Presence Of Colloidal Particles Research Articles

The impact of viscosity asymmetry on phase separating binary mixtures with suspended colloids.

The introduction of neutrally wetting colloidal particles into coarsening binary fluids is known to arrest the dynamics of the phase separation, as the colloids tend to be captured by the growing interfaces to reduce the free energy of the system. This phenomenon has often been studied in systems with symmetric fluid viscosities. In this study, we investigate the behavior of colloidal particles introduced into asymmetric binary fluids with a viscosity contrast. Our results show that due to the broken symmetry the colloidal particles more easily escape from the interface towards the more viscous fluid, which reduces the lifetime of the jammed phase. Moreover, the presence of colloidal particles near the interfaces promotes the formation of micro-droplets with typical sizes comparable to the colloids.

A double rigidity transition rules the fate of drying colloidal drops.

The evaporation of drops of colloidal suspensions plays an important role in numerous contexts, such as the production of powdered dairies, the synthesis of functional supraparticles, and virus and bacteria survival in aerosols or drops on surfaces. The presence of colloidal particles in the evaporating drop eventually leads to the formation of a dense shell that may undergo a shape instability. Previous works propose that, for drops evaporating very fast, the instability occurs when the particles form a rigid porous solid, constituted of permanently aggregated particles at random close packing. To date, however, no measurements could directly test this scenario and assess whether it also applies to drops drying at lower evaporation rates, severely limiting our understanding of this phenomenon and the possibility of harnessing it in applications. Here, we combine macroscopic imaging and space- and time-resolved measurements of the microscopic dynamics of colloidal nanoparticles in drying drops sitting on a hydrophobic surface, measuring the evolution of the thickness of the shell and the spatial distribution and mobility of the nanoparticles. We find that, above a threshold evaporation rate, the drop undergoes successively two distinct shape instabilities, invagination and cracking. While permanent aggregation of nanoparticles accompanies the second instability, as hypothesized in previous works on fast-evaporating drops, we show that the first one results from a reversible glass transition of the shell, unreported so far. We rationalize our findings and discuss their implications in the framework of a unified state diagram for the drying of colloidal drops sitting on a hydrophobic surface.

Phase diagram of two-patch colloids with competing anisotropic and isotropic interactions

Patchy particles are considered to be a good model for protein aggregation. We propose a novel method to generate different structures of glucose isomerase protein such as chains, crystals and bundles by utilising aggregation of two-patch colloidal particles in presence of competing isotropic and anisotropic potential. We calculate the equilibrium phase diagram of two-patch colloidal particles and demonstrates the coexistence of different phases like disordered clusters, chains, crystals and bundles depending on the relative strength of isotropic and anisotropic potential. We also show that the formation of network of bundles is metastable against the formation of thermodynamically favored finite sized bundles along with thermodynamically stable crystals. These bundles appear to be helical in structure similar to that observed in sickle cell hemoglobin. The simulation results show that the method can characterize phase behaviour of glucose isomerase protein, which provides a novel tool to unveil self-assembly mechanism of protein under different conditions.

Effect of bentonite particles’ presence on two-dimensional chromium transmission

The co-transport of pollutants with colloidal particles to lower depths of groundwater and porous environments has been demonstrated in many studies in recent three decades. Despite the numerous researches, all experimental and numerical studies of pollutant transfer in the presence of colloidal particles have been carried out in one dimension, which causes significant errors in this phenomenon. In this study, the two-dimensional transfer experiment of chromium in the presence of bentonite colloidal particles is done in saturated porous media. In order to conduct the experiment in two-dimensional conditions, the sampling was done in central and lateral of the last experiment column section. The results have been demonstrated that the transmission along the longitudinal direction is higher than lateral in the three tests of the transfer of chromium, bentonite, and chromium in the presence of bentonite colloidal particles at the beginning of the experiment, and due to completed mixing in the section, it reached to a constant value as lateral samples. While the presence of bentonite colloidal particles facilitates the transfer of chromium in both longitudinal and lateral directions, increasing the bentonite colloidal particle concentration causes more getting stuck of colloid particles between the sand grains and reduction of the chromium transfer in both longitudinal and lateral directions. So, it can be concluded that transfer in the lateral direction is lower in bentonite colloidal particles compared with chromium, and the reason is the bentonite colloidal particles getting stuck between sand grains, which is exacerbated by increasing the concentration of the bentonite. Also, due to the chromium co-transport with colloid particles in the fraction of chromium total transport, increasing the bentonite concentration causes decreasing the chromium lateral transfer.

Experimental investigation on sludge dewatering using granulated blast furnace slag as skeleton material.

The highly compressible nature of sludge and the presence of colloidal particles cause difficulties in sludge dewatering. Reducing the moisture content in secondary sludge is a key factor in reducing the capital costs, operational costs, and transportation costs in wastewater management. This investigation concerned the combined utilization of quicklime and granulated blast furnace slag (GBFS) to improve sludge dewatering. The experimental work included the initial characterization of the sludge and granulated blast furnace slag and evaluation of the dewatering ability of the treated sludge (CST, moisture content, turbidity, zeta potential, and heavy metal and biopolymer contents). Optimization using the Box-Behnken design (BBD) was carried out with various operational parameters, and the best performance was found to be at a pH of 10.2, a dose of 0.34g/g DS, and a contact time of 14min. A characterization study was carried out by scanning electron microscopy (SEM) in conjunction with EDS, X-ray diffractometry (XRD), and Fourier transform infrared spectroscopy (FTIR) to confirm the structural features (dense), elemental composition, and the presence of different functional groups. Hence, this study concluded that the use of quicklime with granulated blast furnace slag is suitable for conditioning during sludge dewatering. Graphical abstract.

Diagnostics of the technical condition of transformers according to the color characteristics of transformer oil

This paper presents the results of a research of transformer oil in a visual way. The high information content of the optical radiation scattered and transmitted through the oil is shown. By the color of the radiation, it is possible to determine such characteristics of the oil as acid number, dielectric loss tangent, the presence of colloidal particles, their concentration and size, as well as the presence of aromatic compounds in the oil, changes in their molecular composition and concentration. By the presence of aromatic compounds and colloidal particles, it is possible to visually state the development of thermal and discharge defects in a transformer. This diagnostic system allows to assess the condition of power transformers without shutting them down, make decisions on their further operation without the use of expensive equipment and at the initial stage to identify the changes that are significant and necessary. This is due to the high cost of the transformer, its importance in terms of the reliability of power supply to consumers, the complexity of determining damages and defects at an early stage of development.

The Influence of Salinity, pH, Temperature and Particles on Produced Water Oil Quantification Precision and Accuracy with Confocal Laser Fluorescence Microscopy

The present study investigates the effects of different produced water parameters, such as salinity, pH, temperature, and presence of colloidal particles, in oil quantification using confocal laser fluorescence microscopy (CLFM). The study simulates different produced water samples, which typically contains a mixture of oil, salts, and different concentrations of particles. The accuracy of the quantification was not affected by the environmental condition for any of the conditions investigated. On the other hand, under extreme environmental conditions, such as high pH (pH 8), salinity (250000 ppm), and temperatures (60 °C), the precision of the CLFM oil quantification was reduced. Changes in the average oil droplet size upon variation of the environmental conditions generally correlated with the change in CLFM measurement precision. Interfacial tension and DLVO interactions were further evaluated to gain a better mechanistic understanding of how the environmental conditions affect the size or colloidal st...

Structure and behaviour of vesicles in the presence of colloidal particles.

This review highlights recent studies that investigate the structural changes and behaviour of synthetic vesicles when they are exposed to colloidal particles. We will show examples to demonstrate the power of combining particles and vesicles in generating exciting supracolloidal structures. These suprastructures have a wide range of often responsive behaviours that take advantage of both the mechanical and morphological support provided by the vesicles and the associated particles with preset functionality. This review includes applications spanning a variety of disciplines, including chemistry, biology, physics and medicine.

Colloidal fouling of nanofiltration membranes: A novel transient electrokinetic model and experimental study

Fouling of nanofiltration (NF) membranes by colloidal matter is a commonly encountered phenomenon, adversely influencing the permeate quality and membrane life. In this work, a transient electrokinetic model has been developed to predict the permeate flux and observed rejection of NF membranes in presence of colloidal particles. The cake layer is considered as a swarm of non-interacting, incompressible, spherical, charged particles and the structure is represented using the cell model approach. In the cell model a single particle and a representative volume of the fluid enclosing that particle is considered. The hydrodynamic drag exerted by the stationary colloidal cake layer is obtained by the Stokes–Einstein law and combined with Kuwabara cell model to account for the effect of neighboring particles. The transport of solvent around the charged particles distorts the ionic distribution causing the development of streaming potential and electroosmotic back flow. The model provides valuable insight into application of this phenomenon in colloidal fouling of membranes, in light of the classical Levine–Neale cell model of electrophoresis. This model is then coupled with film theory to appraise the permeate flux decline and salt rejection during the filtration processes. To validate the model, cross flow NF experiment was conducted with silica particles and sodium chloride solution over a wide range of operating conditions.

Self-organizing hybrid systems chitosan succinamide–silver iodide sol and their hemocompatibility

Self-organization of a water-soluble chitosan derivative, chitosan succinamide sodium salt, in the presence of colloidal particles of silver iodide sol was studied. The polymer–colloid disperse system formed is essentially a polymer–inorganic nanocomposite in which chitosan succinamide macromolecules act as a stabilizer of inorganic nanoparticles. The reaction of the system components leads to the formation of a network of intermolecular contacts whose nodes are colloidal particles of silver iodide sol, on which the polymer chains are specifically adsorbed. The chitosan succinamide–silver iodide sol ultradisperse systems exert a stabilizing effect on erythrocyte membranes.

Effect of Nanostructure on Thermal Conductivity of Nanofluids

The presence of colloidal particles is known to increase the thermal conductivity of base fluids. The shape and structure of the solid particles are important in determining the magnitude of enhancement. Spherical particles—the only shape for which analytic theories exist—produce the smallest enhancement. Nonspherical shapes, including clusters formed by colloidal aggregation, provide substantially higher enhancements. We conduct a numerical study of the thermal conductivity of nonspherical structures dispersed in a liquid at fixed volume fraction in order to identify structural features that promote the conduction of heat. We find that elongated structures provide high enhancements, especially if they are long enough to create a solid network (colloidal gel). Cross‐linking further enhances thermal transport by directing heat in multiple directions. The most efficient structure is the one formed by hollow spheres consisting of a solid shell and a core filled by the fluid. In both dispersed and aggregated forms, hollow spheres provide enhancements that approach the theoretical limit set by Maxwell’s theory.

Graphene in the aquatic environment: adsorption, dispersion, toxicity and transformation.

Graphene-family nanomaterials (GFNs) including pristine graphene, reduced graphene oxide (rGO) and graphene oxide (GO) offer great application potential, leading to the possibility of their release into aquatic environments. Upon exposure, graphene/rGO and GO exhibit different adsorption properties toward environmental adsorbates, thus the molecular interactions at the GFN-water interface are discussed. After solute adsorption, the dispersion/aggregation behaviors of GFNs can be altered by solution chemistry, as well as by the presence of colloidal particles and biocolloids. GO has different dispersion performance from pristine graphene and rGO, which is further demonstrated from surface properties. Upon exposure in aquatic environments, GFNs have adverse impacts on aquatic organisms (e.g., bacteria, algae, plants, invertebrates, and fish). The mechanisms of GFNs toxicity at the cellular level are reviewed and the remaining unclear points on toxic mechanisms such as membrane damage are presented. Moreover, we highlight the transformation routes of GO to rGO. The degradation of GFNs upon exposure to UV irradiation and/or biota is also reviewed. In view of the unanswered questions, future research should include comprehensive characterization of GFNs, new approaches for explaining GFNs aggregation, environmental behaviors of metastable GO, and the relationship between dispersion of GFNs and the related adsorption properties.

Comparison of Colorimetric and ICP Methods of Phosphorus Determination in Soil Extracts

The traditional method for quantifying phosphorus (P) in Manitoba soil extracts is the molybdate blue–ascorbic acid colorimetric method. The shift from this traditional method to newer and more sophisticated analytical methods such as inductively coupled plasma (ICP) optical emission spectroscopy for P determination in soil extract could have serious implications on agronomic and environmental P management. Thus, the objectives of this study were to compare P determination by colorimetric and ICP methods in four extractants, namely Olsen, Mehlich 3, CaCl2, and water extraction methods and to evaluate the possibility of developing conversion equations for P determination for the two methods in Manitoba soils. A laboratory experiment was conducted to establish relationships between P determination by colorimetric and ICP methods. Sixty surface soil samples (30 manured and 30 nonmanured) were collected from across Manitoba and extracted with Mehlich 3 reagent, Olsen solution, calcium chloride (CaCl2) solution, and deionized water. Extractable P in the extract was determined by colorimetric (Col-P) and ICP (ICP-P) methods. The concentrations of P measured by the two methods were statistically analyzed. Mean comparison showed that P amounts determined by ICP in Mehlich 3, water, and CaCl2 solutions were significantly greater than those determined by colorimetric method (P < 0.05) in the study. The differences between P determinations by the two analytical methods in the extractants were probably due to the presence of organic P, which was included in ICP determination but not in colorimetric determination. The influence of other factors such as the presence of colloidal particles on the P that was determined by the two methods could not be ruled out. However, Olsen P determined by the colorimetric method was not significantly different from the values determined by ICP (P > 0.05) probably because the alkaline nature of this extractant enhanced the hydrolysis of organic P in the extract, thus including organic P in the colorimetric determination of P. There were significant correlations between the two methods of P determination in the various extracting solutions with correlation coefficients ranging between 0.94 and 1.00. The two methods of P determination were linearly related for all the extracting solutions.

Impact of natural water colloids and cations on the rejection of pharmaceutically active and endocrine disrupting compounds by nanofiltration

The rejection of pharmaceutically active (PhACs) and endocrine disrupting compounds (EDCs) via a nanofiltration (NF) membrane was investigated as a function of naturally occurring colloidal and suspended particles, and cations. NF rejection of PhAC/EDCs was evaluated using a surface water that had been pre-treated by fluidized ion exchange (FIEX) to remove the humic fraction of dissolved organic matter yet retain the colloidal particles, and FIEX-pretreated water with cations added (Ca2+, Mg2+, Na+). The presence of natural colloidal and suspended particles resulted in a significant decrease in the rejection of most neutral PhAC/EDCs, attributable to enhanced hydrophobic interactions (solute partitioning) at the membrane surface. The rejection of ionic compounds was governed by electrostatic interactions with the membrane surface and was not significantly affected by the presence of colloidal particles. The addition of cations to FIEX-pretreated water did not generally impact rejection of most compounds. While past research has investigated colloidal accumulation-associated NF/RO rejection of organic micropollutants, this study confirmed that colloidal particles indigenous to a typical surface water matrix negatively impact nanofiltration of PhAC/EDCs.

Molecular level dispersion of graphene in polymer matrices using colloidal polymer and graphene

A novel and environmentally friendly method based on mixing of colloidal polymer particles and graphene sheets has been developed. It is found that colloidal polymers can be employed to stabilize graphene oxide (GO) sheets during reduction to graphene. Adsorption of polymer particles at the surface of graphene layers seems to be underlying mechanism of stabilization of graphene sheets. Surface polarity of the polymer particles is crucial for the successful stabilization of graphene layers. Presence of colloidal particles at the surface of graphene prohibits restacking and agglomeration of nanolayers, resulting in fine dispersion of graphene throughout the polymeric matrix. Formation of strong bond between polar segments of the polymer chain and oxygen groups of graphene sheets generates a strong interface improving final properties of the composites. Inclusion of merely 2wt% of graphene into an acrylic resin resulted in an increase of 522% and 242% in modulus and hardness, respectively.

Mechanically Reinforcing Polyacrylate/Polyacrylamide Hydrogels through the Addition of Colloidal Particles

AbstractPolyacrylamide is a popular material for many bio-related applications ranging from electrophoretic separation to cellular supports. A limitation of polyacrylamide-based hydrogels, however, is their mechanical compliance. The current study examines the effect of colloidal particles as a reinforcing filler phase to enhance the mechanical stiffness of polyacrylamide-polyacrylate hydrogels. Measurements with oscillatory rheology show that for a fixed polymer volume fraction, the presence of colloidal particles with various surface modifications generally results in an increase of the shear storage modulus of the hydrogel-particle composite. Interestingly, this study indicated that no discernable trends can be linked between the values of the shear storage modulus and the particle surface characteristics.

Ion partitioning at the oil–water interface as a source of tunable electrostatic effects in emulsions with colloids

We present a combined experimental and theoretical investigation of the surprisingly strong electrostatic effects that can occur in mixtures of low- and high-polar liquids (e.g. oil-water emulsions), here in the presence of colloidal particles. For our experiments, we used confocal microscopy imaging, supplemented with electrophoresis and conductivity measurements. Theoretically, we studied our systems by means of a modified Poisson-Boltzmann theory, which takes into account image charge effects and the electrostatic self-energies of the micro-ions in the different dielectric media. Our results show that the unequal partitioning of micro-ions between the two liquid phases is the common driving force behind most of the observed electrostatic effects. The structural signatures of these effects typically develop on a time scale of hours to days and are qualitatively well-described by our theory. We demonstrate how the partitioning process and its associated phenomena can be controlled by shifting the balance of the interlocked ionic dissociation and partitioning equilibria. Moreover, we present strong experimental proof that the two-dimensional colloidal crystals at the oil-water interface are due to long-ranged Coulombic repulsion through the oil phase. The acquired insight in the role of electrostatics in oil-water emulsions is important for understanding the interactions in particle-stabilized ('Pickering') and charge-stabilized emulsions, emulsion production, encapsulation and self-assembly.

Preparação e caracterização de substratos SERS ativos: um estudo da adsorção do cristal violeta sobre nanopartículas de prata

The structural characterization of molecules used in the sterilization of blood for transfusions, such as crystal violet (CV), is relevant for understanding the action of these prophylactic drugs. The characterization is feasible by surface enhanced resonance Raman spectroscopy (SERRS) of CV in solution or on surfaces. The limit of detection of CV by SERRS, in the presence of colloidal particles, using 514.5 nm as excitation radiation, was found to be around 1 ppb. The characterization of CV was also made by SERS, by using different active-particles-containing substrates, proving the versatility of this technique for the study of such structures. The results suggest that the controlled production of highly efficient SERS-active substrates may allow qualitative and quantitative analysis, with high sensitivity, with potential applications in medical and environmental fields.

Structural reorganization in films of cellulose derivatives in the presence of colloidal particles

Water-cast films of two ethers of cellulose, hydroxypropylcellulose (HPC) and hydroxyethylcellulose (HEC), with dispersed silica particles, were deposited on flat substrates. X-ray specular reflectivity was used to characterize the structure of these solid ca. 1000 Å thick films as a function of the added colloidal fraction. It was shown that the structural changes resulting from increasing amounts of incorporated silica particles pass through distinctively different routes in the case of HPC- and HEC-based films. However, the structures in the two cases are similar at sufficiently high colloidal fraction.

Effect of chlorine on adsorption/ultrafiltration treatment for removing natural organic matter in drinking water

In drinking water treatment, prechlorination is often applied in order to control microorganisms and taste-and-odor-causing materials, which may influence organics removal by adsorption and membrane filtration. Thus, the addition of chlorine into an advanced water treatment process using a hybrid of adsorption and ultrafiltration (UF) was investigated in terms of natural organic matter (NOM) removal and membrane permeability. A comparison between two adsorbents, iron oxide particles (IOP) and powdered activated carbon (PAC), was made to understand the sorption behavior for NOM with and without chlorination. Chlorine modified the properties of dissolved and colloidal NOM in raw water, which brought about lower TOC removal, during IOP/UF. The location of IOPs, whether they were in suspension or in a cake layer, affected NOM removal, depending on the presence of colloidal particles in feedwater. Chlorine also played a role in reducing the size of particulate matter in raw water, which could be in close association with a decline in permeate flux after chlorination.