Electrical Double Layer Interaction Research Articles

Streaming potential method for characterizing interaction of electrical double layers between rice roots and Fe/Al oxide-coated quartz in situ.

The interaction between rice roots and Fe/Al oxide-coated quartz was investigated through zeta potential measurements and column leaching experiments in present study. The zeta potentials of rice roots, Fe/Al oxide-coated quartz, and the binary systems containing rice roots and Fe/Al oxide-coated quartz were measured by a specially constructed streaming potential apparatus. The interactions between rice roots and Fe/Al oxide-coated quartz particles were evaluated/deduced based on the differences of zeta potentials between the binary systems and the single system of rice roots. The zeta potentials of the binary systems moved in positive directions compared with that of rice roots, suggesting that there were overlapping of diffuse layers of electric double layers on positively charged Fe/Al oxide-coated quartz and negatively charged rice roots and neutralization of positive charge on Fe/Al oxide-coated quartz with negative charge on rice roots. The greater amount of positive charges on Al oxide led to the stronger interaction of Al oxide-coated quartz with rice roots and the more shift of zeta potential compared with Fe oxide. The overlapping of diffuse layers on Fe/Al oxide-coated quartz and rice roots was confirmed by column leaching experiments. The greater overlapping of diffuse layers on Al oxide and rice roots led to more simultaneous adsorptions of K+ and NO3- and greater reduction in leachate electric conductivity when the column containing Al oxide-coated quartz and rice roots was leached with KNO3 solution, compared with the columns containing rice roots and Fe oxide-coated quartz or quartz. When the KNO3 solution was replaced with deionized water to flush the columns, more K+ and NO3- were desorbed from the binary system containing Al oxide-coated quartz and rice roots than from other two binary systems, suggesting that the stronger electrostatic interaction between Al oxide and rice roots promoted the desorption of K+ and NO3- from the binary system and enhanced overlapping of diffuse layers on these oppositely charged surfaces compared with other two binary systems. In conclusion, the overlapping of diffuse layers occurred between positively charged Fe/Al oxides and rice roots, which led to neutralization of opposite charge and affected adsorption and desorption of ions onto and from the charged surfaces of Fe/Al oxides and rice roots.

Mathematical modeling of magnetic field guided colloidal particle deposition with significant electric double layer interactions

Mathematical modeling of magnetic field guided colloidal particle deposition with significant electric double layer interactions

Synergistic stabilization of Pickering emulsions by in situ modification of kaolinite with non ionic surfactant

Synergistic stabilization of decane/water emulsions with a combination of kaolinite and non ionic surfactant SPAN-80 is explored. Pure kaolinite being charged and very hydrophilic is a poor stabilizer of emulsions even when sufficient quantity of salt is added to screen electrical double layer interactions. However, the hydrophobicity (via. contact angle) of kaolinite can be tuned with increasing concentration of SPAN-80 leading to very stable O/W emulsions when both kaolinite and SPAN-80 are used. This is due to increase in hydrophobicity of kaolinite particles due to surfactant adsorption which enables them to get adsorbed at oil/water interface more efficiently. Adsorption of kaolinite at emulsion droplets is demonstrated through fluorescently labeled kaolinite. Emulsions phase inverted from O/W to W/O at very high concentrations of surfactant. This phase inversion is due to competitive adsorption of excess unadsorbed surfactant. Other general features such as the effect of salt, pH, oil/water ratio on emulsion formation, stability, type and droplet size has been studied.

Electrokinetically induced thermofluidic transport of power-law fluids under the influence of superimposed magnetic field

This paper presents a theoretical analysis of non-Newtonian (power-law obeying) fluid in a narrow confinement subjected to the combined consequences of interfacial electrokinetics, rheology, and superimposed magnetic field. We devote special attention on the exploitation of magnetic field and power-law exponent, in the development of induced streaming potential and thermofluidic energy transfer characteristics over small scales. In an effort to do so, going beyond the Debye-Hückel limit, we first derive an expression for streaming potential by invoking the consequences of strong EDL (electrical double layer) interactions in the narrow fluidic passage and finite conductance of the Stern layer. In particular, we solve thermal energy transport equation with an illustrative case of classical uniform wall heat flux boundary and considering the volumetric heat generation effects due to viscous dissipation as well as Joule heating. Our results demonstrate that the applied magnetic field imparts a retarding influence on the induced streaming potential development, whereas, it results in enhancement of heat transfer rate. Moreover, additional influences of power law index show reduction in heat transfer as well as the streaming potential magnitude. We unveil the optimal combinations of power law index and the magnetic field which lead to the minimization of the global total entropy generation in the system. We believe that theoretical results presented in this research will be useful in the development of novel narrow fluidic energy efficient devices under electrokinetic modulation.

Effect of Approach Velocity on Thin Liquid Film Drainage between an Air Bubble and a Flat Solid Surface

The dynamic drainage process of the liquid film trapped between an air bubble and a flat silica surface over a wide range of hydrodynamic conditions is studied by a newly developed instrument called integrated thin liquid film force apparatus (ITLFFA) under different salt concentrations. The ITLFFA allows the simultaneous measurement of interaction forces and spatiotemporal film thickness with accurate control of bubble approach velocity in a large range of Reynolds number from 0.005 to 135. Our study demonstrates that increasing the bubble approach velocity plays a significant role in the hydrodynamic pressure and fluid flow within the draining film promoting dimple formation and longer drainage time. The drainage time also depends on the competition between the electrical double-layer and van der Waals interactions, which are repulsive in our system, resulting in a flat equilibrium film at the end. The evolution of the draining film is analyzed using the Stokes–Reynolds–Young–Laplace (SRYL) model. Compa...

Manipulating electrokinetic conductance of nanofluidic channel by varying inlet pH of solution

The electrokinetic conductivity of micro-/nanofluidic systems, which strongly depends on the local solution properties (e.g., pH and ionic strength), has wide applications in nanosystems to control the system performance and ion rectification. Accurate and active manipulation of this parameter is proven to be very challenging since, in nanoscale, the ion transport is particularly dominated by the acquired surface charge on the solid–liquid interfaces. In this study, we propose an approach to manipulate the nanochannel electrokinetic conductivity by changing the pH value of the solution at the inlet in order to impose asymmetrical conditions inside nanochannel. The variable surface charge of walls is determined by considering the chemical adsorption on the solid–liquid interface and the electrical double layer interaction. The presented numerical model, which couples Poisson–Nernst–Planck and Navier–Stokes equations, can fully consider the electro-chemo-mechanical transport phenomena and predict the electrokinetic conductivity of nanofluidic channels with good accuracy. Modeling results show that the electrokinetic conductivity of the nanofluidic systems can be regulated by varying the solution pH at the inlet. It is revealed that the stronger electric double layers interaction can enhance the sensitivity of the nanochannel electrokinetic conductance to the inlet pH. This unique behavior of the nanochannel electrokinetic conductivity could broaden potential applications in biomedical, energy, and environmental systems using nanofluidic devices.

Yolk/Shell Colloidal Crystals Incorporating Movable Cores with Their Motion Controlled by an External Electric Field.

Yolk/shell particles composed of a submicrometer-sized movable core and a silica shell are promising building blocks for novel optical colloidal crystals, because the locations of cores in the shell compartment can be reversibly changed by using external stimuli. Two dimensional arrays of yolk/shell particles incorporating movable cores were prepared by a self-assembly method. The movable cores of colloidal crystals in water could be observed with an optical microscope under application of external electric field. The motions of inner silica cores depended on the electric field strength and frequency and were categorized into three cases: (1) Random Brownian motion, (2) anisotropic motion of cores moving in a direction orthogonal to a field, and (3) suppressed motion fixed in the center of shell compartment. Random Brownian motion of cores was scarcely affected by field strength when a high frequency (in the MHz range) electric field was applied. On the other hand, an increase in field strength at low-frequency fields (kHz) transiently changed the core motion from (1) to (2) and a further increase in field strength changed it from (2) to (3). When the silica core was incorporated in a large void a stronger electric field was needed to suppress its motion than when it was in a small void. The high responsivity to electric fields in a low-frequency range indicated the importance of electric double layer (EDL) interaction between core and inner shell in controlling the core location in yolk/shell colloidal crystals. It was also shown that movable titania cores in yolk/shell particles required a low-frequency field with a high strength to change from the random to anisotropic motion. The result suggested that the electrostatic interaction between EDLs of the silica core and the inner silica wall could be stronger than that between EDLs of the titania core and the silica shell.

Mean distance of two Brownian particles trapped in a suspended droplet and its dependence on the Debye length

Abstract The Brownian motion of two particles confined near the bottom of a suspended droplet was considered in order to examine the electrical double-layer interaction between them. The mean distance between the particles was expressed as a function of the Debye screening length. We report the application of Brownian particle trajectories for the experimental determination of the Debye screening length between gold particles trapped within a water droplet. This was computed through a comparison of the mean distance measured by observing the Brownian motion with its theoretical value.

Variation of Local Surface Properties of an Air Bubble in Water Caused by Its Interaction with Another Surface.

Surface and hydrodynamic forces acting between an air bubble and a flat mica surface in surfactant-free water and in 1 mM KCl solution have been investigated by observing film drainage using a modified surface force apparatus (SFA). The bubble shapes observed with the SFA are compared to theoretical profiles computed from a model that considers hydrodynamic interactions, surface curvature, and disjoining pressure arising from electrical double layer and van der Waals interactions. It is shown that the bubble experiences double-layer forces, and a final equilibrium wetting film between the bubble and mica surfaces is formed by van der Waals repulsion. However, comparison with the theoretical model reveals that the double-layer forces are not simply a function of surface separation. Rather, they appear to be changed by one of more of the following: the bubble's dynamic deformation, its proximity to another surface, and/or hydrodynamic flow in the aqueous film that separate them. The same comments apply to the hydrodynamic mobility or immobility of the air-water interface. Together the results show that the bubble's surface is "soft" in two senses: in addition to its well-known deformability, its local properties are affected by weak external forces, in this case the electrical double-layer interactions with a nearby surface and hydrodynamic flow in the neighboring aqueous phase.

Surface charge-induced EDL interaction on the contact angle of surface nanobubbles.

The contact angle (CA) of surface nanobubbles is believed to affect the stability of nanobubbles and fluid drag in micro/nanofluidic systems. The CA of nanobubbles is dependent on size and is believed to be affected by the surface charge-induced electrical double layer (EDL). However, neither of these of attributes are well understood. In this paper, by introducing an EDL-induced electrostatic wetting tension, a theoretical model is first established to study the effect of EDLs formed near the solid-liquid interface and the liquid-nanobubble interface on the gas phase CA of nanobubbles. The size-dependence of this EDL interaction is studied as well. Next, by using atomic force microscopy (AFM), the effect of the EDL on nanobubbles' gas phase CA is studied with variable electrical potential at the solid-liquid interface, which is adjusted by an applied voltage. Both the theoretical and the experimental results show that the EDLs formed near the solid-liquid interface and the liquid-nanobubble interface lead to a reduction of gas phase CA of the surface nanobubbles because of an electrostatic wetting tension on the nanobubble due to the attractive electrostatic interaction between the liquid and nanobubble within the EDL, which is in the nanobubbles' outward direction. An EDL with a larger zeta potential magnitude leads to a larger gas phase CA reduction. Furthermore, the effect of EDL on the nanobubbles' gas phase CA shows a significant size-dependence considering the size dependence of the electrostatic wetting tension. The gas phase CA reduction due to the EDL decreases with increasing nanobubble height and increases with the nanobubble's increasing curvature radius, indicating that a surface charge-induced EDL could possibly explain the size dependence of the gas phase CA of nanobubbles.

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.

Evaporation, viscous flow, and electrostatic interaction of charged interfaces in the apparent contact line region

We consider evaporation of an aqueous solution near an apparent contact line separating a macroscopically dry area of a heated solid substrate and a constant-curvature meniscus far away from the substrate. Viscous flow, described by a lubrication-type model, is coupled to the interaction of electrical double layers formed near the solid-liquid and liquid-vapor interfaces. The electrostatic interaction is described using the nonlinear Poisson-Boltzmann equation and is shown to affect both normal and shear stress balances at the deformable interface. For steady configurations, we find that the apparent contact line region becomes wider and the total evaporation rate there increases as the substrate potential is increased. Motion of the apparent contact line in response to changes in the substrate temperature is also investigated. The contact line speed is found to increase when the electrostatic effects are incorporated into the model.

Electric Double-Layer Interaction between Dissimilar Charge-Conserved Conducting Plates.

Small metallic particles used in forming nanostructured to impart novel optical, catalytic, or tribo-rheological can be modeled as conducting particles with equipotential surfaces that carry a net surface charge. The value of the surface potential will vary with the separation between interacting particles, and in the absence of charge-transfer or electrochemical reactions across the particle surface, the total charge of each particle must also remain constant. These two physical conditions require the electrostatic boundary condition for metallic nanoparticles to satisfy an equipotential whole-of-particle charge conservation constraint that has not been studied previously. This constraint gives rise to a global charge conserved constant potential boundary condition that results in multibody effects in the electric double-layer interaction that are either absent or are very small in the familiar constant potential or constant charge or surface electrochemical equilibrium condition.

Hydrophobic nano-asperities in control of energy barrier during particle–surface interactions

To explain differences in colloidal interactions for spherical hydrophobic particles, a theoretical analysis of the interaction potential was carried out for a model rough particle interacting with a smooth and flat surface in an electrolyte solution. The attractive hydrophobic interaction potential was added to repulsive retarded van der Waals and repulsive electrical double layer interaction potentials. The rough microscopic particles were modeled as spheres decorated with nano-sized hemispherical asperities. Parameters that reflect common flotation separation systems were selected for testing this theoretical model and computation of the energy barrier applicable to particle–surface interactions. It was found that hydrophobic asperities with the radius of only a few nanometers reduced the energy required for particle attachment to a hydrophobic surface by several times. The value of this energy barrier was reduced by as much as two orders of magnitude when the radius of nano-sized asperities increased to a few tens of nanometers. Theoretical analysis also revealed that surface coverage of microscopic particles by nano-sized asperities was not as important as the size of the asperities.

Particle Deposition and Removal of Relevance to Wet Processing in Semiconductor Manufacturing

Removal of particulate contaminants from surfaces is a critical area in the processing of wafers to build integrated circuits and is typically done using wet chemical formulations. Strategies for particle removal require an understanding of particle deposition mechanisms. In the first part of this review paper, colloid chemical principles underlying particle deposition on surfaces is discussed. Specifically, the importance of van der Waals and electrical double layer interaction energy on particle–surface interaction is reviewed. This is followed by a description of commonly used particle removal methods in wafer processing, viz., megasonic cleaning, brush cleaning, and nanospray cleaning. The importance of particle deposition conditions used in research on particle removal efficiency is highlighted through a study on the effect of aging.

Heterocoagulation in Bidisperse Magnetorheological Fluids Containing Like-Charged Nanosized and Micron Particles Without a Magnetic Field

Based on extended Derjaguin–Landau–Verwey–Overbeek theory, a heterocoagulation model is proposed for magnetorheological (MR) fluids containing like-charged nanosized and micron particles without a magnetic field. This model considers three major interactions, namely van der Waals attraction, electrical double layer (EDL) interaction, and steric repulsion. The EDL interaction has been identified as the most important factor. The surface potential ratio β (ψ2/ψ1) between two dissimilar particles with like charge plays an important role in controlling the change of EDL interaction. At higher β ratios, the EDL interaction becomes attractive when the surface separation falls within a certain range. Two groups of MR fluid samples have been used in experimental studies based on electroacoustic measurements. In the first group, the ratio and the sum of the zeta potentials between carbonyl iron particles and ceria were 4 and −734.57 mV, respectively. In the second group, these parameters were 1.38 and −108.17 mV, respectively. The experimental results suggested that the second group did not undergo heterocoagulation, whereas the first group showed extensive heterocoagulation. The difference in surface potentials between particles of two different phases has been found to be critical for determining the state of dispersion or heterocoagulation in concentrated MR fluid systems.

Experimental characterization of the nanoparticle size effect on the mechanical stability of nanoparticle-based coatings.

We present an experimental investigation of the mechanical stability of silica nanoparticle-based coatings as a function of the size of the nanoparticles. The coatings are built following a layer-by-layer procedure, alternating positive and negative surface charges. The mechanical stability of the multilayers is studied in water, on the basis of an ultrasonic cavitation test. The resistance of the coating to cavitation is found to remarkably increase with decreasing the size of the nanoparticles, indicating an increase of the cohesive energy density. The relative contribution of van der Waals and electrical double-layer interactions to the stability of the multilayer is discussed toward their size dependence.

Effects of polyethyleneimine–phosphonate–carboxylic copolymers on the dispersion of boehmite particles

Novel polyethyleneimine–phosphonate–carboxylic copolymers with an increasing number of carboxylate and phosphonate groups have been synthesised. The presence of positively charged amino groups and negatively charged carboxylate and phosphonate groups influenced the adsorption of these copolymers on boehmite colloidal particles and their dispersant ability in solution at pH values below and above the isoelectric point (iep) of boehmite. It was found that the addition of negatively charged carboxylate groups to the polyethyleneimine polymer backbone had a positive effect on polymer adsorption density and affinity for the boehmite surface while the phosphonate groups had a negative effect. The adsorption of these copolymers on the boehmite surface is largely controlled by electrostatic attractions with the positively and negatively charged aluminium sites below and above the iep of boehmite, respectively. The changes in yield stress of the boehmite particle suspension following copolymer adsorption are largely explained by electrical double layer interaction between the boehmite particles, but also by van der Waals or steric interactions between the polymer-coated particles.

Coatings of Fe/Al Hydroxides Inhibited Acidification of Kaolinite and an Alfisol Subsoil Through Electrical Double-Layer Interaction and Physical Blocking

Variably charged soils confer a different pattern of soil chemical properties compared with a homogeneously charged colloidal system. The relative contents of soil mineralogical constituents and their interaction play important roles in the variation of charge characteristics and other chemical properties of the soils. In this study, coating and simple mixing of iron (Fe)/aluminum (Al) hydroxides with kaolinite and an Alfisol subsoil were made for comparative study of their effect on the electrochemical and acidity properties of kaolinite and Alfisol subsoil after electrodialysis. Transmission electron microscopy and X-ray diffraction analyses indicated that Fe hydroxide coating was more effective than their mixing in physically blocking the kaolinite surface and decreasing the peak intensity of XRD for kaolinite. Coated Fe hydroxides were also more effective than the mixed ones in shifting zeta potential in a positive value direction, decreasing effective cation exchange capacity, and inhibiting acidification of kaolinite and Alfisol subsoil, whereas there was little difference between coated and mixed amorphous aluminum hydroxide (Al(OH)3). The effect of coated Fe/Al hydroxides on effective cation exchange capacity of electrodialyzed kaolinite and Alfisol subsoil varied irreversibly with ionic strength of the bathing solutions. All the results demonstrated that coatings of Fe/Al hydroxides could decrease effective negative charge and inhibit acidification of kaolinite and Alfisol subsoil mainly through two mechanisms: diffuse double-layer overlapping between oppositely charged particles and physical blocking of kaolinite and Alfisol subsoil during electrodialysis. Therefore, Fe/Al hydroxides can act as antiacidification agents in variably charged soils.

Boehmite suspension behaviour upon adsorption of methacrylate–phosphonate copolymers

Two novel methacrylate–phosphonate copolymers were successfully synthesised with varying proportions of methacrylate and phosphonate groups. The dispersant ability of the copolymers was investigated using boehmite colloidal suspensions as a function of pH and polymer concentration. The adsorption and electrochemical behaviour of these methacrylate–phosphonate copolymers onto the boehmite surface was studied as a function of polymer concentration at pH values below and above the IEP of boehmite.It was found that the anionic copolymers adsorbed slightly more on boehmite at pH values below the boehmite IEP (pH9.4) than above the IEP due to electrostatic attraction with the positively charged aluminate hydroxide groups at the boehmite surface. As a result, boehmite becomes more negatively charged, increasing electrostatic repulsion between boehmite particles and therefore the stability of the boehmite particulate suspension, especially at alkaline pH values around the IEP. It was also found that, for a boehmite surface partially covered by adsorbed copolymer, heterogeneous electrical double layer interaction could occur between a positively charged bare boehmite patch (pH<IEP) and the polymer covered patch, resulting in increased electrical attraction between particles. The increased electrical attraction causes the suspension to be less stable when compared to that either in the absence of polymer or at full polymer surface coverage. Very little differences between the two copolymers were observed in their boehmite adsorption or in their particle dispersion ability which is likely to be due to the low proportion of phosphonate groups that were able to be incorporated in these polymers.