Electrical Double Layer Forces Research Articles

Influence of electrical double-layer dispersion forces and size dependency on pull-in instability of clamped microplate immersed in ionic liquid electrolytes

Plate-type clamped microplate is of the most common constructive elements for developing in-liquid-operating devices. While the electromechanical behavior of clamped microplate in non-liquid environments has exclusively been addressed in the literature, no theoretical studies have yet been conducted on precise modeling of the clamped microplate in electrolyte liquid. Herein, the electromechanical response and instability of the clamped microplate immersed in ionic electrolyte media are investigated. The electrochemical force field is determined using double layer theory and linearized Poisson–Boltzmann equation. The presence of dispersion forces, i.e., Casimir and van der Waals attractions, are included in the theoretical model considering the correction due to the presence of liquid media between the interacting surfaces (three-layer model). To this end, a kind of microplate has been designed, i.e., a square microplate with all edges clamped supported. The strain gradient elasticity is employed to model the size-dependent structural behavior of the clamped microplate. To solve the nonlinear constitutive equation of the system, Extended Kantorovich Method, is employed and the pull-in parameter of the microplate are extracted. Impacts of the dispersion forces and size effect on the instability characteristics are discussed as well as the effect of ion concentration and potential ratio. It is found that the significant difference between the pull-in instability parameters in the modified strain gradient theory and the classical theory for thin microplates is merely due to the consideration of size effect parameter in the modified strain gradient theory. To confirm the validity of formulations, the numerical values of the results are compared. The results predicted via the aforementioned approach are in excellent agreement with those in the literature. Some new examples are solved to demonstrate the applicability of the procedure.

Adsorption, Aggregation, and Deposition Behaviors of Carbon Dots on Minerals.

The increased production of carbon dots (CDs) and the release and accumulation of CDs in both surface and groundwater has resulted in the increasing interest in their research. To assess the environmental behavior of CDs, the interaction between CDs and goethite was studied under different environmental conditions. Electrokinetic characterization of CDs suggested that the ζ-potential and size distribution of CDs were affected by pH and electrolyte species, indicating that these factors influenced the stability of CDs in aqueous solutions. Traditional Derjaguin-Landau-Verwey-Overbeek theory did not fit well the aggregation process of CDs. Results of the effects of pH and ionic strength suggested that electronic attraction dominated the aggregation of CDs. Compared with other minerals, hydrogen-bonding interactions and Lewis acid-base interactions contributed to the aggregation of CDs, in addition to van der Waals and electrical double-layer forces. Adsorption isotherms and microscopic Fourier transformed infrared spectroscopy indicated that chemical bonds were formed between CDs and goethite. These findings are useful to understand the interaction of CDs with minerals, as well as the potential fate and toxicity of CDs in the natural environment, especially in soils and sediments.

Electrical Double-Layer and Ion Bridging Forces between Symmetric and Asymmetric Charged Surfaces in the Presence of Mono- and Divalent Ions.

An atomic force microscope, employing the colloidal probe technique, was used to study the interactions between six different combinations of silane-functionalized silica surfaces in NaCl and CaCl2 solutions. The surfaces consisted of monolayers of the apolar trimethoxy(octyl)silane, the positively charged (3-aminopropyl)trimethoxysilane, and the negatively charged (3-mercaptopropyl)trimethoxysilane. The interactions between the three symmetric systems, as well as between the three asymmetric combinations of surfaces, were measured and compared to calculated electrical double-layer forces. The results demonstrated that the long-range interactions between the surfaces in all cases were dominated by double-layer forces, while short-range interactions, including adhesion, were dominated by ion bridging forces in the cases where both interaction surfaces favored adsorption of calcium ions. The study thus also demonstrates how surface force studies in mono- and divalent salt solutions can be used as an analytical tool for probing specific functional groups on heterogeneous surfaces.

Design of latex-layered double hydroxide composites by tuning the aggregation in suspensions.

Colloidal stability of polymeric latex particles was studied in the presence of oppositely charged layered double hydroxide (LDH) platelets of different interlayer anions. Adsorption of the LDH particles led to charge neutralization and to overcharging of the latex at appropriate concentrations. Mixing stable colloidal suspensions of individual particles results in rapid aggregation once the LDH adsorption neutralizes the negative charges of the polymer spheres, while stable suspensions were observed at high and low LDH doses. The governing interparticle interactions included repulsive electrical double layer forces as well as van der Waals and patch-charge attractions, whose strength depended on the amount of LDH particles adsorbed on the latex surface. The type of the LDH interlayer anions did not affect the colloidal stability of the samples. Structural investigation of the obtained latex-LDH composites revealed that the polymer spheres were completely coated with the inorganic platelets once their concentration was sufficiently high. These results are especially important for designing synthetic routes for hybrid systems in suspensions, where stable colloids are required for uniform film-formation and for the homogeneous distribution of the inorganic filler within the composite materials.

Adsorbed Organic Material and Its Control on Wettability

Laboratory core flood and field scale tests have demonstrated that 5–40% more oil can be released from sandstone reservoirs by injecting low salinity water, rather than high salinity fluids, such as seawater or formation water. The effect has been explained by a change in wettability of the minerals that form the pore surfaces, as a result of the decrease in divalent cation concentration. We have previously demonstrated that, even for solvent cleaned core samples, mineral surfaces retain a significant quantity of carbon containing material and this affects wettability and response to changed salinity. Here we quantified the response of sandstone core plug material in its preserved state (i.e., after storage in kerosene) and after the same core plug material was treated with ethanol and ozone to remove adsorbed organic compounds. We used the chemical force microscopy (CFM) mode of atomic force microscopy (AFM) to directly measure the adhesion force for two types of molecules on pore surfaces of individual sand grains that were plucked from an oil reservoir core plug. We functionalized AFM tips with alkane or carboxylate, so they resembled tiny oil droplets and measured adhesion to the sand grain surfaces in artificial seawater (ASW; 35,600 ppm) and in ASW diluted to ∼1,500 ppm (ASW-low). Both before and after the ethanol/ozone treatment, and for both the alkane and the carboxylate functionalized tips, the adhesion was lower in ASW diluted to ∼1,500 ppm than in ASW. For both alkane and carboxylate, the difference in adhesion between ASW and ASW-low was higher before the ethanol/ozone treatment. We attribute this change in response to the salinity dependent force caused mainly by the electric double layer (EDL) at the sand grain surfaces. We interpret the higher adhesion difference, before a very thorough ethanol/ozone treatment, to be a result of the loss of the organic material that was originally adsorbed on these surfaces, which adds to the charge density and thereby to the salinity dependent EDL force. Investigating the same area on the same pore surface, before and after removal of the organic material, demonstrates without doubt that it is organic material that causes the low salinity response, not the underlying mineral surface.

Filtration of aqueous colloidal ceria slurries using fibrous filters – An experimental and simulation study

Abstract A combined experimental and computational study of fibrous filters for removal of large hydrosols, essential to minimize defects during chemical mechanical polishing, was performed. Dilute aqueous suspensions of colloidal ceria particles, of known size distribution, were filtered and the filter efficiencies were measured for different particle sizes and pH, then converted to single fiber efficiencies. The particle size distributions were also measured for the influent and effluent streams. In a series of numerical simulations, the Navier-Stokes equation was solved for a single fiber using the ANSYS-FLUENT computational fluid dynamics commercial package. For dilute suspensions, the motion of the dispersed particles in the size range of 35–600 nm was tracked in the Lagrangian reference frame including the effects of hydrodynamic drag, lift, gravity, hydrodynamic retardation, Brownian, van der Waals and electric double layer forces. The electric double layer and van der Waals forces were incorporated in the calculations by developing a user defined function. Particular attention was given to the effect of Brownian excitations, as well as the electric double layer and van der Waals forces - which have been neglected in many of the previous models - on the overall fiber collection efficiency for different particle sizes and charges. The simulated fiber efficiencies and particle size distributions compared very well with experimental results.

Specific Ion Effects and pH Dependence on the Interaction Forces between Polystyrene Particles.

Colloidal interactions have been extensively studied due to the wide number of applications where colloids are present. In general, the electric double layer force and the van der Waals interaction dominate the net force acting between two colloids at large separation distances. However, it is well accepted that some other phenomena, especially those acting at short separation distances, might be relevant and induce substantial changes in the force profiles. Within these phenomena, those related to the surface contact angle, the hydration degree of the ions, or the pH, may dominate the force profiles features, not only at short distances. In this paper, we analyzed the effect of the pH and counterion type on the long-range as well as short-range forces between polystyrene colloidal particles by using the colloidal probe technique based on AFM. Our results confirm that the features of the force profiles between polystyrene surfaces are strongly affected by the pH and hydration degree of the counterions in solution. Additionally, we performed a study of the role of the pH on the wettability properties of hydrated and nonhydrated polystyrene sheets to scan the wettability properties of this material with pH. Contact angle measurements confirmed that the polystyrene surface is hydrophobic in aqueous solutions over the entire range of pHs investigated. These results are in good agreement with the features observed in the force profiles at low pH. At high pH, a short-range repulsion similar to the one observed for hydrophilic materials is observed. This repulsion scales with the pH, and it also depends on the hydration degree of the ions in solution. This way, the short-range forces between polystyrene surfaces may be tunable with the pH, and its origin does not seem to be related to the hydrophobicity of the material.

Visual investigation of the effects of clay minerals on enhancement of oil recovery by low salinity water flooding

Experimental study of Low-Salinity Water flooding (LSWF) in sandstone cores by core flooding indicated the presence of fine particles of clay minerals in the effluent. Also, migration of clay particles is considered as one of the major mechanisms for improving oil recovery by LSWF. In addition, it is believed that the presence of clay minerals is one of the necessary conditions for a positive impact of LSWF because clay/crude interaction plays an essential role in the initial wettability of porous media. However, a clear role of clay minerals in this process has not been identified. The aim of this study is to investigate oil recovery enhancement by fines migration at micromodel scale during LSWF. To this end, kaolinite and sodium bentonite were utilized as migratory and swelling clays in the glass micromodel to create clayey porous media. The results indicated that when the porous medium lacked clay minerals, LSWF did not enhance oil recovery. In the clay-coated porous medium that was free of connate water, the crude oil was adsorbed on the pore surfaces, and under this condition, LSWF caused the migration of clay particles with clinging oil droplets due to the electrical double layer force, which improved oil recovery and water wetness. If the porous medium contained clay minerals and connate water, the crude oil did not stick on the pore surfaces. Hence, in both seawater flooding and LSWF, film-flow was observed, which meant that migration of fines by LSWF did not contribute to the oil recovery enhancement. Our work showed that LSWF would be effective as the secondary recovery method if polar compounds of crude oil were adsorbed on the pore surfaces, which means that the initial wettability of porous media must be mixed-wet. LSWF in the clay-coated porous media with high cation-exchange-capacity clay in the primary mode increased the interstitial velocity in some pore paths due to pore-plugging by swelling of clay and finally led to sectional sweeping.

A review of principles and applications of magnetic flocculation to separate ultrafine magnetic particles

Magnetic separation has been used in industries to concentrate or remove magnetic minerals/particles for many years. The separation of ultrafine magnetic particles is significantly influenced by aggregation between particles due to various external and interparticle forces, such as gravity, magnetic attraction, van der Waals, electrical double-layer, hydrodynamic, and Brownian diffusion forces. This review focuses on the principles of the magnetic flocculation and separation of micrometer-sized particles in solution. Potential energies between particles are linked to the particle aggregation (i.e. stability), sedimentation and dispersion in applied magnetic fields. Prediction and control of magnetic flocculation are achieved by simulating particle motions around the surface of the magnetic separators using various mathematical models, with some large-scale applications of magnetic flocculation are being demonstrated.

Controlling droplet bouncing and coalescence with surfactant

The collision between aqueous drops in air typically leads to coalescence after impact. Rebounding of the droplets with similar sizes at atmospheric conditions is not generated, unless with significantly large pressure or high impact parameters exhibiting near-grazing collision. Here we demonstrate experimentally the creation of a non-coalescent regime through addition of a small amount of water-soluble surfactant. We perform a direct simulation to account for the continuum and short-range flow dynamics of the approaching interfaces, as affected by the soluble surfactant. Based on the immersed-boundary formulation, a conservative scheme is developed for solving the coupled surface-bulk convection–diffusion concentration equations, which presents excellent mass preservation in the solvent as well as conservation of total surfactant mass. We show that the Marangoni effect, caused by non-uniform distributions of surfactant on the droplet surface and surface tension, induces stresses that oppose the draining of gas in the interstitial gap, and hence prohibits merging of the interfaces. In such gas–liquid systems, the repulsion caused by the addition of surfactant, as frequently observed in liquid–liquid systems such as emulsions in the form of an electric double-layer force, was found to be too weak to dominate in the attainable range of interfacial separation distances. These results thus identify the key mechanisms governing the impact dynamics of surfactant-coated droplets in air and imply the potential of using a small amount of surfactant to manipulate impact outcomes, for example, to prevent coalescence between droplets or interfaces in gases.

Interactions between elemental selenium and hydrophilic/hydrophobic surfaces: Direct force measurements using AFM

Understanding the surface interactions between elemental selenium (Se0) and solid substrates is of both fundamental and practical importance in biological systems, water treatment processes, and microelectromechanical/nanoelectromechanical systems where Se0 is present. In this work, for the first time, surface interactions between a Se0 sphere and substrates of varying hydrophobicity, including silica, octadecyltrichlorosilane (OTS) modified silica, and electrodeposited Se0 film, were directly measured in aqueous solutions at different pH and salinity conditions using an atomic force microscope (AFM). In 1mM NaCl, electrical double layer forces and van der Waals forces dominated the interactions between Se0 sphere and hydrophilic silica, and the force-distance profiles could be well fitted by classic Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Additional hydrophobic attraction was found to play a role in the interactions between Se0 sphere and hydrophobic surfaces (i.e., OTS modified silica, and electrodeposited Se0 film), with Se0-OTS showing relatively larger hydrophobic decay length (D0∼1.3nm) than Se0-Se0 (D0∼1nm). In 0.5M NaCl, the electrical double layer interaction was significantly compressed. The change of zeta potentials of Se0, OTS and silica surfaces with pH showed good agreement and same trend as that of the fitted surface potentials based on the force measurements. This work provides useful information regarding the interaction mechanism of Se0 and surfaces of varying hydrophobicity in aqueous solutions.

Temperature- and pH-Responsive Benzoboroxole-Based Polymers for Flocculation and Enhanced Dewatering of Fine Particle Suspensions.

Random copolymers based on N-isopropylacrylamide (NIPAAm) containing 2-aminoethyl methacrylamide hydrochloride (AEMA) and 5-methacrylamido-1,2-benzoboroxole (MAAmBo) were synthesized and subsequently evaluated for their performance in solid-liquid separation at various pH and temperatures. The strong interactions between benzoboroxole residues and kaolin hydroxyl groups were evaluated for the first time in the flocculation of fine particle suspensions. The lower critical solution temperatures (LCSTs) of PAMN decreases because of the hydrophobic nature of the benzoboroxole moieties, resulting in strong hydrophobic interaction at temperatures higher than the LCSTs. Temperature and pH responsive polymer, P(AEMA51-st-MAAmBo76-st-NIPAM381) (denoted as PAMN) shows the ability to induce fastest settling at a low dosage of 25 ppm and under the condition of pH 9 and 50 °C. The accelerated settling rate is considered to be due to the strong adhesion of benzoboroxole residues to the kaolin hydroxyl groups, the electrical double layer force, and the hydrophobic force. During condensation phase, increasing the pH of sediment to pH 11 could attain the most compact structure. Random copolymers containing benzoboroxole groups act as dispersants (due to pH-responsive character) rather than flocculants at pH 11, providing repulsive force that enables particles to rearrange their position and consolidate well. Through a two-step solid-liquid separation including settling phase and consolidation phase, rapid settling and compact sediment are feasible simultaneously.

Cell shape recognition by colloidal cell imprints: energy of the cell-imprint interaction.

The results presented in this study are aimed at the theoretical estimate of the interactions between a spherical microbial cell and the colloidal cell imprints in terms of the Derjaguin, Landau, Vervey, and Overbeek (DLVO) surface forces. We adapted the Derjaguin approximation to take into account the geometry factor in the colloidal interaction between a spherical target particle and a hemispherical shell at two different orientations with respect to each other. We took into account only classical DLVO surface forces, i.e., the van der Waals and the electric double layer forces, in the interaction of a spherical target cell and a hemispherical shell as a function of their size ratio, mutual orientation, distance between their surfaces, their respective surface potentials, and the ionic strength of the aqueous solution. We found that the calculated interaction energies are several orders higher when match and recognition between the target cell and the target cell imprint is achieved. Our analysis revealed that the recognition effect of the hemispherical shell towards the target microsphere comes from the greatly increased surface contact area when a full match of their size and shape is produced. When the interaction between the surfaces of the hemishell and the target cell is attractive, the recognition greatly amplifies the attraction and this increases the likelihood of them to bind strongly. However, if the surface interaction between the cell and the imprint is repulsive, the shape and size match makes this interaction even more repulsive and thus decreases the likelihood of binding. These results show that the surface chemistry of the target cells and their colloidal imprints is very important in controlling the outcome of the interaction, while the shape recognition only amplifies the interaction. In the case of nonmonotonous surface-to-surface interaction we discovered some interesting interplay between the effects of shape match and surface chemistry which is discussed in the paper. The results from this study establish the theoretical basis of cell shape recognition by colloidal cell imprints which, combined with cell killing strategies, could lead to an alternative class of cell shape selective antimicrobials, antiviral, and potentially anticancer therapies.

Molecular-scale quantitative charge density measurement of biological molecule by frequency modulation atomic force microscopy in aqueous solutions

Surface charge distributions on biological molecules in aqueous solutions are essential for the interactions between biomolecules, such as DNA condensation, antibody–antigen interactions, and enzyme reactions. There has been a significant demand for a molecular-scale charge density measurement technique for better understanding such interactions. In this paper, we present the local electric double layer (EDL) force measurements on DNA molecules in aqueous solutions using frequency modulation atomic force microscopy (FM-AFM) with a three-dimensional force mapping technique. The EDL forces measured in a 100 mM KCl solution well agreed with the theoretical EDL forces calculated using reasonable parameters, suggesting that FM-AFM can be used for molecular-scale quantitative charge density measurements on biological molecules especially in a highly concentrated electrolyte.

The effect of ionic strength on oil adhesion in sandstone--the search for the low salinity mechanism.

Core flood and field tests have demonstrated that decreasing injection water salinity increases oil recovery from sandstone reservoirs. However, the microscopic mechanism behind the effect is still under debate. One hypothesis is that as salinity decreases, expansion of the electrical double layer decreases attraction between organic molecules and pore surfaces. We have developed a method that uses atomic force microscopy (AFM) in chemical force mapping (CFM) mode to explore the relationship between wettability and salinity. We functionalised AFM tips with alkanes and used them to represent tiny nonpolar oil droplets. In repeated measurements, we brought our “oil” close to the surface of sand grains taken from core plugs and we measured the adhesion between the tip and sample. Adhesion was constant in high salinity solutions but below a threshold of 5,000 to 8,000 ppm, adhesion decreased as salinity decreased, rendering the surface less oil wet. The effect was consistent, reproducible and reversible. The threshold for the onset of low salinity response fits remarkably well with observations from core plug experiments and field tests. The results demonstrate that the electric double layer force always contributes at least in part to the low salinity effect, decreasing oil wettability when salinity is low.

Coalescence behavior of oil droplets coated in irreversibly-adsorbed surfactant layers

Coalescence between oil caps with irreversibly adsorbed layers of nonionic surfactant is characterized in deionized water and electrolyte solution. The coalescence is characterized using a modified capillary tensiometer allowing for accurate measurement of the coalescence time. Results suggest two types of coalescence behavior, fast coalescence at low surface coverages that are independent of ionic strength and slow coalescence at high coverage. These slow coalescence events (orders of magnitude slower) are argued to be due to electric double layer forces or more complicated stabilization mechanisms arising from interfacial deformation and surface forces. A simple film drainage model is used in combination with measured values for interfacial properties to quantify the interaction potential between the two interfaces. Since this approach allows the two caps to have the same history, interfacial coverage and curvature, the results offer a tool to better understand a mechanism that is important to emulsion stability.

Probing the interaction between air bubble and sphalerite mineral surface using atomic force microscope.

The interaction between air bubbles and solid surfaces plays important roles in many engineering processes, such as mineral froth flotation. In this work, an atomic force microscope (AFM) bubble probe technique was employed, for the first time, to directly measure the interaction forces between an air bubble and sphalerite mineral surfaces of different hydrophobicity (i.e., sphalerite before/after conditioning treatment) under various hydrodynamic conditions. The direct force measurements demonstrate the critical role of the hydrodynamic force and surface forces in bubble-mineral interaction and attachment, which agree well with the theoretical calculations based on Reynolds lubrication theory and augmented Young-Laplace equation by including the effect of disjoining pressure. The hydrophobic disjoining pressure was found to be stronger for the bubble-water-conditioned sphalerite interaction with a larger hydrophobic decay length, which enables the bubble attachment on conditioned sphalerite at relatively higher bubble approaching velocities than that of unconditioned sphalerite. Increasing the salt concentration (i.e., NaCl, CaCl2) leads to weakened electrical double layer force and thereby facilitates the bubble-mineral attachment, which follows the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory by including the effects of hydrophobic interaction. The results provide insights into the basic understanding of the interaction mechanism between bubbles and minerals at nanoscale in froth flotation processes, and the methodology on probing the interaction forces of air bubble and sphalerite surfaces in this work can be extended to many other mineral and particle systems.

Developed Mathematical Equation for Predicting Turbidity Removal Using Synthetic Fiber Filter

A new mathematical model for predicting the contact efficiency of a single collector in the treatment of turbid water is presented in this study. The removal mechanisms applied were interception, diffusion, and sedimentation. In order to obtain the model for the single-collector efficiency, the effect of the density current caused by turbidity and differences in temperature was considered and the impact of multiple-size particles was also included when calculating the respective mechanisms. The sticking coefficient was also calculated, including the effect of the van der Waals attraction energy and electrical double layer forces. The result of the modeling indicated that the predicted efficiency using the developed equation showed good agreement with the experimental values over a wide range of parameters and the increases and decreases in the model performance were simulated very well. The quality of the data was analyzed and this indicated that the experimental work and the developed model showed fairly good agreement.

Influence of Ag+ interaction on 1D droplet array spacing and the repulsive forces between stimuli-responsive nanoemulsion droplets.

This paper reports results on the effect of interaction of Ag(+) on 1D droplet array spacing and the repulsive forces between stimuli-responsive nanoemulsion droplets, stabilized with an anionic surfactant--sodium dodecyl sulfate--and a diblock polymer--poly(vinyl alcohol)-vinyl acetate. The repulsive interaction is probed by measuring the in-situ equilibrium force-distance in the presence of Ag(+) using the magnetic chaining technique. At a constant static magnetic field, emulsion droplets form 1D array that diffract visible light. A large blue-shift in the diffracted light is observed in the presence of interacting Ag(+) because of the reduction in the interdroplet spacing within the 1D array. The in-situ equilibrium force-distance measurement results show that the onset of repulsions and magnitude of repulsive forces are strongly influenced by the presence of Ag(+) in ppb levels. This suggests that the Ag(+) ions screen the surface charges through the formation of both Stern and diffuse electric double layer and produces a dramatic blue-shift in surfactant-stabilized emulsion, whereas a dramatic conformational change in the adsorbed polymer layer causes a reduction in the 1D array spacing in the diblock polymer stabilized emulsion. The force-distance results are compared with the predictions of electrical double-layer and repulsive steric forces. The droplet array shows an excellent selectivity to Ag(+) due to the strong interaction of Ag(+) with the stabilizing moieties at the oil-water interface. The possible mechanisms of interaction of Ag(+) with surfactant and polymer are discussed. The dramatic decrease in the 1D array spacing in the presence of Ag(+) may find promising practical applications in the development of optical sensors for selective detection of cations with ultrahigh sensitivity.

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.