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Electronic paper displays rely on electrokinetic effects in nonpolar solvents to drive the displacement of colloidal particles within a fluidic cell. While Electrophoresis (EP) is a well-established and frequently employed phenomenon, electro-osmosis (EO), which drives fluid flow along charged solid surfaces, has not been studied as extensively. We hypothesize that by exploiting the interplay between these effects, an enhanced particle transport can be achieved. In this study, we experimentally investigate the combined effects of EP and EO for colloidal particles in non-polar solvents, driven by an electric field. We use astigmatism micro-particle tracking velocimetry (A- μ PTV) to measure the motion of charged particles within model fluidic cells. Using a simple approach that relies on basic fluid flow properties we extract the contributions due to EP and EO, finding that EO contributes significantly to particle transport. The validity of our approach is confirmed by measurements on particles with different magnitudes of charge, and by comparison to numerical simulations. We find that EO flows can play a dominant role in the transport of particles in electrokinetic display devices. This can be exploited to speed up particle transport, potentially yielding displays with significantly faster switching times. Interplay of electrokinetic effects : Driven by the applied electric field, both electro-osmosis (EO, top left), which drives a flow along the surfaces of the fluidic cell, and electrophoresis (EP, top right), which drives a migration of particles relative to the background liquid, occur in our system. A typical example of the resultant particle velocity field (bottom) illustrates the important role of EO on particle transport in the fluidic cell. • Studied electrokinetics of particles in nonpolar solvent using astigmatism micro-PTV. • Both electrophoresis (EP) and electro-osmosis (EO) play important roles. • Combination of EO and EP could be exploited in faster switching e-paper displays. [ABSTRACT FROM AUTHOR]

[Display omitted] To understand the shielding of electrokinetics of colloidal particles by polymer coating, we measured the electrophoretic mobility of negatively charged polystyrene sulfate latex (PSL) adsorbed with electrostatically neutral polyethylene oxide (PEO) chains with various molecular weights under different ionic strengths. We confirmed that substantial adsorbed neutral polymer on the particle surface would decrease the absolute value of electrophoretic mobility. Even though the polymer layer is sufficiently thicker compared to the thickness of electric double layer (EDL), the electrophoretic mobility (EPM) never vanishes, which indicates the incompleteness of electrokinetic shielding by an adsorbed neutral polymer. To relate such interesting phenomena, a simple mathematical model has been proposed to evaluate the electrophoretic mobility, assuming the presence of a scaling structure of adsorbed permeable polymer layer does not influence the Poisson–Boltzmann distribution of ions in the electric double layer (EDL). An analytical expression of electrophoretic mobility under Debye-H u ¨ ckel approximation has been derived using the method of Ohshima-Kondo theory, which successfully justifies the experimentally obtained data. [ABSTRACT FROM AUTHOR]

This study explored the influence of frozen ball milling on the physicochemical properties and functional characteristics of glutinous rice protein. After grinding glutinous rice protein at 0 min, 10 min, 20 min, 30 min and 40 min, physicochemical indexes showed that with the extension of milling time, the particle size of glutinous rice protein decreased significantly, the free sulfhydryl content increased first and then decreased, the surface hydrophobicity increased gradually, the α-helix content decreased first and then increased, the β-sheet content decreased gradually, and the secondary structure was transformed. However, the electrophoresis bands did not change obviously before and after frozen ball milling. Functional indexes showed that the solubility of glutinous rice protein increased first and then decreased after frozen ball milling. With the increase of the frozen ball milling time, the emulsification activity of glutinous rice protein tended to increase first and then decrease. The emulsifying stability of glutinous rice protein decreased after undergoing freezing and ball milling, showing a notable decrease from 21.25% before frozen ball milling to 8.42% after 40 min of ball milling. This indicates that frozen ball milling is an effective method for producing modified glutinous rice protein products with new structure and characteristics. • Frozen ball milling is an effective method for producing modified glutinous rice protein products. • Freeze ball milling improves the solubility and emulsifying activity of glutinous rice protein. • Freezing ball milling alters the spatial structure of glutinous rice protein. [ABSTRACT FROM AUTHOR]

[Display omitted] Separations of particles and cells are indispensable in many microfluidic systems and have numerous applications in chemistry and biomedicine. The interface of aqueous two-phase system (ATPS) can act as a liquid filter. Under electric field stimuli, the selective transfer of targets across the liquid–liquid interface are expected for particles and cells separation. The separations of particles and cells based on ATPS electrophoresis in a microfluidic chip were investigated. A systematical study of the mechanism of ATPS electrophoresis was performed first by employing polystyrene (PS) particles. Subsequently, the separations of particles and microalgae cells were demonstrated. The electrophoretic transfer of particles across the interface of ATPS is determined by multi-parameters, including the strength of electric pulse, particle size, zeta potential, and hydrophobicity of the particle. The continuous separations of particles/cells can be achieved through the controllable transfer of target particles/cells across the interface under electric pulses in a microfluidic chip. By simply turning the magnitude of the applied electric pulse, the technique is suitable for different purposes, for example, the separations of particles and cells, purification of cells, and viability identification of cells. This tunable separation approach opens opportunities in multidimensional particle and cell sorting for the fields of seed selection of microorganisms, environmental assessment, and biomedical research. [ABSTRACT FROM AUTHOR]

[Display omitted] The traditional model of the Isolated Double Layer (DL) becomes inadequate in concentrated dispersions when the distance between particles becomes comparable to the Debye length and DLs overlap. The notion of "overlapping DLs" was introduced to Electrophoretic theory 60 years ago by Prof. T. Overbeek's group. The theory posed in that paper and a subsequent publication by Long and Ross predicts a decline of electrophoretic mobility due to DLs overlap. There is also more recent theory that describes electrokinetics at the extreme case of complete DLs overlap. We call it "quasi-homogeneous DL theory". It predicts an increase of electrophoretic mobility. We conducted an experimental study to verify which theoretical prediction is correct. We used an equilibrium dilution protocol, which allowed us to maintain the same interface-bulk electrochemical equilibrium at all volume fractions, ranging from 1 %vl up to 36 %vl (56 %wt). Electroacoustics were applied for measuring electrophoretic mobility and zeta potential. They remain constant up to 15% vl. At the higher volume fraction, where DLs become overlapping, they increase. This confirms prediction of "quasi-homogeneous DL theory" at least on qualitative level. [ABSTRACT FROM AUTHOR]

[Display omitted] Electrophoresis of a dielectric fluid droplet with arbitrary surface potentials is investigated theoretically in this study. A pseudo-spectral method based on Chebyshev polynomials is adopted to solve the governing electrokinetic equations. Droplet mobilities are expressed as functions of electrolyte strength for fluid droplets with various viscosities and surface potentials. Effects of various electrokinetic parameters upon the droplet motion are investigated extensively. It is found, among other things, that the viscosity-dependence of the droplet mobility is synchronized with the presence of a separate axisymmetric exterior vortex flow surrounding the droplet, in addition to the axisymmetric interior vortex flow induced by the spinning motion of the charged surface. With its presence, the more viscous a fluid droplet is, the faster it moves; otherwise, the viscosity-dependence is the other way around. Critical points are discovered for highly charged droplets, at which the droplet surface becomes immobile and the interior fluid becomes motionless, just like a rigid solid particle. The orientation of the interior vortex flow changes each time passing these critical points, accompanied by the onset or shutdown of the exterior vortex flow. The results are useful in various practical applications such as drug delivery. [ABSTRACT FROM AUTHOR]

Homoaggregation and heteroaggregation involving amidine and sulfate latex particles in the presence of the anionic surfactant octyl sulfate (OS) is studied by light scattering. This surfactant causes a charge reversal of the amidine particles. This reversal induces a rapid homoaggregation near the charge reversal point. In the presence of the same surfactant, the sulfate particles remain negatively charged and stable. The heteroaggregation process is probed in mixed suspensions of amidine and sulfate latex particles with multi-angle time-resolved dynamic light scattering. This technique allows differentiating between the contributions of homoaggregation and heteroaggregation, and permits to measure the heteroaggregation rate. By optimally choosing the sizes of the particles, one can optimize the contrast and extract heteroaggregation stability ratio over a wide range. The heteroaggregation rate is fast at low OS concentrations, where the two particles are oppositely charged. This rate slows down at higher OS concentrations due to double layer repulsion between the negatively charged particles. However, the onset of this slow heteroaggregation occurs at lower OS concentrations than for homoaggregation. The reason for this shift is that the double layer repulsion between two OS-decorated amidine particles is weaker than between one sulfate particle and one OS-decorated amidine particle. These measurements compare favorably with calculations with the theory by Derjaguin, Landau, Verwey, and Overbeek (DLVO). These calculations suggest that constant potential boundary conditions are more appropriate than the ones of constant charge. In the system studied, the present light scattering technique permits to extract heteroaggregation stability ratios over almost three orders of magnitude. This study is the first of its kind, where such a large range is being probed. [ABSTRACT FROM AUTHOR]

Within the framework of analytical theories for soft surface electrophoresis, soft particles are classically defined by a hard impermeable core of given surface charge density surrounded by a polyelectrolyte shell layer permeable to both electroosmotic flow and ions from background electrolyte. This definition excludes practical core-shell particles, e.g. dendrimers, viruses or multi-layered polymeric particles, defined by a polyelectrolytic core where structural charges are distributed and where counter-ions concentration and electroosmotic flow velocity can be significant. Whereas a number of important approximate expressions has been derived for the electrophoretic mobility of hard and soft particles, none of them is applicable to such generic composite core-shell particles with differentiated ions- and fluid flow-permeabilities of their core and shell components. In this work, we elaborate an original closed-form electrophoretic mobility expression for this generic composite particle type within the Debye-Hückel electrostatic framework and thin double layer approximation. The expression explicitly involves the screening Debye layer thickness and the Brinkman core and shell hydrodynamic length scales, which favors so-far missing analysis of the respective core and shell contributions to overall particle mobility. Limits of this expression successfully reproduce results from Ohshima's electrophoresis theory solely applicable to soft particles with or without hard core. [ABSTRACT FROM AUTHOR]

The classical problem of the electrophoretic motion of a spherical particle has been treated theoretically by Overbeek in his 1941 PhD thesis and almost 40 years later by O'Brien & White. Although both approaches used identical assumptions, the details are quite different. Overbeek solved for the pressure, velocity fields as well as the electrostatic potential, whereas O'Brien & White obtained the electrophoretic mobility without the need to consider the pressure and velocity explicitly. In this paper, we establish the equivalence of these two approaches that allow us to show that the tangential component of the fluid velocity has a maximum near the surface of the particle and outside the double layer, the velocity decays as 1 / r 3 , where r is the distance from the sphere, instead of 1 / r in normal Stokes flow. Associated with this behavior is that of an irrotational outer flow field. This is consistent with the fact that a sphere moving with a constant electrophoretic velocity experiences zero net force. A study of the forces on the particle also provides a physical explanation of the independence of the electrophoretic mobility on the electrostatic boundary conditions or dielectric permittivity of the particle. These results are important in situations where inter-particle interaction is considered, for instance, in electrokinetic deposition. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Hypothesis Cellulose nanofibres produced by TEMPO-mediated oxidation can form gels. This study presents a proof-of-concept for gel electrophoresis with nanocellulose (NC). Experiments TEMPO-oxidised cellulose nanofibre dispersion is chemically cross-linked by inducing amide linkages to produce gel slabs for electrophoretic separation. Nanocellulose gel slabs 1 cm thick containing Tris/Borate/EDTA (TBE) buffer were casted. Different cross-linker types and ratios are investigated to assess the migration of conventional electrophoresis tracking dyes. Findings Tracking dyes (bromophenol blue and orange G) can diffuse within the gel at different rates and therefore separate. Changing the cross-linker length from EDA to HMDA (C2- to C6-chain) increases the overall network pore size resulting in a faster migration rate for both bromophenol blue and orange G. Increasing the cross-linker concentration stabilises the HMDA-NC gel (no extension) during the electrophoresis run without any effect on the dye migration rate. Increasing the voltage increases the migration rates for both orange G and bromophenol blue. Further development is required to cast the gels evenly and to prevent bubble formation during the cross-linking process. This will enable to effectively separate mixtures of proteins. Nanocellulose gels can become a novel substrate for sustainable biomedical separation and diagnostics by electrophoresis. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract This paper proposes a simple and versatile method for the determination of the zeta potential of a channel wall and discusses the values measured for the surface of frozen solvents, which are not only of scientific interest but also of potential use for microfluidic platforms. The zeta potential of the solid surface is an important parameter for discussing its electrokinetic properties, the distribution and reaction of ions in an electric double layer, and the fluidic behavior in the space surrounded by the surface. While the zeta potential of colloidal matters can be determined from their electrophoretic mobility, it is often difficult to determine that of a bulk material. In this paper, the zeta potential of a microchannel fabricated in a frozen solvent is determined by measuring the apparent mobility of microparticles as the probe. The electrophoretic mobility of the microparticles has been measured in advance using microchip electrophoresis under various conditions. This approach allows us to determine the zeta potential of water-ice and frozen cyclohexane. We discuss the pH dependence of the zeta potential of ice and also effects of the NaCl concentration on that of ice and frozen cyclohexane. [ABSTRACT FROM AUTHOR]

Platinum (Pt) free micro/nanomotors (MNMs) using a low content of fuels are highly desired for many applications. Herein, we demonstrate that cathodic electrofabrication can produce modified MnO 2 based microtubes and microrods as highly efficient MNMs in hydrogen peroxide (H 2 O 2 ) as low as 0.2%. The speed of graphene/Ag-MnO 2 micromotors could be smartly regulated using a surfactant and the maximum speed of an individual micromotor exceeds 1.3 mm s −1 in 0.5% H 2 O 2 . The propelling force and output power of the micromotors are 3.4 and 10 times as high as those of the best Pt-based micromotors reported. These Ag-MnO 2 based micromotors are envisioned to be a great promise for practical applications from biomedical delivery to environmental decontamination. [ABSTRACT FROM AUTHOR]

miRNAs are key cellular regulators and their dysregulation is associated with many human diseases. They are usually produced locally in a spatiotemporally controlled manner to target mRNAs and regulate gene expression. Thus, developing chemical tools for manipulating miRNA with spatiotemporal precise is critical for studying miRNA. Herein, we designed a strategy to control miRNA biogenesis with light controllable inhibitor targeting the pre-miRNA processing by Dicer. By conjugating two non-inhibiting units, a low affinity Dicer inhibitor and a pre-miRNA binder, through a photocleavable linker, the bifunctional molecule obtained could inhibit miRNA production. Taking advantage of the photocleavable property of the linker, the bifunctional inhibitor can be fragmented into separate non-inhibiting units and therefore be deactivated by light. We expect that this strategy could be applied to generate chemical biological tools that allow light-mediated spatiotemporal control of miRNA maturation and contribute to the study of miRNA function. [ABSTRACT FROM AUTHOR]

Electrophoretic mobility and time resolved light scattering are used to measure the effect on charging and aggregation of amidine and sulfate latex particles of different oxyanions namely, phosphate, arsenate, sulfate, and selenate. In the case of negatively charged sulfate latex particles oxyanions represent the coions, while they represent counterions in the case of the positively charged amidine latex. Repulsive interaction between the sulfate latex surface and the coions results in weak ion specific effects on the charging and aggregation. On the other hand the interaction of oxyanions with the amidine latex surface is highly specific. The monovalent dihydrogen phosphate ion strongly adsorbs to the positively charged surface and reverses the charge of the particle. This charge reversal leads also to the restabilization of the amidine latex suspension at the intermediate phosphate concentrations. In the case of dihydrogen arsenate the adsorption to amidine latex surface is weaker and no charge reversal and restabilization occurs. Similar differences are seen between the sulfate and selenate analogues, where selenate adsorbs more strongly to the surface as compared to the sulfate ion and invokes charge reversal. The present results indicate that ion specificity is much more pronounced in the case of counterions. [ABSTRACT FROM AUTHOR]

Hypothesis The thermoresponse of poly( N -isopropylacrylamide) stabilised particles is influenced by the presence of salt and is dependent on the concentration, and ions present. The conformation and electrophoretic mobility of core/shell PNIPAM brush modified silica particles is expected to vary as a function of these specific ion effects. Experiments The thermoresponse of PNIPAM brush modified silica particles was investigated via dynamic light scattering and electrophoretic mobility measurements between 5 and 45 °C in the presence of 11 different salt solutions. Findings Specific ion effects were observed in the presence of salt solutions for concentrations between 50 and 1000 mM. The temperature response could be mapped to a master curve unlike PNIPAM brush behaviour on planar substrates. The magnitude of brush layer lower critical solution temperature reduction was found to follow the order F −  > CH 3 CO 2 −  > Cl −  > NO 3 −  ∼ Br −  > I −  > SCN − for the potassium series and Na +  > K +  > Cs +  > Li +  ∼ NH 4 + for the chloride salts. The electrophoretic mobility of the modified particles in the presence of 100 mM potassium salts increased in magnitude as the brush layer collapsed and also with the chaotropic nature of the anion. [ABSTRACT FROM AUTHOR]

In this paper we present experimental results on the electrokinetic behavior of planar gibbsite particles in concentrated suspensions. The dc electrophoretic mobility measurements are in this case of little significance, as they are scarcely informative. In the present investigation, we show that the dielectric dispersion and dynamic electrophoresis can in contrast provide such information. The complicating factors are of course the non-spherical shape and the finite particle concentration, as no complete theory of these phenomena exists for such systems. We propose to use first of all a model of dynamic electrophoresis of spheroids in which the effect of volume fraction is considered by means of an approximate theory previously obtained for spheres, based on the evaluation of electrical and hydrodynamic interactions between particles. In addition, the role of volume fraction on the high frequency inertial relaxation is also ascertained and used to obtain a volume fraction-independent radius of the gibbsite spheroids. A similar approach is used for the evaluation of dielectric dispersion data. Both the dynamic mobility and dielectric constant dependencies on frequency were obtained for gibbsite suspensions of different volume fractions in 0.5 mM KCl. The theoretical treatments elaborated were applied to these data, and a coherent picture of the geometrical and electrical characteristics of the particles was obtained. [ABSTRACT FROM AUTHOR]

Interleukin-8 (IL-8) is an angiogenic CXC chemokine that plays an important role in both the development and progression of several human malignancies including prostate cancer (PC). A single nucleotide polymorphism (SNP) at −251 upstream of the transcriptional start site of the IL-8 gene has been shown to influence its production. The effects of IL-8 are mediated by two highly related chemokine receptors, CXCR1 and CXCR2. The present study investigated the influence of the IL-8 and CXCR2 gene variation on susceptibility and clinicopathological characteristics of PC in a group of Brazilian subjects. Methods: Two hundred and one patients and 185 healthy controls were enrolled in a case-control study. Blood was collected for DNA extraction; typing of IL-8 −251 T/A and CXCR2 +1208 C/T genes was performed by polymerase chain reaction with sequence-specific primers (PCR-SSP), followed by agarose gel electrophoresis. Risk association between the genotypes, PC susceptibility and tumor characteristics was estimated by odds ratio (OR) and 95% confidence intervals (95% CI) using logistic regression analysis, after adjusting for age at diagnosis. Results: A significant association was found between the heterozygous CXCR2 +1208 CT genotype and stage of PC. The CXCR2 +1208 CT genotype was significantly less frequent in patients with clinical stage T3-T4 compared to T1-T2 (56.7 versus 80.5%). Our findings suggest that carriers of the CXCR2 +1208 CT genotype had a protective effect for advanced PC (CT versus CC: adjusted OR = 0.25; P = 0.02). No association was observed between the SNP for IL-8 −251 T/A and clinicopathological parameters of PC. Conclusion: These results indicated that the CXCR2 +1208 CT genotype is less frequent in advanced stages of PC, suggesting that this chemokine receptor plays a role in the pathogenesis of this disease. [ABSTRACT FROM AUTHOR]

Comet assay is an efficient test to detect genotoxic compounds based on observation of DNA damage. The aim of this work was to compare the results obtained from the comet assay in two different type of cells extracted from the root tips from Lactuca sativa L. and human blood. For this, Spent Pot Liner (SPL), and its components (aluminum and fluoride) were applied as toxic agents. SPL is a solid waste generated in industry from the aluminum mining and processing with known toxicity. Three concentrations of all tested solutions were applied and the damages observed were compared to negative and positive controls. It was observed an increase in the frequency of DNA damage for human leukocytes and plant cells, in all treatments. On human leukocytes, SPL induced the highest percentage of damage, with an average of 87.68%. For root tips cells of L. sativa the highest percentage of damage was detected for aluminum (93.89%). Considering the arbitrary units (AU), the average of nuclei with high levels of DNA fragmentation was significant for both cells type evaluated. The tested cells demonstrated equal effectiveness for detection of the genotoxicity induced by the SPL and its chemical components, aluminum and fluoride. Further, using a unique method, the comet assay, we proved that cells from root tips of Lactuca sativa represent a reliable model to detect DNA damage induced by genotoxic pollutants is in agreement of those observed in human leukocytes as model. So far, plant cells may be suggested as important system to assess the toxicological risk of environmental agents. [ABSTRACT FROM AUTHOR]

High-performance electrochromic films based on tungsten oxide hydrate ([WO 2 (O 2 )H 2 O]·1.66H 2 O) colloidal nanocrystals with fast switching speed were fabricated by laser ablation in a mixture of water and hydrogen peroxide followed by electrophoretic methods. Through electrophoretic deposition, the nanoparticles in the colloids synthesized by laser ablation aggregated onto the FTO coated glass substrate forming a lager cell with a uniform size of around 200 nm, which subsequently self-assembled into a porous tungsten oxide hydrate film. By optimizing the electrophoretic time (800 s) and voltage (−0.5 V), the mesh-like porous tungsten oxide hydrate film achieved a wide optical modulation of 32% at 632 nm, fast coloration and bleaching response speed of 7.8 s and 1.7 s respectively due to the synergetic effect of the unique atomic structure of [WO 2 (O 2 )H 2 O]·1.66H 2 O and porous structure with large surface area that facilitates the ion insertion/extraction. Thus the tungsten oxide hydrate can be a promising electrochromic material for practical applications. [ABSTRACT FROM AUTHOR]

Aqueous particle suspensions of many kinds are stabilized by the electrostatic potential developed at their surfaces from reaction with water and ions. An important and less well understood aspect of this stabilization is the dependence of the electrostatic surface potential on particle size. Surface electrostatics are typically probed by measuring particle electrophoretic mobilities and quantified in the electrokinetic potential ( ζ ), using commercially available Zeta Potential Analyzers (ZPA). Even though ZPAs provide frequency-spectra (histograms) of electrophoretic mobility and hydrodynamic diameter, typically only the maximal-intensity values are reported, despite the information in the remainder of the spectra. Here we propose a mapping procedure that inter-correlates these histograms to extract additional insight, in this case to probe particle size-dependent electrokinetics. Our method is illustrated for a suspension of prototypical iron (III) oxide (hematite, α -Fe 2 O 3 ). We found that the electrophoretic mobility and ζ -potential are a linear function of the aggregate size. By analyzing the distribution of surface site types as a function of aggregate size we show that site coordination increases with increasing aggregate diameter. This observation explains why the acidity of the iron oxide particles decreases with increasing particle size. [ABSTRACT FROM AUTHOR]

The deposition of poly(amido amine) dendrimers on mica at various pHs was studied by the atomic force microscopy (AFM) and in situ streaming potential measurements. Bulk characteristics of dendrimers were acquired by using the dynamic light scattering (DLS) and the laser Doppler velocimetry (LDV). The hydrodynamic radius derived from DLS measurements was 5.2 nm for the ionic strength of 10 −2 M and pH range 4–10. The electrophoretic mobility, the zeta potential and the number of electrokinetic charges per molecule were derived as a function of pH from the LDV measurements. It was revealed that the dendrimers are positively charged for pH up to 10. This promoted their deposition on negatively charged mica substrate whose kinetics was quantitatively evaluated by direct AFM imaging and streaming potential measurements interpreted in terms of the electrokinetic model. The desorption kinetics of dendrimers under flowing conditions from monolayers of various coverage was also studied. It was revealed that dendrimer deposition was partially reversible for pH above 5.8. The acid-base properties of the dendrimer monolayers deposited on mica were characterized. [ABSTRACT FROM AUTHOR]

Hypothesis: Sodium dioctylsulfosuccinate (Aerosol OT or NaAOT) is a well-studied charging agent for model poly(methyl methacrylate) (PMMA) latexes dispersed in nonpolar alkane solvents. Despite this, few controlled variations have been made to the molecular structure. A series of counterion-exchanged analogs of NaAOT with other alkali metals (lithium, potassium, rubidium, and cesium) were prepared, and it was expected that this should influence the stabilization of charge on PMMA latexes and the properties of the inverse micelles. Experiments: The electrophoretic mobilities of PMMA latexes were measured for all the counterion-exchanged AOT analogs, and these values were used to calculate the electrokinetic or ζ potentials. This enabled a comparison of the efficacy of the different surfactants as charging agents. Small-angle scattering measurements (using neutrons and X-rays) were performed to determine the structure of the inverse micelles, and electrical conductivity measurements were performed to determine the ionized fractions and Debye lengths. Findings: Sodium AOT is a much more effective charging agent than any of the other alkali metal AOTs. Despite this, the inverse micelle size and electrical conductivity of NaAOT are unremarkable. This shows a significant non-periodicity in the charging efficiency of these surfactants, and it emphasizes that charging particles in nonpolar solvents is a complex phenomenon. [ABSTRACT FROM AUTHOR]

In this study, we improve on our 3D steady-state model of electrophoretic motion of spherical particles in bounded fluidic channels (Liu et al., 2014) to include the effect of nonsymmetric electrolytes, and further validate this improved model with detailed comparisons to experimental data. Specifically, we use the experimentally-measured particle mobilities from the work of Semenov et al. (2013), Napoli et al. (2011), and Wynne et al. (2012) to determine the corresponding particle zeta potentials using our model, and compare these results with classical theory. Incorporating the effects of nonsymmetric electrolytes, EDL polarization, and confinement, we show that our improved model is applicable to a wide range of practical experimental conditions, for example, particles that have high zeta potentials in a bounded channel filled with nonsymmetric electrolyte solutions, where classical theory is not applicable. In addition, we find that when electrolyte concentration is comparable to the concentration of hydronium or hydroxide ions, the complicated composition of ions increases the particle mobility. Finally, increased electrophoretic mobility can be observed when buffer solutions (phosphate or borate) were used as electrolyte solutions in experiments as opposed to simple symmetric electrolytes. [ABSTRACT FROM AUTHOR]

Considering recent applications of electrophoresis conduced in nanoscaled devices, where particle–particle interaction can play a role, we studied for the first time the electrophoresis of two rigid spheres along their center line, taking account of the hydrodynamic, electric, and van der Waals interactions between them. Under the conditions of constant surface potential and surface charge density, the influences of the level of surface potential/charge density, the bulk salt concentration, and the particle–particle distance on their electrokinetic behaviors are examined. Numerical simulation reveals that these behaviors are much more complicated and interesting than those of isolated particles. In particular, we show that care must be taken in choosing an appropriate particle concentration in relevant experiment to avoid obtaining unreliable mobility data. [ABSTRACT FROM AUTHOR]

In this paper a procedure for selecting the enhancing solutions in electrokinetic remediation experiments is proposed. For this purpose, dredged marine sediment was contaminated with fuel, and a total of 22 different experimental conditions were tested, analysing the influence of different enhancing solutions by using three commercial non-ionic surfactants, one bio-surfactant, one chelating agent, and one weak acid. Characterisation, microelectrophoretic and electrokinetic remediation trials were carried out. The results are explained on the basis of the interactions between the fuel, the enhancing electrolytes and the matrix. For one specific system, the electrophoretic zeta potential, ( ζ ), of the contaminated matrix in the solution was found to be related to the electroosmotic averaged ζ in the experiment and not to the efficiency in the extraction. This later was correlated to a parameter accounting for both contributions, the contaminant and the enhancing solution, calculated on the basis of differences in the electrophoretic ζ in different conditions which has allowed to propose a methodology for selection of enhancing solutions. [ABSTRACT FROM AUTHOR]

The effect of surfactants on the properties of Pickering emulsions stabilized by cellulose nanocrystals (CNCs) was investigated. Electrophoretic mobility, interfacial tension, confocal microscopy and three-phase contact angle measurements were used to elucidate the interactions between anionic CNCs and cationic alkyl ammonium surfactants didecyldimethylammonium bromide (DMAB) and cetyltrimethylammonium bromide (CTAB). Both surfactants were found to adsorb onto CNCs with concentration-dependent morphology. At low concentrations, individual surfactant molecules adsorbed with alkyl tails pointing outward leading to hydrophobic CNCs. At higher concentrations, above the surfactant’s apparent critical micelle concentration, surfactant aggregate morphologies on CNCs were inferred and the hydrophobicity of CNCs decreased. DMAB, which has two alkyl tails, rendered the CNCs more hydrophobic than CTAB which has only a single alkyl tail, at all surfactant concentrations. The change in CNC wettability from surfactant adsorption was directly linked to emulsion properties; adding surfactant increased the emulsion stability, decreased the droplet size, and controlled the internal phase of CNC Pickering emulsions. More specifically, a double transitional phase inversion, from oil-in-water to water-in-oil and back to oil-in-water, was observed for emulsions with CNCs and increasing amounts of DMAB (the more hydrophobic surfactant). With CNCs and CTAB, no phase inversion was induced. This work represents the first report of CNC Pickering emulsions with surfactants as well as the first CNC Pickering emulsions that can be phase inverted. The ability to surface modify CNCs in situ and tailor emulsions by adding surfactants may extend the potential of CNCs to new liquid formulations and extruded/spray-dried materials. [ABSTRACT FROM AUTHOR]

The diffusiophoresis of a soft, pH-regulated particle comprising a rigid core and a polyelectrolyte (PE) layer in an aqueous salt solution containing multiple ionic species is modeled theoretically. We show that the diffusiophoretic behavior of a soft particle can be different appreciably from that of a rigid one. In particular, both the sign and the magnitude of the mobility of a soft particle can vary with the friction coefficient of its PE layer. In an aqueous KCl solution, if that coefficient is sufficiently large, the particle always moves towards the opposite direction as that of the applied concentration gradient, regardless of the pH level, an interesting observation which has not been reported previously. In an aqueous NaCl solution, if pH is sufficiently low, the particle mobility increases with increasing friction coefficient, an interesting and unexpected finding. The results obtained provide valuable and necessary information for both interpreting experimental data and design diffusiophoresis devices. [ABSTRACT FROM AUTHOR]

We image visible light scattered from dispersions of charged spherical nanoparticles propagating through a passivated agarose gel during electrophoresis. By analyzing one-dimensional light intensities along different lanes, we measure the mobility distributions of the nanoparticles and thereby infer their size distributions, which become time-independent after adequate propagation and separation have occurred. For a given large-pore passivated agarose gel, experiments using monodisperse, surfactant-free, sulfate-stabilized, polystyrene nanopheres establish the propagation distance as a function of time for a range of different sphere radii having known surface charges. As bands of monodisperse nanospheres propagate through the gel, the bands become smeared, developing asymmetric tails as some nanospheres experience additional delays compared to others of the same size. After background subtraction, these bands, including their tails, can be fit well using a modified log–normal distribution, yielding deconvolution parameters that vary with propagation distance and transit time. To demonstrate the approach for complex nanosphere dispersions, such as a multi-modal mixture or a broadly polydisperse nanoemulsion, we measure scattered light intensities as a function of propagation distance and time during gel-EP. Iterative deconvolution using a modified log–normal point-spread function, which changes shape according to propagation distance and time, directly yields unsmeared, high-resolution electrophoretic mobility distributions, from which detailed particle size distributions are inferred. [ABSTRACT FROM AUTHOR]

Abstract: Gel electrophoresis (gel–EP) has been used for decades to separate charged biopolymers, such as DNA, RNA, and proteins, yet propagation of other charged colloidal objects, such as nanoparticles, during gel–EP has been studied comparatively little. Simply introducing anionic nanoparticles, such as sulfate–stabilized polystyrene nanospheres, in standard large-pore agarose gels commonly used for biomolecules does not automatically ensure propagation or size-separation because attractive interactions can exist between the gel and the nanoparticles. Whereas altering the surfaces of the nanoparticles is a possible solution, here, by contrast, we show that treating a common type I–A low-electroendoosmosis agarose gel with a passivation agent, such as poly-(ethyleneglycol), enables charged nanoparticles to propagate through large-pore passivated gels in a highly reproducible manner. Moreover, by taking advantage of the significant optical scattering from the nanoparticles, which is not easily measurable for biopolymers, relative to scattering from the gel, we perform real-time, light-scattering, video-tracking gel–EP. Continuous optical measurements of the propagation of bands of uniformly sized nanospheres in passivated gels provides the propagation distance, L, and velocity, v, as a function of time for different sphere radii, electric field strengths, gel concentrations, and passivation agent concentrations. The steady-state particle velocities vary linearly with applied electric field strength, E, for small E, but these velocities become non-linear for larger E, suggesting that strongly driven nanoparticles can become elastically trapped in the smaller pores of the gel, which act like blind holes, in a manner that thermal fluctuations cannot overcome. Based on this assumption, we introduce a simple model that fits the measured v(E) in both linear and non-linear regimes over a relevant range of applied voltages. [Copyright &y& Elsevier]

Highlights: [•] High resolution (50nm) nondestructive tomographic technique is used in this study. [•] Closed-packed structure, grain boundary and defect area are clearly defined. [•] An fcc close-packed packing sequence (ABCA) of polystyrene microspheres is identified. [•] The orientation variation in stacking direction between two grains is determined. [•] 3D simulation of inverse opal with (111) plane has been done. [Copyright &y& Elsevier]

Abstract: Hypothesis: Silica nanoparticles can be dispersed in organic solvents (organosols) using surfactants, such as didodecyldimethylammonium bromide (DDAB). DDAB analogs prepared with lathanide tetrahalide counterions, either a high-magnetic moment ion (HoCl3Br, DDAH) or low-magnetic moment one (NdCl3Br, DDAN), are expected to produce charged particles, but only DDAH-stabilized dispersions are expected to be magnetically responsive. Experiments: Phase-analysis light scattering (PALS) measurements have been performed to determine the charge on DDAH- and DDAN-stabilized organosols. Magnetic sedimentation experiments have been performed to determine whether or not the silica dispersions are magnetically responsive. Sedimentation was monitored both by visual observations and UV–vis spectroscopy. Findings: Both DDAH and DDAN organosols are negatively charged, the same as DDAB-stabilized nanoparticles. The DDAH-stabilized nanoparticles are found to respond to a magnetic field, whereas the DDAN-stabilized nanoparticles do not. This opens up possibilities for creating nanoparticle dispersions in nonpolar solvents which can be tailored to respond to desired external stimuli. [Copyright &y& Elsevier]

Highlights: [•] Electrokinetics of monodisperse charged silica spheres in ethanol were studied. [•] Dynamic and electrophoretic mobility were compared at low and high salt. [•] Electroacoustics agrees with laser Doppler electrophoresis at high ionic strength. [•] At low ionic strength, dynamic mobility by far exceeds electrophoretic mobility. [•] Is the model system not as simple as it seems, is the theory inadequate, or both? [Copyright &y& Elsevier]

Highlights: [•] Electrophoresis considering self-induced nonuniform surface charge is modeled. [•] Self-induced nonuniform surface charge is most important when surface potential is high. [•] Competition of several factors yields complicated and interesting behaviors. [•] Influence of types of background salt on particle mobility can be significant. [Copyright &y& Elsevier]

Highlights: [•] Monodisperse PGMA particles carrying COOH or NH2 groups were developed. [•] Electrophoretic mobilities and ζ potential values of the particles were determined. [•] Poly(glycidyl methacrylate)/Ag nanocomposite microspheres were prepared. [•] The composite microspheres were used as efficient radioiodine scavenger. [Copyright &y& Elsevier]

Highlights: [•] We test recent proposals that an uncharged particle can have a non-zero electrophoretic mobility. [•] We show that a steady mobility is impossible because of charge polarisation at the interface. [•] Although motion is possible in an ac field, we show that the uncharged theory does not fit experimental data. [•] Thus the uncharged mobility hypothesis cannot account for standard electrophoresis observations. [ABSTRACT FROM AUTHOR]

Highlights: [•] Theoretical modelling of concentrated “realistic salt-free suspensions”. [•] Influence of CO2 and H2O derived ionic species. [•] Added non-equilibrium dissociation–association kinetic equations. [•] Augmented electroviscous coefficient and DC electrophoretic mobility. [ABSTRACT FROM AUTHOR]

Highlights: [•] Uncharged and Weakly-charged nano-hydrogels have negative electrophoretic mobility. [•] H-bonding in the dipole-layer is hypothesized to be responsible for these effects. [•] Introduction of glycine to test this hypothesis leads to sharpened mobility distributions. [•] The latter effect is related to Kohlrausch-boundary effects. [•] Alternative theoretical treatments are presented. [Copyright &y& Elsevier]

Highlights: [•] Deposition kinetic depends on the suspension conductivity. [•] For low dispersion conductivities, deposition is controlled by particle diffusion. [•] When conductivities are high the forming deposit resistance governs the deposition kinetic. [•] For high conductivities, the electric field is focused on the anodic film. [Copyright &y& Elsevier]

Highlights: [•] Electrophoresis of a pH-regulated, zwitterionic soft cylinder with boundary modeled. [•] Liquid phase contains multiple ionic species. [•] Effect of double layer polarization considered. [•] Results gathered provide necessary information for device design. [Copyright &y& Elsevier]

Highlights: [•] Safranin was used as a dispersant for electrophoretic deposition of materials. [•] Carbon nanotubes, graphene and polypyrrole nanofibers were deposited cathodically. [•] Graphene–carbon nanotubes and graphene polypyrrole nanofiber composites were obtained. [•] Composite films were studied for electrodes of electrochemical supercapacitors. [•] The composite electrodes showed high capacitance and low resistance. [ABSTRACT FROM AUTHOR]

Highlights: [•] Evaporation of TiO2–water nanofluid droplets under direct current (DC). [•] Droplet internal flow of nanoparticles under DC electric field differs from AC. [•] Electrophoretic motion of nanoparticles preferential to advective one. [•] Smoother receding of the contact line and more homogeneous deposits. [ABSTRACT FROM AUTHOR]

Highlights: [•] We report the electrokinetic response of montmorillonite particles. [•] The relaxation frequencies shifted to lower frequencies with decreasing ionic strength. [•] This shift is in qualitative agreement with the model’s prediction. [•] We need a Stern layer conductance to fit the amplitude of the dipole coefficients. [•] The quantitative deviations are due to the limitation of the theory. [ABSTRACT FROM AUTHOR]

Abstract: The plant-infecting mastreviruses (family Geminiviridae) express two distinct replication-initiator proteins, Rep and RepA. Although RepA is essential for systemic infectivity, little is known about its precise function. We therefore investigated its role in replication using 2D-gel electrophoresis to discriminate the replicative forms of Maize streak virus (MSV) mutants that either fail to express RepA (RepA−), or express RepA that is unable to bind the plant retinoblastoma related protein, pRBR. Whereas amounts of viral DNA were reduced in two pRBR-binding deficient RepA mutants, their repertoires of replicative forms changed only slightly. While a complete lack of RepA expression was also associated with reduced viral DNA titres, the only traces of replicative intermediates of RepA− viruses were those indicative of recombination-dependent replication. We conclude that in MSV, RepA, but not RepA–pRBR binding, is necessary for single-stranded DNA production and efficient rolling circle replication. [Copyright &y& Elsevier]

Abstract: Cathodic electrophoretic deposition (EPD) method has been developed for the fabrication of thin films from aqueous solutions of crystal violet (CV) dyes. The films contained rod-like particles with a long axis oriented perpendicular to the substrate surface. The proposed deposition mechanism involved cataphoresis of cationic CV+ species, base generation in the cathodic reactions, and charge neutralization at the electrode surface. The assembly of rod-like particles was governed by π–π interactions of polyaromatic CV molecules. The deposition kinetics was studied by quartz crystal microbalance. CV dyes allowed efficient dispersion of multiwalled carbon nanotubes (MWCNTs) and graphene in water at relatively low CV concentrations. The feasibility of cathodic EPD of MWCNT and graphene from aqueous suspensions, containing CV, has been demonstrated. The deposition yield was investigated at different CV concentrations and deposition voltages. The relatively high deposition yield of MWCNT and graphene indicated that CV is an efficient dispersing, charging, and film forming agent for EPD. Electron microscopy data showed that at low CV concentrations in MWCNT or graphene suspensions and low deposition voltages, the films contained mainly MWCNT or graphene. The increase in the CV concentration and/or deposition voltage resulted in enhanced co-deposition of CV. The EPD method developed in this investigation paves the way for the fabrication of advanced nanocomposites by cathodic electrodeposition. [Copyright &y& Elsevier]

Abstract: Electric field induced particle–particle interactions and assembly are of great interest due to their useful applications in micro devices. The behavior of particles becomes more complex if multiple particles interact with each other at the same time. In this paper, we present a numerical study of two dimensional DC dielectrophoresis based particle–particle interactions and assembly for multiple particles using a hybrid immersed interface-immersed boundary method. The immersed interface method is employed to capture the physics of electrostatics in a fluid media with suspended particles. Particle interaction based dielectrophoretic forces are obtained using Maxwell’s stress tensor without any boundary or volume integration. This electrostatic force distribution mimics the actual physics of the immersed particles in a fluid media. The corresponding particle response and hydrodynamic interactions are captured through the immersed boundary method by solving the transient Navier–Stokes equations. The interaction and assembly of multiple electrically similar and dissimilar particles are studied for various initial positions and orientations. Numerical results show that in a fluid media, similar particles form a chain parallel to the applied electric field, whereas dissimilar particles form a chain perpendicular to the applied electric field. Irrespective of initial position and orientation, particles first align themselves parallel or perpendicular to the electric field depending on the similarity or dissimilarity of particles. The acceleration and deceleration of particles are also observed and analyzed at different phases of the assembly process. This comprehensive study can be used to explain the multiple particle interaction and assembly phenomena observed in experiments. [Copyright &y& Elsevier]

Abstract: Electric fields are commonly used to deposit colloidal particles on electrode surfaces and can even be used in directed assembly. The electric field beneath each particle changes as the particle approaches the wall; the proximity of the wall breaks the fore/aft symmetry and drives complicated flows that exert forces on the particle. While two limiting cases have been partially analyzed, constant electrode potential and uniform current density, the full problem has not been explored. Here, the electroosmotic flows in the region between the particle and the electrode are analyzed and the forces are computed for arbitrary electrode kinetic boundary conditions. Finite element analysis is employed to explore the effect of the current distribution beneath a particle on the net force acting on it. Previously established dimensionless kinetic parameters are used to scale between the two limiting cases. The forces on particles are an order of magnitude larger than the bulk electrophoretic force and are profoundly sensitive to the current distribution beneath the particle as it approaches the electrode. [Copyright &y& Elsevier]

Abstract: The effect of SDS on the electrokinetic behavior of TiO2 and Al2O3 was studied by electrophoresis at various solid-to-liquid ratios. Additionally, the effect of CTAB on electrokinetic curves of Al2O3 single crystal and of Al2O3 particles was studied by streaming potential. At a sufficiently low solid-to-liquid ratio, the electrokinetic potential was negative and almost pH-independent in the presence of SDS and positive and pH-independent in the presence of CTAB. Further decrease in the solid-to-liquid ratio had a limited effect on the course of the electrokinetic curves. At a sufficiently high solid-to-liquid ratio, the electrokinetic potential was not affected by the presence of the surfactant. At moderate solid-to-liquid ratios, the electrokinetic potential in the presence of SDS was negative and almost pH-independent at very high and at very low pH, and less negative or even positive electrokinetic potential (more positive at higher solid-to-liquid ratios) was observed at moderate pH with a peak 1 to 2 pH units below the pristine IEP. The inspection of the results (obtained at single solid-to-liquid ratio) from the literature confirmed the above trends, also for oxides other than TiO2 or Al2O3. The range of solid-to-liquid ratios, which can be covered by electrophoresis is limited by insufficient signal, and by insufficient transparency at low and at high solid-to-liquid ratios, respectively. The available range of solid-to-liquid ratios can be extended by using the electroacoustic method. Apparently, the significance of the solid-to-liquid ratio in the electrokinetic studies of oxide-ionic surfactant systems is underrated. To our best knowledge, this is the first systematic study of such an effect ever published, and in many publications, the solid-to-liquid ratio was not reported and probably not even controlled. [Copyright &y& Elsevier]

Abstract: We study the charging behavior of polystyrene and polymethyl methacrylate particles with different functional surface groups in water and in decane containing either ionic (AOT) or nonionic surfactant (Span 85). Electrophoretic mobilities in the nonpolar media are measured as a function of surfactant concentration and the applied electric field strength by phase analysis light scattering (PALS); acid–base characteristics of the particles and the surfactant are investigated via contact angle measurement and interfacial tensiometry, and the residual water content of the non-aqueous dispersions is assessed by Karl Fischer titration. The results suggest a competition of several mechanisms for particle charging in nonpolar media. At high concentrations of the nonionic surfactant, particle charging becomes insensitive to the functional surface groups responsible for charging in aqueous dispersions, but consistent with a charge transfer between the polymer surface and the surfactant due to acid–base interactions, which can be rationalized in terms of measurable acid–base parameters. By contrast, particle charging in nonpolar solutions of the ionic surfactant (with significantly larger amounts of residual water) suggests a strong influence of surface headgroup ionization, and of dissociated surfactants adsorbed to the particle surface. [Copyright &y& Elsevier]

Abstract: Charging and aggregation of negatively charged carboxyl latex particles in the presence of positively charged linear oligoamines containing 1–6 amine groups were investigated by electrophoretic mobility and dynamic light scattering. The oligoamines of low valence resemble simple inert salts and destabilize the suspensions by screening their charge. The oligoamines of higher valence induce overcharging at low concentrations, whereby destabilization is triggered by charge neutralization. At higher concentrations, destabilization is also induced by screening. The onset of first fast aggregation regime scales with the inverse six power of the valence in agreement with the Schulze–Hardy rule. The aggregation rates can be relatively well described by the DLVO theory which indicates that the interactions are governed by van der Waals and electrostatic double layer forces. [Copyright &y& Elsevier]

Abstract: Electrophoresis of a single charged porous sphere in an infinite medium of electrolyte solution is investigated theoretically. The porous sphere is treated as a Brinkman medium with uniformly distributed electric charges. General electrokinetic equations including the full nonlinear Poisson equation are employed as the governing equations, which are then solved with a pseudo-spectral method based on Chebyshev polynomials. Key parameters of electrokinetic interest are examined for their effects on particle motion. Motion-deterring nonlinear effects, the condensation effect and the double layer polarization effect, are separated from each other and examined in detail for their respective impact on the particle motion. The Debye–Hückel approximation is found to overestimate the particle mobility severely: Up to ten times for a porous sphere both highly charged and highly permeable in some situations, which is attributed to the polarization effect. Convenient charts of correction factors for this overestimation are provided to facilitate the usage by interested experimental researchers in the field of the study of polyelectrolytes, such as DNA and proteins, which are well modeled as charged porous spheres. [Copyright &y& Elsevier]