Zeta Potential Distribution Research Articles

Fluorescence imaging technique of surface electrostatic potential using evanescent wave illumination

The electrostatic potential at a solid-liquid interface (i.e., the zeta potential) is a dominant factor in electric adsorption and microchannel flows. This study proposes a fluorescence-based technique for obtaining color image of modified surface and directly measuring zeta potential. The evanescent wave is used as an excitation light for anions and cations that emit fluorescence at two different wavelengths. Patterns of self-assembled monolayers in a closed microchannel were visualized and their zeta potential distributions were measured. This technique will contribute to development of technical applications in the fields of microfluidics and material science.

Behaviour of a starch as a viscosity modifier for aerial lime-based mortars

Different dosages of a commercialized potato starch were added to aerial lime-based mortars in order to check its efficiency as a rheological modifier. Several fresh state properties of the mortars were studied: consistency, density, air content, water retention capacity, setting time and evolution when applied on support. The effect of the starch on ζ-potential of the lime particle surface as well as the particle size distribution and viscosity changes in lime pastes were also assessed in order to elucidate the action mechanism of the polymer. The behaviour of this starch polymer was found to be strongly dosage-dependent: it acted as a thickener when the incorporated dosage was up to 0.30% of lime weight; conversely, above that dosage, it behaved as a plasticizer. The thickening effect took place because polymer molecules were adsorbed onto lime particles acting as a flocculant, as confirmed by zeta-potential and particle size distribution results. For large amounts of polymer, steric hindrance and electrostatic repulsive forces appeared, leading to a dispersion mechanism which explained the plasticizing effect as well as the fresh mortar behaviour.

Folate receptor mediated intracellular gene delivery using the charge changing solid lipid nanoparticles

Compared to viral carriers, non-viral gene delivery systems showed good biocompatibility and safety, but low transfection efficiencies. Fortunately, the mechanism of folic acid uptake by cells to promote targeting and internalization could improve transfection rates. In this study, folate-chitosan and one kind of cholesterol derivatives CHETA (Cholest-5-en-3β-yl[2-[[4-[(carboxymethyl)dithio]-1-iminobutyl]amino]ethyl] carbamate, C36H61N3O4S2) were synthesized to prepare the charge changing Solid Lipid Nanoparticles (Folate-chitosan−CHETA−Sln) by a reverse micelle-double emulsion method. The resulted particles showed the distributions of size and zeta potential were 254.5 ± 20 nm and −40.5 ± 0.8 mV, respectively. The image observed by scanning electron microscopy (SEM) showed that Folate-chitosan−CHETA−Sln was spherical in shape. Moreover, after reaction with a disulfide reducing agent dithiothreitol (DTT), the zeta potential changed from negative to positive (20.5 ± 1.9 mV). The results of transfection showed that Folate-chitosan–CHETA−Sln enhanced the reporter gene expression against a folate receptor over-expressing cell line (SKOV3 cells) compared to a folate receptor deficient cell line (A549 cells) and did not induce obvious cytotoxicity against HEK 293 cells. In addition, the presence of serum did not affect the transfectivity of Folate-chitosan−CHETA−Sln complexes. In conclusion, Folate-chitosan−CHETA−Slns with proper physical characteristics and high transfection efficiency might act as a novel non-viral gene delivery system.

Calibration-free concentration determination of charged colloidal nanoparticles and determination of effective charges by capillary isotachophoresis

Although colloidal nanoparticles show an electrophoretic heterogeneity under the conditions of capillary electrophoresis, which can be either due to the particle-size distribution and/or the particle shape distribution and/or the zeta-potential distribution, they can form correct isotachophoretic zones with sharp-moving boundaries. Therefore, the technique of isotachophoresis permits to generate plugs in which the co-ions and counter ions of the original colloidal solution are removed and replaced by the buffering counter ions of the leading electrolyte. It is shown that analytical isotachophoresis can be used to measure directly, without calibration, the molar (particle) concentration of dispersed ionic colloids provided that the transference number and the mean effective charge number of the particles (within the isotachophoretic zone) can be determined with adequate accuracy. The method can also be used to measure directly the effective charge number of biomacromolecules or colloidal particles, if solutions with known molar (particle) concentration can be prepared. The validity of the approach was confirmed for a model solution containing a known molar concentration of bovine serum albumin.

Electrophoresis of a Cylindrical Particle with a Nonuniform Zeta Potential Distribution Parallel to a Charged Plane Wall

An analytical study is presented for the steady, transverse electrophoretic motion of a circular cylindrical particle with an arbitrary angular distribution of its surface potential parallel to a plane wall prescribed with the potential distribution consistent with the applied electric field. The electric double layers adjacent to the solid surfaces are assumed to be very thin with respect to the particle radius and spacing between the surfaces. The two-dimensional electrostatic and hydrodynamic governing equations are solved using cylindrical bipolar coordinates, and the typical electric field line, equipotential line, and streamline patterns are exhibited. The explicit formulas for the electrophoretic and angular velocities of the particle are obtained with the contribution from the electroosmotic flow produced by the interaction between the applied electric field and the thin double layer adjacent to the plane wall. To apply these formulas, one only has to calculate the leading multipole moments of the...

Characterisation of titanium tetrachloride and titanium sulfate flocculation in wastewater treatment

Flocculation with titanium tetrachloride (TiCl(4)) and titanium sulfate (Ti(SO(4))(2)) was investigated in terms of different coagulant doses, pH, turbidity, dissolved organic carbon (DOC), UV-254, colour, zeta potential, particle size and molecular weight distribution. The two coagulants were compared with the commonly used coagulants such as ferric chloride (FeCl(3)) and aluminium sulfate (Al(2)(SO(4))(3)). Titanium tetrachloride showed the highest turbidity removal, while titanium sulfate showed the highest reduction of UV-254 and colour at all pH values. The four coagulants were found to have similar organic removal up to 60-67% and resulted in similar organic removal in terms of various MW ranges. The decantability of the settled flocs was very high for titanium tetrachloride, titanium sulfate and ferric chloride compared with aluminium sulfate. The dominating coagulation mechanisms for titanium tetrachloride and titanium sulfate are still to be studied, since different precipitation reactions might take place at different pH even without flocculant addition. Titanium tetrachloride and titanium sulfate were found as effective new coagulants in wastewater treatment not only in terms of organic matter removal, but also in sludge reduction through the production of titanium dioxide.

Effect of nonionic and ionic surfactants on zeta potential and dispersion properties of carbon black powders

Dispersion of carbon black powders in aqueous medium was investigated by using anionic surfactant sodium oleate and a series of nonionic surfactants which were selected systematically to represent varying degrees of ethoxylation. Single and binary mixtures of the nonionic and ionic surfactants were employed in zeta potential and particle size measurements and a high affinity of surfactants on carbon black powders was beheld as they significantly changed the zeta potential and size distribution of the powders. But, noticeable differences between the surfactants were also observed, for example, as the nonionic surfactants reduced the absolute magnitude of zeta potential of powders in a wide pH range of 3.0–11.0, Na oleate made the zeta potential of the powders more negative under similar experimental conditions. The carbon black suspensions were agitated in a vessel having a standard geometry and the particle size measurements were carried out at desired time intervals without disturbance of the suspensions and interruption of agitation. Effect of surfactants on stability and dispersion of the powders were recognized with the reduction in mean particle sizes, as, in the absence of surfactant, the mean particle size could not be reduced below 24.0 μm even after 210 min of stirring, it could be reduced to 5.35 μm after 120 min of stirring in the presence of only 30 g/L of nonionic surfactant. Generally, it was found that nonionic surfactants could wet and stabilize carbon black powders in aqueous medium better than anionic surfactant. The reason was explained by molecular structure and bulk properties of surfactants.

Membrane characterizations for mitigation of organic fouling during desalination and wastewater reclamation

Measurements of contact angle, zeta potential, and pore size distribution for clean, cationic surfactant coated, and organic fouled membranes, were conducted to obtain membranes properties, from perspectives of organic fouling mitigation. Interaction between natural organic matter (NOM) and the membrane surface was investigated using contact angle measurements, with the results being attempted to be used for mitigation of NOM fouling. Several different membranes, one nanofiltration (NF; NE70), one ultrafiltration (UF; GM), and three reverse osmosis (RO; SR, BE, FRM3) membranes, were tested. With NOM fouled membranes, contact angles obtained from the sessile drop method increased compared to corresponding clean membranes. For cationic surfactant coated membranes, contact angles measured with NaCl and sea salts solutions were substantially lower than those measured with deionized pure water, implying the cationic surfactant modification can have a potential to reduce hydrophobic organic fouling during desalination or relatively high salts containing wastewater reclamation processes. For NOM fouled membranes, contact angle increases and the surface charge increases negatively compared to corresponding clean membranes; the membrane surface exhibits greater hydrophobicity and less negative charge, which is supported by the FTIR spectrum measurements.

Fabrication of a silica ceramic membrane using the aerosol flame deposition method for pretreatment focusing on particle control during desalination

A silica membrane was fabricated using the aerosol flame deposition (AFD) method under different sintering temperatures. It was characterized, in terms of roughness, pure water permeability, contact angle, zeta potential, and effective pore size distribution. Membrane performance was evaluated with respect to removal of Suwannee River humic acids and polystyrene particles with different sizes. Both membrane thickness and pure water permeability decreased with increasing sintering temperature. The effective pore sizes of synthesized membranes ranged from 6.5 to 8.0 µm. Polystyrene particles with sizes higher than 7 μm were almost completely removed by the synthesized ceramic membranes; however, no removal for humic acids was measured with the ceramic membranes tested.

The fundamentals of nano- and submicro-scaled ceramic particles incorporation into electrodeposited nickel layers: Zeta potential measurements

Nano- and submicro-scaled ZrO 2 particles were codeposited into Ni matrix by an electrochemical plating process using a Watts bath. The incorporation has been studied in relation to dispersion stability. The ZrO 2 particles were characterized through zeta potential electro-acoustic measurements and particle size distribution. SEM and EDX analysis of the codeposited layers were performed to characterise the coating morphology and to determine the particle concentration in the layer. A content up to 10 vol.% of ZrO 2 was found in Ni matrix. As electrostatic repulsion within the dispersion increases, particle agglomeration slows down and the concentration of non-agglomerated particles rises resulting in an enhanced amount of particles incorporated in the electroplated Ni layers. The effect of electrophoresis and diffusion on particle transport to the cathode is discussed.

Self-assembled honokiol-loaded micelles based on poly(ɛ-caprolactone)-poly(ethylene glycol)-poly(ɛ-caprolactone) copolymer

Self-assembled polymeric micelles are widely applied in drug delivery system (DDS). In this study, honokiol (HK) loaded micelles were prepared from biodegradable poly(ɛ-caprolactone)-poly(ethylene glycol)-poly(ɛ-caprolactone) (PCEC) copolymers. Micelles were prepared by self-assembly of triblock copolymer PCEC in distilled water triggered by its amphiphilic character without any organic solvent. Drug loading and encapsulation efficiency were determined by adjusting the weight ratio of HK and PCEC. The particle size and zeta potential distribution of obtained micelles were determined using Malvern laser particle sizer, and spherical geometry were observed on atomic force microscope (AFM). Otherwise, the thermo-sensitivity of honokiol-loaded micelles was monitored. And the cytotoxicity results of drug loaded micelles showed that the encapsulated honokiol remained potent antitumor effect. Moreover, in vitro release profile demonstrated a significant difference between rapid release of free honokiol and much slower and sustained release of HK-loaded micelles. These results suggested that we have successfully prepared honokiol-loaded micelles in an improved method which is safer and more efficient. The prepared micelles might be potential carriers for honokiol delivery in cancer chemotherapy.

Chaotic mixing in a microchannel utilizing periodically switching electro-osmotic recirculating rolls

In this study, active mixing in a microchannel with spatiotemporal variations in zeta potential distributions was investigated theoretically. In this mixing system, the primary flow is a pressure-driven flow (i.e., parabolic flow), and the electro-osmotic recirculating rolls induced by the heterogeneous zeta potential distributions act as the perturbation source. By timewise alterations of two different electro-osmotic recirculating flow fields, chaotic mixing can be induced. Blob deformation, Poincaré map, and Lyapunov exponent analyses were employed to describe the behaviors of the particle motion in this active mixing system. Finally, the optimal time-switching period was identified, which was also verified through direct numerical simulations.

Optimization of zeta potential distributions for minimal dispersion in an electroosmotic microchannel

Optimization of the zeta potential distributions at the walls for minimal dispersion in an electroosmotic microchannel is performed based on the variational approach. In the present problem, the governing equations are the steady flow equations and the unsteady mass transport equation. Based on the calculus of variations and the method of Lagrange multiplier, the Euler–Lagrange equations are derived in the form of coupled partial differential equations. The coupled equations of the state variables and the adjoint variables are solved by the FDM method iteratively. The original and adjoint flow equations are reformulated using the streamfunction-vorticity method to eliminate the pressure and the adjoint pressure in the equations. It is found that the dispersion can be reduced drastically by controlling the zeta potentials at the channel walls in an optimal way. The results of the optimal solutions are expected to provide an insight for the design of zeta potential control systems. The methodology used in this work may find various applications in the area of the micro-total-analysis-system (μTAS).

Micromixing using induced-charge electrokinetic flow

The mixing effect of induced-charge electrokinetic flow (ICEKF) in a rectangular microchannel with embedded conducting hurdles is investigated in this paper. A correction method is suggested to estimate numerically the induced zeta potential on the conducting surface. Two-dimensional pressure-linked Navier–Stokes equation is used to model the flow field in the channel. The numerical results show flow circulations generated from the induced non-uniform zeta potential distribution along the conducting hurdle surfaces. It is demonstrated that the local flow circulations provide effective means to enhance the flow mixing between different solutions. The mixing enhancement effect is experimentally validated using PDMS based microchannels with embedded platinum hurdles. The dependence of the degree of mixing enhancement on the hurdle geometries and hurdle numbers is also predicted. The mixing using ICEKF described in this paper can be used in various microfluidics and lab-on-a-chip applications.

Influence of Surface Charge Distributions and Particle Size Distributions on Particle Attachment in Granular Media Filtration

Filtration experiments were performed with a laboratory-scale filter using spherical glass beads with 0.55 mm diameter as collectors. Suspensions were made with Min-U-Sil 5 particles, and two different methods (pH control and polymer dosing) were used for destabilization. In the pH control experiments, all particles had negative surface charge, and those with lower (absolute value) charge were selectively attached to the collectors, especially during the early stage of filtration. This selective attachment of the lower charged particles caused the zeta potential distribution (ZPD) of the effluent to move to a more negative range. However, the ZPD of the effluent did not continue moving to more negative values during the later stages of filtration, and this result was attributed to two reasons: ripening effects and detachment of flocs. In the polymer experiments, substantial differences were found between experiments performed with negatively charged particles (underdosing) and those with positively charged particles (overdosing). With under-dosing, the results were similar to the pH control experiments (which also had negatively charged particles), but with overdosing, the effluent's ZPDs in the early stages did not overlap with those of the influent and more highly charged particles were removed more efficiently than lesser-charged particles. It is hypothesized that, despite a substantial period of pre-equilibration of media and coagulant, this equilibrium shifted when particles were also added. It was assumed that coagulant molecules previously adsorbed to the particles desorbed and subsequently attached to the filter media because of surface area differences in the particle and filter media.

Characterization of kaolin dispersion using acoustic and electroacoustic spectroscopy

The objective of this work is the investigation of the kaolin dispersion by the ultrasonic techniques. In contact with aqueous solution clay minerals show cation - exchange properties and certain degree of dissolution or rather selective leaching of components. The work is divided into two main parts - determination of zeta potential and particle size distribution. The first part is focused on measuring of zeta potential. Effects of concentration of solid, different kind of electrolytes (0.01 M KCl, 0.01 M MgCl2 and 0.01 M CaCl2), pH and temperature of the dispersions are investigated. The isoelectric points (IEP) of kaolin suspension are about pH 4-5. Electrolytes containing monovalent cations such as K+ become zeta potential more negative compared to the values obtained with water. Such behavior is explained by the exchange of K+ ions with H+ ions in the system. When the electrolyte is formed by divalent cations such as Mg2+ or Ca2+, the values of zeta potential become less negative than zeta potential of kaolin in water. The second part is focused on the determination of particle size distribution with respect to dispersing conditions, such as the optimal dispersing agent (Na2SiO3, (NaPO3)6, Na4P2O7 or Busperse), time and power of ultrasonication and also the tracking of dispersion stability that is expressed by the measuring of particle size distribution during certain time period.

Dispersion-Flocculation Behavior of Fine Lead Particles in an Organic Solvent

Methyl ethyl ketone (MEK) is a good solvent for polyvinyl chloride (PVC) and it has been proposed for use in PVC recycling. In the recycling process, fine particles of 3PbO·PbSO 4 ·H 2 O, used as a thermal stabilizer in PVC products, are dispersed and not dissolved in the solvent. To establish methods for removing of 3PbO·PbSO 4 ·H 2 O particles from the solvent, factors affecting the dispersion-flocculation behavior of the particles in MEK were investigated. The zeta potential and particle distribution of 3PbO·PbSO 4 ·H 2 O particles in MEK solutions containing known amounts of H 2 O were measured. Above 5 vol%H 2 O in MEK solutions, the zeta potential of 3PbO·PbSO 4 ·H 2 O particles approached zero and the flocculation of particles was achieved. In addition, it was found that Pb 2+ and Cl - affect the zeta potential of the particles. These results indicate that the dispersion-flocculation behavior of lead particles can be influenced by the concentration of H 2 O, Pb 2+ , and Cl - in MEK.

Electrophoresis of a Colloidal Sphere in a Spherical Cavity with Arbitrary Zeta Potential Distributions and Arbitrary Double-Layer Thickness

The electrophoretic motion of a dielectric sphere situated at the center of a spherical cavity with an arbitrary thickness of the electric double layers adjacent to the particle and cavity surfaces is analyzed at the quasisteady state when the zeta potentials associated with the solid surfaces are arbitrarily nonuniform. Through the use of the multipole expansions of the zeta potentials and the linearized Poisson-Boltzmann equation, the equilibrium double-layer potential distribution and its perturbation caused by the applied electric field are separately solved. The modified Stokes equations governing the fluid velocity field are dealt with using a generalized reciprocal theorem, and explicit formulas for the electrophoretic and angular velocities of the particle valid for all values of the particle-to-cavity size ratio are obtained. To apply these formulas, one only has to calculate the monopole, dipole, and quadrupole moments of the zeta potential distributions at the particle and cavity surfaces. In some limiting cases, our result reduces to the analytical solutions available in the literature. In general, the boundary effect on the electrophoretic motion of the particle is a qualitatively and quantitatively sensible function of the thickness of the electric double layers relative to the radius of the cavity.

Effects of CMP Slurry Chemistry on Agglomeration of Alumina and Copper Surface Hardness

The influence of common slurry additives on the colloidal behavior of alumina suspensions and the surface characteristics of copper were investigated. The effects of the addition of glycine and H2O2 to aqueous suspensions of alpha-alumina at various pH values were studied by zeta potential and agglomerate size distribution measurements. Depending on the state of copper in solution, alumina agglomerate size was found to either increase or decrease. Nanohardness of 1 µm copper films deposited onto 30 nm Ta on a silicon wafer was measured after exposure to the same slurry solutions and was found to be significantly affected by pH and addition of chemical additives. The agglomeration behavior and hardness measurements suggest that the states of the copper in solution or on the surface are consistent with potential-pH diagrams.

Investigation of multimodal zeta potential and size distribution in chemical pulp process water

Multimodal zeta potential distribution in chemical birch pulp process water was studied by filtrating the water into fractions and subsequently measuring zeta potential, charge quantity, turbidity and organic substances. Filtrations were made using 12 microm, 1.6 microm, 1.2 microm, 0.45 microm and 0.1 microm membranes. The number of populations with different zeta potentials diminished with filtration. With the unfiltrated water, 12 microm and 1.6 microm filtrates, three or four different zeta potentials were observed. When the filtration was performed with a 1.2 microm membrane or smaller, only two populations of different zeta potentials were detected. The charge quantity steadily approached zero from unfiltrated water towards a 1.6 microm fraction filtrate. After that, it remained constant. Turbidity constantly decreased when using smaller membranes. The amount of wood extractives decreased to half with 0.1 microm filtration. No significant difference in the amount of carbohydrates and lignin between the filtrated fractions and the unfiltrated water was detected. A comparison dealing with particle size analysis between two different apparatuses was also made.