Low Zeta Potential Research Articles

Dynamic electrophoretic mobility of a spherical colloidal particle with a hydrodynamically slipping surface in an oscillating electric field

A theory of the dynamic electrophoresis of a spherical colloidal particle with a slip surface in an oscillating electric field is developed. The slipping length on the particle surface, which is the measure of the degree of the particle surface hydrophobicity, is introduced. The general expression of the particle electrophoretic mobility and its approximate analytic expressions for a particle carrying a low zeta potential are derived.

The influence of extracellular polymeric substances on the coagulation process of cyanobacteria

The hydrophobicity and flocculation properties of cyanobacterial cells are closely related to their extracellular polymeric substances (EPS). During the treatment of drinking water, the coagulation and removal of EPS-wrapped cyanobacterial particles from natural water sources is very difficult. In this work, a series of surface characteristics of cyanobacterial cells with different EPS fractions were analyzed to evaluate their influences on the coagulation process. With the removal of EPS, the coagulation efficiency of cyanobacteria was gradually improved. The intracellular microcystin release showed that the cyanobacterial cells in each EPS removal phase were almost intact with few broken cells. The surface of cyanobacterial cells had higher hydrophobicity and lower zeta potentials with each step of the EPS extraction, which improved the ratio of particles that were in an unstable state. Furthermore, the deeper the EPS extraction phase, the larger the decreased in size of cyanobacterial particles, thus increasing their specific surface area for adsorption with coagulant. It was concluded that the coagulation mechanism of EPS-wrapped cyanobacterial particles was: the cyanobacterial cells were first peeled off through attraction by opposite charges from the coagulant, and then they were adsorbed before settling down. This study provides a scientific basis for the removal of cyanobacteria by enhancing coagulation.

Formulation and evaluation of hyaluronic acid-based mucoadhesive self nanoemulsifying drug delivery system (SNEDDS) of tamoxifen for targeting breast cancer

The present study was intended to develop a papain grafted S-protected hyaluronic acid-lithocholic acid co-block (PAP-HA-ss-LCA) polymeric excipient as an amphiphilic muco permeating stabilizer for targeting breast cancer epithelial cells overexpressed with CD44 receptors. The mucopermeating, stabilizing and targeting capability of the PAP-HA-ss-LCA polymeric excipient was investigated by manufacturing tamoxifen (TMX) loaded self-nanoemulsifying drug delivery system (SNEDDS). TMX loaded PAP-HA-ss-LCA incorporated SNEDDS (TMX-PAP-HA-ss-LCA SNEDDS) were characterized for their surface chemistry, drug release, permeation enhancement, biocompatibility and antitumor activity. FTIR spectroscopic analysis showed successful synthesis of PAP-HA-ss-LCA polymer. X-ray diffraction (XRD) showed the amorphous form of TMX inside SNEDDS. The observed hydrodynamic diameter of TMX-PAP-HA-ss-LCA SNEDDS was 367.5 nm. Furthermore, Hyaluronic Acid-based Mucoadhesive Self Nanoemulsifying Drug Delivery System (SNEDDS) of TMX showed homogeneity in synthesis with low polydispersity and negative zeta potential due to stabilization with PAP-HA-ss-LCA polymer. The distinct spherical shape of the nanodroplets was evident by transmission electron microscopy (TEM). In vitro release kinetics indicated approximately >80% release within 48 h under sink conditions. Ex-vivo permeation study displayed 7.11-folds higher permeation of TMX by TMX-PAP-HA-ss-LCA in contrast to pure TMX. The biocompatibility study proved that SNEDDS formulation was safe and compatible against macrophages. In vitro cytotoxicity studies demonstrated that TMX-PAP-HA-ss-LCA SNEDDS could efficiently kill MCF-7 breast cancer cells as compared to the native TMX drug. Systemic toxicity studies proved the non-toxic nature of TMX-PAP-HA-ss-LCA in contrast to pure TMX. Based on these evidences, TMX-PAP-HA-ss-LCA SNEDDS formulation seems to be promising mucopermeating, augmented intracellular uptake with strong targeting potential for anti-proliferative activity.

Numerical study of electroosmotic slip flow of fractional Oldroyd-B fluids at high zeta potentials.

In this paper, an investigation of the electroosmotic flow of fractional Oldroyd-B fluids in a narrow circular tube with high zeta potential is presented. The Navier linear slip law at the walls is considered. The potential field is applied along the walls described by the nonlinear Poisson-Boltzmann equation. It's worth noting here that the linear Debye-Hückel approximation can't be used at the condition of high zeta potential and the exact solution of potential in cylindrical coordinates can't be obtained. Therefore, the Matlab bvp4c solver method and the finite difference method are employed to numerically solve the nonlinear Poisson-Boltzmann equation and the governing equations of the velocity distribution, respectively. To verify the validity of our numerical approach, a comparison has been made with the previous work in the case of low zeta potential and the excellent agreement between the solutions is clear. Then, in view of the obtained numerical solution for the velocity distribution, the numerical solutions of the flow rate and the shear stress are derived. Furthermore, based on numerical analysis, the influence of pertinent parameters on the potential distribution and the generation of flow is presented graphically.

An evaluation of Acacia mearnsii tannin as an aluminum corrosion inhibitor in acid, alkaline, and neutral media

AbstractThe electrochemical behavior of aluminum in tannin from Acacia mearnsii bark was evaluated by potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) in media under three different pH conditions: acid, alkaline, and neutral. A relationship among pH, polymerization grade (PG), zeta potential, surface, and electrochemical properties was observed in the inhibition performance of the tannin. At high pH, the oligomer structure of the tannin was affected, resulting in a low PG (4) and high zeta potential (−75 mV), and consequently, the inhibition efficiency decreased (68%) in comparison with that in acid (99%) and neutral media (96%). The values obtained indicate a physisorption mechanism for the aluminum corrosion inhibition in the studied conditions.

Rapid determination of emulsion stability by rheology-based thermal loop test

This study aimed to determine the stability of oil-in-water emulsions using the thermal loop test as a novel method. Samples with xanthan gum concentrations of 0.1 g, 0.2 g, 0.3 g, 0.4 g or 0.5 g/100 g were subjected to 10 thermal cycles from 5 to 23 °C (low-temperature stability test) and 23–45 °C (high-temperature stability test). In the low-temperature stability test, the relative change of G* for the samples (Δ) was 4.15%, 2.82%, 1.32%, 1.17%, and 4.68%, respectively. In the high-temperature stability test, the Δ values were 7.7%, 0.58%, and 7.22% for samples 3–5, respectively. However, samples 1 and 2 had dramatic changes in G*. This was also confirmed by a visual test, zeta potential measurement, polydispersity index, and particle size distribution. Moreover, a low zeta potential, high polydispersity indexes, and phase separations yielded high Δ values. This study implies that the thermal loop test could be successfully applied to determine the emulsion stability in food emulsions.

Comparative study on the properties of lignin isolated from different pretreated sugarcane bagasse and its inhibitory effects on enzymatic hydrolysis

Five sugarcane bagasse lignin samples, namely, dilute sulfuric acid (DSAL), sodium hydroxide (SHL), ethanol (EL), hot liquid water (HLWL)-pretreated residual solids, and raw material (cellulolytic enzyme lignin, CEL), were extracted. Comparative studies on the physicochemical properties of isolated lignin, nonproductive adsorption of cellulase by lignin, and its effect on enzymatic hydrolysis was performed. Results showed that the molecular weight and homogeneity of lignin remarkably decreased after pretreatment compared with CEL. Lignin with low negative zeta potential, high phenolic hydroxyl group content and hydrophobicity exhibited strong nonproductive adsorption performance to cellulase. This phenomenon was positively correlated with it's inhibitory effect on enzymatic hydrolysis. Compared with the control (without lignin), the Avicel conversion rate (40 mg lignin/200 mg Avicel) decreased by 10.74%, 9.28%, 8.73%, 4.22%, and 2.80% after digestion of Avicel for 72 h with the presence of EL, SHL, CEL, HLWL, and DSAL, respectively.

Electrokinetic properties of chemically modified jute fabrics

In this work, the electrokinetic properties of alkali and oxidatively modified jute fabrics were studied. In contrast to the control fabric, chemically modified jute fabrics had a small positive zeta potential in the basic pH range, which could be attributed to the presence of sodium cations (originating from the undertaken chemical modifications) on their surfaces. At lower pH values, the samples modified under milder alkali and oxidative conditions had about 2.2?3.5 times lower zeta potential since the protonation process led to the formation of a higher positive charge in the electrochemical double layer, causing higher adsorption of Cl- (originating from the electrolyte). On the other hand, more intensive chemical modifications increased the zeta potential at lower pH values due to the increased amount of carboxyl groups and the ability of the fibres for water retention and hence swelling. The isoelectric point of the fabrics, having lower zeta potentials than that of the control fabric, was shifted towards higher pH values, indicating to a lower contribution of surface acidic groups of the fabrics. In the case of extensive oxidation conditions (60 and 90 min), the isoelectric point was shifted toward lower pH values because of lignin removal and the mentioned higher availability of newly formed carboxyl groups.

Titanium dioxide nanotubes incorporated into bleaching agents: physicochemical characterization and enamel color change.

Titanium dioxide nanotubes are nanostructures that can accelerate the oxidation reaction of bleaching procedures and promote a more effective whitening effect. Objective This study evaluated physicochemical properties of bleaching agents incorporated with titanium dioxide (TiO2) nanotubes, and the effects on tooth color change at different periods.Methodology 40 premolars were treated according to the following groups (n=10): CP - 10% carbamide peroxide (1 hour daily/21 days); CPN - CP incorporated into TiO2; HP - 40% hydrogen peroxide (three 40-minute sessions/7 days apart); HPN - HP incorporated into TiO2. Color shade was evaluated at five different periods (baseline, after 7, 14 and 21 days of bleaching, and 7 days after end of treatment) according to Vita Classical, CIELab and CIEDE2000 scales. Mean particle size (P), polydispersity (PO) and zeta potential (ZP) were evaluated using dynamic light scattering. Data on the different variables were analyzed by mixed model tests for measures repeated in time (ZP e L*), generalized linear models for measures repeated in time (P, PO, Vita Classical and b*), and Friedman and Mann-Whitney tests (a* and color change/ΔE and ΔE00).Results CP and CPN presented higher P, higher PO and lower ZP than HP and HPN (p≤0.05). All groups showed a significant decrease in Vita Classical color scores after 7 days of bleaching (p<0.05), and HPN presented a greater significant reduction than the other groups. L* increased in TiO2 presence, in all groups, without any differences (p>0.05) in bleaching time. A significant reduction occurred in the a* and b* values for all the groups, and HPN presented lower a* and b* values (p<0.05) than CPN. ΔE was clinically noticeable after 7 days, in all groups, and all groups resulted in a perceptible color change according to ΔE00.Conclusion TiO2 did not influence physicochemical properties of the bleaching agents. HPN presented more effective tooth bleaching than CPN.

A highly stable hydroxylated graphene/ethylene glycol-water nanofluid with excellent extinction property at a low loading for direct absorption solar collectors

In order to explore a graphene-containing nanofluid with good dispersion stability as the working fluid for a low-temperature direct absorption solar collector (DASC), firstly, two kinds of functionalized graphene, hydroxylated graphene (GOH) and carboxylated graphene (GCOOH), were dispersed into a mixture of ethylene glycol (EG) and water (1:1 mass ratio), at the same loadings. It is found that, although the obtained GOH nanofluid exhibits a slight lower zeta potential than the GCOOH one, its optical absorption property is obviously higher. Consequently, GOH was employed to prepare the EG-water based nanofluids at different loadings, followed by the investigations on their optical absorption and thermophysical properties, photo-thermal conversion performance, and dispersion stability. It is shown that, at a loading as low as 0.007 wt%, the transmittance of the corresponding GOH/water-EG nanofluid is reduced to zero, and its extinction coefficient is 100 times higher than that of the base fluid. Under the illumination of 1000 W/m2, the 0.007 wt% GOH/EG-water nanofluid can reach a high final temperature of 55 °C. More significantly, the zeta potential of the 0.007 wt% GOH/EG-water nanofluid increases with temperature and reaches 47.63 mV at 60 ℃, suggesting its good dispersion stability at the elevated temperatures. These good characteristics of the GOH/EG-water nanofluid make it a very promising working fluid for a low temperature DASC.

Propensity of gypsum precipitation using surface energy approach

In-depth knowledge of the mechanisms underlying the precipitation, and deposition of precursors would help to rigorously scale formation. This, in turn, is closely associated with the solid/fluid interfacial interactions. In this study, the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, rather than total surface energy, is sought to investigate the precipitation phenomenon for an aqueous solution containing gypsum. To do so, intermolecular interaction energies are evaluated for two identical gypsum particles immersed in brine where the gypsum surface energy and its components play a pivotal role. The resultant findings show that Lewis acid-base and Lifshitz-van der Waals interactions referred to as the grouped determinative interaction (GDI) would project whether precipitation takes place or not. Even though the electrostatic double layer interaction is one to three orders of magnitude lower than the last two, especially at lower zeta potentials as well as at smaller Debye-Hückel lengths, nonetheless it gains significance as the brine salinity decreases. Finally, the precipitation of gypsum particles from an aqueous solution would increase when the two gypsum particles (precursor particles) having Lewis base polarity less than unity, are located at distances below 7 nm.

Surface and colloid properties of biochar and implications for transport in porous media

Biochar contains a large amount of colloidal particles. Biochar colloids are generated (1) during pyrolysis of the feedstock, where some of the biochar formed is in the colloidal size fraction, and (2) by the breakdown of larger biochar particles. Here, we review the surface and colloid properties of biochar and the implications for transport of biochar colloids in porous media. We discuss the origin of biochar colloids and their physical and chemical properties relation to feedstock and pyrolysis temperature. We then review the transport of colloidal biochar in sand columns and soils and relate the transport behavior to surface characteristics. We finally examine the effects of aging, i.e., natural and simulated environmental weathering, on the surface properties of biochar colloids. Biochar colloids tend to have lower zeta potential and lower aromaticity than the bulk biochar. Due to their smaller size, biochar colloids are more stable in aquatic environments and more mobile in the subsurface than the parent biochar particles. Like the parent biochar material, pristine biochar colloids contain a variety of hydrophobic functional groups (e.g., alkyl, aromatic), and become more hydrophilic as the biochar ages. At environmentally relevant pH, biochar colloids are negatively charged.

Electrophoretic mobility of a cylindrical colloidal particle with a slip surface

General expressions of the electrophoretic mobility-zeta potential relationship for a cylindrical colloidal particle with a hydrodynamically slipping surface in an aqueous electrolyte solution under a transverse or tangential electric field are obtained on the basis of the Navier boundary condition. Approximate expressions for the electrophoretic mobility of cylindrical particles carrying a low zeta potential are derived. As in the case of a sphere, the electrophoretic mobility of a cylinder increases with increasing slip length, which characterizes the hydrophobicity of the particle surface.

Immunomodulating action of the 3-phenylcoumarin derivative 6,7-dihydroxy-3-[3',4'-methylenedioxyphenyl]-coumarin in neutrophils from patients with rheumatoid arthritis and in rats with acute joint inflammation.

To examine whether free (3-PD-5free) and/or liposomal (3-PD-5lipo) 6,7-dihydroxy-3-[3',4'-methylenedioxyphenyl]-coumarin (3-PD-5) (1) modulate the effector functions of neutrophils from patients with rheumatoid arthritis under remission (i-RA) and with active disease (a-RA), in vitro; and (2) exert anti-inflammatory effect in a rat model of zymosan-induced acute joint inflammation. Incorporation of 3-PD-5 into unilamellar liposomes of soya phosphatidylcholine and cholesterol was efficient (57.5 ± 7.9%) and yielded vesicles with low diameter (133.7 ± 18.4nm), polydispersity index (0.39 ± 0.06), and zeta potential (- 1.22 ± 0.34mV). 3-PD-5free (1µM) and 3-PD-5lipo (3µM) equally suppressed elastase release and reactive oxygen species generation in neutrophils from healthy subjects and i-RA and a-RA patients, stimulated with immune complexes. 3-PD-5free (20µM) suppressed the release of neutrophil extracellular traps and chemotaxis in vitro, without clear signs of cytotoxicity. 3-PD-5lipo (1.5mg/kg, i.p.) diminished joint edema and synovial infiltration of total leukocytes and neutrophils, without changing the synovial levels of TNF-α, IL-1β, and IL-6. Altogether, the results reported herein indicate that 3-PD-5 is a promising modulator of the early stages of acute joint inflammation that can help to diminish not only excessive neutrophil infiltration in the synovia but also neutrophil activation and its outcomes in RA patients.

Development of amphotericin B-loaded propionate Sterculia striata polysaccharide nanocarrier

This work was aimed at the production and characterization of a new nanocarrier based on a Sterculia striata polysaccharide (SSP) modified via acylation reaction with propionic anhydride. Nanocapsules of propionated SSP (PSSP) were produced via spontaneous nanoemulsification process and tested as a potential amphotericin B (AMB) nanocarrier. Stable nanoparticles with a very low polydispersity index (0.08–0.29) and high zeta potential (ζ −42.7 to −53.8 mV) were obtained. Particle size was dependent on the degree of substitution and ranged from 205 to 286 nm. A nanocapsule with a degree of substitution (DS) of 2.53 (NCP 2.53) was selected for encapsulation, biocompatibility, and antifungal evaluation against Candida albicans strains. A maximum of 98.3% AMB encapsulation was achieved. Encapsulated AMB was in its monomeric form and showed good biocompatibility and antifungal activity against four C. albicans strains. Data indicate that PSSP has potential as a nanocarrier system for AMB.

Material-selective separation of mixed microparticles via insulator-based dielectrophoresis.

Insulator-based dielectrophoresis (iDEP) has become a powerful tool for biomicrofluidic separation and analysis because it is capable to selectively separate biological particle systems according to properties like size, material, and shape. However, it has rarely been used to solve challenging separation problems involving nonbiological particles, namely, for systems that are prone to particle agglomeration. Here, we demonstrate material-selective separation of nonbiological systems, i.e., polystyrene and gold-coated polystyrene particles of two different sizes, using iDEP at high accuracy. For this purpose, we present a method to generate fluorescent gold-coated particles. We further introduce a method to reduce the static backpressure that builds up between in- and outlet reservoir due to electroosmotic flow. Moreover, we found that particle agglomeration makes their separation impossible when conventional iDEP routines are applied. Therefore, two solutions to reduce particle agglomeration are presented: A combination of AC and DC potentials and adjustment of pH and conductivity of the suspending medium. Both approaches allow separating particles under challenging conditions such as initially low absolute particle zeta potentials and high particle concentrations. Since those conditions can also be present in biological iDEP separation processes, the results are of general value for biological and nonbiological iDEP operations.

Analysis of entropy generation in biomimetic electroosmotic nanofluid pumping through a curved channel with joule dissipation

Biomimetic designs are increasingly filtering into new areas of technology in recent years. Such systems exploit characteristics intrinsic to nature to achieve enhanced adaptivity and efficiency in engineering applications. Peristaltic propulsion is an example of such characteristics and in the current article it is explored as a feasible mechanism for deployment in electrokinetic pumping of nanofluids through a curved distensible conduit as a model for a bioinspired smart device. The unsteady mass, momentum, energy and nanoparticle concentration conservation equations for a Newtonian aqueous ionic fluid under an axial electrical field are formulated and simplified using lubrication approximations and low zeta potential (Debye Hückel linearization). A dilute nanofluid is assumed with Brownian motion and thermophoretic body forces present. The reduced non-dimensional conservation equations are solved with the symbolic software, Mathematica 9 via the NDSolve algorithm for velocity, temperature, nano-particle concentration distributions for low zeta potential. An entropy generation analysis is also conducted. The influence of curvature parameter, maximum electroosmotic velocity (Helmholtz-Smoluchowski velocity), inverse EDL thickness parameter, zeta potential ratio and Joule heating parameter on transport characteristics is evaluated with the aid of graphs and contour plots. Temperature profiles are elevated with positive Joule heating and reduced with negative Joule heating whereas the opposite behaviour is observed for the nano-particle concentrations.

Tuning with Phosphorylcholine Grafts Improves the Physicochemical Properties of PLL/pDNA Nanoparticles at Neutral pH

The improvement of biological properties of polycations is a fundamental step to overcome their limitations as non-viral gene carriers. This work studied the effect of phosphorylcholine (PC) groups on the physicochemical properties of poly(L-lysine) (PLL)/pDNA nanoparticles. Phosphorylcholine-grafted PLL derivatives (PLL-PC) containing increasing proportions of PC were obtained by the reductive amination reaction with phosphoryl glyceraldehyde and characterized by 1H NMR, FTIR, and GPC measurements. The PLL-PC derivatives were used to prepare polyplexes with pDNA and their properties were evaluated by fluorescence, gel electrophoresis and dynamic light scattering (DLS) measurements. The PLL-PC derivatives were able to interact with pDNA at low N/P ratios in physiological pH to form stable polyplexes having lower zeta potentials, as evidenced by the gel electrophoresis and zeta potentials measurements. A degree of grafting of 10% increased the in vitro transfection efficiency of PLL and a degree of 20 mol% of PC groups provided colloidal stability in physiological saline solution at neutral pH. Overall, the PC-PLL derivatives exhibited improved physicochemical properties and have significant potential for further studies as non-viral gene transfer agents.

Characterization of Self-Microemulsifying Dosage Form: Special Emphasis on Zeta Potential Measurement

The emulsion is a disperse system which is thermodynamically unstable. To improve the stability of the disperse system microemulsion or nanoemulsion was prepared to improve thermodynamic stability. Zeta potential is a physical property which is exhibited by any particle in suspension/emulsion, i.e., in colloidal dispersion. It can be used to optimize the formulations of suspensions and emulsions. Zeta potential is the measure of overall charges acquired by particles in a particular medium and is considered as one of the benchmarks of stability of the colloidal system. As a rule of thumb, suspensions/dispersed system with zeta potential above 30 mV (absolute value) are physically stable. Suspensions with a potential above 60 mV show excellent stability. Suspensions below 20 mV are of limited stability; below 5 mV they undergo pronounced aggregation if the system is stabilized by the electrostatic mechanism. If the values are low for visually stable emulsions, it could be attributed to steric repulsion between approaching molecules, i.e., system is sterically stabilized. Such sterically stabilized colloidal systems though they have low zeta potential values are found to be stable during storage. Tween is well accepted steric stabilizer for colloidal systems. Stability of such a visually stable emulsion or microemulsions should be carried out under accelerated or long-term stability conditions to confirm the globule size and zeta potential on aging.

Lignin prepared from different alkaline pretreated sugarcane bagasse and its effect on enzymatic hydrolysis

Sugarcane bagasse (SCB) was pretreated by sodium hydroxide (SH), alkaline ethanol (AE) and alkaline hydrogen peroxide (AHP), and the solid residue with similar lignin content after different pretreatment was selected. Enzymatic saccharification with different substrates was performed at 2%, 10%, and 20% (w/v) solid loading. After that, the lignin from different substrate was extracted and its structure was characterized. Furthermore, the adsorption capability of isolated lignin to cellulase and its effect on enzymatic hydrolysis were studied. The results showed that, as the substrate content increased from 2% (w/v) to 20% (w/v), the glucose yield after digestion of SH, AE, and AHP pretreated SCB reduced by 41.8%, 35.4%, and 28.7%, respectively. The inhibitory effect of different prepared lignin on the digestibility of Avicel was as follows, SH pretreated lignin (SHL) > cellulase enzymatic hydrolysis lignin (CEL) > AE pretreated lignin (AEL) > AHP pretreated lignin (AHPL), which exhibited positive correlation with its non-productive adsorption capability to cellulase. Lignin samples with low negative zeta potential, high hydrophobicity and high ration of syringyl (S) to guaiacyl (G) were unfavorable for the enzymatic saccharification of cellulose.