Surface Charge Density Measurements Research Articles

Electrical Responses of Modified Mineral Surfaces as Observed With Spectral Induced Polarization and Atomic Force Microscopy

AbstractAtomic force microscopy (AFM) and spectral induced polarization (SIP) are widely used to investigate the electrical properties of mineral surfaces at vastly different scales of measurement. We compare AFM and SIP measurements made on two different materials (glass beads and silica gel) subjected to etching, deposition of iron oxide particles, and inclusion of calcite grains. We found that the treatments produced qualitatively consistent behaviors in the AFM and SIP data. Direct AFM measurements of surface charge density for silica and calcite surfaces were quantitatively compared to values estimated from the SIP results using a grain polarization model. No statistically significant difference (at a 95% confidence level) was found between the surface charge density of silica estimated by AFM (2.3 ± 6.6 mC/m2 for glass beads and 1.6 ± 0.1 mC/m2 for silica gel) versus SIP (5.4 ± 4.4 mC/m2 for glass beads and 1.6 ± 0.5 mC/m2 for silica gel). The surface charge density for calcite determined by AFM (43.5 ± 12.9 mC/m2) was approximately 19 times higher than that found for silica. While the charge density of calcite surfaces determined by SIP was also generally higher than that found for silica, different treatments produced significantly different values between 4.7 and 258 mC/m2 (with a maximum 95% CI of ±8.7 mC/m2). Several possible explanations exist for the range of the observed SIP measurements, including aging of the calcite surfaces. Overall, this study suggests the potential for the complementary use of AFM and SIP measurements to constrain future investigations of polarization mechanisms in porous media.

Slide electrification of drops at low velocities.

Slide electrification of drops is mostly investigated on tilted plate setups. Hence, the drop charging at low sliding velocity remains unclear. We overcome the limitations by developing an electro drop friction force instrument (eDoFFI). Using eDoFFI, we investigate slide electrification at the onset of drop sliding and at low sliding velocities ≤ 1 cm s-1. The novelty of eDoFFI is the simultaneous measurements of the drop discharging current and the friction force acting on the drop. The eDoFFI tool facilitates control on drop length and width using differently shaped rings. Hereby, slide electrification experiments with the defined drop length-to-width ratios >1 and <1 are realized. We find that width of the drop is the main geometrical parameter which determines drop discharging current and charge separation. We combine Kawasaki-Furmidge friction force equation with our finding on drop discharging current. This combination facilitates the direct measurement of surface charge density (σ) deposited behind the drop. We calculate σ ≈ 45 μC m-2 on Trichloro(1H,1H,2H,2H-perfluorooctyl)silane (PFOTS) and ≈20 μC m-2 on Trichloro(octyl)silane (OTS) coated glass surfaces. We find that the charge separation by moving drops is independent of sliding velocity ≤ 1 cm s-1. The reverse sliding of drop along the same scanline facilitates calculation of the surface neutralization time constant. The eDoFFI links two scientific communities: one which focuses on the friction forces and one which focuses on the slide electrification of drops.

Selected Textural and Electrochemical Properties of Nanocomposite Fillers Based on the Mixture of Rose Clay/Hydroxyapatite/Nanosilica for Cosmetic Applications.

In order to improve the properties and characteristics of rose clay composites with acai, hydroxyapatite (HA), and nanosilica, the systems were mechanically treated. This treatment provides the preparation of better nanostructured composites with natural and synthetic nanomaterials with improved properties. The materials were characterized using XRD, nitrogen adsorption and desorption, particle sizing, zeta potential, and surface charge density measurements. For the systems tested in the aqueous media, the pH value of the point of zero charge (pHPZC) ranges from 8 to 9.9. However, the isoelectric point (pHIEP) values for all composites are below pH 2. This large difference between pHPZC and pHIEP is due to the complexity of the electrical double layer (EDL) and the relation of these points to different layers of the EDL. The tested samples as composite/electrolyte solutions are colloidally unstable. The toxicity level of the ingredients and release of anthocyanins as bioactive substances from acai in the composites were determined. The composites demonstrate an enhanced release of anthocyanins. There are some regularities in the characteristics depending on the type of components, morphology, and textural features of solids. The morphological, electrochemical, and structural characteristics of the components have changed in composites. The release of anthocyanins is greater for the composites characterized by minimal confined space effects in comparison with rose clay alone. The morphological, electrochemical, and structural characteristics allow us to expect high efficiency of composites as bioactive systems that are interesting for practical applications in cosmetics.

Ion-mediated desorption of asphaltene molecules from carbonate and sandstone structures

As more and more oil recovery scenarios use seawater, the need to identify the possible mechanisms of wettability state changes in oil reservoirs has never been greater. By using molecular dynamics simulations, this study sheds light on the effect of ions common to seawater (Ca2+, K+, Mg2+, Na+, Cl−, HCO3−, SO4 2−) on the affinity between silica and carbonate as the traditional rock types and asphaltene molecules as an important contributing factor of reservoir oil wetness. In the case of carbonate and silica being the reservoir rock types, the measured parameters indicate good agreement with each other, meaning that (HCO3 − & SO4 2−) and (Na+ & Cl−) ions reached maximum bonding energies of (25485, 25511, 4096, and −4093 eV, respectively). As with the surface charge density measurements, the results of the non-bonding energies between the individual atomic structures agree with those from the simulation cell. In the presence of a silica surface, the radial distribution function (RDF) results determine that the peak of the maximum value for the distribution of the ions is 4.2. However, these values range from 3 to 6.6, suggesting that different ions perform better under the influence of carbonate rock. As these ions are distributed in the simulation box along with the adsorption domain, the conditions for sequestering asphaltene from the rock surface are made ideal for dissolution and removal. At equal ion strength, measuring the distance between the center of mass of rocks and asphaltene structures reveals a maximum repulsion force of 22.1 Å and a maximum detachment force of 10.4 Å in the presence of SO4 2− and Na+ ions on carbonate and silica surfaces.

Surface charge density measurement of a single protein molecule with a controlled orientation by AFM

The spatial distribution of functional groups causes a charge distribution that often has a close relationship with its biofunctions. To understand them of the protein molecules, measurements of the charge distribution under physiological conditions are desired. Atomic force microscopy (AFM) has been utilized to measure the surface charge density by measuring the electric double layer (EDL) force caused by the overlap of the EDLs on the surfaces of the AFM tip and the biomolecule. Here, we demonstrated the surface charge density measurement of a single streptavidin (SA) protein molecule by the three-dimensional force mapping method based on frequency modulation AFM (FM-AFM). The SA has a strong affinity to biotin because of the electrostatic interactions between the molecules. Therefore, the surface charge density measurements of the biotin-binding sites and other surface areas of the molecule have been anticipated. However, the surface charge density of the surfaces other than the biotin-binding side has never been measured. We demonstrate the surface charge density measurement of the top surface of the single SA molecule, which is perpendicular to the biotin-binding sides, with a controlled orientation using DNA origami as a template by FM-AFM in an electrolyte solution. The surface charge density of the top surface of the SA molecule was estimated by fitting the experimental force curves to the Derjaguin-Landau-Verwey-Overbeck theory. We found that the surface charge density of the top surface of the SA molecule is comparable to those reported earlier for the biotin-binding sides of the molecule. We expect that, by using the DNA origami technology, one can control the orientation of a biomolecule attached to the substrate and measure the surface charge density of the specific surface areas of the biomolecule to obtain information that will help us to understand the relationship between their structures and functions.

Alginic acid as a stabilizer of zirconia suspensions in the presence of cationic surfactants

The influence of hydrocarbon (CTAB), fluorocarbon (S-106-A) and silicone (C-Si) cationic surfactants: on stability, adsorption and electrokinetic properties of the alginic acid (AA)/zirconia (ZrO2) suspensions was studied. The results obtained from the spectrophotometric measurements indicate on very high effectiveness of the surfactants in stabilization of the studied systems. This is due to the formation of multimolecular complexes between alginic acid and the surfactants. The existence of these complexes was confirmed by the surface tension and the zeta potential measurements. Presented studies also enabled the estimation of the conditions under which the complexes are effectively created and the determination of their character. These findings were also confirmed by the adsorption data. Moreover, the surface charge density measurements proved that the adsorption of AA or the AA/surfactant complexes changes the structure of the electrical double layer. The presented results may find applications in the fields of functionalized materials.

Microfabricated and multilayered PLGA structure for the development of co-cultured in vitro liver models

One of the main advantages of having an in vitro model is the possibility of reducing toxic effects of drugs on human body and evaluate their response to pharmacological treatments to improve the efficacy of a patient-specific therapy. The limitation of such in vitro model is the use of monolayer hepatocytes cultures that show some problems of protein secretion and hepatic functionality. In order to overcome these drawbacks, we present two innovative multilayer structures based on micro-stamped poly(lactic-co-glycolic acid) (PLGA) structures and hepatocytes and fibroblast co-cultures. In particular, the first model consisted of 1 up to 5 layers of PLGA seeded with the previously cited co-culture, while the second model consisted of various sandwich structures of PLGA functionalised (or not) with collagen and seeded with hepatocytes and/or fibroblasts. A mechanical analysis, contact angle and surface charge density measurements were carried out. After these preliminary tests, a metabolic analysis was performed evaluating glucose consumption and urea and albumin production over a culture period of 11 days. Results showed promising application of these in vitro liver models, in particular considering the field of cirrhotic liver treatment.

Changes in the CMC/ZrO2 system properties in the presence of hydrocarbon, fluorocarbon and silicone surfactants

The influence of cationic surfactants: hydrocarbon - myristyltrimethylammonium bromide (MTAB), silicone - Silquat J2 (C-Si) and fluorine one (S-106A) on the stabilizing properties of the carboxymethyl cellulose (CMC)/zirconia (ZrO2) system was studied using the spectrophotometric measurements. The obtained results prove that all used polysaccharide/surfactant mixtures can be used as stabilizers of zirconia suspensions, however, the CMC/S-106A mixture is the most effective. The reason for that is formation of the CMC/S-106A complexes with 1:2 stoichiometry and their adsorption on the metal oxide surface. In order to find possible mechanisms of stabilization the CMC adsorption on the ZrO2 was studied. To obtain some information on the structure of the polysaccharide/surfactant/oxide adsorption layer, the surface charge density measurements were conducted. The obtained results can be applied in the fields of ceramics and catalysis.

Does Flexoelectricity Drive Triboelectricity?

The triboelectric effect, charge transfer during sliding, is well established but the thermodynamic driver is not well understood. We hypothesize here that flexoelectric potential differences induced by inhomogeneous strains at nanoscale asperities drive tribocharge separation. Modeling single asperity elastic contacts suggests that nanoscale flexoelectric potential differences of ±1-10 V or larger arise during indentation and pull-off. This hypothesis agrees with several experimental observations, including bipolar charging during stick slip, inhomogeneous tribocharge patterns, charging between similar materials, and surface charge density measurements.

The effect of ionic and non-ionic surfactants and pH on the stability, adsorption and electrokinetic properties of the alginic acid/alumina system

The influence of ionic (CTAB; SDS) and non-ionic (TX-100; TX-165 and TX-405) surfactants as well as pH of the solution on the stability, adsorption and electrokinetic properties of the alginic acid (AA)/alumina (Al2O3) suspensions was studied. The results obtained using the spectrophotometric method show that the addition of ionic surfactants is an effective way to obtain stable AA/Al2O3 suspensions whereas the changes in pH are not sufficient. Surface tension measurements together with the adsorption data show that the macromolecules of alginic acid are able to form complexes with CTAB, however, they compete for the adsorption centers on the metal oxide surface with SDS. Non-ionic surfactants do not affect alginic acid adsorption. The electrokinetic measurements (surface charge density and zeta potential measurements) prove that adsorption of alginic acid on Al2O3 with or without surfactants changes the structure or the compact and diffused parts of the electric double layer. It should be emphasized that the alginic acid/surfactant/alumina system has not been studied before which confines its possible applications in the fields of functionalized materials.

Influences of styrene-acrylate latexes on cement hydration in oil well cement system at different temperatures

Influences of styrene-acrylate (SA) latexes on cement hydration were investigated by isothermal calorimetry and the mechanism wasdiscussed. Super-retardation phenomenon caused by addition of SA latexes on oil well cement hydration was found at 80°C by setting time measurement. Quantitative analysis of hydrolysis of SA latexes in cementitious systems and their effect on cement hydration were investigated by FTIR, zeta potential and surface charge density measurements. Results show that the hydrolysis of ester groups in acrylate units is significantly accelerated by elevated temperature in alkaline condition. The continuous production of carboxyl groups promotes the adsorption of polymer particles on the surface of cement grains and/or leads to continuous Ca2+ sequestration from pore solution. These two aspects are the causes of the super-retardation effect. It is concluded that unless special chemistry is involved in the preparation of SA latexes, such as construction of core-shell structure of the colloidal particles, SA latexes with high content of acrylate units, due to the severe hydrolysis of the ester groups in the polymer chains, are not recommended to be used in oil well cement system.

Impact of lysozyme on stability mechanism of nanozirconia aqueous suspension

The effect of lysozyme (LSZ) presence on the zirconium(IV) oxide (ZrO2) aqueous suspension stability was examined. The applied zirconia contains mesopores (with a diameter about 30nm) and its mean particle size is about 100nm. To determine the stability mechanism of ZrO2 suspension in the biopolymer presence, the adsorption and electrokinetic (surface charge density and zeta potential) measurements were performed in the pH range 3–10. The lysozyme adsorption on the nanozirconia surface proceeds mainly through electrostatic forces. Under solid-polymer repulsion conditions, there is no adsorption of lysozyme (pH<6, CNaCl 0.01mol/dm3). The increase of solution ionic strength to 0.2mol/dm3 causes screening of unfavourable forces and biopolymer adsorption becomes possible. The LSZ addition to the ZrO2 suspension influences its stability. At pH 3, 4.6 and 7.6, slight improvement of the system stability was obtained. In turn, at pH 9 considerable destabilization of nanozirconia particles covered by polymeric layers occurs.

周波数変調原子間力顕微鏡を用いた溶液環境下のナノスケール電位・電荷密度計測

Surface charges on nanometer-scale structures in liquids play an essentially important role in various physical, chemical and biochemical phenomena such as ionic adsorptions, microscopic electrode reactions and specific ligand bindings. These molecular-scale interactions are mediated through local electric double layers (EDLs) formed by the counter ions in electrolyte solution. Although static-mode atomic force microscopy (AFM) including colloidal probe AFM is a powerful technique for surface charge density measurements and EDL analysis on a submicron scale in liquids, precise surface charge density analysis with molecular resolution has not been realized because of its limitation of the resolution and the electrical force detection sensitivity. Here recent molecular-scale surface charge measurements of self-assembled micellar structures and biomolecules by three-dimensional (3D) force mapping based on frequency modulation AFM are presented.

Adsorption and electrokinetic properties in the system: Beta-cyclodextrin/alumina in the presence of ionic and non-ionic surfactants

Abstract The influence of some ionic and non-ionic surfactants (CTAB, SDS, TX-100 and TX-405) on the adsorption of β-cyclodextrin (β-CD) at the surface of alumina using the spectrophotometric measurements was determined. The additional information concerning the process of oligosaccharide-surfactant complexation was obtained by the use of the surface tension measurements. The obtained results show that there is no competitive adsorption between the β-cyclodextrin and surfactants but the adsorption of the oligosaccharide-surfactant complexes takes place. β-CD creates the complexes characterized by 2:1 stoichiometry with CTAB and TX-100 whereas these with SDS and TX-405 have 1:1 stoichiometry. The structure of the adsorption layer in the oligosaccharide/surfactant/metal oxide system was determined using the thickness of adsorption layer, the zeta potential and the surface charge density measurements. The lack of information the worldwide literature concerning this subject in together with the ability of β-cyclodextrin possessing chelating properties toward surfactants to modify the alumina surface was the motivations of this study. The obtain results create new possibilities in the fields of functionalized materials especially such as adsorbents, catalysis and drug delivery systems.

Study on the influence of surfactants on the adsorption and electrokinetic properties of the system: Cationic starch/alumina

The aim of this paper was to investigate the influence of some surfactants of different chemical character (SDS, CTAB, TX-100 or their equimolar mixtures) on the adsorption and electrokinetic properties of the cationic starch (CS)/alumina system. The obtained results show that CS creates multilayer complexes with SDS, TX-100 and their mixture, but does not interact with CTAB. The reason for that is connected with chemical character of the polyelectrolyte and the above-mentioned surface active agents. Formation of complexes was confirmed by the surface tension measurements and by the measurements of surfactants adsorption at the alumina surface in the presence and absence of CS. The crucial information about both the electrokinetic properties of the system and the structure of the adsorption layer was obtained from the surface charge density and zeta potential measurements. The obtained data showed the specific structure of the adsorption layer polymer/surfactant/metal oxide. According to the results the polymer is directly bonded to the surface whereas the surfactants are present in the upper parts of the electrical double layer.

Investigation of removal possibilities of chromium(III) oxide from water solution in the presence of albumins

System destabilization is a highly desirable phenomenon during colloidal impurity removal from sewages and wastewaters. Therefore, in this study, the stability of chromium(III) oxide suspension in the absence and presence of albumins [bovine serum albumin (BSA), ovalbumin (OVA), human serum albumin (HSA)] was investigated. Based on the analysis of experimental results, i.e., measurements of adsorption amount, electrokinetic potential, and metal oxide surface charge density as well as system stability, the mechanism of the suspension stabilization/destabilization was proposed. The examined system without the albumins is relatively stable at pH 3, 4.6, and 9 (TSI = 34.8, 36.6, 34.22, respectively), which is associated with the electrostatic stabilization phenomenon. In turn, the least stable is the suspension at pH 7.6 (TSI = 55.43). This is the result of the adsorbent zero surface charge. Regardless of solution pH, the BSA, OVA, or HSA adsorption causes an increase in the system stability (17.55 < TSI < 30). Probably, the steric stabilization is involved in this phenomenon, which results from the mutual repulsion of the adsorption layers formed on the solid surface. Thus, it can be concluded that the albumin presence in the industrial wastewaters impedes the chromium(III) oxide removal.

Molecular-scale investigations of structures and surface charge distribution of surfactant aggregates by three-dimensional force mapping

Surface charges on nanoscale structures in liquids, such as biomolecules and nano-micelles, play an essentially important role in their structural stability as well as their chemical activities. These structures interact with each other through electric double layers (EDLs) formed by the counter ions in electrolyte solution. Although static-mode atomic force microscopy (AFM) including colloidal-probe AFM is a powerful technique for surface charge density measurements and EDL analysis on a submicron scale in liquids, precise surface charge density analysis with single-nanometer resolution has not been made because of its limitation of the resolution and the detection sensitivity. Here we demonstrate molecular-scale surface charge measurements of self-assembled micellar structures, molecular hemicylinders of sodium dodecyl sulfate (SDS), by three-dimensional (3D) force mapping based on frequency modulation AFM. The SDS hemicylindrical structures with a diameter of 4.8 nm on a graphite surface were clearly imaged. We have succeeded in visualizing 3D EDL forces on the SDS hemicylinder surfaces and obtaining the molecular-scale charge density for the first time. The results showed that the surface charge on the trench regions between the hemicylinders was much smaller than that on the hemicylinder tops. The method can be applied to a wide variety of local charge distribution studies, such as spatial charge variation on a single protein molecule.

Determination of the Surface Charge Density and Temperature Dependence of Purple Membrane by Electric Force Microscopy

We report here the measurement of the temperature-dependent surface charge density of purple membrane (PM) by using electrostatic force microscopy (EFM). The surface charge density was measured to be 3.4 × 10(5) e/cm(2) at room temperature and reaches the minimum at around 52 °C. The initial decrease of the surface charge density could be attributed to the reduced dipole alignment because of the thermally induced protein mobility in PM. The increase of charge density at higher temperature could be ascribed to the weakened interaction between proteins and the lipids, which leads to the exposure of the charged amino acids. This work could be a benefit to the direct assessment of the structural stability and electric properties of biological membranes at the nanoscale.

Surface Charge Density Measurements

This paper is devoted to the Kelvin probe technique which is noncontacting method for the quantitative evaluation of an electric field, surface potential, and surface charge distribution. It does not change the physical state of the object under test. Lack of contact with the measured object assures that there is no charge transfer between the meter and the tested surface. This article investigates the uses and limitations of Kelvin probe-based instruments for surface charge density measurements of dielectric materials.

Size and Structure Characterization of Dye Flocs during Coagulation of Reactive Black 5 Dye

AbstractThis paper deals with results from laboratory scale experiments with model dye effluents comprising of the commercially used textile diazo dye, CI “Reactive Black 5”, coagulated with ZETAG type primary coagulants. Size and structure analysis of flocs in coagulated dye sludge was undertaken in order to evaluate their separation abilities. The particle size distribution was estimated by use of a Galai CIS‐100 particle counting system working on a time‐of‐transition principle, while their fractal dimension was obtained from laser scattering instrument in LALS mode. An image analysis of the flocculated dye‐sludge has also been carried out. In parallel to the flocs characterization, the measurement of surface charge density of coagulated dye sludge was performed with the aim of linking surface charge data with the floc characteristics, and on this basis, to outline the predominant mechanism of color removal. It was found that flocs produced at optimal dosage are characterized by large sizes and a high value of fractal dimension, which is manifested in a very good level of color removal by sedimentation. The evident correlation between the surface charge density progression of coagulated dye flocs and color removal, suggests adsorption and charge neutralization as the predominant mechanism of dye destabilization.