Electric Double Layer Repulsion Research Articles

Different effects of temperature and salinity on permeability reduction by fines migration in Berea sandstone

Hot water injection into geothermal aquifers is considered in order to store energy seasonally. Berea sandstone is often used as a reference formation to study mechanisms that affect permeability in reservoir sandstones. Both heating of the pore fluid and reduction of the pore fluid salinity can reduce permeability in Berea sandstone. These effects could be caused by mobilisation of fines by increasing the repulsive electrical double layer forces among sandstone grains and the fines. We investigated the reversibility and the dependence on flow velocity and flow direction of the permeability change by means of flow through experiments and examined thin sections of samples prior to and after tests. A permeability reduction at 20°C with decreasing salinity was not reversed by restoring the salinity, whereas a permeability reduction due to heating to 80°C was reversible by restoring the temperature to 20°C. A reversible permeability increase with increasing flow rate was observed at 80°C but not at 20°C. We observed no difference in the distribution of kaolinite clay minerals in thin sections of untested and tested samples. Dissolution of iron bearing carbonates and precipitation of iron hydroxides was observed but no effect on permeability was found. The experimental results suggest that different mechanisms are responsible for permeability reduction depending on temperature and salinity.

Rate of Bubble Coalescence following Quasi-Static Approach: Screening and Neutralization of the Electric Double Layer

Air-bubble coalescence in aqueous electrolytic solutions, following quasi-static approach, was studied in order to understand its slow rate in purified water and high rate in electrolytic solutions. The former is found to be due to surface charges, originating from the speciation of dissolved CO2, which sustain the electric double layer repulsion. Rapid coalescence in electrolytic solutions is shown to occur via two different mechanisms: (1) neutralization of the carbonaceous, charged species by acids; or (2) screening of the repulsive charge effects by salts and bases. The results do not indicate any ion specificity. They can be explained within the DLVO theory for the van der Waals and electric double layer interactions between particles, in contrast to observations of coalescence following dynamic approach. The present conclusions should serve as a reference point to understanding the dynamic behavior.

Polyelectrolyte adsorption, interparticle forces, and colloidal aggregation

This review summarizes the current understanding of adsorption of polyelectrolytes to oppositely charged solid substrates, the resulting interaction forces between such substrates, and consequences for colloidal particle aggregation. The following conclusions can be reached based on experimental findings. Polyelectrolytes adsorb to oppositely charged solid substrates irreversibly up to saturation, whereby loose and thin monolayers are formed. The adsorbed polyelectrolytes normally carry a substantial amount of charge, which leads to a charge reversal. Frequently, the adsorbed films are laterally heterogeneous. With increasing salt levels, the adsorbed mass increases leading to thicker and more homogeneous films. Interaction forces between surfaces coated with saturated polyelectrolyte layers are governed at low salt levels by repulsive electric double layer interactions, and particle suspensions are stable under these conditions. At appropriately high salt levels, the forces become attractive, principally due to van der Waals interactions, but eventually also through other forces, and suspensions become unstable. This situation can be rationalized with the classical theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO). Due to the irreversible nature of the adsorption process, stable unsaturated layers form in colloidal particle suspensions at lower polyelectrolyte doses. An unsaturated polyelectrolyte layer can neutralize the overall particle surface charge. Away from the charge reversal point, electric double layer forces are dominant and particle suspensions are stable. As the charge reversal point is approached, attractive van der Waals forces become important, and particle suspensions become unstable. This behaviour is again in line with the DLVO theory, which may even apply quantitatively, provided the polyelectrolyte films are sufficiently laterally homogeneous. For heterogeneous films, additional attractive patch-charge interactions may become important. Depletion interactions may also lead to attractive forces and suspension destabilization, but such interactions become important only at high polyelectrolyte concentrations.

Deposition of silica nanoparticles onto alumina measured by optical reflectometry and quartz crystal microbalance with dissipation techniques

Understanding of the interactions between particles and the substrate is important for successful sol–gel deposition of thin films. We have studied the deposition of silica nanoparticles on alumina coated surfaces in aqueous electrolytes by optical reflectometry (OR) and a quartz crystal microbalance with dissipation (QCM-D). The deposition of negatively charged silica nanoparticles on positively charged alumina was primarily controlled by the electric diffuse double layer interactions between the substrate and the deposited particles, modulated by the counter-ion release. The build-up of a negative charge on the positively charged substrate resulted in a decrease in the deposition rate with increasing surface coverage. Higher surface coverage of silica nanoparticles was obtained at low pH than at high pH conditions, due to reduced electric diffuse double layer repulsion between the silica nanoparticles. The deposition was enhanced at high pH by increasing the concentration of NaCl due to compression of the electric diffuse double layer. In particular, the repulsion between the silica nanoparticles was efficiently screened at a concentration of NaCl higher than 100mM and thick silica layers could be deposited at pH=6 and 8.

Chemistry of the calcite/water interface: Influence of sulfate ions and consequences in terms of cohesion forces

Calcite suspensions are used to mimic the behavior of more complex cementitious systems. Therefore the characterization of calcite–water interface in strong alkaline conditions, through ionic adsorption, electrokinetic measurements, static rheology and atomic force microscopy is a prerequisite. Calcium, a potential determining ion for calcite, adsorbs specifically onto the weakly positively charged calcite surface in water. This leads to an increase of the repulsive electric double layer force and thus weakens the particle cohesion. Sulfate adsorption, made at constant calcium concentration and ionic strength, significantly increases the attractive interactions between the calcite particles despite its very low adsorption. This is attributed to a lowering of the electrostatic repulsion in connection with the evolution of the zeta potential. The linear relationship found between the yield stress and ζ2 proves that the classical DLVO theory applies for these systems, contrary to what was previously observed with C–S–H particles under the same conditions.

Effects of Water Chemistry on Aggregation and Soil Adsorption of Silver Nanoparticles

ObjectivesIn this study, we investigated the influence of ionic strength and natural organic matter (NOM) on aggregation and soil adsorption of citrate-coated silver nanoparticles (AgNPs).MethodsTime-resolved dynamic light scattering measurements and batch adsorption experiments were used to study their aggregation and soil adsorption behaviors, respectively.ResultsThe aggregation rate of AgNPs increased with increasing ionic strength and decreasing NOM concentration. At higher ionic strength, the AgNPs were unstable, and thus tended to be adsorbed to the soil, while increased NOM concentration hindered soil adsorption. To understand the varying behaviors of AgNPs depending on the environmental factors, particle zeta potentials were also measured as a function of ionic strength and NOM concentration. The magnitude of particle zeta potential became more negative with decreasing ionic strength and increasing NOM concentration. These results imply that the aggregation and soil adsorption behavior of AgNPs were mainly controlled by electrical double-layer repulsion consistent with the Derjaguin-Landau-Verwey-Overbeek theory.ConclusionsThis study found that the aggregation and soil adsorption behavior of AgNPs are closely associated with environmental factors such as ionic strength and NOM and suggested that assessing the environmental fate and transport of nanoparticles requires a thorough understanding of particle-particle interaction mechanisms.

Zeta-Potential Investigation and Experimental Study of Nanoparticles Deposited on Rock Surface To Reduce Fines Migration

Summary Fines migration is a noticeable problem in petroleum-production engineering. Plugging of throats in porous media occurs because of detachment of fine particles from sand surfaces. Thus, the study of interactions between fines and pore surfaces and the investigation of governing forces are important factors to consider when describing the mechanism of the fines-release process. The main types of these forces are electric double-layer repulsion (DLR) and London–van der Waals attraction (LVA). It may be possible to alter these forces with nanoparticles (NPs) as surface coatings. In comparison with repulsion forces, NPs increase the effect of attraction forces. In this paper, we present new experiments and simple modeling to observe such properties of NPs. For this purpose, the surfaces of pores were coated with different types of NPs: magnesium oxide (MgO), silicon dioxide (SiO2), and aluminum oxide (Al2O3). A zeta-potential test was used to examine changes in the potential of the pore surfaces. Total interaction energy was then mathematically calculated to compare different states. Total interaction energy is a fitting criterion that gives proper information about the effect of different NPs on surface properties. Consequently, total interaction plots are found to be suitable tools for selecting the best coating material. On the basis of experimental results, the magnitude of change in zeta potential for the MgO NP was 45 mV. Our model demonstrated that the magnitude of the electric DLR in comparison with the LVA of the probe and plate surface was considerably diminished when MgO NPs were used to coat the surface of the plate, which agrees completely with our experimental observation.

Surfactant-Mediated Control of Colloid Pattern Assembly and Attachment Strength in Evaporating Droplets

This study demonstrates that the pattern assembly and attachment strength of colloids in an evaporating sessile droplet resting on a smooth substrate can be controlled by adding nonionic solutes (surfactant) to the solution. As expected, increasing the surfactant concentration leads to a decrease in initial surface tension of the drop, σ(0). For the range of initial surface tensions investigated (39-72 mN m(-1)), three distinct deposition patterns were produced: amorphous stains (σ(0) = 63-72 mN m(-1)), coffee-ring stains (σ(0) = 48-53 mN m(-1)), and concentric rings (σ(0) = 39-45 mN m(-1)). A flow-displacement system was used to measure the attachment strength of the dried colloids. Characteristic drying regimes associated with the three unique pattern formations are attributed to abrupt transitions of contact line dynamics during evaporation. The first transition from slipping- to pinned-contact line was found to be a direct result of the competition between mechanical instability of the droplet and the friction generated by pinned colloids at the contact line. The second transition from pinned- to recurrent-stick-rip-slip-contact line was caused by repeated liquid film rupturing from evaporation-intensified surfactant concentration. Data from flow-displacement tests indicate that attachment strength of dried particles is strongest for amorphous stains (lowest surfactant concentration) and weakest for concentric rings (highest surfactant concentration). The mechanism behind these observations was ascribed to the formation and adsorption of micelles onto colloid and substrate surfaces as the droplet solution evaporates. The range of attachment forces observed between the colloids and the solid substrate were well captured by extended-DLVO interactions accounting for van der Waals attraction, electric double layer repulsion, and micelle-protrusion repulsion. Both empirical and theoretical results suggest that an increasingly dense layer of adsorbed micellar-protrusions on colloid and substrate surfaces acts as a physical barrier that hinders strong van der Waals attractive interactions at close proximity. Thereby, colloid stains dried at higher surfactant concentrations are more easily detached from the substrate when dislodging forces are applied than stains dried at lower surfactant concentrations.

Collective effects on thermophoresis of colloids: a microfluidic study within the framework of DLVO theory

Collective effects on thermophoresis of aqueous particle suspensions are studied experimentally and theoretically. A microfluidic device is used to characterize thermophoretic transport of 100 nm, 500 nm and 1 μm particles of various concentrations in deionized (DI) water. Our experimental findings show two interesting collective effects on the Soret coefficient of colloids: (i) for smaller particles (e.g., 100 nm and 500 nm), a sign change of the Soret coefficient is observed when increasing the particle concentration; (ii) for larger particles (e.g., 1 μm), a negative Soret coefficient is always seen. A model is derived to account for the collective effect on the thermophoresis of colloids using the well-known Derjaguin–Landau–Verwey–Overbeek (DLVO) theory that combines the van der Waals (VDW) attraction and the electric double layer (EDL) repulsion. Such DLVO interactions in an inhomogeneous particle suspension can exert an additional force on particles and thus modify the mass transport of particles under both temperature and concentration gradients and also alter the corresponding Soret coefficient. It is found that the proposed theoretical model can favorably explain our experimental observations.

Estimation of Water Film Thickness in Geological Media Associated with the Occurrence of Gas Entrapment

When water and entrapped gas co-exist in pore spaces of a geological medium, a water film is formed on grain surfaces, which potentially influences chemical reaction and mass transport. We developed a model to estimate the film thickness in a geological medium using a concept of disjoining pressure associated with the electric double layer repulsion force and van der Waals force. The model indicates that the thickness of the water film associated with the occurrence of gas entrapment is controlled by the diameter of pore (the diameter of meniscus), and that larger pores have thicker water films. Examples of the relationship between pore size distribution and film thickness are shown.

Stabilization of Ceramics Particles with Anionic Polymeric Dispersants

The dispersion of colloidal ceramic particles in an aqueous media using a charged polymer has been investigated extensively. Most often, such a dispersion is obtained by an electrosteric mechanism. The stabilizing forces that result from electrical double layer repulsion and/or steric interaction must be sufficiently large in magnitude to provide an energy barrier against aggregation. Several factors, such as pH, temperature and ionic strength, nature, structure and molecular weight of the polyelectrolyte and its degree of dissociation can affect the respective contribution of electrostatic and steric interactions. In this study we applied silver nanoparticles prepared by reduction method with modifications. The hydroxyapatite was obtained from pork bone sludge. Polymer system contained poly(acrylic acid) and poly(ethylene glycol). The effects of dispersant structure on particle stabilization were investigated through properties of the suspensions. Viscosity and sedimentation height measurements indicated that addition of the dispersants improve particle stabilization. A dispersants were characterized using Scanning electron microscopy (SEM) with BSE detector (Back Scaterred Electrons), X-ray diffraction (XRD) and pH determination.

Aggregation of nano-sized alum–humic primary particles

In order to understand the mechanism of floc formation and growth in coagulation process, effect of zeta potential and surface characteristic of nano sized primary particles on coagulation efficiency were investigated by coagulation of humic acid with alum in this study. It was demonstrated that only 1min rapid mixing was enough for adsorption of humic acid onto the precipitates of alum, and 15min flocculation (slow mixing) only induced the formation and growth of flocs. The primary particle size of alum–humic flocs was near 50nm and spherical. Mathematical model deduced from Derjaguin–Landau–Verwey–Overbeek (DLVO) theory showed that the formation of micro-flocs (or lag time) was determined by the square value of zeta potential of nano-sized primary particles and intensity of Brownian motion, which is closely related to water temperature. There was an absolute critical zeta potential, i.e. 13.5mV in this study, determining whether two nano-sized particles could overcome the energy barrier consisted of Van der Waals force and electrical double layer repulsion force to allow floc formation to occur at a certain temperature. The Brownian motion determined whether the nano-sized primary particles (aluminum hydroxide precipitates with humic acid) had the opportunity to overcome the repulsive force and cement with each other. Low coagulation efficiency at high latitude area in winter is caused by low collision frequency, which is mainly attributed to the low intensity of Brownian motion at a low temperature. Furthermore, it was demonstrated that aggregation of micro-flocs or their clusters significantly depended on activated sites on the primary particles rather than the zeta potential of primary particles when sweep flocculation dominated the coagulation mechanism if the size of flocs was larger than some value.

Effect of Organic Matter on the Flocculation of Colloidal Montmorillonite: A Modeling Approach

FURUKAWA, Y. and WATKINS, J.L., 2012. Effect of organic matter on the flocculation of colloidal montmorillonite: A modeling approach. The effect of organic matter (OM) on the flocculation of colloidal montmorillonite was investigated through a complementary use of laboratory experiments and computational flocculation modeling. The model, based on Smoluchowski's coagulation model and population balance equation (PBE), was established with two key flocculation parameters: sticking efficiency and breakup parameter. The laboratory flocculation experiments tracked the temporal evolution of the mean floc sizes for aqueous systems with colloidal bare montmorillonite as well as those with montmorillonite and OM (humic acid, chitin, or xanthan gum). The key flocculation parameters were derived and calibrated through the interactive optimization of the model results by juxtaposing against the laboratory results. The calibrated flocculation parameter values revealed that OM has a complex influence on the flocculation behavior of montmorillonite. They also showed that the effect of OM on flocculation depends on the types of OM. For example, xanthan gum does not significantly modify the flocculation behavior of montmorillonite that is primarily determined by the electrical double-layer repulsion (i.e., ζ-potential) and van der Waals attraction [i.e., Derjaguin and Laudau, Verwey and Overbeek (DLVO) interaction energies], whereas chitin modifies both the sticking efficiency and breakup parameter. This study illustrates that there is no universally predictive correlation between DLVO energies or ζ-potential and flocculation parameters, as some OM has little effect on the DLVO interaction of montmorillonite colloids whereas other types of OM exert significant non-DLVO interactions such as repulsive hydration, steric repulsion, and polymer bridging. Further understanding of the physical-chemical properties of OM is needed in order to predict the flocculation behaviors of estuarine and coastal suspended colloids.

Muscovite clay mineral particle interactions in aqueous media

Particle interactions and colloid stability of aqueous clay mineral dispersions play a pivotal role in many unit operations and plant processes (e.g. crystallization, leaching, slurry transport and dewatering). In this study, the nature of the particle interactions, colloid stability and shear rheology of dilute (< 0.1wt.% solid) and concentrated (8–57wt.% solid) muscovite clay mineral dispersions have been investigated under a variety of industrially relevant process conditions in the pH range 1–10. Particle zeta potential profile was found to be distinctly pH-history and pulp solid loading and chemistry mediated, reflecting different isoelectric points and colloid stability at different pH values. For dilute dispersions, muscovite particle zeta potential followed pH-dependent electrokinetic trends typical of siliceous minerals which indicated an isoelectric point (iep) at ~pH 2. For concentrated dispersions, on the other hand, the magnitude of negative particle zeta potentials was markedly lower and the concomitant ieps were significantly higher (in pH range 5–7) compared with the dilute dispersions. Isothermal, batch settling behavior and dispersion rheology for fresh dispersion at pH >3 reflected the predominance of interaction energy potentials of attractive van der Waals and repulsive electrical double layer forces' origin. The particle interactions may be theoretically treated and rationalized in the manner of DLVO theory. At pH <3 and aging at pH 7, completely different trends emerged due to incongruent leaching of the muscovite particles which led to the development of non-DLVO particle interactions.

Effect of Cation Size and Charge on the Interaction between Silica Surfaces in 1:1, 2:1, and 3:1 Aqueous Electrolytes

Application of two complementary AFM measurements, force vs separation and adhesion force, reveals the combined effects of cation size and charge (valency) on the interaction between silica surfaces in three 1:1, three 2:1, and three 3:1 metal chloride aqueous solutions of different concentrations. The interaction between the silica surfaces in 1:1 and 2:1 salt solutions is fully accounted for by ion-independent van der Waals (vdW) attraction and electric double-layer repulsion modified by cation specific adsorption to the silica surfaces. The deduced ranking of mono- and divalent cation adsorption capacity (adsorbability) to silica, Mg(2+) < Ca(2+) < Na(+) < Sr(2+) < K(+) < Cs(+), follows cation bare size as well as cation solvation energy but does not correlate with hydrated ionic radius or with volume or surface ionic charge density. In the presence of 3:1 salts, the coarse phenomenology of the force between the silica surfaces as a function of salt concentration resembles that in 1:1 and 2:1 electrolytes. Nevertheless, two fundamental differences should be noticed. First, the attraction between the silica surfaces is too large to be attributed solely to vdW force, hence implying an additional attraction mechanism or gross modification of the conventional vdW attraction. Second, neutralization of the silica surfaces occurs at trivalent cation concentrations that are 3 orders of magnitude smaller than those characterizing surface neutralization by mono- and divalent cations. Consequently, when trivalent cations are added to our cation adsorbability series the correlation with bare ion size breaks down abruptly. The strong adsorbability of trivalent cations to silica contrasts straightforward expectations based on ranking of the cationic solvation energies, thus suggesting a different adsorption mechanism which is inoperative or weak for mono- and divalent cations.

A facile synthetic strategy for Mg–Al layered double hydroxide material as nanocarrier for methotrexate

Mg–Al layered double hydroxide nanopowders were synthesised by a facile coprecipitation technique at different pH conditions. LDH nanoparticles of higher aspect ratio with an average particle size of 26 nm were obtained at pH 9 whereas a pH of 11.3 resulted in LDH nanoparticles of average size 50 nm with lower aspect ratio and narrower size distribution. LDH–MTX organo–inorganic nanohybrid was produced with an average particle size of 53 nm after intercalation of MTX into the interlayer space of LDH, as evident from the shift of (0 0 3) peak in X-ray diffraction. This was corroborated by the transmission electron micrograph, which showed an increase in average interlayer spacing from 8.00 Å in pristine LDH to 21.4 Å in LDH–MTX nanohybrid. Thermogravimetric analyses showed ∼33.2 wt% MTX loading in the LDH structure. The MTX release profile from Mg–Al LDH–MTX nanohybrid in phosphate buffer saline at pH 7.4 follows Ritger–Peppas kinetics model which demonstrates that the release kinetics is diffusion controlled. An attempt has been made to explain the above observations based on the effect of electrical double layer repulsions on the growth of LDH nuclei, primarily considering significance of the particle morphology in drug delivery application.

Hemin−Graphene Hybrid Nanosheets with Intrinsic Peroxidase-like Activity for Label-free Colorimetric Detection of Single-Nucleotide Polymorphism

This paper demonstrated for the first time a simple wet-chemical strategy for synthesizing hemin-graphene hybrid nanosheets (H-GNs) through the π-π interactions. Significantly, this new material possesses the advantages of both hemin and graphene and exhibits three interesting properties. First, H-GNs have intrinsic peroxidase-like activity, which can catalyze the reaction of peroxidase substrate, due to the existence of hemin on the graphene surface. Second, their dispersion follow the 2D Schulze-Hardy rule, that is to say, the coagulation of H-GNs in electrolyte solution results from the interplay between van der Waals attraction and electric double-layer repulsion. Third, H-GNs exhibit the ability to differentiate ss- and ds-DNA in optimum electrolyte concentration, owing to the different affinities of ss- and ds-DNA to the H-GNs. On the basis of these unique properties of the as-prepared H-GNs, we have developed a label-free colorimetric detection system for single-nucleotide polymorphisms (SNPs) in disease-associated DNA. To our knowledge, this is the first report concerning on SNPs detection using functionalized graphene nanosheets. Owing to its easy operation and high specificity, it was expected that the proposed procedure might hold great promise in the pathogenic diagnosis and genetic diseases.

Stability of kaolinite dispersions in the presence of sodium and aluminum ions

The stability of colloidal kaolinite dispersions in the presence of NaCl and AlCl3 was studied by measuring turbidity, electrophoretic mobility and adsorption. The kaolinite particles coagulated at pH 2.5–3.5 and were dispersed at pH >4.5. These results well obeyed the classic DLVO theory if the mean zeta potential of the kaolinite particles in aqueous solutions was taken into account in the computation of potential energy of electrical double layer repulsion, which suggests that the kaolinite particles might coagulate in the same way as normal colloidal particles. The kaolinite particles in aqueous aluminum salt solution only coagulated at a medium AlCl3 concentration, and formed a stable dispersion at a high salt concentration. This is caused by Stern-layer adsorption of hydrolyzed aluminum species, probably adsorbed on the kaolinite surfaces through hydrogen bonds between the hydroxyl groups of the aluminum species and the oxygen atoms on the kaolinite surfaces.

Helix – Rod transition in a nanospring

A model of helical spring is described whose effective pitch and length are decided by the balance of the attractive van der Waals and repulsive hydration and electrical double layer forces. Also the electric contribution to the curvature free energy is taken into account. The stability of the nanospring is investigated and it is shown that the spring becomes unstable and jumps to its extended state on increase of electrostatic repulsion beyond a limit implying a jump in viscosity of suspension of springs in the solution. The magnitude of the jump and threshold potential are investigated.

Effect of Electric Double Layer Repulsion on Oil Droplet Coalescence Process

AbstractFilm drainage between two droplets approaching each other at constant velocity under the influence of electric double layer repulsion is studied systematically. Based on the lubrication equations, a mathematical model is given to govern the evolution of film drainage between two oil droplets. This model consists of three coupled fourth‐order nonlinear parabolic partial differential equations describing the dynamic evolution of the film thickness, film pressure and surfactant interfacial concentration. The numerical method used is the finite element method. The main objective of this research work is to modify the film pressure equation by considering the electric double layer repulsion. The effects of electric double layer repulsion and viscosity ratio on film drainage are investigated theoretically.