Decane Molecules Research Articles

Molecular insights of condensate trapping mechanism in shale oil reservoirs and its implications on lean gas enhanced oil recovery

The heterogeneous pore structure and the confinement effect of the narrow pore space lead to the differential release/retention phenomenon of hydrocarbons in unconventional reservoirs. So far, the mechanism of this phenomenon, in particular the dynamic process, requires further investigation since it affects the design of gas-based enhanced oil recovery (EOR) operations. In this work, we aim to numerically study the capillary condensate trapping mechanism that causes the differential release phenomenon by conducting molecular dynamics (MD) simulations.In our work, a two-bath MD model is set up, in which two baths are used to mimic the bulk pores and a nano-channel connecting the two baths is used to model the pore throat. Methane (C1) and decane (C10) molecules are used to represent the light and heavy component of the in-situ oil. The MD results show that at the early stage of the primary depletion, the light components release faster than the heavier components, leading to increasing gas oil ratio (GOR) above the system’s bubble point. As depletion continues, heavier hydrocarbons accumulate in the nano-channel due to the confinement effect, while light hydrocarbons tend to remain in the dead-end pores. During the gas EOR process, the injected gas ‘dissolves’ the liquid in the nano-channel and thus enhances the recovery of the ‘trapped’ hydrocarbons.This work systematically investigates the impact of pore throat on the differential release and trapping effect. We demonstrate that a significant amount of light hydrocarbons may be ‘trapped’ during the primary depletion of unconventional reservoirs, due to the capillary condensate trapping effect. The trapped hydrocarbons can be partly recovered through gas injection. Our study has implications for practical EOR operations.

CO2 gas stripped off membranous residual oil from pore surfaces: Effects of temperature, pressure and wettability

The threshold values of CO2 gas stripped off membranous residual oil from the pore walls are not clear under different temperatures, pressures and wettability conditions. The extent to which temperature, pressure and wettability influence CO2 flooding for enhancing the recovery of residual oil in membranous formations also remains uncertain. Therefore, further quantitative characterization is entailed. In this study, the molecular dynamics method was employed to explore CO2 flooding under different temperatures, pressures and wettability conditions, aiming to enhance the production of membranous residual oil. The results reveal that the interaction energy between CO2, decane molecules and pore walls exhibits a decrease with increasing temperature and an increase with increasing pressure, respectively, in distinct wettability scenarios. When the temperature was at or below 363 K and the pressure was not lower than 40 MPa, CO2 gas could detach the membranous residual oil from the pore walls in the water-wet systems. When the temperature was equal to 363 K and the pressure remained under 40 MPa, or the temperature surpassed 363 K, CO2 gas failed to detach the membranous residual oil from the pore walls in the water-wet systems. For the mixed-wet and oil-wet systems, CO2 molecules could not detach the membranous residual oil from the pore walls. The hierarchy of influence regarding temperature, pressure and wettability on the competitive adsorption capacity of CO2 and decane molecules on the pore walls emerged as follows: wettability > temperature > pressure. The findings of this study offer valuable insights into the application of CO2 gas flooding for the exploitation of membranous residual oil on pore walls.

Molecular dynamics simulation of the Stribeck curve: Boundary lubrication, mixed lubrication, and hydrodynamic lubrication on the atomistic level

Lubricated contact processes are studied using classical molecular dynamics simulations for determining the entire range of the Stribeck curve. Therefore, the lateral movement of two solid bodies at different gap height are studied. In each simulation, a rigid asperity is moved at constant height above a flat iron surface in a lubricating fluid. Both methane and decane are considered as lubricants. The three main lubrication regimes of the Stribeck curve and their transition regions are covered by the study: Boundary lubrication (significant elastic and plastic deformation of the substrate), mixed lubrication (adsorbed fluid layer dominates the process), and hydrodynamic lubrication (shear flow is set up between the surface and the asperity). We find the formation of a tribofilm in which lubricant molecules are immersed into the metal surface—not only in the case of scratching, but also for boundary lubrication and mixed lubrication. The formation of a tribofilm is found to have important consequences for the contact process. Moreover, the two fluids are found to show distinctly different behavior in the three lubrication regimes: For hydrodynamic lubrication (large gap height), decane yields a better tribological performance; for boundary lubrication (small gap height), decane shows a larger friction coefficient than methane, which is due to the different mechanisms observed for the formation of the tribofilm; the mixed lubrication regime can be considered as a transition regime between the two other regimes. Moreover, it is found that the nature of the tribofilm depends on the lubricant: While methane particles substitute substrate atoms sustaining mostly the crystalline structure, the decane molecules distort the substrate surface and an amorphous tribofilm is formed.

Influence of an external electric field on the rupture force of decane, 4-decanone, and dicumyl peroxide molecules: Computational insight

To clarify the degradation of the electrical insulation ability of polymeric materials at the molecular level, the effects of an external electric field on the rupture of molecules were evaluated using quantum chemical calculations. Two molecular models were evaluated with the aim of elucidating the physicochemical background of realistic insulation deterioration factors, namely, the effect of oxidation and impurities. The first model was used to evaluate the effect of oxidative degradation of alkane molecules on the C–C bond; maximum rupture force of the C–C bonds of decane and 4-decanone were compared, and it was found to decrease by approximately 13.8 %. It was also clarified that the maximum rupture force changes depending on the applied direction of the external electric field. The second model was used to examine the effect of an external electric field on the decomposition of dicumyl peroxide, which is a cross-linking agent for cross-linked polyethylene. In the decomposition process of dicumyl peroxide, the rupture of cumyl alcohol was found to be strongly influenced by an external electric field. Because the decomposition of cumyl alcohol involves dehydration, it is likely to induce the initiation and propagation of water trees in polyethylene. Therefore, it is important to remove the cumyl alcohol before applying a high voltage.

CNT biodevices for early liver cancer diagnosis based on biomarkers detection- a promising platform

Regarding the serious threat of liver cancer owing to the concealment and hard detection of liver tumors at an early stage, primary diagnosis becomes quite crucial to guarantee human health. So, in this work platinum-decorated single-walled carbon nanotubes (SWCNTs) were proposed as superior nanodevice for the detection of 1-Octen-3-ol (octenol), decane, and hexanal as liver cancer biomarkers in the exhaled breath of the patients. Herein, density functional theory (DFT) calculations have been utilized to scrutinize the structural and electronic properties of pristine and Pt-decorated SWCNTs. Obtained results showed that the gas molecules were weakly physisorbed on the pristine SWCNT with negligible charge transfer and large interaction distances. Contrariwise, after the decoration of the SWCNT with Pt metal atom, significant charges are transferred, and energy adsorption increased. The results disclosed that the energy adsorption has been enhanced, for example, energy adsorption increased two times for decane and hexanal molecules (−1.06, and −1.07 eV) upon adsorption on Pt-decorated SWCNT. Moreover, substantial charges with amount of 0.238, 0.245, and 0.223 e were transferred from octenol, decane, and hexanal to the surface, respectively. So, investigations revealed that these compounds are strongly chemisorbed on Pt-SWCNT with small interaction distances and along with the short recovery time of 1.7, 83.4, and 123 s at room temperature toward octenol, decane, and hexanal, respectively which make it a compelling nanodevice. Considering the findings, Pt-SWCNT is an excellent substrate for the sense of liver cancer biomarkers with desired recovery time and the results demonstrate its feasibility for potential application in the near future in the field of liver cancer diagnosis.

Molecular Dynamics Simulation of the Soret Effect on Two Binary Liquid Solutions with Equimolar n-Alkane Mixtures.

Molecular dynamics is employed to simulate the Soret effect on two binary liquid solutions with equimolar mixtures: normal pentane (n-pentane, nC-5) and normal heptane (n-heptane, nC-7) molecules plus normal decane (n-decane, nC-10) and normal pentane molecules. Moreover, two coarse-grained force field (the CG-FF) potentials, which may depict inter-/intramolecular interactions fairly well among n-alkane molecules, are developed to fulfill such investigations. In addition, thermal diffusion for the mass fraction of each of these n-alkane molecules is simulated under an effect of a weak thermal gradient (temperature difference) exerting on solution systems from their hot to cold boundary sides. Finally, quantities of the Soret coefficient (SC) for two binary solutions are calculated by means of the developed CG-FF potentials, so as to improve the calculation rationality. As a result, first, it is found that molecules with light molar masses will migrate toward the hot boundary side, while those with heavy molar masses will migrate toward the cold boundary one ; second, the SC quantities indicate that they match relevant experimental determinations fairly well, i.e., trends of these SC quantities show inverse proportionality to the thermal gradient on the systems.

Soaking in CO2 huff-n-puff: A single-nanopore scale study

CO2 Huff-n-Puff is a promising method for enhancing the oil recovery from unconventional reservoirs and sequestering CO2. Optimizing the operation of Huff-n-Puff requires a fundamental understanding of the thermodynamic and transport phenomena of CO2 and oil in nanopores. Here, we investigate the soaking step of CO2 Huff-n-Puff in a single, 4 nm-wide calcite pore using molecular dynamics simulations. We show that the CO2 molecules entering the pore can become adsorbed on pore walls and diffuse along with walls or are transported into the pore's interior as free CO2 molecules. Decane molecules are displaced from the pore walls and out of the bulk zone in the pore. Before reaching the pore's end, the movement of the density fronts of adsorbed and free CO2 molecules inside the pore obeys a t1/2 scaling law with effective diffusion coefficients ∼50% smaller than that of bulk CO2. Except at the very beginning period of soaking, the accumulation of adsorbed and free CO2 molecules occurs at a similar rate and follows the diffusive scaling law. These pore-scale results highlight the importance of surface adsorption in the storage and transport of CO2 during the soaking process in unconventional oil reservoirs.

Molecular Dynamics Study on Performance of Olefin Sulfonate at the Decane–Water Interface: Effect of Molecular Architecture

Surfactant flooding has been widely employed to recover the residual oil in the oilfields. Among the various oil-displacing chemicals, olefin sulfonate isomers have been identified as effective chemical agents by many experiments due to the realization of low interfacial tension (IFT) at the oil–water interface, and tolerance for high salinity and high temperature under reservoir conditions. The molecular architecture (e.g. degree of branching) of the surfactant can significantly affect the oil–water interfacial properties and hence its performance. Herein, molecular dynamics simulations were performed to investigate the adsorption processes of alpha olefin surfactant (AOS with single-tailed structure) and internal olefin surfactant (IOS with twin-tailed structure) at the oil (n-decane) - water interface under oil reservoir condition. The results show that IOS can significantly reduce the IFT at high concentrations, and the formed monolayers at the interface are more stable compared with AOS. The steric hindrance effect by the short chain of IOS can inhibit the aggregation behavior, thus leading to larger interfacial coverage, which are favorable to separation of the water and decane phases. The larger distance between the headgroups of IOS molecules is conducive to formation of hydrogen bonds between the surfactant and water molecules, and hence enhances the interaction between the IOS and water molecules at the inerface. Based on the analysis of order parameter, the middle segment of AOS molecules and the long chain of IOS molecules are mainly contributed to the Van der Waals’ interaction between the surfactant alkyl tails and decane molecules. Meanwhile, the twin-tailed structure of IOS has more favorable effective alkyl tail length (i.e. better miscibility with the oil phase) compared with the single-tailed structure of AOS. Consequently, the twin-tailed structure is superior to the single-tailed structure in terms of interfacial performance, and it is strongly suggested for the design of advanced surfactants in EOR implementation.

Molecular Dynamics of Decane Solubilization and Diffusion of Aggregates Consisting of Surfactant and Decane Molecules in Aqueous Solutions

Molecular Dynamics of Decane Solubilization and Diffusion of Aggregates Consisting of Surfactant and Decane Molecules in Aqueous Solutions

Decane structure on a graphite surface with sodium dodecyl sulfate and betaine surfactant mixtures: A molecular dynamics study

Computer simulations of anionic and zwitterionic surfactants were carried out to study decane molecules arrangement on a graphite surface. Systems were constructed with different amount of decane molecules deposited on top of the graphite surface by forming two and four structured layers. Then, Sodium dodecyl sulfate (SDS) and two betaine surfactants, cocoamidopropyl (CAPB) and the N-Dodecyl-N,N-dimethyl- 3-ammomio-1-propanesulfonate (SB3-12), with their mixtures were used to investigate removal of the alkane molecules where different features were observed. Arrangement was analyzed in terms of density profiles and isotherm curves at different surfactant concentrations. It was observed that all surfactants promoted the formation of an additional decane layer suggesting they could produce detachment or removal from the graphite surface. The anionic surfactant present better removal from the surface than the betaine ones whereas in the case of the mixtures the SDS/CAPB one was slightly better than the SDS/SB3-12 one.

Quadrupolar mechanism for vibrational sum frequency generation at air/liquid interfaces: Theory and experiment

Vibrational sum frequency generation (VSFG) spectroscopy has been widely utilized to investigate various interfaces through molecular vibration. VSFG is usually attributed to the breakdown of the inversion symmetry at the interface within the electric dipole approximation. Although the electric dipole approximation is a very good approximation in the isotropic bulk, its validity is questionable at the interface because a large electric field gradient exists in the thin interface region. Thus, the quadrupole contribution may become significant at the interface. Here, we discuss the quadrupole contribution in VSFG from theoretical and experimental viewpoints. We describe a theory as to how the quadrupole contribution appears in experimental VSFG spectra by deriving the vibrational selection rule and discussing the interface selectivity. With this theoretical framework, we examine the mechanism of VSFG at the air/benzene and air/decane interfaces. The accurate determination of the vibrational frequencies realized by heterodyne-detected VSFG spectroscopy reveals that VSFG at the air/benzene interface arises from the quadrupolar mechanism. This means that the observation of VSFG does not imply a molecular alignment so that interfacial benzene molecules may be randomly oriented. Meanwhile, at the air/decane interface, it is concluded that the VSFG signal arises from the ordinary dipolar mechanism. This implies that decane molecules are aligned in a preferential direction at the interface despite their low polarity. This study demonstrates the importance of examining the mechanism of VSFG before discussing the interfacial structure based on VSFG spectra. A strategy to distinguish different mechanisms is also proposed. The present study further shows that the quadrupolar mechanism, if properly taken into consideration, enables us to obtain information about interfacial molecules beyond the restriction of the inversion symmetry breaking required by the dipolar mechanism, through the large electric field gradient localized at the interface.

Estimating Factors Determining Emulsification Capability of Surfactant-Like Peptide with Coarse-Grained Molecular Dynamics Simulation

The ability of surfactant-like peptides to emulsify oil has become the main focus of our current study. We predicted the ability of a series of surfactant-like peptides (G6D, A6D, M6D, F6D, L6D, V6D, and I6D) to emulsify decane molecules using coarse-grained molecular dynamics simulations. A 1-μs simulation of each peptide was carried out at 298 K and 1 atm using MARTINI force field. Simulation system was constructed to consist of 100 peptide molecules, 20 decane molecules, water, antifreeze particles and neutralizing ions in a random configuration. Out of seven tested peptides, M6D, F6D, L6D, V6D, and I6D were able to form emulsion while G6D and A6D self-assembled to order b-strands. A higher hydropathy index of amino acids constituting the hydrophobic tail renders the formation of an emulsion by peptides more likely. By calculating contact number between peptides and decanes, we found that emulsion stability and geometry depends on the structure of amino acids constituting the hydrophobic tail. Analysis of simulation trajectory revealed that emulsions are formed by small nucleation following by fusion to form a bigger emulsion. This study reveals the underlying principle at the molecular level of surfactant peptide ability to form an emulsion with hydrophobic molecules.

Mechanistic Study of Wettability Changes on Calcite by Molecules Containing a Polar Hydroxyl Functional Group and Nonpolar Benzene Rings.

Oil extraction efficiency strongly depends on the wettability status (oil- vs water-wet) of reservoir rocks during oil recovery. Aromatic compounds with polar functional groups in crude oil have a significant influence on binding hydrophobic molecules to mineral surfaces. Most of these compounds are in the asphaltene fraction of crude oil. This study focuses on the hydroxyl functional group, an identified functional group in asphaltenes, to understand how the interactions between hydroxyl groups in asphaltenes and mineral surfaces begin. Phenol and 1-naphthol are used as asphaltene surrogates to model the simplest version of asphaltenes. Adsorption of oil molecules on the calcite {101̅4} surface is described using static quantum-mechanical density functional theory (DFT) calculations and classical molecular dynamics (MD) simulations. DFT calculations indicate that adsorption of phenol and 1-naphthol occurs preferentially between their hydroxyl group and calcite step edges. 1-Naphthol adsorbs more strongly than phenol, with different adsorption geometries due to the larger hydrophobic part of 1-naphthol. MD simulations show that phenol can behave as an agent to separate oil from the water phase and to bind the oil phase to the calcite surface in the water/oil mixture. In the presence of phenol, partial separation of water/oil with an incomplete lining of phenol at the water/oil boundary is observed after 0.2 ns. After 1 ns, perfect separation of water/oil with a complete lining of phenol at the water/oil boundary is observed, and the calcite surface becomes oil-wet. Phenol molecules enclose decane molecules at the water-decane boundary preventing water from repelling decane molecules from the calcite surface and facilitate further accumulation of hydrocarbons near the surface, rendering the surface oil-wet. This study indicates phenol and 1-naphthol to be good proxies for polar components in oil, and they can be used in designing further experiments to test pH, salinity, and temperature dependence to improve oil recovery.

Moving mechanisms of the three-phase contact line in a water-decane-silica system.

The movement of the three-phase contact line with chain molecules in the liquid phase displays more complex mechanisms compared to those in the usual liquid–liquid–solid systems and even to the gas–liquid–solid systems controlled by the traditional single-molecule adsorption–desorption mechanisms. By introducing decane molecules with chain structures, we demonstrate from molecular dynamics insights that the moving mechanism of the contact line in a water–decane–silica system is totally different from traditional mechanisms. Three different wettability-related moving mechanisms including “Roll up”, “Piston” and “Shear” are revealed corresponding to the hydrophilic, intermediate and hydrophobic three-phase wettability, respectively. In the “Roll up” mechanism, the decane molecules are rolled up by the competitively adsorbed water molecules and then move forward under the driving force; when the “Piston” mechanism happens, the decane molecules are pushed by the piston-like water phase owing to the comparable adsorption interactions of the two liquids on the solid surface; in the “Shear” mechanism, the contact line is hard to drive due to the stronger decane–silica interactions but the decane molecules far away from the solid surface will move forward. Besides, the time-averaged velocity of the moving contact line is greatly related to the moving mechanisms. For the “Roll up” mechanism, the contact line velocity increases first and then reaches a steady value; for the “Piston” mechanism, the contact line velocity has a maximum value at the start-up stage and then decreases to a stable value; for the “Shear” mechanism, the contact line velocity fluctuates around zero due to the thermal fluctuation of the molecules. Additionally, the mean distance from Molecular Kinetics Theory increases with decreasing hydrophilicity and the displacement frequency in “Roll up” mechanism is 2 orders of magnitude higher than that in the “Piston” mechanism, further demonstrating the different moving mechanisms from a quantitative point of view.

Structural Properties of Span 80/Tween 80 Reverse Micelles by Molecular Dynamics Simulations.

The sorbitan monooleate (Span 80)/poly(oxyethylene) sorbitan monooleate (Tween 80) reverse micelles (RMs) in the water-in- n-decane microemulsion were studied using the molecular dynamics simulation. The coexistence of the large RMs with the hydrodynamic radii Rh ∼ 10-20 nm and small RMs with Rh ∼ 1-2 nm was previously specified for this system. Models of both surfactants and decane were based on the united-atom approach to allow us to describe the structural properties of the small RMs. The micelles have been self-assembled from an initially homogeneous mixture of surfactant, water, and decane molecules. The dependence of the shape of the RMs on the relative content of surfactants has been established. The inner structure of Span 80, Tween 80, and Span 80/Tween 80 RMs was quantitatively described. Tween 80 molecules penetrate the water core, whereas Span 80 molecules are located on the surface of the RM. The obtained data show that the hydrogen bonds are formed between the surfactant molecules on the surface of the RM and play an important role in the formation of RMs. The water hydrogen bond density distribution in individual and mixed RMs explains the advantages of the mixed surfactant system compared to an individual surfactant.

Extra low friction coefficient caused by the formation of a solid-like layer: A new lubrication mechanism found through molecular simulation of the lubrication of MoS2 nanoslits

Abstract Monolayer molybdenum disulfide (MoS2) is a novel two-dimensional material that exhibits potential application in lubrication technology. In this work, molecular dynamics was used to investigate the lubrication behaviour of different polar fluid molecules (i.e., water, methanol and decane) confined in monolayer MoS2 nanoslits. The pore width effect (i.e., 1.2, 1.6 and 2.0 nm) was also evaluated. Results revealed that decane molecules exhibited good lubricating performance compared to the other two kinds of molecules. The friction coefficient followed the order of decane

Molecular Dynamics Simulation of the Oil Sequestration Properties of a Nonionic Rhamnolipid.

A detailed molecular dynamics simulation study is presented on the behavior of aggregates composed of the nonionic monorhamnolipid α-rhamnopyranosyl-β-hydroxydecanoyl-β-hydroxydecanoate (Rha-C10-C10) and decane in bulk water. A graph theoretical approach was utilized to characterize the size and composition of the many aggregates generated in our simulations. Overall, we observe that the formation of oil in Rha-C10-C10 aggregates is a favorable process. Detailed analysis on the surfactant/oil aggregate shows that larger aggregates are stable. The shape and size of the aggregates are widely distributed, with the majority of the aggregates preferring ellipsoidal or cylindrical structures. Irrespective of the decane concentration in the system, we did not observe free decane in any of the simulations. Further insights into the binding energy of decane were carried out using free-energy perturbation calculations. The results showed that the trapped decane molecules provide stability to the Rha-C10-C10 aggregates of size N = 50 which are shown to be unstable in our previous study and allow for the growth of larger aggregates than pure Rha-C10-C10 in water. The density profile plots show that decane molecules encapsulated inside the aggregate preferred to remain closer to the center of mass. This study points to the feasibility of using this biosurfactant as an environmental remediation agent.

Design and experimental verification of a photoacoustic flow sensor using computational fluid dynamics.

A photoacoustic (PA) sensor for fast and real-time gas sensing is demonstrated. The PA sensor is a stand-alone system controlled by a field-programmable gate array. The PA cell has been designed for flow noise immunity using computational fluid dynamics (CFD) analysis. The aim of the CFD analysis was to investigate and minimize the influence of the gas distribution and flow noise on the PA signal. PA measurements were conducted at different flow rates by exciting molecular C-H stretch vibrational bands of hexane (C6H14) and decane (C10H22) molecules in clean air at 2950 cm-1 (3.38μm) with a custom-made mid-infrared interband cascade laser. We observe a (1σ, standard deviation) sensitivity of 0.4±0.1 ppb (nmol/mol) for hexane in clean air at flow rates up to 1.7L/min, corresponding to a normalized noise equivalent absorption coefficient of 2.5×10-9 W cm-1 Hz-1/2, demonstrating high sensitivity and fast real-time gas analysis. An Allan deviation analysis for decane shows that the detection limit at optimum integration time is 0.25ppbV (nmol/mol).

Effect of Alkyl Chain Length on the Interfacial Dilational Properties of Hydroxy-Substituted Alkyl Benzenesulfonates

Dilational rheological behaviors of adsorption layers of three surfactants, sodium 2-hydroxy-3,5-dioctyl benzene sulfonate (C8C8), sodium 2-hydroxy-3-octyl-5-decyl benzene sulfonate (C8C10), and sodium 2-hydroxy-3-octyl-5-dodecylbenzenesulfonate (C8C12) formed at air–water and decane–water interfaces, have been investigated as a function of concentration and frequency (0.002–0.1 Hz) by the oscillating bubble/drop method. The experimental results show that the dilational moduli of hydroxy-substituted alkyl benzenesulfonates are obviously higher than those of the common surfactants, because the interfacial interactions between alkyl chains are improved drastically by the unique arrangement of C8C8 molecules at the interface. However, the moduli at the decane–water interface are much lower than those at the surfaces because decane molecules will insert into the surfactant molecules adsorbed at the interface and destroy the interactions between alkyl chains. With an increase in the number of carbon atom of 5-alkyl, the surface dilational modulus decreases because the orientation of the surfactant molecules at the surface varies from parallel to tilt. On the other hand, the diffusion-exchange process dominates the interfacial behavior and the interfacial modulus improves with the increase in the length of the alkyl chain.

Wetting Effects and Molecular Adsorption at Hydrated Kaolinite Clay Mineral Surfaces

In this study, classical molecular dynamics simulations have been used to understand the key interactions and surface structure of a set of organic molecules at the hydrated surfaces of the 1:1 clay mineral kaolinite. Decane, decanoic acid, and decanamine have been modeled at both the hydroxylated and silicate surfaces of kaolinite. Additionally, the effect of pH is observed via looking at the protonated decanamine and decanoate anion forms. The key results show that relative affinity of the organic molecules to the kaolinite surface may be readily switched between the hydroxylated and the silicate surfaces according to the pH and the nature of the organic head functional group. Decane molecules readily form droplets atop the silicate surface and do not adsorb to the hydroxyl surface, as do protonated decanoic acids. In stark contrast, decanoate anions do not adsorb to the silicate surface, yet adsorb to the hydroxyl surface through an anion exchange mechanism. Decanamine readily adsorbs to both silicate ...