Suspensions Of Colloidal Particles Research Articles

Rescaled mode-coupling scheme for the quantitative description of experimentally observed colloid dynamics.

We describe experimentally observed collective dynamics in colloidal suspensions of model hard-sphere particles using a modified mode coupling theory (MCT). This rescaled MCT is capable of describing quantitatively the wave-vector and time-dependent diffusion in these systems. Intermediate scattering functions of liquidlike structured dispersions are determined by means of static and dynamic light-scattering experiments. The structure and short-time dynamics of the systems can be described quantitatively employing a multicomponent Percus-Yevick ansatz for the partial structure factors and an effective, one-component description of hydrodynamic interactions based on the semianalytical δγ expansion. Combined with a recently proposed empirical modification of MCT in which memory functions are calculated using effective structure factors at rescaled number densities, the scheme is able to model the collective dynamics over the entire accessible time and wave-vector range and predicts the volume-fraction-dependence of long-time self-diffusion coefficients and the zero-shear viscosity quantitatively. This highlights the potential of MCT as a practical tool for the quantitative analysis and prediction of experimental observations.

Stem cutting: A novel introduction site for transporting water-insoluble particles into tomato (Solanum lycopersicum) seedlings

The introduction of exogenous particles into plants has promising applications in agriculture and biotechnology. Nanoparticles can be transported into plants through foliar application or root uptake. However, both methods have limitations in terms of the size of the particles (<40 nm) that can be transported due to the barriers of the cell wall and cuticle. In the present study, we proposed a novel method to deliver particles of up to 110 nm into plants by cutting the stem of tomato seedlings. We demonstrated for the first time, using water-insoluble silica colloids, that not only nanoparticles but also submicron particles can be transported toward the leaves when the plant stem is used as the entry point of particles. Thirty-five-day-old tomato seedlings were used as the target plants. When the cut stem seedlings were immersed in the colloidal particle suspension for up to 24 h, significant particle accumulation was observed in the nodes and leaves. The relatively low particle concentrations (10 mg/L) allowed effective transport throughout the plants. Silica particles with average diameters of 10 nm and 110 nm were both well transported and moved through the stem. Even after the particles entered the plant, adventitious roots were formed, resulting in the formation of whole plants with roots, stems, and leaves. This method can be applied not only to tomatoes but also to other food crops for various applications in plant biotechnology.

Phase separation of a magnetic fluid: Asymptotic states and nonequilibrium kinetics.

We study self-assembly in a colloidal suspension of magnetic particles by performing comprehensive molecular dynamics simulations of the Stockmayer (SM) model, which comprises spherical particles decorated by a magnetic moment. The SM potential incorporates dipole-dipole interactions along with the usual Lennard-Jones interaction and exhibits a gas-liquid phase coexistence observed experimentally in magnetic fluids. When this system is quenched from the high-temperature homogeneous phase to the coexistence region, the nonequilibrium evolution to the condensed phase proceeds with the development of spatial as well as magnetic order. We observe density-dependent coarsening mechanisms-a diffusive growth law ℓ(t)∼t^{1/3} in the nucleation regime and hydrodynamics-driven inertial growth law ℓ(t)∼t^{2/3} in the spinodal regimes. [ℓ(t) is the average size of the condensate at time t after the quench.] While the spatial growth is governed by the expected conserved order parameter dynamics, the growth of magnetic order in the spinodal regime exhibits unexpected nonconserved dynamics. The asymptotic morphologies have density-dependent shapes which typically include the isotropic sphere and spherical bubble morphologies in the nucleation region, and the anisotropic cylinder, planar slab, cylindrical bubble morphologies in the spinodal region. The structures are robust and nonvolatile, and exhibit characteristic magnetic properties. For example, the oppositely magnetized hemispheres in the spherical morphology impart the characteristics of a Janus particle to it. The observed structures have versatile applications in catalysis, drug delivery systems, memory devices, and magnetic photonic crystals, to name a few.

Flow and Heat Transfer of Micropolar Ferrofluid at Stagnation Point on a Horizontal Flat Plate in the Presence of Magnetic Field and Thermal Radiation

Ferrofluid demonstrates Newtonian or non-Newtonian fluid behaviour depending on the characteristics of ferrofluid. Generally, ferrofluid consists of a stable colloidal suspension of single-domain magnetic particles in a base fluid that can assume non-Newtonian fluid behaviour involving a spin vector and microinertia tensor in flow motion. These two properties possess the theory of micropolar fluid which exhibits microrotational motions and spin inertia in microscopic behaviour. Therefore, this theoretical study is focused to investigate the boundary layer of micropolar ferrofluid flow and heat transfer at the stagnation point on the horizontal flat plate. Magnetite (Fe3O4) nanoparticles and water (H2O) compose in ferrofluid exposed to the magnetic field and thermal radiation is considered. The influences of ferroparticles volume fraction and micropolar parameter on the ferrofluid flow and heat transfer are evaluated mathematically. The partial differential equations have been formulated based on purposed assumptions using Tiwari and Das model and are simplified into ordinary differential equations, which are then solved numerically by Runge-Kutta Fehlberg (RFK45) method. The numerical results of the velocity profile, temperature profile, angular velocity profile, reduced skin friction and reduced Nusselt number are scrutinised in different values of ferroparticles volume fraction and micropolar parameter to estimate the ferrofluid flow and heat transfer. It is found the velocity profile of micropolar ferrofluid flow increases when elevates the ferroparticles volume fraction but decreases when increasing the micropolar parameter. Meanwhile, enlarging ferroparticles volume fraction of micropolar ferrofluid also enhances the temperature profile, reduced skin friction and reduced Nusselt number in the presence of magnetic field and thermal radiation parameter.

Induced phase transformation in ionizable colloidal nanoparticles

Acid–base equilibria directly influence the functionality and behavior of particles in a system. Due to the ionizing effects of acid–base functional groups, particles will undergo charge exchange. The degree of ionization and their intermolecular and electrostatic interactions are controlled by varying the pH and salt concentration of the solution in a system. Although the pH can be tuned in experiments, it is hard to model this effect using simulations or theoretical approaches. This is due to the difficulty in treating charge regulation and capturing the cooperative effects in a colloidal suspension with Coulombic interaction. In this work, we analyze a suspension of ionizable colloidal particles via molecular dynamics (MD) simulations, along with Monte Carlo simulations for charge regulation (MC-CR) and derive a phase diagram of the system as a function of pH. It is observed that as pH increases, particles functionalized with acid groups change their arrangement from face-centered cubic (FCC) packing to a disordered state. We attribute these transitions to an increase in the degree of charge polydispersity arising from an increase in pH. Our work shows that charge regulation leads to amorphous solids in colloids when the mean nanoparticle charge is sufficiently high.Graphical abstract

Bentonite and polymeric support fluids used for stabilization in excavations

Bentonite is a natural and finite mineral resource. Dilute suspensions of sodium montmorillonite clay in water represents bentonite slurries. Suspension and orientation of colloidal clay particles define rheological properties in bentonite slurry (BS). The BS has been used about seventy years to temporarily support the excavations. More recently, polymer support fluids (PSF) gained much popularity and are widely used compared to bentonite support fluids. The PSF are categorized into natural (pure) and synthetic polymers. Physico-chemical properties of PSF are different than BS irrespective of the quite similarity in the mode of action. Synthetic polymer fluids are molecularly engineered fluids that can be a popular alternative of conventional BS deployed as excavation support fluids in different foundation applications such as diaphragm wall panels and pile bores. The synthetically engineered fluids of polymers (water-soluble) are different from conventional BS. The PSF offer additional benefits because their use is cost effective, eco-friendly, and these polymers need smaller site footprint as well as easy preparation, mixing, handling, management and ultimately the final disposal. Nevertheless, synthetic polymers have advantage over bentonite, however, foundation engineers and scientists have also certain concerns about their use because of their performance related issues. For an efficient use of polymers, specific properties and in situ behavior of polymers as well as their sorption onto the soils must be recognized because the polymer concentration in the solution is decreased with time during their use. The present manuscript reviewed the relative performance of excavation support fluids and displayed an arranged marriage of physicochemical and rhelogical properties of natural and synthetic excavation support fluids used in the foundation industry. This information will be highly useful to scientific community for their future ventures and will lay a foundation to understand the mechanisms of stabilization in open and deep excavations.

Effects of tunable hydrophobicity on the collective hydrodynamics of Janus particles under flows

Understanding active colloidal systems with nonequilibrium self-organization is a long-standing, challenging area in material sciences and biology. In this work we use a colloidal suspension of Janus particles to investigate the hydrodynamics that underlies their various morphologies (unilamellar, multilamellar, and striated structures) and rheological properties.

Full dynamic corrections to the Maxwell Garnett mixing formula and corresponding extensions beyond the dipolar approximation

Here we derive a full dynamic extension to the Maxwell Garnett mixing formula for the effective refractive index of a random system of particles that takes proper account of scattering by the particles even for moderate densities. The new formula exhibits the so-called dependent-scattering effects, which are strongest, in relative terms, in colloidal systems with small non-absorbing particles. Then we extend our result to systems of large particles having a multipolar electromagnetic response and offer a new approximation to the effective refractive index for these systems. The resulting formula can also be seen as an extension of the well-known Foldy-Lax approximation through dynamic local-field corrections. This formula reduces to all previously established approximations in the appropriate limits. We compare predictions of this formula for the imaginary part of the effective refractive index with experimental data of colloidal suspensions of non-absorbing particles with sizes comparable to and larger than the wavelength of the incident radiation and find excellent agreement. We provide some new insights into the origin of dependent scattering for systems of very small particles, such as nanofluids in the optical regime, and finally show predictions of the here-derived formulas for the effective refractive index of a system of plasmonic particles, showing redshifts of the resonance which differ from the ones predicted by other approximations.

Entropic analysis of cilia-modulated slip flow of trimetallic nanofluid through electroosmotic corrugated pump in the presence of inclined magnetic field

An incredible eradication of thermal indulgence is required to enhance the flow and heat transfer enhancement in micro/nanofluidic devices. In addition, the rapid transport and instantaneous mixing of colloidal suspensions of metallic particles at nanoscale are exceptionally crucial at ascendency of inertial and surface forces. To address these challenges, the present work is intended to investigate the role of trimetallic nanofluid comprising of three kinds of nano-sized granules (titanium oxide, Silica and Aluminium dioxide) with pure blood through a heated micropump in the presence of inclined magnetic field and axially implemented electric field. To ensure rapid mixing in unidirectional flow, the pump internal surface is lined-up with mimetic motile cilia with slip boundary. The embedded cilia whip in pattern due to dynein molecular motion controlled by time and produce a set of metachronal waves along the pump wall. The shooting technique is executed to compute the numerical solution. In a comparative glance it is revealed that the trimetallic nanofluid exhibits 10% higher heat transfer efficiency as compared to bi-hybrid and mono nanofluids. Moreover, the involvement of electroosmosis results in almost 17% decrease in the heat transfer rate if it values jumps from 1 to 5. The fluid temperature in case of trimetallic nanofluid is higher and thus keeps the heat transfer entropy and the total entropy lower. Furthermore, involvement of thermal radiated and momentum slip significantly contribute in reducing heat losses.

Superbright quantum dots with inorganic caps

Inorganic semiconductor nanocrystals, or quantum dots, are widely used in commercial displays and imaging technology. They could be used in additional optoelectronic applications if their charge-transport properties could be improved without dimming their intense luminescence. A new study reports a way to do that by treating the crystals with metal salts to customize the quantum dots’ surface chemistry ( Nat. Commun. 2023, DOI: 10.1038/s41467-022-35702-7 ). Quantum dots are typically capped with long-chain hydrocarbon ligands to control crystal growth and stabilize the particles in colloidal suspensions. They also form electrically insulating barriers that impede charge flow between particles, a property needed for electronic applications. Replacing the organic ligands with inorganic ones can boost charge transport, but that approach can reduce luminescence by over 75%. Yuanyuan Wang of Nanjing University, Dmitri V. Talapin of the University of Chicago, and coworkers treated organically capped quantum dots with salts of cadmium, zinc, and other

Bacterial nanocellulose membrane as novel substrate for biomimetic structural color materials: Application to lysozyme sensing

The development of optical biosensors based on structural colors generated by short-range ordered colloidal particles is attracting growing interest due to their non-iridescent and non-fading features. In this study, a biomimetic approach using biopolymers for the various steps of sensor construction is presented. Bacterial nanocellulose (BNC) has many foreseen applications in biomedical engineering because of its biocompatibility, good mechanical strength, and large modifiable surface area. Herein, a novel approach is taken by using functionalized BNC as a substrate to build a molecularly imprinted photonic sensing layer. BNC was modified with polydopamine (PDA), which improved the adhesion and mechanical properties of the BNC substrate while providing simultaneously a black background for color saturation. A molecularly imprinted polymer (MIP) also made of PDA was used to create the recognition sites for the biomarker lysozyme. A monodisperse colloidal suspension of silica particles was first synthesized and used as core of the MIP shell, and then the photonic structure was assembled on the PDA-BNC membrane. The biosensor showed a detection limit of about 0.8 nmol L−1 of lysozyme in spiked human serum and demonstrated to be selective against cystatin C. These properties, combined with biocompatible, eco-friendly, and low-cost materials, offer a sustainable sensing platform with great potential for healthcare applications.

Parameter optimization of electrophoretically deposited graphene oxide coating on the frictional characteristics of AISI 52100 alloy steel

Wear-resistant coatings help to extend the life of materials by improving their tribological properties. Among the various coating methods, electrophoretic deposition (EPD) is a simpler, low cost and effective coating method in which the charged particles in colloidal suspension are deposited on the substrate. Graphene oxide (GO) has been coated by different deposition methods, but the optimization of EPD coating factors for improving frictional characteristics has been studied limitedly. This work aims to optimize various parameters of EPD coating such as voltage, deposition time, concentration and sintering temperature for a lower tribological response. Experiments were conducted using the L16 orthogonal array created by the Taguchi optimization method. After sintering the samples, tribological tests were done using a Pin-on-Disc apparatus. The influence of coating parameters and the optimum combination of the factors for a lower coefficient of friction (COF) was found and experimentally validated. A crack density study has been done to study the influence of porosity on frictional characteristics. Results showed that the COF of the optimum GO-coated substrate (0.152) was lowered by 71.33% while comparing with the COF of uncoated substrate (0.53) under the same test conditions.

Climbing Colloidal Suspension

Mixtures of powder and liquid are ubiquitous in nature as well as industries and exhibit complex flowing and deforming behaviors, including sol to gel transition under shear stress. In order to better understand the characteristic features of this type of mixture, we observed the behavior of a mixture of colloidal silica particles and water as a model system under vibration. The mixture showed different states, from powder-like to viscous fluid-like, with increasing content of water. At certain concentrations of silica particles (around 70 wt. %) and under relatively faster vibration (over 17 Hz), we observed that the colloidal suspension of silica particles and water climbed up the wall of a container against gravity. The main purpose of this paper is to report how we can observe the climbing suspension of colloidal silica. The rheological measurements of the climbing suspension demonstrated that the climbing suspension showed shear-thickening behavior, where force chain networks and normal stress differences are considered to develop. Therefore, we speculate that the transient formation and breaking of force networks and normal stress differences under vibration contribute to the occurrence of the climbing suspension. The tunable nature of colloidal suspensions may help to elucidate the climbing mechanism in the future.

МАКРОФИТЫ РОДА POTAMOGETON — БИОИНДИКАТОРЫ НАКОПЛЕНИЯ ТЯЖЕЛЫХ МЕТАЛЛОВ

This work presents the investigation of the content of some heavy metals in the pondweeds of the Lower Volga River Delta within the area of Astrakhan State Biosphere Reserve. Higher aquatic plants extract chemical elements both from bottom sediments and water column. Moreover, the macrophytes, namely the representatives of Potamogeton genus, are capable of extraction and accumulation of the metals dissolved in the water, contained in the suspended colloidal particles, and present on the surface of leaves. This work is aimed at the identification of species-specific features of the typical hydatophytes—aquatic plants of Potamogeton genus—pertaining to the accumulation of heavy metals. The content of chemical elements in the investigated specimens has been identified using atomic absorption spectrometry; the results have been processed with statistical methods. It has been found that all investigated plant species accumulate iron and manganese in the highest quantities and cobalt and cadmium in the lowest. The investigated pondweed species have shown species-specific properties in the accumulation of chemical elements. Potamogeton crispus and Potamogeton lucens are found to be iron concentrating species. Potamogeton lucens also accumulates nickel, iron and manganese, and Potamogeton pectinatus accumulates chrome, cobalt and lead.

Rheology of 3D printable ceramic suspensions: effects of non-adsorbing polymer on discontinuous shear thickening.

Concentrated suspensions of particles at volume fractions (ϕ) ≥ 0.5 often exhibit complex rheological behavior, transitioning from shear thinning to shear thickening as the shear stress or shear rate is increased. These suspensions can be extruded to form 3D structures, with non-adsorbing polymers often added as rheology modifiers to improve printability. Understanding how non-adsorbing polymers affect the suspension rheology, particularly the onset of shear thickening, is critical to the design of particle inks that will extrude uniformly. In this work, we examine the rheology of concentrated aqueous suspensions of colloidal alumina particles and the effects of adding non-adsorbing polyvinylpyrrolidone (PVP). First, we show that suspensions with ϕalumina = 0.560-0.575 exhibited discontinuous shear thickening (DST), where the viscosity increased by up to two orders of magnitude above an onset stress (τmin). Increasing ϕalumina from 0.550 to 0.575 increased the viscosity and yield stress in the shear thinning regime and decreased τmin. Next, PVP was added at concentrations within the dilute and semi-dilute non-entangled regimes of polymer conformation (ϕPVP = 0.005-0.050) to suspensions with constant ϕalumina = 0.550. DST was observed in all cases and increasing ϕPVP increased the viscosity and yield stress. Interestingly, increasing ϕPVP also increased τmin. We posit that the free PVP chains act as lubricants between alumina particles, increasing the stress needed to induce thickening. Finally, we demonstrate through direct comparisons of suspensions with and without PVP how non-adsorbing polymer addition can extend the extrusion processing window due to the increase in τmin.

Wettability-tuned silica particles for emulsion-templated microcapsules.

Pickering emulsions play a significant role in generating advanced materials and have widespread application in personal care products, consumer goods, crude oil refining, energy management, etc. Herein, we report a class of wettability tuned silica-based Pickering emulsifiers which stabilize a diverse range of fluid-fluid interfaces: oil/water, ionic liquid/oil, and oil/oil, and their use to prepare microcapsules via interfacial polymerization. To alter particle wettability, colloidal suspensions of SiO2 particles (22 nm) were modified via silanization with reagents of varied hydrophilicity/hydrophobicity, giving particles that could be dispersed in solvents that became the continuous phase of the emulsions. To test the viability of this system as templates for the fabrication of composite materials, the different particle-stabilized emulsions were coupled with interfacial polymerization, leading to microcapsules with polyurea/silica shells. These results demonstrate that a single particle feedstock can be coupled with fundamental chemical transformation to access a versatile toolkit for the stabilization of diverse fluid interfaces and serve as a template for the preparation of hybrid architectures.

Surface melting of a colloidal glass

Despite their technological relevance, a full microscopic understanding of glasses is still lacking. This applies even more to their surfaces whose properties largely differ from that of the bulk material. Here, we experimentally investigate the surface of a two-dimensional glass as a function of the effective temperature. To yield a free surface, we use an attractive colloidal suspension of micron-sized particles interacting via tunable critical Casimir forces. Similar to crystals, we observe surface melting of the glass, i.e., the formation of a liquid film at the surface well below the glass temperature. Underneath, however, we find an unexpected region with bulk density but much faster particle dynamics. It results from connected clusters of highly mobile particles which are formed near the surface and deeply percolate into the underlying material. Because its thickness can reach several tens of particle diameters, this layer may elucidate the poorly understood properties of thin glassy films which find use in many technical applications.

Improving the clarification quality of industrial wastewater by acoustic method

The gravity clarification method is relatively effective only for extracting coarse suspended particles from industrial wastewater. The removal of medium and fine suspended and colloidal particles and heavy metals at respective treatment facilities requires their preliminary aggregation by chemical, physical, or combined methods, with the use of additional sorbent filters. Irregular removal of bottom sediments results in secondary pollution of industrial wastewater with mineral particles and heavy metals retained by the sediments. In poorly treated industrial effluents, fish die within a few weeks. The key factor, in this case, is the dispersion rather than concentration of suspended solids in the water. The method proposed involves coagulation of finely dispersed suspended solids, colloidal particles, and insoluble heavy metals and their forced settling with simultaneous compaction of bottom sediments in acoustic fields (not only in horizontal settling tanks, but also directly in local and main water sumps of open pits and mines). The paper presents examples of successful application of the integrated acoustic method in the sumps of pits and mines at diamond and gold mining enterprises of the Russian Federation in 2015&ndash;2022. The average underground dewatering efficiency (in local and main mine dewatering) is shown to be 82.1 %, which is 20&ndash;22 % higher than the surface dewatering efficiency (via the settlement pond and two filter channels) of the mine water clarification facility.

The Study of Betulin Particles Containing Hydrogels Prepared by Antisolvent Precipitation

The aim of the study was to investigate the effect of process parameters on the production of hydrogels with antisolvent precipitation using unpurified (UB) and purified (PB) birch outer bark betulin powder samples. Experimental activities are focused on the production of hydrogels using concentration of colloidal dispersions with filtration of UB or PB sample particles obtained by antisolvent precipitation method varying the dilution of saturated (at boiling temperature) ethanol solutions with different water content. During the study the maximum solubility in ethanol at boiling point of PB (22.0 g/L) and UB (55.0 g/L) was determined. For obtaining gel with the highest liquid content (absorption capacity 37.45 g per 1 g of dry matter) from PB by antisolvent precipitation the optimal saturated ethanol solution dilution with water was 12.5 vol%. In the case of UB hydrogel, by dilution of ethanol from 25 to 10 vol%, a gradual decrease of hydrogel dry matter yield and a simultaneous increase of the filtrate dry matter yield can be observed, which is related with leaching of the particles through the filter paper together with a solution and form a colloidal suspension of particles. For obtaining gels with high liquid content from UB the optimal saturated ethanol solution dilution with water was in the range from 20.0 to 12.5 vol% (absorption capacity in average 18 g per 1 g of dry matter). Comparing the chemical compositions of the raw materials and dry matter of hydrogels in the case of PB composition remains quite similar while in UB dry matter composition the betulin content increased from 52 to even 69 wt%. PB at the optimal dilution of 12.5 vol% of ethanol managed to achieve average particle size - 231.7 nm and with UB in the optimal dilution range from 20 to 12.5 vol% the range of average particle size was from 304.7 to 189.8 nm.

Filter Modified with Hydrophilic and Oleophobic Coating for Efficient and Affordable Oil/Water Separation

To mitigate the damage of oil spills, a filter modified with a hydrophilic and oleophobic coating is proposed for affordable and efficient oil separation and recovery from water. The sol–gel method was chosen to produce a colloidal suspension of titanium dioxide particles for its ease of production and its versatility in application for many different substrates, including paper and cloth fabric. After immersing the substrates into a titanium-containing solution, three techniques were applied to increase the production of titanium dioxide—microwave-assisted, refrigeration, and ultra-sonication. Contact angle tests were done to investigate the change in the filter’s oleophobicity. The titanium dioxide present on the surface of the filter was amorphous, but all treatment methods showed an improvement in oleophobicity. All treated filters improved oil filtration performance by up to eighty percent. The filters isolated motor oil from a mixture while allowing water to pass through. The coated filters also displayed photocatalytic activity by degrading methylene blue on its surface when exposed to sunlight, demonstrating the filter’s self-cleaning ability. For real-world applications, the filter can be supported by a stainless mesh for enhanced strength and durability. While being dragged through the water, the filter collects the surface oil, allowing water to pass through via gravity.