Electrical Double Layer Interaction Research Articles

Exploring the mechanisms of calcium carbonate deposition on various substrates with implications for effective anti-scaling material selection

The unexpected scaling phenomena have resulted in significant damages to the oil and gas industries, leading to issues such as heat exchanger failures and pipeline clogging. It is of practical and fundamental importance to understand the scaling mechanisms and develop efficient anti-scaling strategies. However, the underlying surface interaction mechanisms of scalants (e.g., calcite) with various substrates are still not fully understood. In this work, the colloidal probe atomic force microscopy (AFM) technique has been applied to directly quantify the surface forces between calcite particles and different metallic substrates, including carbon steel (CR1018), low alloy steel (4140), stainless steel (SS304) and tungsten carbide, under different water chemistries (i.e., salinity and pH). Measured force profiles revealed that the attractive van der Waals (VDW) interaction contributed to the attachment of the calcium carbonate particles on substrate surfaces, while the repulsive electric double layer (EDL) interactions could inhibit the attachment behaviors. High salinity and acidic pH conditions of aqueous solutions could weaken the EDL repulsion and promote the attachment behavior. The adhesion of calcite particles with CR1018 and 4140 substrates was much stronger than that with SS304 and tungsten carbide substrates. The bulk scaling tests in aqueous solutions from an industrial oil production process showed that much more severe scaling behaviors of calcite was detected on CR1018 and 4140 than those on SS304 and tungsten carbide, which agreed with surface force measurement results. Besides, high salinity and acidic pH can significantly enhance the scaling phenomena. This work provides fundamental insights into the scaling mechanisms of calcite at the nanoscale with practical implications for the selection of suitable anti-scaling materials in petroleum industries.

Clay micromechanics: Numerical modelling of electrical double-layer interactions to develop particle-based models for clay

Discrete element modelling of clays requires defining the interaction energy between two particles. The Derjaguin, Landau, Verwey and Overbeek (DLVO) theory combining the effect of the van der Waals forces and the Coulombic forces due to the double layer of counterions provides a widely accepted framework to characterise the pair potential energy. Solutions of the Poisson-Boltzmann (PB) equation to quantify the Coulombic forces are only available for the case of infinitely extended and uniformly charged facing plates (1D conditions). However, these assumptions are not representative of a clay particle system. Particles should be represented by platelets of finite size and finite thickness, with different charges between the edge and the basal planes. This paper addresses the problem of deriving the Coulombic interaction forces for plates of finite size and thickness in 3D configuration by solving the Poisson-Boltzmann equation numerically via the Finite Element Method (FEM). It is shown that 2D particles (plates of infinitesimal thickness) provide an adequate representation of Coulombic interaction as long as the particles are uniformly charged. The advantage of 2D particles is to reconcile numerical modelling with analytical solutions available in the literature. The use of 2D particles is questionable when considering different charges between basal planes and edges.

Revisiting DLVO theory to inform particle-scale modelling of clays

Particle-scale modelling of clays requires defining an energy-separation function for a pair of platy particles. The Derjaguin, Landau, Verwey and Overbeek (DLVO) theory provides a convenient framework for developing such a function as it embeds the combined effect of pore-fluid temperature, dielectric permittivity, and electrolyte concentration. Therefore, it can underpin the modelling of clay mechanical behaviour associated with thermal and environmental loading. The DLVO theory assumes particle interactions to be controlled by the van der Waals forces and the Coulombic forces via the Electrical Double-Layer (EDL). This paper first explores the 1D EDL interactions via the thermodynamics-based Grand Potential for the case of parallel sheets (with infinitesimal and infinite thickness). For infinitesimal thickness sheets, it is shown that i) the approximate analytical solutions of the Poisson-Boltzmann equation provide a qualitatively robust representation of EDL interactions, ii) the EDL interaction is qualitatively similar regardless of whether the interaction is modelled assuming constant surface charge or surface potential thus eliminating the uncertainty about the most appropriate electrical boundary condition to model EDL interactions; iii) the mechanical pressure required to ‘aggregate’ two sheets interacting via the EDL is finite and not infinite as often assumed in the literature (i.e. van der Waals forces do not need to be invoked to generate the energy barrier that triggers face-to-face aggregation but it remains fundamental for the quantitative definition of the potential energy barrier responsible for particle aggregation). Finally, the paper compares the 1D solutions for infinitely extended particles with the numerical solutions derived for face-to-face finite cuboidal particles with different aspect ratios to investigate the 1D analytical solutions that can conveniently be used as a benchmark in particle-scale modelling.

Probing the surface forces between air bubbles and bitumen via direct force Measurements: Effects of aqueous chemistry

The surface interactions of air bubbles and other components (e.g., particles, oil droplets) significantly influence the operation efficiency of a variety of engineering processes such as oily water treatment, bitumen extraction and flotation. Herein, the surface interactions of air bubbles with two types of Athabasca bitumen samples in aqueous solutions of varying pH, salinity, type of cations and in the presence of surfactants have been systematically characterized using a bubble probe atomic force microscope (AFM) technique. AFM imaging has revealed that exposure to high concentrations of NaCl and CaCl2 solutions or alkaline environments causes roughening of the bitumen surfaces. The results of surface force measurements demonstrate that the interaction and attachment behaviors between bubbles and bitumen are significantly affected by ionic strength, solution pH, and the presence of surfactants. The experimental force measurement results could be accurately described by a theoretical model that incorporates Reynolds lubrication theory and augmented Young-Laplace equation, with the inclusion of disjoining pressure. In low-salinity conditions, the bubble-bitumen interaction is dominated by electric double layer (EDL) repulsion, which prevents surface attachment. This effect is more pronounced at elevated pH conditions. In high-salinity solutions, however, the EDL interactions are significantly reduced, and the hydrophobic interaction becomes the dominant factor, overcoming the van der Waals repulsion and leading to the attachment of bubbles to bitumen surfaces. Raising aqueous pH weakens the bubble-bitumen hydrophobic interaction, whereas the introduction of calcium ions strengthens this interaction, resulting in enhanced surface attachment. Interestingly, even in high-salinity conditions, the presence of a small number of surfactants can inhibit bubble-bitumen contact, mainly caused by reduced hydrophobic attraction and increased steric repulsion. This work provides valuable nanoscale insights into how bubbles and bitumen interact in intricate aqueous environments, and the results show practical implications for controlling similar interfacial phenomena in various engineering processes.

Algae–water–silica interactions in low and high ionic strength environments

The interaction between algae and solid surfaces is of direct interest for the optimization of biofuel production technologies. Silica is particularly relevant due the use of solgel matrices for enhanced growth and ease of processing, where ionic strength variation is an important consideration. Here, an inverted fluorescence experiment is used to perform measurements of the distance between a silica surface and algae in solution. At low ionic strength, the average algae–silica distance is approximately 90 nm but increases to roughly 130 nm at 1 M NaCl, contradicting the prediction based on simple electrical double layer interaction models. These findings illustrate the role of biochemical and electrostatic interactions at charged aqueous interfaces of relevance to biofuel production.

Connecting Colloidal Forces to the Equilibrium Thickness of Particulate Deposits on a Substrate in Contact with a Suspension Using Classical Density Functional Theory

We study contributions of colloidal forces, i.e., hydrophobic, van der Waals, and electrical double layer interactions, to the thickness of a colloidal deposit in equilibrium with an aqueous suspension by using classical density functional theory, which we expand to obtain a Ginzburg-Landau type energy functional. We regard colloidal particles as clusters of molecular segments-a reminiscent of polymer statistical physics and of the classic Hamaker treatment of van der Waals interactions between particles. This approach appropriately accounts for the integral interaction energy between colloidal particles, which may take magnitudes of many times the characteristic molecular thermal energy kBT (Boltzmann constant times temperature). The analysis highlights the well-known insight that entropy is mostly governed by the solvent molecules and gives physical values to the statistical coefficients in a Ginzburg-Landau type energy functional.

A Coarse-Grained Interaction Model for Sodium Dominant Montmorillonite.

Montmorillonite is the main crystalline mineral present in bentonite. It is an absorbent, swelling material; the physical chemistry underlying its ability to absorb water and swell occurs at the nanoscale, governed by electrical double-layer interactions. In turn, absorption and swelling lead to important changes in the macroscopic transport properties of the clay. Mesoscale models can help us establish a link between these nanoscale processes and macroscale properties, notably by providing a detailed description of its pore network. Models on the scale of hundreds to thousands of nanometers are required, which cannot realistically be handled using traditional all-atom molecular dynamics simulations. This work presents a coarse-grained (CG) mesoscale model of sodium montmorillonite. In our model, montmorillonite platelets are represented by two types of particles: central nonhydrogen-bonded particles and edge hydrogen-bonding particles. The particle interactions are described by two-body potentials, which were optimized based on all-atom molecular dynamics simulations. Specifically, several potential mean force calculations involving dry and hydrated montmorillonite were performed, using the ClayFF potential to calculate interatomic forces. The CG model was validated by testing the scalability of the model, testing its ability to reproduce potentials of mean force reported elsewhere in the literature, and by comparing the calculated elastic properties of a system containing 1000 Na montmorillonite platelets to experimentally measured elastic properties of bentonite. The simulated elastic properties obtained using our mesoscale model agree with these experimental values.

Proposition of a bubble-particle attachment model based on DLVO van der Waals and electric double layer interactions for froth flotation modelling

Proposition of a bubble-particle attachment model based on DLVO van der Waals and electric double layer interactions for froth flotation modelling

Electro‐kinetically enhanced mass transport of charged macro‐solutes through a microchannel with porous walls

AbstractElectrokinetics of the solute transport across the porous walls of micro channel is important from its practical application but less explored. Transport of the charged macro‐solutes across perm‐selective walls in a microchannel is investigated. The extended Nernst–Planck equation describes the charged macro‐solutes distribution in the mass transfer boundary layer over the porous wall. The transverse electromigration of the charged macro‐solute either augments or suppresses the concentration polarization and the permeation rate depending on the wall and solute surface potential (attractive or repelling). The wall potential is screened due to the electrical double layer interaction of the wall and charged solute. It is observed that the charged solute concentration over the channel wall enhances by two times in case of oppositely charged interactions (unlike solute and channel wall) compared to like charges. The findings of this study can facilitate understanding of electrokinetic based drug delivery and separation systems involving charged solutes.

Relationship between soil erodibility by concentrated flow and shear strength of a Haplic Acrisol with a cationic polyelectrolyte

To clarify the relationship between rill erodibility in an excess shear stress model for concentrated flow erosion and soil particle–particle interactions, we examined the rill erodibility and aggregation-dispersion behavior of Shimajiri Maaji soil, classified as a Haplic Acrisol, with different amounts of cationic polyelectrolyte poly(diallyldimethylammonium chloride) (PDADMAC). The effect of particle–particle interaction on rill erodibility was determined by performing shear strength measurements and rill erosion experiments as a function of the PDADMAC dose without changing other soil conditions. Moreover, the mechanisms of particle–particle interactions were examined by comparing the electrophoretic mobility (EPM) with the transmission of the supernatant of the soil suspension and soil shear strength. The EPM and transmission showed that the Derjaguin-Landau-Verwey-Overbeek (DLVO) interaction governed the aggregation-dispersion behavior. At the same time, the shear strength monotonically increased with increasing PDADMAC dose, even when charge reversal and electric double layer (EDL) repulsion occurred. This result suggests that the shear strength is sensitive not only to the EDL interaction but also to the interactions, the so-called non-DLVO forces, such as bridging interaction. The difference between transmission and shear strength should be due to the difference in the characteristic length because the transmission is attributed to the collision/approaching process between particles, whereas the shear strength is attributed to the broken/retracting process of particle–particle contact. Rill erodibility decreased with increasing shear strength. Furthermore, our quantitative analysis demonstrated that rill erodibility can be represented by a linear function of shear strength. These results clearly show that a high attractive force between soil particles results in low rill erodibility. The strong particle–particle attraction protects soil particles from peeling off by increasing the shear stress of the flowing water. Our study suggests that shear strength measurement can be used to quickly estimate the effect of soil conditioners on rill erodibility in the field.

Simulation study on the flow behaviors of weak electrolyte solutions in nano-sized and micron-sized pores considering electric double layer interactions

ABSTRACT The interactions between the ions in the weak electrolyte solutions and the charged solid wall result in the formation of an electric double layer (EDL) in nano-sized and micron-sized pores. However, in nano-sized pores, EDLs may be overlapping. Herein, a widely applicable Poisson-Nernst-Planck equation combined with the Navier–Stokes equation was adopted for the flow of weak electrolyte solutions under pressure-driven conditions. Meanwhile, the finite element method was utilized to solve the governing equations and investigate the influence of EDL interactions on flow behaviors in different pore radii (25 nm~5 μm). The results showed that as the pore radius increased, the influence of EDL interactions on fluid flow behaviors first increased and then decreased. The influence of EDL interactions on fluid flow behaviors was the most noticeable when the pore radius was close to the EDL thickness. Furthermore, the influence of EDL interactions appeared to be negligible in the pore radius greater than 5 μm. When EDL interactions were ignored, the volume flow in the pores of the circular, square, and equilateral triangle was increased by about 13%. This study provides new insights into the flow behaviors of weak electrolyte solutions in nano-sized and micron-sized pores.

DC-electrokinetic motion of colloidal cylinder(s) in the vicinity of a conducting wall.

The boundary effects on DC-electrokinetic behavior of colloidal cylinder(s) in the vicinity of a conducting wall is investigated through a computational model. The contribution of the hydrodynamic drag, gravity, electrokinetic (i.e., electrophoretic and dielectrophoretic), and colloidal forces (i.e., forces due to the electrical double layer and van der Waals interactions) are incorporated in the model. The contribution of electrokinetic and colloidal forces are included by introducing the resulting forces as an external force acting on the particle(s). The colloidal forces are implemented with the prescribed expressions from the literature, and the electrokinetic force is obtained by integrating the corresponding Maxwell stress tensor over the particles' surfaces. The electrokinetic slip-velocity together with the thin electrical double layer assumption is applied on the surfaces. The position and velocity of the particles and the resulting electric and flow fields are obtained and the physical insight for the behavior of the colloidal cylinders are discussed in conjunction with the experimental observations in theliterature.

Nanofabricated chitosan/graphene oxide electrodes for enhancing electrosorptive removal of U(VI) from aqueous solution

The radioactive pollution caused by uranium-containing effluents brings serious detriments to environmental safety and human health. Herein the chitosan/graphene oxide (CS/GO) electrodes were nano-fabricated for the effective electrosorption of U(VI) from aqueous solution. The cyclic voltammetry measurements were conducted to determine the specific capacitance of the CS/GO materials. The U(VI) electrosorption was performed on capacitive deionization (CDI) system. The results showed that CS/GO-4 presented best electrosorption performance for U(VI) among various CS/GO materials, which is associated with a well-balanced meso-/micro- porous structure for promoting ion transfer and superior conductivity for ion trapping through electrical double-layer (EDL) interaction. The isotherms could be described by Langmuir model, whereas the kinetics could be fitted by Langmuir model. The maximum removal capacity for U(VI) electrosorption by CS/GO-4 reached 271.2 mg/g at 0.9 V, which was almost double that achieved at 0.0 V. The electrosorption mechanism may involve in the formation of electrical double-layer (EDL) and the coordination of U(VI) by the amine and carboxyl groups of CS/GO materials. The electrosorption-desorption cycles further demonstrated that the potential application of CS/GO electrode materials for the electrosorptive removal of U(VI) from radioactive wastewater.

Nonlinear charge regulation for the deposition of silica nanoparticles on polystyrene spherical surfaces

HypothesisWe describe the deposition behavior of monodispersed silica nanoparticles on polystyrene spherical particles by using modified pairwise DLVO (Derjaguin-Landau-Verwey-Overbeek) interaction force profiles at pH values between two and twelve. Our modified model contains a new nonlinear charge regulation parameter that considers redistribution of ions, which allows us to realistically express the electrical double layer (EDL) interaction forces. ExperimentsSilanol-terminated silica nanoparticles (7.6 ± 0.4 nm), l-lysine-covered silica nanoparticles (7.8 ± 0.4 nm), and polyallylamine hydrochloride-covered polystyrene (PAH/PS) particles (348 ± 1 nm) were synthesized. Then, each type of silica nanoparticle was deposited on the PAH/PS particles at a range of pH values. FindingsOur new regulation parameter describes the realistic redistribution of charges governed by pH, total salt concentration, ionic strength of solution, and separation distance of particles. We find that this regulation parameter can be roughly approximated from the absolute values of theoretically calculated surface charge density and potential distributions, as well as experimentally measured ζ-potentials. Morphological analysis using electron microscopy of the experimental systems shows that the modified pairwise DLVO interaction forces exceptionally describe the deposition behavior of the silica nanoparticles physically adsorbed on the PAH/PS particle substrates.

Steric Interaction of Polyglycerol-Functionalized Detonation Nanodiamonds.

Detonation nanodiamonds have found numerous potential applications in a diverse array of fields such as biomedical imaging and drug delivery. Here, we systematically characterized non-functionalized and polyglycerol-functionalized detonation nanodiamond particles (DNPs) dispersed in aqueous suspensions at different ionic strengths (∼1.0 × 10-7 to 1.0 × 10-2 M) via dynamic light scattering and cryogenic transmission electron microscopy. For these colloidal suspensions, the total potential energies of interactions between a pair of DNPs were theoretically calculated using the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory plus the fitting of the Boltzmann distribution to the interparticle spacing distribution of the colloidal DNPs. These investigations revealed that the non-functionalized DNPs are dispersed in aqueous media through the long-range (>10 nm) and weak (<7 kBT) electrical double-layer repulsive interaction, while the driving force on dispersion of polyglycerol-functionalized DNPs is mostly derived from the short-range (<2 nm) and strong (∼55 kBT) steric repulsive potential barrier generated by the polyglycerol. Moreover, our results show that the truly monodispersed and individually dispersed DNP colloids, forming no aggregates in aqueous suspensions, are available by both functionalizing DNPs by polyglycerol and increasing ionic strength of suspending media to ≳1.0 × 10-2 M.

Interfacial Polyelectrolyte-Surfactant Complexes Regulate Escape of Microdroplets Elastically Trapped in Thermotropic Liquid Crystals.

Polyelectrolytes adsorbed at soft interfaces are used in contexts such as materials synthesis, stabilization of emulsions, and control of rheology. Here, we explore how polyelectrolyte adsorption to aqueous interfaces of thermotropic liquid crystals (LCs) influences surfactant-stabilized aqueous microdroplets that are elastically trapped within the LCs. We find that adsorption of poly(diallyldimethylammonium chloride) (PDDA) to the interface of a nematic phase of 4-cyano-4'-pentylbiphenyl (5CB) triggers the ejection of microdroplets decorated with sodium dodecylsulfate (SDS), consistent with an attractive electrical double layer interaction between the microdroplets and LC interface. The concentration of PDDA that triggers release of the microdroplets (millimolar), however, is three orders of magnitude higher than that which saturates the LC interfacial charge (micromolar). Observation of a transient reorientation of the LC during escape of microdroplets leads us to conclude that complexes of PDDA and SDS form at the LC interface and thereby regulate interfacial charge and microdroplet escape. Poly(sodium 4-styrenesulfonate) (PSS) also triggers escape of dodecyltrimethylammonium bromide (DTAB)-decorated aqueous microdroplets from 5CB with dynamics consistent with the formation of interfacial polyelectrolyte-surfactant complexes. In contrast to PDDA-SDS, however, we do not observe a transient reorientation of the LC when using PSS-DTAB, reflecting weak association of DTAB and PSS and slow kinetics of formation of PSS-DTAB complexes. Our results reveal the central role of polyelectrolyte-surfactant dynamics in regulating the escape of the microdroplets and, more broadly, that LCs offer the basis of a novel probe of the structure and properties of polyelectrolyte-surfactant complexes at interfaces. We demonstrate the utility of these new insights by triggering the ejection of microdroplets from LCs using peptide-polymer amphiphiles that switch their net charge upon being processed by enzymes. Overall, our results provide fresh insight into the formation of polyelectrolyte-surfactant complexes at aqueous-LC interfaces and new principles for the design of responsive soft matter.

The role of small separation interactions in ferrofluid structure

Interparticle interactions in colloids are traditionally modeled by means of the DLVO theory, which includes van der Waals and electrical double layer (EDL) interactions However, the validity range limitations become critical in biocompatible magnetic colloids, requiring a more detailed description of the interactions, especially at small intersurface separations. As magnetic colloids, ferrofluids require an extended DLVO (XDLVO) model that includes magnetic interactions. Moreover, the nanoparticles of biocompatible ferrofluids are usually ionic-surfacted, such that their charged surfactants interact both electrically and sterically. In some of such particles, the charge is usually not located at the surface, but at the outer extremities of the surfactant molecules, and this feature restricts the EDL model validity to larger separation distances. We addressed this problem by means of a model proposed by Schnitzer and Morozov, which employs a generalized Derjaguin approximation that makes the EDL repulsion expression valid for all separations. The van der Waals expression of the DLVO theory is also problematic because it shows an unphysical divergence as the intersurface separation tends to zero, a problem that was circumvented by replacing the expression at small separations with another expression based on cohesion energy and the Born-Mayer repulsion. The modifications proposed here are of interest for research on colloids in general and our Monte Carlo simulations show that they acquire even greater importance when it comes to ferrofluids. The influence of magnetic interparticle interactions on the colloid structure is better gauged using these modifications, which prevent magnetic interactions from being obfuscated by artificially large van der Waals and EDL interactions. This conclusion makes the small separation treatment particularly important for the study of magnetic colloids.

Research progress on oil-water-rock interface interaction in micro-nano porous medium

Low/ultra-low permeability reservoirs have small pores, and the proportion of crude oil directly contacting with the rock and bound by the rock wall is much higher than that of conventional reservoirs, resulting in a large number of oil films difficult to be stripped. This seriously restricts the efficient development of low/ultra-low permeability reservoirs. The traditional adhesion work theory has limitations. A large number of crude oil in micro-nano pore throats is bound by the strong force of rock wall, and the adhesion force between oil film and rock becomes the main factor restricting the oil film peeling effect. This paper introduces the methods of analyzing oil-water-rock microscopic interaction by nanomechanics, such as atomic force microscope and molecular dynamics simulation. Focusing on oil-solid interface, the strong interaction between them is summarized. Nanomechanical analysis of the microscopic interface interactions among oil-water-rock shows that there are not only typical Derjaguin-Landau-Verwey Overbeek (DLVO) interactions (i.e., van der Waals and electrical double-layer interactions), but also non-DLVO interactions, such as hydrophobic and ion bridging interactions. This review focuses on the oil-rock interface interactions, summarizes recent research progress of the adhesion mechanism and the strong interaction between oil-rocks, discusses the challenges faced by efficient stripping of oil film and improving oil recovery in low permeability reservoirs. Finally, challenges and future prospects of this field are discussed.

Two-dimensional colloidal particle assembly in ionic surfactant solutions under an oscillatory electric field

Assembling colloidal particles under oscillatory electric field (OEF) has become an emerging bottom-up technique to synthesize advanced materials and fabricate micro/nano devices. Surfactants have often been used in colloidal dispersions to improve their stability. However, the precise role of surfactants in particle assembly processes under OEF is unknown. Here, we systematically study the effects of ionic surfactants on the colloidal particle assembly process subject to a fixed OEF, by using an anionic surfactant (sodium dodecyl sulfate) and a cationic surfactant (cetyltrimethylammonium bromide). In the concentration range below the critical micelle concentration (CMC), the particles tend to form three different aggregate structures, including randomly close-packed, hexagonally close-packed crystals, and randomly non close-packed structures. In the concentration range at CMC and above, the particles cannot assemble into any aggregate structures under the given OEF. With increasing surfactant concentration, the average interparticle separation distance within the aggregate can be regulated in a wide range. We qualitatively interpret the observed variation of particle assembly behaviors in different surfactant solutions based on the particle/particle interaction energy, implying that the repulsive electric double-layer interaction is significantly enhanced with increasing ionic surfactant concentration and hinders the particles approaching close to the high-energy barrier. These results suggest that the particle aggregate structure and interparticle separation distance of the two-dimensional colloidal assembly can be manipulated by controlling the ionic surfactant concentration according to the requirements of practical applications.

Electrokinetic Mechanisms and Synergistic Effect on Ion-Tuned Wettability in Oil-Brine-Rock Systems

Wettability alteration has been recognized as the dominant mechanism of ion-tuned waterflooding, where the ionic composition of injecting brine is modified to improve oil recovery. Yet mechanisms of ion-tuned wettability have not been fully understood, and there are ongoing debates over the effectiveness and relative contribution of each mechanism. In this paper, ion-tuned wettability in variable oil-brine-rock (OBR) systems over a wide range of ionic compositions is theoretically investigated, with focuses on two electrokinetic mechanisms, double layer expansion (DLE) and multicomponent ion exchange (MIE). Results indicate that the qualitative features of ion-tuned wettability in terms of DLE and MIE in various OBR systems with different surface properties can be divided into two typical types, depending on the electrical double layer (EDL) interaction being repulsive or attractive. With attractive EDL force, both DLE and MIE do not contribute to the water-wetness. While with repulsive EDL force, DLE only takes effect at relatively high concentration and MIE has a significantly larger impact at a low percentage of divalent cation. In addition, DLE and MIE can have a synergistic effect, where one mechanism alone has a negligible effect on wettability but two mechanisms combined have a big impact.