Electrical Double Layer Interaction Research Articles

Steric and electrostatic surface forces on sulfonated PEG graft surfaces with selective albumin adsorption

Addition of ionized terminal groups to PEG graft layers may cause additional interfacial forces to modulate the net interfacial interactions between PEG graft layers and proteins. In this study we investigated the effect of terminal sulfonate groups, characterizing PEG-aldehyde (PEG-CHO) and sulfonated PEG (PEG-SO3) graft layers by XPS and colloid probe AFM interaction force measurements as a function of ionic strength, in order to determine surface forces relevant to protein resistance and models of bio-interfacial interaction of such graft coatings. On the PEG-CHO surface the measured interaction force does not alter with ionic strength, typical of a repulsive steric barrier coating. An analogous repulsive interaction force of steric origin was also observed on the PEG-SO3 graft coating; however, the net interaction force changed with ionic strength. Interaction forces were modelled by steric and electrical double layer interaction theories, with fitting to a scaling theory model enabling determination of the spacing and stretching of the grafted chains. Albumin, fibrinogen, and lysozyme did not adsorb on the PEG-CHO coating, whereas the PEG graft with terminal sulfonate groups showed substantial adsorption of albumin but not fibrinogen or lysozyme from 0.15M salt solutions. Under lower ionic strength conditions albumin adsorption was again minimized as a result of the increased electrical double-layer interaction observed with the PEG-SO3 modified surface. This unique and unexpected adsorption behaviour of albumin provides an alternative explanation to the “negative cilia” model used by others to rationalize observed thromboresistance on PEG-sulfonate coatings.

Inhibition of Acidification of Kaolinite and an Alfisol Subsoil by Iron Oxides Through Electrical Double-Layer Interaction

Iron (Fe) oxides were found to inhibit natural acidification of highly weathered soils from tropical and subtropical regions. The mechanism for the inhibition of the acidification has not been well documented. Electrodialysis was used to simulate natural acidification process in soils under intensive leaching and to investigate mechanism of Fe oxides inhibiting acidification of kaolinite and an Alfisol subsoil. Results indicate that the electrodialysis treatment could release exchangeable base cations from kaolinite and phyllosilicate surfaces of the Alfisol subsoil gradually, produce exchangeable acidity, and ultimately result in strong acidification of the near-neutral kaolinite and Alfisol subsoil. Contrary to the traditional soil acidification principle, addition of Fe oxides to the kaolinite and Alfisol subsoil led to a decrease in effective cation exchange capacity (ECEC) and exchangeable acidity but inhibited the decrease in pH of the kaolinite and Alfisol subsoil during the electrodialysis process. Thus, the presence of Fe oxides could inhibit the acidification of the kaolinite and the Alfisol subsoil. The inhibition of acidification by Fe oxides was related to the amount of Fe oxides added and the surface charges per unit mass of negatively charged kaolinite or Alfisol subsoil and the positively charged Fe oxides carried. Higher content of Fe oxides and larger surface charges per unit mass resulted in a lower ECEC and exchangeable acidity but higher pH and thus weaker acidification of kaolinite or Alfisol subsoil. Changes in ECEC of kaolinite and Alfisol subsoil induced by Fe oxides were completely reversible with changes in ionic strength of the bathing solutions. These results confirm the occurrence of a diffuse layer overlapping on oppositely charged particles and support the hypothesis that Fe oxides inhibit the natural acidification process through an electric double layer overlapping in highly weathered soils.

The Electrochemical Surface Forces Apparatus: The Effect of Surface Roughness, Electrostatic Surface Potentials, and Anodic Oxide Growth on Interaction Forces, and Friction between Dissimilar Surfaces in Aqueous Solutions

We present a newly designed electrochemical surface forces apparatus (EC-SFA) that allows control and measurement of surface potentials and interfacial electrochemical reactions with simultaneous measurement of normal interaction forces (with nN resolution), friction forces (with μN resolution), and distances (with Å resolution) between apposing surfaces. We describe three applications of the developed EC-SFA and discuss the wide-range of potential other applications. In particular, we describe measurements of (1) force-distance profiles between smooth and rough gold surfaces and apposing self-assembled monolayer-covered smooth mica surfaces; (2) the effective changing thickness of anodically growing oxide layers with Å-accuracy on rough and smooth surfaces; and (3) friction forces evolving at a metal-ceramic contact, all as a function of the applied electrochemical potential. Interaction forces between atomically smooth surfaces are well-described using DLVO theory and the Hogg-Healy-Fuerstenau approximation for electric double layer interactions between dissimilar surfaces, which unintuitively predicts the possibility of attractive double layer forces between dissimilar surfaces whose surface potentials have similar sign, and repulsive forces between surfaces whose surface potentials have opposite sign. Surface roughness of the gold electrodes leads to an additional exponentially repulsive force in the force-distance profiles that is qualitatively well described by an extended DLVO model that includes repulsive hydration and steric forces. Comparing the measured thickness of the anodic gold oxide layer and the charge consumed for generating this layer allowed the identification of its chemical structure as a hydrated Au(OH)(3) phase formed at the gold surface at high positive potentials. The EC-SFA allows, for the first time, one to look at complex long-term transient effects of dynamic processes (e.g., relaxation times), which are also reflected in friction forces while tuning electrochemical surface potentials.

Paradox of Stability of Nanoparticles at Very Low Ionic Strength

The scaling of electrical double layer interaction energy from a plate-plate system to a sphere-plate system was reexamined, and it was found that accurate scaling without resorting to the Derjaguin approximation theoretically predicts the destabilization of nanoparticles in water depleted of added electrolyte and, consequentially, a maximum stability at a moderate ionic strength. This theoretical feature re-emphasizes the dual-role nature of added electrolyte that was supported by experimental results of direct surface force measurement but not by those of colloidal stability of nanoparticle deposition/aggregation. Inconsistences between the theoretical prediction and the experimental observation and between experimental observations in different systems were discussed. Possible reasons leading to the inconsistences were explored, including the effect of curvature, the contribution from counterions, the mode of interaction, and the applicability of an equilibrium model to describe the colloidal interaction of a nanoparticle suspension.

DLVO-Based Estimates of Adsorbed Water Film Thicknesses in Geologic CO2 Reservoirs

When supercritical carbon dioxide (scCO(2)) is injected into deep subsurface reservoirs, much of the affected volume consists of pores containing both water and scCO(2), with water films remaining as the mineral-wetting phase. Although water films can affect multiphase flow and mediate reactions at mineral surfaces, little is known about how film thicknesses depend on system properties. Here, the thicknesses of water films were estimated on the basis of considerations of capillary pressure needed for the entry of CO(2) and disjoining pressures in films resulting from van der Waals and electric double-layer interactions. Depth-dependent CO(2) and water properties were used to estimate Hamaker constants for water films on silica and smectite surfaces under CO(2) confinement. Dispersion interactions were combined with approximate solutions to the electric double layer film thickness-pressure relationship in a Derjaguin-Landau-Verwey-Overbeek (DLVO) analysis, with CO(2) as the confining fluid. Under conditions of elevated pressure, temperature, and salinity commonly associated with CO(2) sequestration, adsorbed water films in reservoir rock surfaces are typically predicted to be less than 10 nm in thickness. Decreased surface charge of silica under the acidic pH of CO(2)-equilibrated water and elevated salinity is predicted to compress the electric double layer substantially, such that the dispersion contribution to the film thickness is dominant. Relative to silica, smectite surfaces are predicted to support thicker water films under CO(2) confinement because of greater electrostatic and dispersion stabilization.

Polymeric Coatings on Silver Nanoparticles Hinder Autoaggregation but Enhance Attachment to Uncoated Surfaces

The propensity of silver nanoparticles (AgNPs) having two different polymer coatings (poly(vinylpyrrolidone), PVP, or gum arabic, GA) to aggregate, or to deposit to a reference surface (silica), was explored as a basis for differentiating the effect of surface coating on the stability of nanoparticles in aggregation and in deposition. Surface polymeric coatings stabilize nanoparticles against aggregation as shown by either an increased critical coagulation concentration as for PVP-coated AgNPs (AgPVP) or the absence of observable aggregation even at a high ionic strength as for GA-coated AgNPs (AgGA). In experiments of AgNPs deposition in a silica porous medium, dissimilar surfaces favored deposition, such as the case where polymer coatings were present on the AgNPs but were absent on the porous medium. The increased affinity of the AgNPs for the porous medium in this case may be explained by a shifted contact frontier where electrical double layer interaction is weaker. When coating polymers were introduced to the porous medium and allowed to preadsorb to the silica surfaces, the attachment efficiencies for both the AgPVP and AgGA were reduced due to steric and electrosteric stabilization, respectively. The results suggest that polymeric coatings that are usually deemed as stabilizers (as they indeed are in the case of autoaggregation) might not necessarily stabilize nanoparticles against deposition unless the collector surfaces are also coated with polymer.

The Role of Enamel Proteins in Protecting Mature Human Enamel Against Acidic Environments: A Double Layer Force Spectroscopy Study

Characterisation of the electrostatic properties of dental enamel is important for understanding the interfacial processes that occur on a tooth surface and how these relate to the natural ability of our teeth to withstand chemical attack from the acids in many soft drinks. Whereas, the role of the mineral component of the tooth enamel in providing this resistance to acid erosion has been studied extensively, the influence of proteins that are also present within the structure is not well understood. In this paper, we report for the first time the use of double-layer force spectroscopy to directly measure electrostatic forces on as received and hydrazine-treated (deproteinated) enamel surfaces in solutions with different pH to determine how the enamel proteins influence acid erosion surface potential and surface charge of human dental enamel. The deproteination of the treated samples was confirmed by the loss of the amide bands (~1,300–1,700 cm−1) in the FTIR spectrum of the sample. The force characteristics observed were found to agree with the theory of electrical double layer interaction under the assumption of constant potential and allowed the surface charge per unit area to be determined for the two enamel surfaces. The values and, importantly, the sign of these adsorbed surface charges indicates that the protein content of dental enamel contributes significantly to the electrostatic double layer formation near the tooth surface and in doing so can buffer the apatite crystals against acid attack. Moreover, the electrostatic interactions within this layer are a driving factor for the mineral transfer from the tooth surface and the initial salivary pellicle formation.

Ion-induced hydrophobic collapse of surface-confined polyelectrolyte brushes measured by total internal reflection microscopy

Cationic poly(2-(methacryloyloxy)ethyl trimethylammonium chloride) (PMETAC) brushes are grown from glass slides via surface-initiated atom transfer radical polymerization (SI-ATRP). The interaction potential energy between the surface-grown polyelectrolyte brushes and a 5 μm diameter polystyrene (PS) particle in different electrolyte environments (NaCl and NaClO4) has been directly measured using total internal reflection microscopy (TIRM). At a NaCl concentration of 0.05 mM, the measured interaction potential energy profiles show a long-range repulsion, arising from an electrical double layer interaction between the positively charged PS particle and the charges from the PMETAC layers. Upon addition of 1 mM NaCl, screening effects reduce the separation distance (h) between the PS particle and the surface, accompanied by the collapse of the PMETAC brushes. However, when the sample solution is replaced with a low concentration NaCl (0.05 mM) solution, h returns to the original values, indicating that the brushes resume the extended conformation. A remarkable difference is observed when similar TIRM experiments are carried out in the presence of NaClO4 solution. At the same concentration or ionic strength, NaClO4 causes a much more abrupt decrease in h between the particle and surface than that with NaCl solution. Conversely, flushing the sample cell with highly diluted NaClO4 or pure water cannot restore the original interaction potentials, thus implying an irreversible collapse of the PMETAC brushes in the presence of ClO4− anions. This apparent change in the PMETAC brush characteristics can be associated with the strong ion-pairing interaction between the ClO4− anions and the quaternary ammonium group in the PMETAC brushes, which experiences not only pure charge screening, but also a sharp hydrophilic-to-hydrophobic change of the brush layer. Using TIRM, we have directly measured such an ion-pairing induced collapse transition of surface-confined polyelectrolyte brushes, even at very low specific anion concentrations.

On-chip latex agglutination immunoassay readout by electrochemical impedance spectroscopy

We describe a new class of impedance-based lab-on-chip immunosensors in which the immunoagglutination of latex is monitored by electrochemical impedance spectroscopy (EIS). Antibody-coated latex microspheres agglutinated in the presence of target antigens are precipitated from solution between interdigitated microsized electrodes on a chip. Impedance spectra are reproducibly measured in the 0.1-1 MHz frequency range within several minutes and are shown to be dependent on the aggregate morphology and the sedimentation rates of the agglutinated particles. An equivalent circuit model of the system suggests that the impedance is governed primarily by the electric double layer interactions close to the electrode surface. The effects of sedimentation time, particle type, particle size, and concentration are characterized. The readout method holds promise for developing sensitive miniaturized sensors for rapid immunotesting.

Transport Behavior of Selected Nanoparticles with different Surface Coatings in Granular Porous Media coated with Pseudomonas aeruginosa Biofilm

Well-controlled laboratory column experiments were conducted to understand the influence of Pseudomonas aeruginosa (P. aeruginosa) biofilms on the transport of selected engineered nanoparticles (ENPs) in granular porous media representative of groundwater aquifers or riverbank filtration settings. To understand the importance of particle size on retention in the biofilm-coated granular (quartz sand) matrix, column experiments were carried out using nanosized (20 nm) and micrometer-sized (1 μm) sulfate-functionalized polystyrene latex particles (designated as 20 nSL and 1 mSL, respectively). Additional experiments conducted with nanosized (20 nm) carboxyl-modified latex particles (20nCL) and carboxyl-modified CdSe/ZnS quantum dots (QDs) provide information on the influence of particle surface chemistry on retention. Biofilm grown on the surface of the sand was characterized by total biomass quantification, confocal laser scanning microscopy (CLSM), and electrokinetic analysis. All four particles exhibit increased retention in the biofilm-coated packed bed: e.g., the attachment efficiency (α) of the 1 mSL particle increases from 0.40 to 1.7, whereas α for the 20 nSL particle increases from 0.04 to 0.10 in the biofilm-coated system. Particle surface chemistry can also influence the affinity of the ENPs for the biofilm coating as revealed by the greater attachment of the 20 nSL particle onto the biofilm-coated sand (α = 0.10) than its carboxylated counterpart (α = 0.04). Column experiments conducted using sand coated with growth medium (LB) or extracellular polymeric substances (EPS) extracted from P. aeruginosa biofilms further reveal that particle surface chemistry influences the interaction between the different ENPs and these coated sand surfaces. Namely, coating of sand surfaces with LB medium or bacterial EPS does not affect the transport of the sulfonated nanoparticle, but the LB coating leads to decreased retention of the carboxylated latex nanoparticle. Furthermore, our results show that EPS coatings are not necessarily good surrogates for biofilm-coated sand. Electrokinetic characterization of the clean and coated sand surfaces also reveals that the extent of particle retention is not controlled by electrical double layer interactions. Future studies should thus be aimed at improving our understanding of the fundamental mechanisms (both colloidal and noncolloidal) governing nanoparticle transport and fate in biofilm-laden granular aquatic environments.

Electrokinetic characterization of individual nanoparticles in nanofluidic channels

We electrokinetically characterize properties of single 42-nm polystyrene nanoparticles (NP) in nanofluidic channels imaged with frustrated total internal reflection fluorescence microscopy (fTIRFM). Specifically, we demonstrate fTIRFM of individual NPs in nanofluidic channels shallower than the evanescent field and use the resultant illumination field to gain insight into the behavior and electrokinetic properties of individual NP transport in channels. We find that the electrophoretic mobility of nanoparticles in 100-nm channels is lower than in larger channels or in bulk, presumably due to hindrance effects. Furthermore, we notice a non-intuitive increase in mobility with buffer concentration, which we attribute to electric double layer interactions. Finally, since the evanescent field intensity decreases with distance from the channel wall, we use the measured fluorescence intensity to report probable transverse distributions of free-solution 42-nm polystyrene fluorescent particles. Our method promises to be useful for characterizing nanoscale molecules for many applications in drug discovery, bioanalytics, nanoparticle synthesis, viral targeting, and the basic science of understanding nanoparticle behavior.

Steric-Effect Induced Alterations in Streaming Potential and Energy Transfer Efficiency of Non-Newtonian Fluids in Narrow Confinements

In this work, we explore the possibilities of utilizing the combined consequences of interfacial electrokinetics and rheology toward augmenting the energy transfer efficiencies in narrow fluidic confinements. In particular, we consider the exploitation of steric effects (i.e., effect of finite size of the ionic species) in non-Newtonian fluids over small scales, to report dramatic augmentations in the streaming potential, for shear-thickening fluids. We first derive an expression for the streaming potential considering strong electrical double layer interactions in the confined flow passage and the consequences of the finite conductance of the Stern layer, going beyond the Debye-Hückel limit. With a detailed accounting for the excluded volume effects of the ionic species and their interaction with pertinent interfacial phenomena of special type of rheological fluids such as the power law fluids in the above-mentioned formalism, we demonstrate that a confluence of the steric interactions with the non-Newtonian transport characteristics may result in giant augmentations in the energy transfer efficiency for shear-thickening fluids under appropriate conditions.

Effect of nanoparticle aggregation at low concentrations of TiO2 on the hydrophilicity, morphology, and fouling resistance of PES–TiO2 membranes

This paper reports the fabrication and characterization of polyethersulfone–TiO2 (PES–TiO2) nanoparticle composite membranes made from synthesis casting solution consisting of various compositions of polymer solvents (DMF and EtOH) and TiO2 additive. The results also revealed that the membrane permeation and rejection rates, pore size, and porosity were dependent on the TiO2 and EtOH concentrations. Nanoparticles were characterized by zeta potential measurements, TEM observations, and measurement of particle size distributions. Zeta potential measurements in aqueous solution demonstrated that the TiO2 particles size is dominated by electric double layer interactions. Addition of EtOH promotes the increase of the clusters size as consequence of a double effect: reduction of the dielectric constant of solution and the depletion of the suspension field determined by the action of the polymer chains. The observed effects as result of EtOH addition and increase of TiO2 concentration were similar: both procedures provoked an increase of macrovoid dimensions. The modified membranes by TiO2 incorporation showed a structural change from a sponge-like to a finger-like structure. Strong correlations were observed between the hydrophilicity and the permeability of manufactured membranes. The formation mechanism of TiO2-blended membranes was altered, in a similar way, as result of EtOH at different contents of nanoparticles. Fouling resistance of modified membranes was significantly improved showing that EtOH addition is a suitable procedure for the membrane performance improvement. The rejection potential of membranes is hardly affected by the nanoparticles and EtOH incorporation into the polymeric solution.

A General Poisson−Boltzmann Model with Position-Dependent Dielectric Permittivity for Electric Double Layer Analysis

In this paper, we propose a general Poisson-Boltzmann model for electric double layer (EDL) analysis with the position dependence of dielectric permittivity considered. This model provides physically reasonable property profiles in the EDL region, and it is then utilized to investigate the depletion layer effect on EDL structure and interaction near hydrophobic surfaces. Our results show that both the electric potential and the interaction pressure between surfaces decrease due to the lower permittivity in the depletion layer. The reduction becomes more profound at larger variation magnitude and range. This trend is in general agreement with that observed from the previous stepwise model; however, that model has overestimated the influence of permittivity variation effect. For the thin depletion layer and the relative thick EDL, our calculation indicates that the permittivity variation effect on EDL usually can be neglected. Furthermore, our model can be readily extended to study the permittivity variation in EDL due to ion accumulation and hydration in the EDL region.

Dynamic Response of AFM Cantilevers to Dissimilar Functionalized Silica Surfaces in Aqueous Electrolyte Solutions

The dynamic response of an oscillating microcantilever with a gold-coated tip interacting with dissimilar functionalized silica surfaces was studied in electrolyte solutions with pH ranging from 4 to 9. Silica surfaces were chemically modified, yielding dissimilar surfaces with -Br, -NH(2), and -CH(3) functional group terminations. The relative hydrophobicity of the surfaces was characterized by contact angle measurements. The surface charge of the functionalized surfaces was first probed with commonly used static AFM measurements and serves as a reference to the dynamic response data. The amplitude and phase of the cantilever oscillation were monitored and used to calculate the effective interaction stiffness and damping coefficient, which relate to the electrical double layer interactions and also to distance-dependent hydrodynamic damping at the solid/water interface. The data for the dynamic response of the AFM over silica surfaces as a function of chemical functionalization and electrolyte pH show that the effective stiffness has a distinctive dependence on the surface charge of functionalized silica surfaces. The hydrodynamic damping also correlates strongly with the relative hydrophobicity of the surface. The data reported here indicate that interfacial properties can be strongly affected by changing the chemical composition of surfaces.

Exact Analytical Expressions for the Potential of Electrical Double Layer Interactions for a Sphere−Plate System

Exact, closed-form analytical expressions are presented for evaluating the potential energy of electrical double layer (EDL) interactions between a sphere and an infinite flat plate for three different types of interactions: constant potential, constant charge, and an intermediate case as given by the linear superposition approximation (LSA). By taking advantage of the simpler sphere-plate geometry, simplifying assumptions used in the original Derjaguin approximation (DA) for sphere-sphere interaction are avoided, yielding expressions that are more accurate and applicable over the full range of κa. These analytical expressions are significant improvements over the existing equations in the literature that are valid only for large κa because the new equations facilitate the modeling of EDL interactions between nanoscale particles and surfaces over a wide range of ionic strength.

An experimental study of slip considering the effects of non-uniform colloidal tracer distributions

Various studies have suggested that the no-slip condition may not hold for Newtonian liquids flowing over (for the most part) non-wetting surfaces. This paper describes an experimental study of steady Poiseuille flow at various Reynolds numbers up to 0.12 of four different aqueous monovalent electrolyte solutions through naturally hydrophilic and hydrophobically coated fused-silica channels with a depth of 33 μm. The slip lengths for these flows were estimated using a local method based on a new particle velocimetry technique that determines velocities at three different wall-normal distances within the first 400 nm next to the wall. These results are corrected using direct measurements of the near-wall particle distribution, which is highly non-uniform as expected due to repulsive electric double-layer interactions between the 100 nm tracer particles and the wall. In all cases, the slip lengths were not more than 23 nm and for all but one case, zero within their uncertainties. As illustrated here, the standard assumption of uniformly distributed tracers can significantly increase slip length estimates obtained using local methods and near-wall velocity data.

Effect of active control of electric potential of filter medium on depth filtration

The effect of active control of electric potential of filter medium on depth filtration was explored experimentally. Activated carbon particles were selected as the conductive filter medium. The filter medium potential was controlled with an external DC power supply. Kaolin particles were used as the model suspended solid. The activated carbon and kaolin had negative zeta potential around neutral pH. When the filter medium potential against a counter electrode was greater than or equal to + 0.2 V, rejection rate of particles was 1.8 times higher than that when the potential was less than + 0.2 V. Thus adsorption of particles by interaction of electric double layers was enhanced by maintaining a positive charge on the filter media. Desorption of kaolin trapped on the filter media was also confirmed by changing the filter medium potential from positive to negative. The percentage of kaolin particles desorbed was 11% of the kaolin trapped on the filter media. The desorption rate was not high, but this technique will enhance refreshment of the filter media when combined with back washing.

Acoustic-Wave-Induced Analyte Separation in Narrow Fluidic Confinements in the Presence of Interfacial Interactions

In the present work, we attempt to analyze the influences of acoustic forces, in conjunction with the intrinsic electrokinetic effects as well as the near-wall attractive and repulsive forces, on the transport and size-based separation of charged analytes in a background-pressure-driven flow through a narrow fluidic confinement. By executing a regular perturbation analysis, we establish that the speed of traverse and the extent of spreading (dispersion) of the analyte bands is effectively determined by the ratio of particle to channel heights, channel height relative to the Debye length, and all other significant acoustic and nonacoustic parameters. These factors in tandem may dictate the analyte separation characteristics (quantified by the resolution of separation), in tune with the particular harmonic of the acoustic wave, the strengths of the induced electrical double layer fields, and the van der Waals interaction mechanisms. We quantitatively pinpoint the relationship between the harmonics to be employed and particle sizes to be separated. Our study reveals that there is a critical channel height beyond which the acoustic effects may effectively mask the near-wall interactions and below which the transverse migrative influences induced by the walls may influence the separation characteristics in a rather profound manner. The results implicate an interesting high-efficiency separation regime that can be obtained with a judicious combination of the background flow, energy intensity of the acoustic effects, and induced electrical double layer interactions.

Electric double layers interactions under condition of variable dielectric permittivity

In this paper, a theoretical method has been developed for the electric double layer interaction under condition of the variable dielectric permittivity of water. Using Poisson-Boltzmann equation (PBE), for one plate and two plates having similar or dissimilar constant charge or constant potential, we have investigated the electric double layer potential, its gradient and the disjoining pressure as well as the effect of variation of dielectric permittivity on these parameters. It has been assumed that plates are separated by a specific distance and contain a liquid solution in between. It is shown that reduction of the dielectric permittivity near the interfaces results in compression of electric double layers and affects the potential and its gradient which leads to a decreased electrostatic repulsion. In addition, it is shown that variation of dielectric permittivity in the case of higher electrolyte concentration, leads to a greater change in potential distribution between two plates.