Repulsion Of Particles Research Articles

Effect of interparticle forces on the stability and droplet diameter of Pickering emulsions stabilized by PEG-coated silica nanoparticles

HypothesisAttractive and repulsive interparticle forces influence the stability and structure of Pickering emulsions. The effect these forces have on emulsion behavior must be better understood to improve Pickering emulsions for subsurface applications, including enhanced oil recovery and aquifer decontamination. Past work demonstrates improved emulsion stability with increasing salinity and reduced electrostatic repulsion, possibly because of interparticle networks. We hypothesize that emulsion stability is similarly improved by reducing interparticle steric repulsion. ExperimentsWe assessed the effect of interparticle forces on emulsion stability by generating decane-in-water emulsions. We used polyethylene glycol (PEG)-coated silica nanoparticles with different diameters, surface modification, and salinities to modify either vdW, steric, or electrostatic interactions. We measured emulsion stability using centrifugation, imaged emulsion droplets with optical microscopy, and analyzed images with ImageJ to calculate droplet diameters. FindingsMildly aggregated particles with 0.5–1.0 μmol/m2 surface PEG exhibit the highest emulsion stability. This optimal surface concentration maximizes a trade-off between particle repulsion and aggregation. Droplet diameters are well explained by an energy balance limited coalescence model, generated by solving DLVO equations. We find that while emulsion stability is influenced by interparticle forces, droplet size is dominated by particle-droplet interactions. These results demonstrate the potential of surface modification to significantly improve emulsion stability.

Insights into setting time, rheological and mechanical properties of chitin nanocrystals- and chitin nanofibers-cement paste

Chitin, the second most abundant biopolymer in nature, is available in the seafood industry's waste streams. In this pioneering study, chitin from waste shrimp shells was processed into chitin nanocrystals and nanofibers (Ch-NCs and Ch-NFs) for evaluation in the cement paste. The results show Ch-NCs delayed the final set time by up to 106 min, likely by electrostatic repulsion of cement particles, but Ch-NFs imparted only a max 78-min delay. Furthermore, the viscosity of fresh cement paste increased with Ch-NFs but did not significantly change with Ch-NCs. These different outcomes are attributed to more mobility of Ch-NCs rods versus the Ch-NFs network. In addition, nanochitin forms at 0.05 wt% of cement significantly increased 28d flexural strength by ∼40% and compressive strength by up to ∼12%. The encouraging results of this study indicate the promise of nanochitins in tailoring fresh and hardened properties of cement-based materials for target applications.

Interactions between coarse and fine galena and quartz particles and their implications for flotation in NaCl solutions

In this study we have investigated the interactions between coarse and fine galena and quartz particles and their implications for flotation in NaCl solutions. Tested were four different particle systems: (CC) Coarse galena/Coarse quartz, (CF) Coarse galena/Fine quartz, (FC) Fine galena/Coarse quartz and (FF) Fine galena/Fine quartz. The flotation experiments were carried out on the four particle systems in NaCl concentrations of 10 mM and 100 mM, at pH 9. It was found that the recovery was the highest for the CC particle system, and the lowest for the FF particle system. The experiments also indicated that the recovery improved for the higher NaCl concentration.As part of this study, we calculated the total interaction free energy as a function of separation distance for each pairwise combination of particles and bubbles, for each test condition. It was found that for all particle systems, galena/quartz interactions are dominated by repulsion. The interactions between two galena particles indicated attraction as the dominating force, while the interactions between quartz particles showed repulsion in 10 mM NaCl, which changed to attraction with an increase in NaCl concentration. Galena/air bubble interactions were controlled by repulsive electrostatic interactions in 10 mM NaCl, but these interactions became attractive in 100 mM NaCl salt solutions. On the other hand, the quartz/air bubble interactions were always repulsive, irrespective of the NaCl concentration. Based on these theoretical predictions, we postulate that the stronger repulsion of quartz particles away from the air bubbles could be the driving force for galena recovery.

On the possibility of electrostatically generated infrasound during thunderstorms

Acoustic emissions from lightning discharges are usually attributed to two mechanisms. The audible part of their spectrum mainly results from the shock wave generated by the heating of the lightning channel. On the other hand, the infrasonic component is associated with the conversion to sound of the electrostatic energy stored in the thundercloud. While there is a broad scientific consensus on the former mechanism, the latter process is still controversial. The electrostatic mechanism was proposed by C. T. R. Wilson in 1921 and can be summarized as follows. Due to the electrostatic repulsion of the charged particles, the pressure within a thundercloud is lower than outside. At discharge, the electrostatic field collapses, and the sudden air volume contraction produces an acoustic pulse. This work examines the existing theoretical models of the electrostatic mechanism with the data observed for thundercloud dimensions, charge densities, and total charges. Our results show that, although possible, this mechanism, as currently described, cannot explain observations. Our findings might support the hypothesis that the heating of the lightning channel is responsible for the generation of both infrasound and audible sound. However, a definitive answer remains precluded and requires a better understanding of cloud formation and electrification processes.

Effects of Organic Agriculture in Structure and Organic Carbon Adsorption at Colloidal Scale in Marginal Olive Groves, Characterized by the Extended DLVO Model

Relationship between macroscopic and microscopic behavior of soils is a difficult issue, especially when dealing with complex properties such as structure or carbon sequestration, but it is necessary for a suitable understanding of the agricultural soil quality. In this work, we used the extended-DLVO theory to compute total energy of interaction between particles (kT), of three soils over granodiorites. This parameter allows predicting the tendency to aggregate formation at the colloidal scale, being the basis of soil structure. Furthermore, we characterized the mechanism and adsorption capacity of humic molecules on mineral surfaces, and its influence in the interaction energy, by means of the adsorption isotherms. The aim was to compare first the effects of organic farming on conventionally managed soils and, second, to compare these with a non-cultivated forest soil under Mediterranean climate. When total energies are negative (particle attraction), or positive (particle repulsion) but near 0 kT (<100 kT), then particle flocculation occurs and the structure at colloidal scale can be developed. Total energy was less in the forest sample and greater in the soil of conventional groves, with intermediate values in organic farming soil. This indicates a tendency toward particle flocculation and more stability of the structure at colloidal scale in less disturbed soils, agreeing with other soil physical properties such as the total porosity (50, 41 and 37% in forest, organic and conventional plots, respectively) or the aggregate stability index (0.94, 0.73 and 0.66, respectively), which followed the same trend. Of the three components of the total energy of interaction, the acid-base force was a key factor. This component, related with the electron-donor component of surface free energy, γ−, yielded a strong attractive force (−150 kT at 3 nm) when calcium solutions were analyzed for the forest soil. This indicates a clear hydrophobic character of this sample. Because the mineralogical composition of the samples is quite similar, hydrophobicity should be attributed to the organic carbon content of the forest soil, which is much higher than that of the cultivated ones (12.03 vs. 1.44% and 0.88% in organic and conventional farms, respectively), proving to be an essential element for the development of the structure at the colloidal level.

Study on the preparation of coal wastewater slurry from salt/alkali wastewater

Combining experimental research and simulation calculation, the effect of high-concentration salt/alkali wastewater on the preparation of coal wastewater slurry (CWWS) was studied. The research on the slurry-ability of CWWS shows that Na+ in NaCl will be electrically neutralized with the negative charge on the coal, the electrostatic repulsion of particles will decrease, and the viscosity will increase. In the presence of HCO3c, negative charge increases on coal particles, the apparent viscosity decreases by 42 mPa·s compared with the absence of HCO3−. In the CO32− systems, the pH is 8.25. Higher pH indicates that there are more OH−. Because CO32− is easy to combine with water to form a stable structure, and the strong polar effect of OH− is also easy to bind water molecules, forming a stable water molecule layer configuration on the coal, which hinders the adsorption of sodium lignosulfonate (SL), resulting in a decrease in steric hindrance effect, which is not conducive to the dispersion of particles. The molecular dynamics (MD) simulation results confirmed the existence of the neutralization of Na+ and the negative charge on coal in the NaCl system. The adsorption energies (Eadsorption) of each system were negative, indicating that the dispersant was easily adsorbed on the coal. However, in the CO32− system, the absolute value of Eadsorption was lower than that the pure water system, indicating that the presence of CO32− is not conducive to the adsorption of SL. The self-diffusion coefficient(D) of Na2CO3 system is lower than that of coal/water/SL system, NaCl system, and NaHCO3 system. It shows that the presence of CO32− can significantly reduce the migration rate of water molecules and is easy to bind water molecules. The presence of HCO3− is also easy to bind water molecules, but it is weaker than CO32−. The migration and diffusion rate of water molecules in the saline-alkali mixed system decrease. This may be mainly affected by CO32−, which easily binds water molecules on the coal surface and hinders the adsorption of SL.

Wall Repulsion of Charged Colloidal Particles during Electrophoresis in Microfluidic Channels.

Electrophoresis describes the motion of charged particles suspended in electrolytes when subjected to an external electric field. Previous experiments have shown that particles undergoing electrophoresis are repelled from nearby channel walls, contrary to the standard description of electrophoresis that predicts no hydrodynamic repulsion. Dielectrophoretic (DEP) repulsive forces have been commonly invoked as the cause of this wall repulsion. We show that DEP forces can only account for this wall repulsion at high frequencies of applied electric field. In the presence of a low-frequency field, quadrupolar electro-osmotic flows are observed around the particles. We experimentally demonstrate that these hydrodynamic flows are the cause of the widely observed particle-wall interaction. This hydrodynamic wall repulsion should be considered in the design and application of electric-field-driven manipulation of particles in microfluidic devices.

Experimental study of highly alkaline motor oils in express diagnostics by drop test method

In order to maintain the reliability and durability of the internal combustion engine during the operation of machines, systematic and operational monitoring of the state and level of technical fluids is necessary, where the most informative indicator is the change in the state of motor oils. The drop test method has been used for express diagnostics of motor oil for many years. Grades of oils with high base number, which are mainly used for high-speed internal combustion engines when diagnosing the state of these oils using the drop test on the surface of the filter used for analysis (Blue Tape filter paper), do not form zones in the form of rings, the change in diameter of which allows evaluating the operational properties of the operating motor oil. The study established that when analyzing the preservation of the properties of strongly alkaline motor oils (assessment of the contamination coefficient, dispersing properties), a spot of dirty oil is formed on the chromotogram of filter paper thus showing the filter structure. Theoretical studies revealed that the segregation into zones during the analysis of motor oils with strongly base number does not occur due to the action of electrical forces leading to the repulsion of contaminant particles. Electrical forces arise due to changes in molecules and alkali when a drop of oil flows through the surface of the filter, this interaction continues, and therefore, to analyze strongly alkaline motor oils, the base number must be neutralized, and a correction factor for the neutralizer must be introduced. The paper presents the results of experimental studies to determine the effective neutralizer of the alkalinity of a working motor oil in the process of diagnosing oil by the drop test, which made it possible to obtain concentric zones on the surface of filter paper to calculate the dispersing ability and other estimated oil indicators.

Microemulsions in the driven Widom-Rowlinson lattice gas.

An investigation of the two-dimensional Widom-Rowlinson lattice gas under an applied drive uncovered a remarkable nonequilibrium steady state in which uniform stripes (reminiscent of an equilibrium lamellar phase) form perpendicular to the drive direction [R. Dickman and R. K. P. Zia, Phys. Rev. E 97, 062126 (2018)10.1103/PhysRevE.97.062126]. Here we study this model at low particle densities in two and three dimensions, where we find a disordered phase with a characteristic length scale (a "microemulsion") along the drive direction. We develop a continuum theory of this disordered phase to derive a coarse-grained field-theoretic action for the nonequilibrium dynamics. The action has the form of two coupled driven diffusive systems with different characteristic velocities, generated by an interplay between the particle repulsion and the drive. We then show how fluctuation corrections in the field theory may generate the characteristic features of the microemulsion phase, including a peak in the static structure factor corresponding to the characteristic length scale. This work lays the foundation for understanding the stripe phenomenon more generally.

Numerical simulation of contact and separation of magnetic particles under uniform magnetic field

Under the action of an external magnetic field, the magnetic particles will be arranged along the direction of the magnetic field. The laws of physics that control these processes are well described in the literature. However, when the magnetic particles move in the fluid, the magnetic particles with different initial distances have different mutual influences, so there will be different laws of motion. Therefore, based on the motion theory of magnetic particles in Stokes fluid, this article discusses the motion law of the contact and separation of two circular magnetic particles in Newtonian fluid. First, we conduct theoretical and simulation modeling of two magnetic particles under the action of a uniform magnetic field, and verify the correctness of the simulation through experiments; secondly, we use numerical simulation to study the angle of repulsion and attraction of magnetic particles at different initial distances, and analyze at the same time the changes in the trajectory, speed, torque and force of magnetic particles in the process of motion are studied. Finally, the influence of external field conditions on the phenomenon of contact and separation of magnetic particles is studied. The study found that even when the initial angle between the magnetic particles is 90° with the direction of the magnetic field, the magnetic particles with different initial distances will repel under the action of repulsive force and then contact again and keep repelling these two states, a better explanation the reason for the agglomeration of magnetic particles at close range is explained.

Importance of Substrate-Particle Repulsion for Protein-Templated Assembly of Metal Nanoparticles.

We study the protein-directed assembly of colloidal gold nanoparticles on de novo designed protein nanofiber templates. Using sequential assembly on glass substrates, we attach positively charged gold nanoparticles to protein nanofibers engineered to have a high density of negatively charged surface residues. Using a combination of electron and optical microscopy, we measure the density of particle attachment and characterize binding specificity. By varying nanoparticle size and pH of the solution, we explore the importance of charge-dependent particle-fiber and particle-substrate interactions. We find an inverse correlation between particle size and attachment density to protein nanofibers, attributed to the balance between size-dependent electrostatic particle-fiber attraction and particle-substrate repulsion. We show pH-dependent particle attachment density and binding specificity in relation to the protonation fraction of each assembly layer. Finally, we employ hyperspectral scattering microscopy to draw conclusions about particle density and interparticle spacings of optically observable particle assemblies.

Mineralogical and physico-chemical properties of halloysite-bearing slip surface material from a landslide during the 2018 Eastern Iburi earthquake, Hokkaido

Destructive landslides were triggered by the 6.7 Mw Eastern Iburi earthquake that struck southern Hokkaido, Japan, on 6 September 2018. Heavy rainfall on 4 September in addition to intermittent rainfall around the Iburi Tobu area saturated and weakened the slope-forming materials (mostly altered volcanoclastic soils), making them susceptible to failure because of the earthquake’s strong ground motion. Most of the shallow landslides exhibited long runouts along gentle hill slopes, with characteristic halloysite-bearing slip surface at the base of the volcanic soils. This study investigated the mineralogical and physico-chemical properties of the slip surface material with the aim of understanding weakening and post-failure behaviors during the landslides. Halloysite in the slip surface had irregular-to-hollow-spherical morphology with higher mesopore volumes than tubular halloysite, which is related to a high capacity for water retention after rainfall. To reproduce possible chemical changes in the slip surface during rainfall, the sample was immersed in varying amounts of rainwater; solution pH increased and ionic strength decreased with increasing water content. These findings, alongside electrophoretic analysis, suggest that rainwater infiltration could have increased the absolute zeta potential value of the slip surface material. It is suggested that rainfall before the earthquake enhanced the colloidal stability of halloysite particles within the slip surface, owing to an increase in electrostatic repulsion. This decreased the material’s cohesive strength, which might have led to destabilization of the slope during ground shaking generated by the earthquake, and subsequent high-mobility flow after failure.Irregular-to-hollow-spherical halloysite on the slip surface of a shallow landslide triggered by the 6.7 Mw Eastern Iburi earthquake. Rainfall before the earthquake enhanced electrostatic repulsion of halloysite particles (owing to solution pH increase and ionic strength decrease), which might have led to destabilization of the slope.

Active phase separation by turning towards regions of higher density

Studies of active matter, from molecular assemblies to animal groups, have revealed two broad classes of behavior: a tendency to align yields orientational order and collective motion, whereas particle repulsion leads to self-trapping and motility-induced phase separation. Here, we report a third class of behavior: orientational interactions that produce active phase separation. Combining theory and experiments on self-propelled Janus colloids, we show that stronger repulsion on the rear than on the front of these particles produces non-reciprocal torques that reorient particle motion toward high-density regions. Particles thus self-propel toward crowded areas, which leads to phase separation. Clusters remain fluid and exhibit fast particle turnover, in contrast to the jammed clusters that typically arise from self-trapping, and interfaces are sufficiently wide that they span entire clusters. Overall, our work identifies a torque-based mechanism for phase separation in active fluids, and our theory predicts that these orientational interactions yield coexisting phases that lack internal orientational order.

Photo-switchable imprinted adsorbent towards a selective phenol recovery from wastewater

• Synthesis of wettability UV switchable adsorbent for a selective phenol adsorption. • Synergy of photosensitive TiO 2 with hydrophobic crosslinker to reverse wettability. • Extremely high phenol adsorption capacity of 8.24 mg-phenol/m 2 -adsorbent. • Easy recovery of 98% phenol from the saturated adsorbent. • Robust regeneration performance of the adsorbent upon cyclic testing. Here we report the design and synthesis of a novel surface imprinted adsorbent, with an UV-switchable wettability towards an efficient and highly selective phenol recovery from wastewater. The high selectivity of phenol is achieved through surface molecularly imprinted cavities featuring a smart phenol identification function, whilst the UV-switchable wettability is accomplished by the co-loading of nano-sized, photosensitive TiO 2 and hydrophobic 3-(trimethoxysilyl) propyl methacrylate imprinted layer. Through numerous adsorption experiments and extensive characterizations including FESEM, TEM, FT-IR, BET, XRD, XPS, and synchrotron NEXAFS, it is confirmed that upon a prior 0.5 h - long UV irradiation, the imprinted surface of the as-synthesized adsorbent can be switched from hydrophobic to hydrophilic, which in turn results in an equilibrated adsorption capacity of 8.24 mg-phenol/m 2 -adsorbent that are superior over all the reported values. More intriguingly, with the progress of the adsorption in the dark, the surface of the adsorbent can be gradually reversed to hydrophobic. This in turn enhances the repulsion of particles from the aqueous phase, leading to a quick self-agglomeration and precipitation of the spent adsorbent for an easy recovery. Moreover, 98% of the adsorbed phenol can be recovered via a subsequent washing by methanol, and the regenerated adsorbent is also confirmed to exhibit a nearly stable adsorption capacity upon five cycles.

Improved dispersion of clay-rich tailings in seawater using sodium polyacrylate

Stabilization of synthetic clay-rich tailings in seawater with sodium polyacrylate (NaPA) has been studied by measurements of yield stress, viscoelastic moduli, zeta potential, and particle chord length distribution. The tailings are kaolin-quartz and sodium montmorillonite-quartz mixtures in seawater at pH 8 at which all surfaces are anionic. The yield stress of both tailings decays exponentially with the dose of NaPA. Reducing the initial value of yield stress to a preset fraction (1-1/e) requires 52 g/ton NaPA for kaolin-quartz and 31 g/ton NaPA for montmorillonite-quartz tailing. At these dosages, in the linear viscoelastic range, both tailings respond similarly to the presence of NaPA, increasing their liquid-like character and suspension stability. The stabilizing action of NaPA is supported by a slight increase of the negative zeta potential and a clear shift of the particle size distribution to the finer sizes. The underlying stabilizing mechanism involves steric-electrostatic repulsion of the clay particles. These results suggest an alternative to improve the management of clay-rich tailings in processes that use raw seawater at natural pH.

Wirelessly powered dielectrophoresis of metal oxide particles using spark-gap Tesla coil.

Wirelessly powered dielectrophoresis (DEP) of metal oxide particles was performed using a spark-gap Tesla coil (TC). The main contribution of this work is the simplification of the conventional DEP setup that requires attaching wires directly to the electrodes. Wireless power from the TC generates a high output frequency and voltage, which corresponds to that used for the DEP. Therefore, a spark-gap TC was built and utilized to conduct the DEP process. Metal oxides (ZnO and Fe2O3) were used as targets for the assembly. The results showed that the wirelessly powered DEP technique via a TC was successful in assembling the metal oxide particles. Positive and negative DEP phenomena were observed. Positive DEP occurred during ZnO assembly, making particles chain grow 0.92mm toward the sparks within 60 s. Negative DEP was observed during Fe2O3 assembly, where the repulsion of particles formed a void around the sparks with a 1.45mm radius. The mechanism of this wireless DEP system is discussed.

Optimizing electrostatic cleaning for dust removal on gecko-inspired adhesives

Gecko-inspired adhesives are one of the most promising forms of controllable adhesives for a wide range of applications, especially robotic gripping, perching, and climbing. One impediment to the technology's success is the negative effect of dust and other contaminants, which can significantly decrease adhesion in real-world environments. Previous work has shown that electrostatic forces were capable of removing adhered dust on the surface of gecko-inspired adhesives and that a two-phase square wave input to the electrostatic element with the lowest possible frequency produced the highest cleaning efficiency. In this work, dust particle size, electrode geometry (electrode width and gap), duty cycle of the exciting wave, peak-peak voltage of the electrodes, and the thickness of dielectric layer (the gecko-inspired microstructures) are evaluated experimentally and in simulation. Moreover, three possible electrostatic particle removal mechanisms were modeled to explain their relative importance: repulsion, sliding, and rolling. Results indicate that the highest cleaning efficiency for all particle sizes occurs with the highest possible peak-peak voltage when the electrode width and gap are 400 μm and 300 μm, respectively. The results also show the highest cleaning efficiencies are produced using a duty cycle of 50% on the thinnest samples of the gecko-inspired microstructures, where electrodes are closer to particles. Finally, particle sliding and particle rolling are the dominant factors in electrostatic cleaning of gecko-inspired adhesives, while particle repulsion plays a limited role.

Properties of Rising Multiple CO2 Droplets under Contamination of SO2: Understanding Scenarios of Leakage to Seawater

Nguyen, T.H.T.; Park, S.W., and Ahn, J., 2020. Properties of rising multiple CO2 droplets under contamination of SO2: Understanding scenarios of leakage to seawater. Journal of Coastal Research, 36(4), 805–811. Coconut Creek (Florida), ISSN 0749-0208.Research on impacts of impurities on the rising of liquid droplets in other liquids is still quite limited, especially when it comes to the behavior of multiple particles. The properties of rising multiple CO2 droplets under contamination of SO2 are investigated in a scenario in which they may leak to the seawater from a pipeline or facility in a Carbon Capture and Storage (CCS) project. The interaction between droplets and their rising properties such as velocity were examined. The results of numerical simulation show that the presence of SO2 changes particles' shape and their rising velocities significantly compared with the single droplet case. This SO2 contamination also caused the repulsion of impure particles even when they were placed close to each other, which was observed as coalescence in the pure CO2 case. Results will help in understanding the impacts of contamination on the rise of multiple CO2 droplets such as that leaked by future CCS operations.

Simultaneous high-frequency Super-Radiance and low-frequency Coherent Spontaneous Radiation from ultrarelativistic electrons in a waveguide

Terahertz generation of high- and low-frequency pulses from an ultrarelativistic electron bunch, which move in a waveguide placed in an undulator, has been studied. If the length of the bunch is less than the low-frequency wavelength, its radiation under certain conditions stabilizes the length of the bunch and largely compensates for the velocity spread introduced by the particle repulsion. This leads to a significant improvement in the micro-bunching of electrons and increases the energy of the radiated high-frequency pulses.

Effect of charging solid particles on their growth process and parameters of microwave discharge in liquid n-heptane

A zero-dimensional non-stationary model of a microwave discharge in liquid n-heptane at atmospheric pressure with continuous argon injection into the plasma region is presented. The model includes equations for the kinetics of neutral and charged plasma components, equations describing the formation and growth of solid particles from the decomposition products of n-heptane, and an equation for the microwave field strength in plasma. The description of the coagulation process takes into account the electrostatic repulsion of solid particles due to their charge. The kinetics of charged particles is described taking into account their death on the surface of negatively charged solid particles formed in plasma. To determine the coefficients of the reaction rates in mechanisms of direct electron impact, the electron energy distribution function obtained by solving the Boltzmann equation is used. Calculations have shown that the plasma quasineutrality is mainly supported by the charge of solid particles, and the electron concentration is 1–2 orders of magnitude less than the total ion concentration. An increase in the averaged microwave field was noted in comparison with the case that does not take into account charging. Charging of the solid particles does not affect the composition of the main gas-phase products, but leads to the suppression of the coagulation process for large solid particles, which leads to a change in the size distribution function of the solid particles formed in the plasma.