Suspensions Of Colloidal Particles Research Articles

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 2015–2022. The average underground dewatering efficiency (in local and main mine dewatering) is shown to be 82.1 %, which is 20–22 % 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.

Distribution, source and behavior of rare earth elements in surface water and sediments in a subtropical freshwater lake influenced by human activities

As tracers, rare earth elements (REEs) can reflect the influence of human activities on the environmental changes in aquatic systems. To reveal the geochemical behavior of REEs in a water–sediment system influenced by human activities, the contents of REEs in the surface water and sediment in the Chaohu Lake Basin were measured by inductively coupled plasma mass spectrometry (ICP–MS). The results show that the ΣREE contents in the surface water are 0.10–0.850 μg L−1, the ΣREE contents in the sediments are 71.14–210.01 μg g−1, and the average contents are 0.24 μg L−1 and 126.72 μg g−1, respectively. Almost all water and sediment samples have obvious light REE (LREE) enrichment, which is the result of the input of LREE-rich substances released by natural processes and human activities (industrial and agricultural production). Under the alkaline water quality conditions of Chaohu Lake, REEs (especially LREEs) are easily removed from water by adsorption/coprecipitation reactions with suspended colloidal particles, which leads to the enrichment of LREEs in sediments. The Ce anomaly of the water–sediment system is related to the oxidation environment, while the Eu anomaly is related to the plagioclase crystallization. Significant Gd anomalies was observed in the downstream of rivers flowing through urban areas, which was related to the anthropogenic Gd wastewater discharged by hospitals. The ∑REE–δEu and provenance index (PI) discrimination results are consistent, indicating that the sediments in Chaohu Lake mainly come from rivers flowing through the southwest farmland. Furthermore, the spatial distribution of REEs shows that these tributaries are significantly affected by agricultural activities. The distribution and accumulation of REEs in Chaohu Lake are the result of the interaction of natural and human processes. The results can provide a scientific reference for the distribution and environmental behavior of REEs in aquatic environments disturbed by human beings.

A Review of the Advances and Challenges in Measuring the Thermal Conductivity of Nanofluids.

Fluids containing colloidal suspensions of nanometer-sized particles (nanofluids) have been extensively investigated in recent decades with promising results. Driven by the increase in the thermal conductivity of these new thermofluids, this topic has been growing in order to improve the thermal capacity of a series of applications in the thermal area. However, when it comes to measure nanofluids (NFs) thermal conductivity, experimental results need to be carefully analyzed. Hence, in this review work, the main traditional and new techniques used to measure thermal conductivity of the NFs are presented and analyzed. Moreover, the fundamental parameters that affect the measurements of the NFs’ thermal conductivity, such as, temperature, concentration, preparation of NFs, characteristics and thermophysical properties of nanoparticles, are also discussed. In this review, the experimental methods are compared with the theoretical methods and, also, a comparison between experimental methods are made. Finally, it is expected that this review will provide a guidance to researchers interested in implementing and developing the most appropriate experimental protocol, with the aim of increasing the level of reliability of the equipment used to measure the NFs thermal conductivity.

Investigation on spray combustion characteristics of Boron-Loaded slurry fuel in a Swirl-Stabilized combustor

For many decades, liquid hydrocarbon fuels are being used to propel air-breathing engines. However, the energy content of liquid hydrocarbon fuels has reached close to its limitation. Any further improvement in energy value is quite difficult through chemical methods. Slurry fuels, which are colloidal suspensions of solid energetic particles in liquid fuel, became a potential alternative fuel. Among several solid additives, boron is considered the best choice because of its higher heating values. However, our knowledge about boron-loaded slurry fuel is very limited. Therefore, here in this study, we experimentally investigated the combustion characteristics of boron/Jet A-1 slurry fuel spray in a swirl-stabilized combustor. A particle loading of 10% by weight is considered here for the experiment. The feed boron, as well as the burnt boron samples, were characterized using standard material characterization techniques in order to understand the surface morphology, oxidation behavior, and active boron content. The combustion characteristics of slurry fuel were analyzed through spectroscopy and BO2* chemiluminescence imaging. Positive thermal contribution from boron combustion was quantified via temperature measurements at three different radial locations of the combustor exit. The spectroscopy and chemiluminescence signatures indicate that combustion of boron particles occurs downstream of the dump plane. The exit temperature of boron-laden slurry fuel measured at all three different radial locations is higher compared to neat Jet A-1. An increment of 19% in exit temperature was observed in the case of boron slurry fuel relative to neat Jet A-1. The X-ray diffractograms (XRD) and thermogravimetric analysis (TGA) show the complete oxidation of boron particles.

Photonic Crystal-Enhanced Photodynamic Antibacterial Therapy

Photonic Crystal-Enhanced Photodynamic Antibacterial Therapy

Effects of interactions, structure formation, and polydispersity on the dynamic magnetic susceptibility and magnetic relaxation of ferrofluids

Linear response theory relates the decay of equilibrium magnetisation fluctuations in a ferrofluid to the frequency-dependent response of the magnetisation to a weak ac external magnetic field. The characteristic relaxation times are strongly affected by interactions between the constituent particles. Similarly, the relaxation of an initially magnetised system towards equilibrium in zero field occurs on a range of timescales depending on the structure of the initial state, and the interactions between the particles. In this work, ferrofluids are modelled as colloidal suspensions of spherical particles carrying point dipole moments, and undergoing Brownian motion. Recent theoretical and simulation work on the relaxation and linear response of these model ferrofluids is reviewed, and the effects of interactions, structure formation, and polydispersity on the characteristic time scales are outlined. It is shown that: (i) in monodisperse ferrofluids, the timescale characterising the collective response to weak fields increases with increasing interaction strength and/or concentration; (ii) in monodisperse ferrofluids, the initial, short-time decay is independent of interaction strength, but the asymptotic relaxation time is the same as that characterising the collective response to weak fields; (iii) in the strong-interaction regime, the formation of self-assembled chains and rings introduces additional timescales that vary by orders of magnitude; and (iv) in polydisperse ferrofluids, the instantaneous magnetic relaxation time of each fraction varies in a complex way due to the role of interactions.

Coupling Flotation Rate Constant and Viscosity Models

In a flotation process, the particle–bubble and particle–particle interactions are key factors influencing collection efficiencies. In this work, the generalized Sutherland equation collision model and the modified Dobby–Finch attachment model for potential flow conditions were used to calculate the efficiencies of particle–bubble collision and attachment, respectively, for a flotation particle size of 80 μm. The negative effects of increase in the suspension viscosity due to the presence of fine particles on the flotation performance of fine particles have been reported, but there is no overarching model coupling the suspension viscosity and the flotation performance in the literature. Therefore, our study addressed this very important research gap and incorporated the viscosity model as a function of solid concentration, shear rate, and particle size into a flotation rate constant model that was proposed and conducted for the first time. This is quite a unique approach because the previously developed flotation rate constant model has never been coupled with a suspension rheology model taking into account the solid particle concentration and shear rate, although they are very important flotation variables in practice. The effect of the presence of ultra-fine/fine particles on the viscosity of the suspension and the flotation efficiencies and rate constant of flotation particle size of 80 μm were also investigated in order to better understand the mechanism of the problematic behavior of ultra-fine/fine particles in flotation. This coupling study started with the simplest case: flowing suspensions of inert, rigid, monomodal spherical particles (called hard spheres). Even for hard spheres, the effect of shear rate and particle size which produces deviation from the ideal case (constant viscosity at constant temperature regardless of shear rate) was clearly identified. It was found that the suspension viscosity increases with the decrease in fine/ultra-fine particle size (i.e., 1 µm–8 nm) and at higher solid particle concentration. Then, the colloidal particle suspensions, where interparticle forces play a significant role, were also studied. The suspension viscosity calculated for both cases was incorporated into the flotation efficiencies and rate constant models and discussed in terms of the effects of the presence of ultra-fine and fine particles on the flotation kinetics of flotation particle size of 80 μm.

Membrane diafiltration for enhanced purification of biologically active compounds from goji berries extracts

• The recovery of phenolic compounds from aqueous goji berries extract was investigated. • Three tight ultrafiltration membranes with different cut-off (1, 2.5 and 3.5 kDa) were studied. • Diafiltration was implemented to improve the separation of phenolic compounds from sugars. • Membrane performance was evaluated in terms of productivity and selectivity towards target compounds. • All selected membranes allowed high recovery of phenolic compounds into the retentate. Goji berries represent a valuable source of phenolic compounds with a strong antioxidant and free radical scavenging activity combined to huge quantities of small sugars. This study was aimed at evaluating the potential of three tight ultrafiltration (UF) membranes with molecular weight cut-off (MWCO) from 1.0 to 3.5 kDa in the fractionation of phenolic compounds from sugars in the aqueous extract of dried goji berries. The aqueous extract produced in optimized conditions of water-to-solid ratio and temperature (6.66 mL/g and 65 °C, respectively) was preliminarily clarified by UF in order to remove suspended solids and colloidal particles. A membrane diafiltration (DF) process was developed in order to fractionate phenolic compounds from sugars with selected UF membranes from the clarified extract. The membrane performance was evaluated in terms of productivity and selectivity towards target compounds. All selected membranes allowed high recovery (more than 80%) of phenolic compounds into the retentate. On the other hand, the yield of carbohydrates increased in the permeate by increasing the diafiltration volume. Among the selected membranes, the 2.5 kDa membrane allowed to reduce the concentration of total carbohydrates from 26.5 up to 2.2 g glucose/L (a reduction of 91.7%) in a diafiltration/batch concentration process producing a concentrated extract enriched in phenolic compounds of interest for pharmaceutical or nutraceutical applications.

Efficient removal of both positively and negatively charged colloidal contaminants using amphoteric starch-based flocculants synthesized by low-pressure UV initiation

• Amphoteric starch-based flocculants were synthesized by low-pressure UV initiation. • Amphoteric starch-based flocculants show high flocculation performance. • Amphoteric starch-based flocculants exhibit low salts sensitivity. • Flocculation mechanism includes charge neutralization, patching and bridging. Surface charges of the suspended colloidal particles in real water can be either negative or positive. Flocculation is one of the most widely used technologies in water treatment. A series of amphoteric starch-based flocculants (denoted as ASBFs) with the same chemically modified functional groups but different charge degrees and intrinsic viscosities were successfully via low-pressure ultraviolet initiation and used for the removal of different charged contaminants from water. The characterization results confirmed the successful grafting acrylamide (AM) and 2-methacryloyloxyethyl) trimethyl ammonium chloride (DMC) onto carboxymethyl starch. Different influencing factors, including flocculant dosage, contaminants concentration, pH of solution, stirring speed, sedimentation time and various salts, were investigated systematically. ASBFs with eco-friendliness exhibited high flocculation property, low optimal dosage and low salts sensitivity, for not only kaolin, but also hematite suspensions. The zeta potential (ZP) measurement suggested that the removal mechanism mainly includes charge neutralization, patching and bridging.

Quality Assessment of Water from Some Selected Sources in Pokhara, Nepal

The present study was carried out to analyze and compare the physicochemical properties of water from Seti Gandaki river, Kali stream, irrigation canal, bore well and potable sources in Pokhara Metropolitan-1, Kaski, Nepal by using standard techniques. Observed properties from different sources were compared to each other and with recommended standard World Health Organization (WHO) values. The result of the study showed that the large number of physical and chemical parameters such as color odor, temperature, specific gravity, relative turbidity, suspended solid (SS), total dissolved solid (TDS), total solid (TS), pH, electrical conductivity (EC), alkalinity, carbonate, bicarbonate, residual sodium carbonate (RSC), boron, chloride, sulphate, nitrate and nitrite-N, calcium hardness, magnesium hardness, total hardness, oil and grease, phenol, surfactants were within the permissible limit of WHO. The observed color of river water and irrigation water was glacial creamy white due to excess of cream white colored suspended colloidal particles in water. The analyzed amount of iron for the sample from different sources was more than that of permissible limit of WHO standard and iron amount was much more for bore well sample. On the basis of analyzed result and WHO standard values, it was concluded that potable water, bore well water and stream water can be used for washing, bathing, irrigation, and industrial purposes after proper treatments. In this study, most of the physicochemical and organic parameters were also analyzed but not the microbiological species.

Particle Separation through Diverging Nanochannels via Diffusiophoresis and Diffusioosmosis

Colloid separation from dilute solutions is of significant relevance in a multitude of technological applications. Here we use numerical simulations to investigate a recently proposed particle separation technique based on diffusiophoresis. Diffusiophoresis refers to the chemotactic migration of particles induced by local chemical gradients that allows for efficient particle manipulation. It can act in a cooperating or competing manner with respect to fluid advection, and is usually accompanied by diffusioosmosis that refers to the bulk flow adjacent to a solid surface. We consider a microfluidic setup with cocurrent flow in two horizontal channels connected by vertical diverging nanochannels, where the top flow contains suspended colloidal particles and solute at a low concentration and the bottom flow contains solute at a higher concentration. We analyze the fluid, solute, and particle dynamics to show that the particle motion is driven into the diverging nanochannels under the combined influence of fluid advection and diffusiophoresis, the latter arising due to the imposed solute gradient. Selective separation and characterization of the particles based on their size and surface charge can be achieved, whose efficiency can be improved by controlling the diffusiophoretic mobility of the particle, solute P\'eclet number, and imposed solute gradient. Diffusioosmosis can enhance or inhibit the diffusiophoretic separation, depending on the surface charge of the solid surfaces.

Turbulence-induced formation of emulsion gels

Emulsion gels have a wide range of applications. We report on a facile and versatile method to produce stable emulsion gels with tunable rheological properties. Gel formation is triggered by subjecting a mixture containing aqueous colloidal particle (CP) suspensions and water-immiscible liquids to intense turbulence, generated by low frequency (20 kHz) ultrasound or high-pressure homogenization. Through systematic investigations, requisite gel formation criteria are established with respect to both formulation and processing, including ratio/type of liquid pairs, CP properties, and turbulence conditions. Based on the emulsion microstructure and rheological properties, inter-droplet bridging and CP void-filling are proposed as universal stabilization mechanisms. These mechanisms are further linked to droplet-size scaling and sphere close-packing theory, distinctive from existing gel-conferring models. The study thereby provides the foundation for advancing the production of emulsion gels that can be tailored to a wide range of current and emerging applications in the formulation and processing of food, cosmetics or pharmaceutical gels, and in material science.

Features of colloidal silica deposits dip coated onto porous alumina membranes from aqueous suspensions

The present work is directed towards understanding the development of coating morphologies and the accompanying hydrodynamics of suspension flows during dip coating on porous substrates. Colloidal silica particles are deposited from aqueous suspension onto nanoporous alumina membranes. The choice of colloidal silica as the model system is motivated by its popularity in fabrication of antireflection coatings, and as nanostructured material templates for electrochemical and catalytic applications. Nanoporous alumina as substrate is notable for its chemical and thermal stability, and its ability to form self-organized pore structures. The objective here is to characterize the dependence of coating morphologies on membrane pore size, wettability, dip coating speed, and size of colloidal particles in suspension. A coating regime map is formulated based on different morphologies obtained for coatings deposited under different operating parameter spaces. The map indicates existence of two perceptibly distinct regimes which emanate from particle-induced interfacial deformation of the meniscus: Scarcely populated particulate deposition regime and densely packed coating regime having significant amount of particle deposition. The experimental results are analysed and explained using numerical results from earlier mathematical models in literature which cater to modified Landau-Levich formulation for porous substrates, as well as the hydrodynamics of colloidal assembly on moving substrates.

Hierarchical Microphase Behaviors of Chiral Block Copolymers under Kinetic and Thermodynamic Control

Hierarchical Microphase Behaviors of Chiral Block Copolymers under Kinetic and Thermodynamic Control

Nanodiamond Colloids heat transfer behavior in electronics thermal management – an experimental study

ABSTRACT This article reports the heat transfer data obtained from experimenting a novel functionalized nanodiamond (fND) colloid. In this functionalization technique, the nanodiamonds are coupled with molecules of the host fluid via carboxylic bonds, leading to a de-aggregated and fully stable nanodiamond colloid. The colloid flows through a conduction cold plate where the system cools the electronic component, leading to the resultant heat dissipation. This surface modification on the fully functionalized nanodiamonds ensures ultimate stability of the colloidal suspension of nanodiamond particles. The heat transfer experiments were performed with different concentrations of nanodiamond (0.05, 0.10, and 0.20 wt.%) and under a turbulent flow regime (6,400 < Re < 17,000). The closed-loop heat transfer apparatus utilizes a pump equipped with a variable frequency drive to study the pumping power at various flow rates and fND concentrations. The experimental results of this paper show the remarkable effect of low-concentrated fND additives on enhancing the heat-transfer coefficient of the deionized water. The results show up to a 70% enhancement in the heat transfer coefficient compared to the base fluid at the same pumping power using a 0.20 wt.% fND. The nanodiamond colloid has shown no sedimentation after remaining stored over two years after synthesis.

Aggregation and breakup of colloidal particle aggregates in shear flow: A combined Monte Carlo - Stokesian dynamics approach

A method for the simulation of aggregation and breakup processes in colloidal particle suspensions is presented. The method combines a Monte Carlo algorithm to determine, on the basis of probabilistic considerations, the sequence of aggregation and breakup events, and a Discrete Element Method, built in the framework of Stokesian dynamics and contact mechanics, to accurately reproduce them. Liquid-solid suspensions subject to a uniform shear stress are investigated. The model is seen to be able to reproduce the typical dynamic steady state which is observed in colloidal suspensions under severe shearing, in which the effects of aggregation and breakup balance each other. The structural properties of the aggregates and the dynamics of the aggregation and breakup phenomena are characterized in detail. Both fragmentation and erosion are seen to contribute to the breakup process, which is characterized by an exponent similar to the one reported in the literature for compact clusters.

Recent advances in using nanofluids in renewable energy systems and the environmental implications of their uptake

It has been more than two decades since the discovery of ‘nanofluids’ – mixtures of common liquids and solid nanoparticles with at least one dimension below 100 nm in size. While colloidal suspensions of particles (which include larger particles) have been studied for several decades, the term ‘nanofluids’ designates fluid systems that have enhanced thermal and optical properties. Although barriers to their commercial adoption remain, the field of nanofluids has continued to grow. Many studies have considered the effects of adding nanoparticles on the thermal efficiency and exergy efficiency of renewable energy systems particularly solar systems, however, few have investigated their potential for emission reductions. Critically, since renewable energy technologies aim to reduce the environmental impact of energy systems, this review focuses on whether nanofluids provide a net environmental benefit. Thus, in addition to providing a comprehensive overview of this body of literature from an environmental perspective, this review also highlights areas for future work that could help ensure that nanofluids have a net positive environmental impact in renewable energy systems going forward. • The applications of nanofluid in renewable energy systems are discussed in detail. • Nanofluid preparation, characterization, related principles and technologies are presented. • Green synthesis methods of nanofluid preparation, CO 2 emissions, and life cycle assessment are explored. • The key challenges associated with the use of nanofluid in practical applications are listed. • Tackling the environmental impacts of nanofluid would pave way for broader applications.