retraction, respectively. This allows showing the force pathway is due the structural change in that particular interaction, leading to possible energy dissipation from the retraction. In the adhesion point, the system is in the local minimum potential upon the interaction energy Eint vs distance Z curve. Likewise, the tip is retracted only from the point where the interaction energy of tip/MMT is reached close to zero (maximum point). Hence, if there is hysteresis, another force pathway corresponding to energy dissipation is obtained. The energy dissipation is obtained from the difference between the force pathways upon the approach and retraction of the tip on the surface.33 This is just the hysteresis curve due the nonconservative forces in the tip/MMT interaction. During all the approach and retraction processes, Z is the distance between the center of mass in the tip fixed part, i.e., the three sites of the silicon bulk passivated by hydrogen, and the MMT surface site. Although there are small distortions of the surface sites after optimization, the silicate surface is rather rigid. Approximately, we ensured that Z varies by 0.10 Å steps. These finest increments in Z allow indeed one to accurately capture hysteresis loops from different points obtained between the approach and the retraction force pathways.50 The MMT site O2 was particularly used as the reference point to obtain Z due to its upmost position in the surface. This leads to a normalization of the distance Z with respect to other sites O1 and O3. Thereby, the range of the distances Z between tH and the MMT surface started in the tip release point, from 6.24 Å, until the maximum points of 4.24, 4.56, and 3.39 Å, respectively, on the oxygen sites O1, O2, and O3. For tSA on the sites O1, O2, and O3, it was started from 7.82 Å until, respectively, 5.76, 5.92, and 5.76 Å. Last, tEG approaches toward the sites O1, O2, and O3 from 10.36 Å until, respectively, 7.47, 6.57, and 7.31 Å. The interaction energy Eint(Z) was calculated from each energy difference between the tip/MMT adsorbed system (tH/ MMT, tSA/MMT, or tEG/MMT), the isolated tip (tH, tSA, or tEG), and the pristine surface (MMT) through the expression

Figure 1. (A) Projection view of the montmorillonite (MMT) on the plane (001) to show the different types of oxygen sites: O1 and O2 in the edge and O3 inside the siloxane cavity. The siloxane cavity is represented by a hexagon in blue, where the blue area is probed from O1, O2, and O3. Models of Si probe tips: (B) hydrogenated (tH), (C) sulfonic acid (tSA), and (D) ethylene glycol (tEG).

composed of one aluminosilicate layer and formula unit Al2Si4O10(OH)2. The NC-AFM probe tip model is composed by three hydrogenated silicons to represent the bulk atoms and an outermost atom one for functionalization as the simplest model of the silicon tip proposed by Oyabu et al.48 This Si site was bonded to one hydrogen to make an explicit hydrophobic probe tip of (H3Si)3−Si−H (tH) (Figure 1B). Thus, from this we replaced this hydrogen site by two types of hydrophilic functional groups to obtain explicit tips of (H3Si)3−Si−SO2− OH (tSA) (Figure 1C) and (H3Si)3−Si−OCH2CH2−OH (tEG) (Figure 1D). For MMT (001) surface calculations with tH, tSA, and tEG, the MMT unit cell was replicated for obtaining a = 10.50 Å and b = 18.34 Å. Additionally, for the approach and retraction processes of the probe tips on the clay surface, we increased the vacuum layer through the converged basal d spacing to isolate the top of the small cluster of probe tip from the bottom of the next MMT layer. Thus, we used d = 13.00 Å for the inclusion of the tips tH and tSA (c = 20.09 Å) and d = 23.00 Å for tEG (c = 30.09 Å). We used a fine converged kinetic energy cutoff for charge density, almost eight times the kinetic energy cutoff for wave functions. The calculations with pseudofunctions much softer lead to use a smaller set of plane waves. However, due to the non-norm conservation, the cutoff for charge density is required to be higher.61 Accurately, this allows for better describing the system and the vacuum layer. Our calculations were performed with fine converged kinetic energy cutoff of 816.00 eV for wave functions and 6800.00 eV for charge density, sampled in the Brillouin zone in the Γ point only. The structural optimizations are performed using the Broyden− Fletcher−Goldfarb−Shanno (BFGS) algorithm,70,71 with convergence criteria for the total energy of 2.7 × 10−3 eV along the calculated Hellmann−Feynman72 forces until residual force components were less than 0.08 nN. In the MMT, the surface silicate sheet and sites in its respective octahedral sheet are

Eint(Z) = Etip/MMT(Z) − Etip − EMMT

(1)

From the interaction energy Eint of the tip/MMT interface that was more accurately described with vdW-DF, the shortrange microscopic force Fsr(Z) was obtained from the gradient of Eint(Z) according to Fsr(Z) = − C

∂Eint(Z) ∂Z

(2) DOI: 10.1021/acs.jpcc.6b01319 J. Phys. Chem. C XXXX, XXX, XXX−XXX

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aluminosilicates like montmorillonite (MMT) clays in the surface (001). In our previous work,7 we simulated the topographic NCAFM image of the MMT surface using an implicit tip of silicon nitride. As described by Chan et al.,45 the force Fts was calculated by the first-principles potential with a fictitious tip. Thus, we obtained the bright and dark spots corresponding for each site present in the MMT (001) surface, being possible to observe the atomic-scale contrast corresponding to the different positions for the basal oxygen sites O1 and O2 (bright) and the hydroxyl group O3 (dark). This was enough to characterize the main sites in the MMT surface by NC-AFM calculations. In this situation, the main surface sites are found to be two types of basal oxygen sites (O1 and O2) besides the oxygen site of the hydroxyl group (O3) in the siloxane region that also takes place in the processes of surface interaction. Then it is possible to probe all siloxane cavity region at the MMT surface through the interactions on the sites O1, O2, and O3 shown in Figure 1A. The results for the interaction between tH/O1, tH/O2, tH/O3, tSA/O1, tSA/O2, tSA/O3, tEG/O1, tEG/O2, and tEG/O3 are discussed below. 3.1. Hydrogenated Tip (tH). We started our study from the approach and retraction processes of tH toward the MMT surface sites O1 (tH/O1), O2 (tH/O2), and O3 (tH/O3), which are shown in the interaction energy Eint, short-range force Fsr, and normalized frequency shift Δf n in Figure 2A, 2B, and 2C, respectively. In this case, the noncontact distance D = 4.56 Å between tH and the top site O2 of the analyzed silicate surface was used for Δf n. Further, it was possible to analyze Fsr in the tH/O1 and tH/O3 interactions under 4.56 Å. In the approach processes, tH acts through attractive forces that preferentially decrease the distance Z regarding the site O3, with Eint = −0.61 eV at the adhesion point for Z = 4.14 Å. However, by continuing to approach, the presence of the hydrogenated tip mainly increases the repulsion forces at the interface with the siloxane cavity (O3). The force in the maximum point is thus Fsr = 2.76 nN for tH/O3. All parameters for the systems tH/O1, tH/O2, and tH/O3 are presented in detail in Table 1. Thereafter, the retraction processes of tH from the sites O1, O2, and O3 were started after the maximum points obtained in the approximation. According to Figure 2A and 2B, any hysteresis loop in the interaction energy curves going back the release points of the tip was not observed. Therefore, the force pathways Fts during approach and retraction are considered to be equivalent. Overall, the approximation followed by the retraction of tH leads to a single type of structure in the adhesion point for the system tH/O1 (Figure 2D). Likewise, the same situation was observed for tH/O2 (Figure 2E) and tH/O3 (Figure 2F). By analyzing the structural parameters described in Figure 2D−F, the hydrogen site of the MMT hydroxyl group (Hs) is closer to the site O1 while it decreases the distance between of the hydrogen site of the tip (Ht) and O1 in the system tH/O1. This behavior is also found to occur in the system tH/O3. Then there may be equilibrium between the possible bonds Ht−O1 and Hs−O1 that favors the adhesion. Accordingly, in both systems tH/O1 and tH/O3 the tip interacts preferentially on the site O1 by Ht−O1−Hs in the silicate sheet to decrease the repulsive forces. Thus far, probing the tH/MMT interaction was the first indication that the site O1 would be the surface site most affected by the hydrophilicity increasing through the functionalization of the Si probe tip. Nevertheless, as shown in Figure

which was found to be similar to the sum of the forces on the not optimized sites in the hydrogenated silicon bulk. In particular, to determine the frequency shift, it is important to obtain the total force (Fts) between the experimental AFM tip (t) and the sample surface (s). Fts is approximately the sum of the short-range (Fsr) and long-range van der Waals (FvdW) forces.36,49 Taking into account the tip models of simulations, Fsr and FvdW depend on the suitable microscopic and not suitable macroscopic parts of the experimental tip, respectively.36,49 Given that the tip models used in first-principles calculations display only the microscopic part and FvdW(Z) is independent of the surface site,36 the force effects of the not explicit macroscopic part of the tip can be calculated from FvdW (Z) = −

AHR 6Z2

(3)

where AH = 0.62 eV is the typical value of the Hamaker constant73 for silicon35 and R = 100 Å is the radius of the sphere of the Si macroscopic part used by Caciuc et al.35,36 in an arbitrarily shaped body. Consequently, the additional correction for FvdW using the Hamaker constant is not employed for energy. Fts(Z) = Fsr(Z) + FvdW(Z) is used to calculate the frequency shift Δf(D) = f − f 0 according to Δfn (D) =

1 2π

∞

∫D

Fts(Z) dZ Z−D

(4)

where D is the distance Z of the nearest tip/MMT interaction, which exhibits a greater influence in Fts. Δf n(D) = cZA3/2Δf/f 0 is the normalized frequency shift. This term Δf n has the advantage to be independent of the experimental parameters of spring constant cZ, oscillation amplitude A, and mechanical eigenfrequency f 0 of the cantilever.35 In the limit of infinitesimal increments in Z, we expressed the interaction parameters in the tip/MMT interface. The distances (σ) and the minimum energies (ϵ) were obtained from the Lennard− Jones 12-6 potential fit of the interaction energy Eint vs distance Z curves ⎡⎛ σ ⎞12 ⎛ σ ⎞6 ⎤ Eint(Z) = 4ϵ⎢⎜ ⎟ − ⎜ ⎟ ⎥ ⎝Z⎠ ⎦ ⎣⎝ Z ⎠

(5)

Keeping the same structural conformations for the isolated tip and surface obtained in the optimization of the system tip/ MMT, i.e., without further optimization to avoid any spurious effect due to atomic displacements, the charge density differences at the maximum and adhesion interfaces were calculated according to Δρ = ρ[tip/MMT] − ρ[tip] − ρ[MMT]

(6)

where ρ[tip/MMT], ρ[tip], and ρ[MMT] are, respectively, the charge densities of the systems tip + MMT, the isolated tip, and the MMT (001) surface. All molecular graphics were generated by the XCRYSDEN package.74

3. RESULTS AND DISCUSSION Our study is based in the noncontact AFM (NC-AFM) simulation through an explicit hydrogenated Si probe tip (tH). In particular, this structural model of the Si tip was used to achieve the functionalized tips by sulfonic acid (tSA) and ethylene glycol (tEG). Furthermore, the sample surface to be probed is a silicate sheet obtained from the exfoliation5,75 of D


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Table 1. Main Parameters Obtained in Each Tip/MMT Interface upon the Approach (a) and Retraction (r) Processes of the Explicit Si Tips (hydrogenated (tH), sulfonic acid (tSA), and ethylene glycol (tEG)) Probing the Oxygen Sites O1, O2, and O3 Present at the Silicate Surface (s) of Montmorillonite (MMT)a Eint

Z

Fsr

tips

surface sites

processes

max

adh

adh

max

tH

O1 O2 O3 O1 O2 O3 O1

a,r a,r a,r a,r a,r a,r a r a,r a,r

4.24 4.56 3.39 5.76 5.92 5.76 7.47 7.47 6.57 7.49

5.03 5.31 4.14 6.80 6.90 6.80 8.97 8.77 7.57 8.57

−0.47 −0.38 −0.61 −0.52 −0.53 −0.54 −0.25 −0.28 −0.32 −0.33

1.90 1.57 2.76 1.80 1.85 1.80 0.91 0.97 1.08 1.02

tSA

tEG

O2 O3 a

The curves and the structures related to the maximum (max) and adhesion (adh) points are shown in Figures 2, 3, and 4 for tH, tSA, and tEG, respectively. Distance Z, interaction energy (Eint), and shortrange force (Fsr) are, respectively, in Å, eV, and nN. Eint and Fsr are about zero in max and adh points, respectively.

possible creation of tSA (reaction r1) and tEG (reaction r2) from the sulfonic acid and ethylene glycol molecules were used, respectively t OH + RSA → t SA + H 2O

(r1)

t OH + REG → t EG + H 2O

(r2)

where R = H. The isolated tip model of (H3Si)3−Si−OH (tOH) was simulated in the same computational procedure shown for tSA and tEG, replacing the hydrogen site by a hydroxyl group in tH. The formation energies for reactions r1 and r2 are 0.20 and −0.08 eV, respectively. These energies were calculated from eq 1 for the difference between the sum of the products and the reactants. Whereas it is common to use organic spacers in functionalization with SA,76 tSA and tEG may be even more easily obtained from it as well as specific alkyl termination77 tips. We do not propose here the functionalization of Si tips with spacers to avoid further increase the computational cost. Although this is a limitation in our work with respect the functionalized NPs, the particular effect of the interaction between the functional groups and the surface sites is presented. 3.2. Tip of Sulfonic Acid (tSA). Following the study, by increasing both hydrophilicity and probe tip size, it was possible to observe greater similarity between the sites O1, O2, and O3 under the probing of tSA, respectively, studied by approach and retraction processes in systems tSA/O1, tSA/O2, and tSA/O3. The interaction energy Eint, short-range force Fsr, and normalized frequency shift Δf n are shown in Figure 3A, 3B, and 3C, respectively. For Δf n, the limit for the noncontact distance between tSA and the MMT surface is D = 5.92 Å on the top site O2. Below this it was also to get Fsr at the maximum points of the systems tSA/O1 and tSA/O3. According to the approach of the tip, tSA adheres on the studied surface sites with Eint ≈ 0.50 eV in similar distance Z ≈ 6.90 Å. Even on the region of the site O3, the basal sites O1 and O2 may thus influence the tip. Despite the tSA/O2 interface displaying the same energy Eint and distance Z as tSA/

Figure 2. Interaction energy Eint, short-range force Fsr, and normalized frequency shift Δf n for the variation of the distance Z between the probe tip (t) and the montmorillonite (MMT) surface (s). Approach (a) and retraction (r) processes of the explicit hydrogenated Si tip (tH) probing the oxygen sites O1, O2, and O3 present at the silicate surface of MMT. Variation of the bond distances dHt−O1, dHt−O2, and dHs−O1 in Angstroms for the maximum and adhesion points at the interaction interfaces. Subscripts t and s represent the site H in the tip and surface layer, respectively. (A) Eint vs Z, (B) Fsr vs Z, (C) Δf n vs D, (D) tH/O1, (E) tH/O2, and (F) tH/O3.

2B after the approach and retraction processes, the general behavior of the force curves for probing the MMT surface by tH showed larger distinction between the regions on the sites O1, O2, and O3. On the other hand, the greater variation of the normalized frequency shift to probe the sites O1, O2, and O3 is due to the stiffness of tH upon both approach and retraction processes of the tip. This can be varied from different hydrophilicity and size of functional groups. For the functionalized Si tip model, this is based on hydroxylated silica nanoparticles (NPs) covered by functional groups of surfactants25 to obtain a more effective EOR. Therefore, in addition to these NPs, the AFM tips studied here may also be created. For justify this, two usual reactions for the E


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repulsion forces are present. Although the variation of the repulsion forces between O1 and O2 may be intensified, no considerable divination of the attraction forces is obtained. Therefore, unlike tH, tSA exhibits small variation of the normalized frequency shift on the MMT sites, making not clear a possible decreased affinity of SA toward site O2 (Figure 3C). The results of the structural parameters showed the distances dHs−O1 remain similar in the maximum and adhesion points of the systems tSA/O1(Figure 3D) and tSA/O3 (Figure 3F). This behavior was not obtained previously in the approach of tH on sites O1 and O3, in which the distance dHs−O1 decreases. Accordingly, the interaction of tSA on the MMT surface does not lead to equilibrium of bonds Hs−O1 and Ht− O1, unlike that previously observed to tH. tSA tends to be preferably closer to site O2 in the adhesion point, with dHt−O1 = 2.58 Å and dHt−O2 = 2.19 Å for the systems tSA/O1 (Figure 3D) and tSA/O2 (Figure 3E), respectively. Then tSA may also be selective toward O2, even though this site is the less hydrophilic one in the silicate sheet due to its slightest interaction and the hydroxyl group within the layered surface. 3.3. Tip of Ethylene Glycol (tEG). Lastly, we analyzed the approach and retraction processes between tEG and the MMT surface sites O1 (tEG/O1), O2 (tEG/O2), and O3 (tEG/O3). The interaction energy Eint, short-range force Fsr, and normalized frequency shift Δf n are shown in Figure 4A, 4B, and 4C, respectively. Unlike tH and tSA, Fsr at the maximum points of the systems tEG/O1 and tEG/O3 are in regions above the noncontact distance for Δf n between tEG and the top site O2, which is D = 6.57 Å. Seemingly, the curves for the tEG approach show less correspondence for the interaction on sites O1 and O3. Similar adhesion energies are found for different distances Z between tEG and the surface sites. However, according to the shortrange force Fsr, O1 and O3 display similar probing behavior as tEG, as well as the previous one obtained for tSA. In addition, a small energy barrier particularly was overcome on O2 in Z = 8.27 Å before the adhesion point. This adds almost −0.10 eV in the interaction energy in a closer contact region for tEG/O2. Better than tSA, our results show tEG is able to increase the selectivity on the site O2. All parameters for the systems tEG/ O1, tEG/O2, and tEG/O3 are presented in detail in Table 1. In the retraction process of tEG, it is possible observe the formation of hysteresis due to two force solutions during the forward and backward movements of the tip from Z = 7.57 (repulsion region) and 7.97 Å (attraction region) for the systems tEG/O1 and tEG/O2, respectively (Figure 4A). In particular, the hysteresis in the retraction of tEG right after the maximum point on the site O1 is related to energy dissipation onto the functionalized tip. This energy difference between the approach and the retraction pathways in tEG/O1 provides a hysteresis mainly in the repulsion region, increasing the repelling forces from noncontinuous frequency shift. On the other hand, for the system tEG/O2, the hysteresis region just after the adhesion point in the retraction was influenced by the tip in order to reduce the energy barriers in the approach. In the system tSA/O3, no hysteresis was found. In addition to tSA, tEG causes slight changes in the normalized frequency shift on the sites O1, O2, and O3 (Figure 4C). Due the energy dissipation at the region of repulsion forces in nearest distances D between tEG and O1, the normalized frequency shift decreases upon the tip retraction. On the other hand, after the approach on site O2,

Figure 3. Interaction energy Eint, short-range force Fsr, and normalized frequency shift Δf n for the variation of the distance Z between the probe tip (t) and the montmorillonite (MMT) surface (s). Approach (a) and retraction (r) processes of the explicit Si tip of sulfonic acid (tSA) probing the oxygen sites O1, O2, and O3 present at the silicate surface of MMT. Variation of the bond distances dHt−O1, dHt−O2, and dHs−O1 in Angstroms for the maximum and adhesion points at the interaction interfaces. The subscripts t and s represent the site H in the tip and surface layer, respectively. (A) Eint vs Z, (B) Fsr vs Z, (C) Δf n vs D, (D) tSA/O1, (E) tSA/O2, and (F) tSA/O3.

O1 and tSA/O3 in the adhesion point, O2 is slightly distinguished by the repulsive forces. Nevertheless, tSA is able to probe likewise the region of the siloxane cavity when compared to tH. All parameters for the systems tSA/O1, tSA/ O2, and tSA/O3 are presented in detail in Table 1. Soon after the tSA retraction processes, there were not new structures in the adhesion points from those obtained in the approach processes in tSA/O1 (Figure 3D), tSA/O2 (Figure 3E), and tSA/O3 (Figure 3F). As seen for tH, no hysteresis curve is obtained for tSA. Even so, it was taken into account in analogous probing of tSA on the sites O1 and O3. Indeed, the system tSA/O2 displays lower interaction affinity onto the region of repulsion Fts (Figure 3A). tSA moves away from hydrophilic behavior on site O2 in the region in which the F


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the nonconservative process. Therefore, on site O1, the energy is extensively dissipated locally over the hydrophilic hydroxyl group in tEG, no tilt the tip. Despite the energy dissipated in the tEG/O1 interface, the MMT surface was not affected. This may be due to the more likely hydrogen bond between the layer inner hydroxyl group and the site O1 (dHs−O1 = 2.37 Å). In the energy dissipation mechanism, MMT regains in the pristine configuration, since the surface is not permanently deformed, and the structural modification of the EG hydroxyl group takes place upon retraction of the tip. The hysteresis thus is displayed as a result of the different force solutions accessible in the repulsion region for tEG/O1. On the other hand, no dissipation is obtained for the system tEG/O2 in Figure 4E. Even though the approximation of the tip on the site O2 leads the tEG to tilt toward the siloxane cavity, the tip remains in this same position during the entire retraction process without any change in the adhesion point for the system tEG/O2. The larger tip tilt on the site O2 is caused by repulsion short-range forces without energy dissipation, displaying tilt angles of 65.62° and 58.57° in the maximum and adhesion points, respectively (Figure 4E). When EG is positioned on site O2, the tip tilt leads to the energy gain to overcome possible energy barriers upon the approach with similar energy variation seen for the dissipation on O1. This implies that long hydrophilic groups may be affected by other interaction ways on the MMT surface. Finally, the EG tip is not affected on the surface site O3 (Figure 4F). Like in the system tEG/O1, the tip remains without any tilt in the system tEG/ O3. Therefore, among the three different behaviors for tEG, the EG group is preferably drawn to a basal site (O1 and O2) even if it is positioned on the siloxane cavity (O3). 3.4. Hydrophilic Selectivity. The magnitude of the interaction energies previously seen resemble physisorption, but important selectivity results were obtained. To parametrize the hydrophilic selectivity of the tips, we evaluated the fit of the curves shown in Figure 2A of tH, in Figure 3A of tSA, and in Figure 4A of tEG from eq 5 for the Lennard−Jones 12-6 potential. The energy (ϵ) and distance (σ) parameters obtained from this fit are in Table 2. The likeness in the selectivity was observed in the interactions of the hydrophilic tSA and tEG tips toward the oxygen sites O1, O2, and O3, while the hydrophobic tH displays a different behavior. If it is taking into account the approach and retraction pathways obtained from a type of tip probing one type of surface site, i.e., in each system probed by tH and tSA, the parameters ϵ are the same for the Lennard−Jones 12-6 potential fit, as it is seen in Table 2. In particular, for the systems tEG/O1 and tEG/O2 that, respectively, display hysteresis and tip tilt, these parameters tend to not be similar upon their approach and retraction processes. However, the alike parameters ϵ achieved from the force pathways in the tEG retraction on O1 and O2 display no specific basal site for the interaction. For this reason, this increases the hydrophilic selectivity between the EG functional group and the MMT surface. By molecular dynamics simulations, Li et al.31 showed indeed that the interaction between surfactants with nonionic groups and mineral surfaces is essential for the oil detachment. Moreover, in order to better describe the possible interaction Ht−O1−Hs in the silicate sheet by tH, the lower interaction affinity of tSA on O2, and the hysteretic interaction of tEG on O1, we calculated the charge density difference according to eq 6 for the systems tH/O1, tSA/O2, and tEG/O1, respectively. This guideline can display the bonding charge density arising

Figure 4. Interaction energy Eint, short-range force Fsr, and normalized frequency shift Δf n for the variation of the distance Z between the probe tip (t) and the montmorillonite (MMT) surface (s). Approach (a) and retraction (r) processes of the explicit Si tip of ethylene glycol (tEG) probing the oxygen sites O1, O2, and O3 present at the silicate surface of MMT. Variation of the bond distances dHt−O1, dHt−O2, and dHs−O1 in Angstroms for the maximum and adhesion points at the interaction interfaces. Subscripts t and s represent the site H in the tip and surface layer, respectively. (A) Eint vs Z, (B) Fsr vs Z, (C) Δf n vs D, (D) tEG/O1, (E) tEG/O2, and (F) tEG/O3. θ1 = 65.62° and θ2 = 58.57°.

the tEG tilt reaches a retraction with small variation of Δf n when compared to the tH and tSA tips. Our results also suggest that in the hysteresis curves in tEG, differently to what occurs in tH and tSA, the retraction process displays a new adhesion point only in the system tEG/O1 due to the energy dissipated. According to Figure 4D, tEG is not in the same position in the adhesion points upon the approach and retraction; two different minima for the same distance between EG and the surface site O1 were obtained for the system tEG/O1. The dissipated energy of 0.10 eV was calculated as the area between the two force curves for the tip. This typical value for a hydrogen bond was large enough to lead to the displacement of tEG on the surface site O1 during G


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not easily obtained in such aluminosilicate clays, as seen in tH/ O1. Therefore, the influence of the AFM tip size and hydrophilicity to probe the MMT surface is remarkable. Meanwhile, unlike tH, the interfacial charge density is indeed due to the hydrophilic behavior from the SA and EG groups toward the surface. There is an increase of charge density in the adhesion interface between the functional groups and MMT, confirming mainly the greater hydrophilic selectivity on the MMT surface. Although tSA provides a less hydrophilic influence on site O2 in the region of repulsive forces, this does not affect the tip/MMT interaction in the adhesion point of the system tSA/O2 (Figure 5B). Nevertheless, tip tilt can often be necessary due to the size increase of hydrophilic tips. The energy barriers that arise in the less hydrophilic interaction on O2 must thus be overcome even in the region of repulsive forces, as discussed in the system tEG/O2. On the other hand, regardless of the functionalized tip size, both oxygen sites O1 and O2 are specific in the hydrophilic interactions under tEG without tilt. On sites O1 and O2, the interaction charge density is displayed in the adhesion (approach) and maximum points of the system tEG/O1 (Figure 5C), repectively. Then even though the interaction between tEG and site O1 is weakened after the energy dissipated on the hydroxyl group, the tip found another force pathway upon the retraction process from a possible hydrophilicity also on site O2. However, the absence of charge density seen in the adhesion point upon tEG retraction confirms the presence of hysteresis without the influence of the MMT surface. For this reason, the basal oxygen sites O1 and O2 may be selectively hydrophilic by the possible interaction with the studied nonionic groups in the absence of interlayer ions.

Table 2. Distance (σ) in Each Well-Depth of Minimum Energy (ϵ) for the Lennard−Jones 12-6 Potential Fit of the Interaction Energy Eint vs Distance Z Curves in the Approach (a) and Retraction (r) Processes of the Explicit Si Tips (hydrogenated (tH), sulfonic acid (tSA), and ethylene glycol (tEG)), Probing the Oxygen Sites O1, O2 and O3 Present at the Silicate Surface (s) of Montmorillonite (MMT)a parameters ϵ

σ

systems

a

r

a

r

tH/O1 tH/O2 tH/O3 tSA/O1 tSA/O2 tSA/O3 tEG/O1 tEG/O2 tEG/O3

0.49 0.38 0.70 0.54 0.51 0.55 0.23 0.34 0.30

0.49 0.38 0.70 0.54 0.51 0.55 0.28 0.30 0.30

4.24 4.60 3.41 5.80 5.93 5.81 7.54 6.60 7.51

4.24 4.60 3.41 5.80 5.93 5.81 7.49 6.60 7.51

The fit results were obtained according eq 5. The parameters ϵ and σ are in eV and Å, respectively.

a

from the most probable interaction effect of the tip on the surface charge distribution. The depletion of charge density is only seen between the hydrophobic silicon tip and MMT. Hydrophobic tH is not influenced by electrostatic interactions in the adhesion point of the system tH/O1 (Figure 5A), which

4. CONCLUSIONS Our simulations are based on first-principles calculations with inclusion of van der Waals (vdW) forces. From the explicit model of the hydrogenated silicon probe tip and its functionalization with sulfonic acid (SA) and ethylene glycol (EG) groups on the MMT surface sites, the short-range microscopic forces led to two major findings: (1) the calculations ensured complex interaction forces with hysteresis mechanisms for NC-AFM and particularly to improve EOR, and (2) it shows the SA and EG functional groups are more selective than the hydrophobic Si tip on the MMT basal oxygen sites. According to 1, the proposed models of functionalized AFM tips were used to probe the interaction between surfactants and the MMT surface sites in 2. Accordingly, our results are important to demonstrate relevant selectivity ways from the interaction between surfactant functional groups and the different MMT surface sites. Regarding the hydrophilic tips, nonconservative processes lead to energy dissipation mainly in the region of repulsion forces on site O1, seen in tEG. Besides, even without having a direct interaction with the intralayer hydroxyl group, site O2 is also able to be selective in the presence of a hydrophilic functional group, seen in both tSA and tEG. The tip tilt can eliminate small energy barriers after this tilt upon attraction. On site O3 in the siloxane cavity, the hydrophilic tips are preferentially attractive by the site O1. In short, we concluded that both basal oxygen sites O1 and O2 are selective by the hydrophilicity and size increase of nonionic groups. Even though our work is related to the pyrophyllite-like structure, the calculations of frequency shift may also be a reference to check the influence of natural isomorphic substitutions in MMT

Figure 5. Charge density differences for the maximum and adhesion points at the main interaction interfaces according to eq 6. Approach (a) and retraction (r) processes of the explicit Si tips (hydrogenated (tH), sulfonic acid (tSA), and ethylene glycol (tEG)), probing the oxygen sites O1 and O2 present at the silicate surface (s) of montmorillonite (MMT). (A) tH/O1, (B) tSA/O2, and (C) tEG/O1. Isosurface of 0.001 electrons × Bohr−3. Green and blue colors indicate increase and depletion of charge density, respectively.

may be related to greater proximity of the hydrogenated silicon bulk with respect to the surface. In the maximum point, the repulsive forces do not unsettle the bond Ht−O1−Hs probably due to higher tip stiffness. Since the site O1 usually shows hydrophilic behavior in the siloxane structure of aluminosilicate surfaces, a possible combination of bonds Ht−O1−Hs between the clay inner hydroxyl group, site O1, and a hydrophobic tip is H


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(13) Sánchez, V. M.; Miranda, C. R. Modeling Acid Oil Component Interactions with Carbonate Reservoirs: A First-Principles View on Low Salinity Recovery Mechanisms. J. Phys. Chem. C 2014, 118, 19180−19187. (14) Underwood, T.; Erastova, V.; Cubillas, P.; Greenwell, H. C. Molecular Dynamic Simulations of Montmorillonite-Organic Interactions Under Varying Salinity: An Insight into Enhanced Oil Recovery. J. Phys. Chem. C 2015, 119, 7282−7294. (15) Wever, D. A. Z.; Picchioni, F.; Broekhuis, A. A. Polymers for Enhanced Oil Recovery: A Paradigm forStructure-Property Relationship in Aqueous Solution. Prog. Polym. Sci. 2011, 36, 1558−1628. (16) Wang, Z.; Le, X.; Feng, Y.; Zhang, C. The Role of Matching Relationship between Polymer InjectionParameters and Reservoirs in Enhanced Oil Recovery. J. Pet. Sci. Eng. 2013, 111, 139−143. (17) Iglauer, S.; Wu, Y.; Shuler, P.; Tang, Y.; Goddard, W. A., III New Surfactant Classes for Enhanced Oil Recovery and Their Tertiary Oil Recovery Potential. J. Pet. Sci. Eng. 2010, 71, 23−29. (18) Amirianshoja, T.; Junin, R.; Idris, A. K.; Rahmani, O. A Comparative Study of Surfactant Adsorption by Clay Minerals. J. Pet. Sci. Eng. 2013, 101, 21−27. (19) Ma, K.; Cui, L.; Dong, Y.; Wang, T.; Da, C.; Hirasaki, G. J.; Biswal, S. L. Adsorption of Cationic and Anionic Surfactants on Natural and Synthetic Carbonate Materials. J. Colloid Interface Sci. 2013, 408, 164−172. (20) de Lara, L. S.; Voltatoni, T.; Rodrigues, M. C.; Miranda, C. R.; Brochsztain, S. Potential Applications of Cyclodextrins in Enhanced Oil Recovery. Colloids Surf., A 2015, 469, 42−50. (21) Shaddel, S.; Tabatabae-Nejad, S. A. Alkali/Surfactant Improved Low-Salinity Waterflooding. Transp. Porous Media 2015, 106, 621− 642. (22) Raffa, P.; Wever, D. A. Z.; Picchioni, F.; Broekhuis, A. A. Polymeric Surfactants: Synthesis, Properties, and Links to Applications. Chem. Rev. 2015, 115, 8504−8563. (23) Sertchook, H.; Elimelech, H.; Makarov, C.; Khalfin, R.; Cohen, Y.; Shuster, M.; Babonneau, F.; Avnir, D. Composite Particles of Polyethylene @ Silica. J. Am. Chem. Soc. 2007, 129, 98−108. (24) Zapata, P. A.; Belver, C.; Quijada, R.; Aranda, P.; Ruiz-Hitzky, E. Silica/Clay Organo-Heterostructures to Promote Polyethylene-Clay Nanocomposites by in situ Polymerization. Appl. Catal., A 2013, 453, 142−150. (25) Rigo, V. A.; de Lara, L. S.; Miranda, C. R. Energetics of Formation and Hydration of Functionalized Silica Nanoparticles: An Atomistic Computational Study. Appl. Surf. Sci. 2014, 292, 742−749. (26) Zhu, J.; Zhu, L.; Zhu, R.; Tian, S.; Li, J. Surface Microtopography of Surfactant Modified Montmorillonite. Appl. Clay Sci. 2009, 45, 70−75. (27) Heinz, H. Clay Minerals for Nanocomposites and Biotechnology: Surface Modification,Dynamics and Responses to Stimuli. Clay Miner. 2012, 47, 205−230. (28) Sodeifian, G.; Daroughegi, R.; Aalaie, J. Study of Adsorptive Behavior of Sulfonated Polyacrylamideonto Carbonate Rock Particles to Enhance Oil Recovery. Korean J. Chem. Eng. 2015, 32, 2484−2491. (29) Yu, X.; Pu, W.; Chen, D.; Zhang, J.; Zhou, F.; Zhang, R.; Gu, S. Degradable Cross-Linked Polymeric Microsphere forEnhanced Oil Recovery Applications. RSC Adv. 2015, 5, 62752−62762. (30) Wang, Y.; He, Z.; Liu, Q.; Huang, H. Synthesis and Characterization of Polymerizable Epoxy Resin Surfactants. J. Appl. Polym. Sci. 2015, 132, 42598. (31) Li, X.; Xue, Q.; Zhu, L.; Jin, Y.; Wu, T.; Guo, Q.; Zheng, H.; Lu, S. How to Select an Optimal Surfactant Molecule to Speed up the OilDetachment from Solid Surface: A Computational Simulation. Chem. Eng. Sci. 2016, 147, 47−53. (32) Eastman, T.; Zhu, D.-M. Adhesion Forces between SurfaceModified AFM Tips and a Mica Surface. Langmuir 1996, 12, 2859− 2862. (33) Morita, S.; Giessibl, F. J.; Wiesendanger, R. Noncontact Atomic Force Microscopy; Springer Verlag: Berlin, Heidelberg, 2009.

toward the experimental AFM tip. Therefore, this study implies important signatures of possible oscillation amplitude due to no stiffness of different functionalized tips to describe the main interactions in the tip/MMT interface, in this case to probe the different hydrophilicity in systems of polymeric surfactants through the selectivity of −OH groups on aluminosilicate surfaces.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone: +55 11 3091 7009. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Advanced Energy Consortium: http://www.beg.utexas.edu/aec/. Member companies include BP America Inc., BG Group, Petrobras, Repsol, Schlumberger, Statoil, Shell, and Total. The authors acknowledge the financial support provided by the Brazilian agencies Fapesp and CNPq. We acknowledge the computational support of CENAPAD-SP and UFABC supercomputer facilities by performed calculations. We would like to thank the anonymous reviewers for insightful suggestions and Dr. Oscar S. C. Macollunco for the help to obtain the frequency shift curves.

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REFERENCES

(1) Sellin, P.; Leupin, O. X. The Use of Clay as an Engineered Barrier in Radioactive-Waste Management - A Review. Clays Clay Miner. 2013, 61, 477−498. (2) Lavikainen, L. P.; Hirvi, J. T.; Kasa, S.; Schatz, T.; Pakkanen, T. A. Stability of Dioctahedral 2:1 Phyllosilicate Edge Structures Based on Pyrophyllite Models. Theor. Chem. Acc. 2015, 134, 112. (3) Briones-Jurado, C.; Agacino-Valdés, E. Brønsted Sites on AcidTreated Montmorillonite: A Theoretical Study with Probe Molecules. J. Phys. Chem. A 2009, 113, 8994−9001. (4) Voora, V. K.; Al-Saidi, W. A.; Jordan, K. D. Density Functional Theory Study of Pyrophyllite and M-Montmorillonites (M = Li, Na, K, Mg, and Ca): Role of Dispersion Interactions. J. Phys. Chem. A 2011, 115, 9695−9703. (5) Mintova, S.; Jaber, M.; Valtchev, V. Nanosized Microporous Crystals: Emerging Applications. Chem. Soc. Rev. 2015, 44, 7207− 7233. (6) Lavikainen, L. P.; Tanskanen, J. T.; Schatz, T.; Kasa, S.; Pakkanen, T. A. Montmorillonite Interlayer Surface Chemistry: Effect of Magnesium Ion Substitution on Cation Adsorption. Theor. Chem. Acc. 2015, 134, 51. (7) Alvim, R. S.; Miranda, C. R. First Principles Characterization of Silicate Sites in Clay Surfaces. Phys. Chem. Chem. Phys. 2015, 17, 4952−4960. (8) Fonseca, C. G.; de Carvalho, G. S. G.; Wypych, F.; Diniz, R.; Leitão, A. A. Na+ as a Probe to Structural Investigation of Dehydrated Smectites Using NMR Spectra Calculated by DFT. Appl. Clay Sci. 2016, 126, 132−140. (9) Buckley, J. S.; Lord, D. L. Wettability and Morphology of Mica Surfaces After Exposure to Crude Oil. J. Pet. Sci. Eng. 2003, 39, 261− 273. (10) Kumar, K.; Dao, E.; Mohanty, K. K. AFM Study of Mineral Wettability with Reservoir Oils. J. Colloid Interface Sci. 2005, 289, 206− 217. (11) Hou, B.-f.; Wang, Y.-f.; Huang, Y. Mechanistic Study of Wettability Alteration of Oil-Wet Sandstone Surface Using Different Surfactants. Appl. Surf. Sci. 2015, 330, 56−64. (12) Abidin, A. Z.; Puspasari, T.; Nugroho, W. A. Polymers for enhanced oil recovery technology. Procedia Chem. 2012, 4, 11−16. I


Article


Bonds in Atomic Force Microscopy Images. J. Phys. Chem. C 2015, 119, 14195−14200. (56) Kohn, W.; Sham, L. J. Self-Consistent Equations Including Exchange and Correlation Effects. Phys. Rev. 1965, 140, A1133− A1138. (57) Payne, M. C.; Teter, M. P.; Allan, D. C.; Arias, T. A.; Joannopoulos, J. D. Iterative Minimization Techniques for ab initio Total-Energy Calculations: Molecular Dynamics and Conjugate Gradients. Rev. Mod. Phys. 1992, 64, 1045−1097. (58) Perdew, J. P.; Wang, Y. Accurate and Simple Analytic Representation of the Electron-Gas Correlation-Energy. Phys. Rev. B: Condens. Matter Mater. Phys. 1992, 45, 13244−13249. (59) Quantum-Espresso is a community project for high-quality quantum-simulation software, based on density-functional theory. See http://www.quantum-espresso.org and http://www.pwscf.org (accessed June 16, 2016). (60) Scandolo, S.; Giannozzi, P.; Cavazzoni, C.; de Gironcoli, S.; Pasquarello, A.; Baroni, S. First-Principles Codes for Computational Crystallography in the Quantum-ESPRESSO Package. Z. Kristallogr. Cryst. Mater. 2005, 220, 574−579. (61) Giannozzi, P.; Baroni, S.; Bonini, N.; Calandra, M.; Car, R.; Cavazzoni, C.; Ceresoli, D.; Chiarotti, G. L.; Cococcioni, M.; Dabo, I.; et al. QUANTUM ESPRESSO: A Modular and Open-Source Software Project for Quantum Simulations of Materials. J. Phys.: Condens. Matter 2009, 21, 395502. (62) Makov, G.; Payne, M. C. Periodic Boundary Conditions in ab initio Calculations. Phys. Rev. B: Condens. Matter Mater. Phys. 1995, 51, 4014−4022. (63) Vanderbilt, D. Soft Self-Consistent Pseudopotentials in a Generalized Eigenvalue Formalism. Phys. Rev. B: Condens. Matter Mater. Phys. 1990, 41, 7892−7895. (64) Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865−3868. (65) Perdew, J. P.; Burke, K.; Wang, Y. Generalized Gradient Approximation for the Exchange-Correlation Hole of a Many-Electron System. Phys. Rev. B: Condens. Matter Mater. Phys. 1996, 54, 16533− 16539. (66) Zhang, Y.; Yang, W. Comment on “Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1998, 80, 890. (67) Dion, M.; Rydberg, H.; Schröder, E.; Langreth, D. C.; Lundqvist, B. I. Van der Waals Density Functional for General Geometries. Phys. Rev. Lett. 2004, 92, 246401. (68) Thonhauser, T.; Cooper, V. R.; Li, S.; Puzder, A.; Hyldgaard, P.; Langreth, D. C. Van der Waals Density Functional: Self-Consistent Potential and the Nature of the van der Waals Bond. Phys. Rev. B: Condens. Matter Mater. Phys. 2007, 76, 125112. (69) Román-Pérez, G.; Soler, J. M. Efficient Implementation of a van der Waals Density Functional: Application to Double-Wall Carbon Nanotubes. Phys. Rev. Lett. 2009, 103, 096102. (70) Billeter, S. R.; Turner, A. J.; Thiel, W. Linear Scaling Geometry Optimisation and Transition State Search in Hybrid Delocalised Internal Coordinates. Phys. Chem. Chem. Phys. 2000, 2, 2177−2186. (71) Billeter, S. R.; Curioni, A.; Andreoni, W. Efficient Linear Scaling Geometry Optimization and Transition-State Search for Direct Wavefunction Optimization Schemes in Density Functional Theory Using a Plane-Wave Basis. Comput. Mater. Sci. 2003, 27, 437−445. (72) Feynman, R. P. Forces in Molecules. Phys. Rev. 1939, 56, 340− 343. (73) Argento, C.; French, R. H. Parametric Tip Model and ForceDistance Relation for Hamaker Constant Determination from Atomic Force Microscopy. J. Appl. Phys. 1996, 80, 6081−6090. (74) Kokalj, A. XCrySDen - A New Program for Displaying Crystalline Structures and Electron Densities. J. Mol. Graphics Modell. 1999, 17, 176−179. Code available from http://www.xcrysden.org/ (accessed June 16, 2016). (75) Jia, F.; Song, S. Preparation of Monolayer Muscovite through Exfoliation of Natural Muscovite. RSC Adv. 2015, 5, 52882−52887. (76) Van Rhijn, W. M.; De Vos, D. E.; Sels, B. F.; Bossaert, W. D.; Jacobs, P. A. Sulfonic Acid Functionalised Ordered Mesoporous

(34) Hassenkam, T.; Skovbjerg, L. L.; Stipp, S. L. S. Probing the Intrinsically Oil-Wet Surfaces of Pores inNorth Sea Chalk at Subpore Resolution. Proc. Natl. Acad. Sci. U. S. A. 2009, 106, 6071−6076. (35) Caciuc, V.; Hölscher, H.; Weiner, D.; Fuchs, H.; Schirmeisen, A. Noncontact Atomic Force Microscopy Imaging Mechanism on Ag(110): Experiment and First-Principles Theory. Phys. Rev. B: Condens. Matter Mater. Phys. 2008, 77, 045411. (36) Caciuc, V.; Hölscher, H. Ab initio Simulation of Atomic-Scale Imaging in Noncontact Atomic Force Microscopy. Nanotechnology 2009, 20, 264006. (37) Eaton, P.; West, P. Atomic Force Microscopy; Cambridge University Press: Cambridge, U.K., 2011. (38) Welker, J.; Weymouth, A. J.; Giessibl, F. J. The Influence of Chemical BondingConfiguration on Atomic Identification by Force Spectroscopy. ACS Nano 2013, 7, 7377−7382. (39) Boneschanscher, M. P.; Hämäläinen, S. K.; Liljeroth, P.; Swart, I. Sample Corrugation Affects theApparent Bond Lengths in Atomic Force Microscopy. ACS Nano 2014, 8, 3006−3014. (40) Neu, M.; Moll, N.; Gross, L.; Meyer, G.; Giessibl, F. J.; Repp, J. Image Correction for Atomic Force Microscopy Images with Functionalized Tips. Phys. Rev. B: Condens. Matter Mater. Phys. 2014, 89, 205407. (41) Weymouth, A. J.; Hofmann, T.; Giessibl, F. J. Quantifying Molecular Stiffnessand Interaction with Lateral Force Microscopy. Science 2014, 343, 1120−1122. (42) Hofmann, T.; Pielmeier, F.; Giessibl, F. J. Chemical and Crystallographic Characterization of the Tip Apexin Scanning Probe Microscopy. Phys. Rev. Lett. 2014, 112, 066101. (43) Jarvis, S. P. Resolving Intra- and Inter-Molecular Structure with Non-Contact Atomic Force Microscopy. Int. J. Mol. Sci. 2015, 16, 19936−19959. (44) Kim, M.; Chelikowsky, J. R. CO Tip Functionalization in Subatomic Resolution Atomic Force Microscopy. Appl. Phys. Lett. 2015, 107, 163109. (45) Chan, T.-L.; Wang, C. Z.; Ho, K. M.; Chelikowsky, J. R. Efficient First-Principles Simulation of Noncontact Atomic Force Microscopy for Structural Analysis. Phys. Rev. Lett. 2009, 102, 176101. (46) Zhong, W.; Overney, G.; Tománek, D. Limits of Resolution in Atomic Force Microscopy Images of Graphite. Europhys. Lett. 1991, 15, 49−54. (47) Tóbik, J.; S̆tich, I.; Terakura, K. Effect of Tip Morphology on Image Formation in Noncontact Atomic Force Microscopy: InP(110). Phys. Rev. B: Condens. Matter Mater. Phys. 2001, 63, 245324. (48) Oyabu, N.; Pou, P.; Sugimoto, Y.; Jelinek, P.; Abe, M.; Morita, S.; Pérez, R.; Custance, O. Single Atomic Contact Adhesion and Dissipation in Dynamic Force Microscopy. Phys. Rev. Lett. 2006, 96, 106101. (49) Kantorovich, L.; Hobbs, C. Probing the Si(001) Surface with a Si Tip: An ab initio Study. Phys. Rev. B: Condens. Matter Mater. Phys. 2006, 73, 245420. (50) Bamidele, J.; Li, Y. J.; Jarvis, S.; Naitoh, Y.; Sugawara, Y.; Kantorovich, L. Complex Design of Dissipation Signals in NonContact Atomic Force Microscopy. Phys. Chem. Chem. Phys. 2012, 14, 16250−16257. (51) Jarvis, S. P.; Kantorovich, L.; Moriarty, P. Structural Development and Energy Dissipation in Simulated Silicon Apices. Beilstein J. Nanotechnol. 2013, 4, 941−948. (52) Sang, H.; Jarvis, S. P.; Zhou, Z.; Sharp, P.; Moriarty, P.; Wang, J.; Wang, Y.; Kantorovich, L. Identifying Tips for Intramolecular NCAFM Imaging via in situ Fingerprinting. Sci. Rep. 2014, 4, 6678. (53) Sweetman, A.; Jarvis, S. P.; Rahe, P.; Champness, N. R.; Kantorovich, L.; Moriarty, P. Intramolecular Bonds Resolved on a Semiconductor Surface. Phys. Rev. B: Condens. Matter Mater. Phys. 2014, 90, 165425. (54) Guo, C.-S.; Van Hove, M. A.; Ren, X.; Zhao, Y. High-Resolution Model for Noncontact Atomic Force Microscopy with a Flexible Molecule on the Tip Apex. J. Phys. Chem. C 2015, 119, 1483−1488. (55) Guo, C.-S.; Xin, X.; Van Hove, M. A.; Ren, X.; Zhao, Y. Origin of the Contrast Interpreted as Intermolecular andIntramolecular J


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The Journal of Physical Chemistry C Materials as Catalysts for Condensation and Esterification Reactions. Chem. Commun. 1998, 317−318. (77) Wu, J.; Liu, F.; Chen, G.; Wu, X.; Ma, D.; Liu, Q.; Xu, S.; Huang, S.; Chen, T.; Zhang, W.; et al. Effect of Ionic Strength on the Interfacial Forces between Oil/Brine/Rock Interfaces: A Chemical Force Microscopy Study. Energy Fuels 2016, 30, 273−280.

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