Concentration Of Colloidal Particles Research Articles

Modeling order–disorder boundaries of colloidal dispersions in organic solvents using interaction force measurements

HypothesisThe formation of soft colloidal crystals, which are nonclose-packed ordered arrays of colloidal particles suspended in a solvent, is dictated by a single physical factor that yields a fixed threshold at order–disorder boundaries for different experimental conditions such as ion concentration, solvent type, and particle size. Identifying the determinant factor and its threshold value should enable the prediction of the critical concentrations of colloidal particles to form soft colloidal crystals. ExperimentsSoft colloidal crystals were fabricated using a series of monohydric alcohols as dispersion media and reflectance spectra were measured to locate order–disorder boundaries. The interaction forces acting between particles were also measured by employing atomic force microscopy. FindingsThe interparticle forces at the order–disorder boundaries exhibited a universal threshold that was independent of the solvent types including alcohols and water. Therefore, the determinant factor for the formation of soft colloidal crystals was determined to be the force acting between the particles. Furthermore, a priori calculation of this critical force and consequently the critical particle concentration in colloidal systems was demonstrated by referring to the pressure at the liquid-to-solid transition in a hard sphere system (Alder transition).

ДИСПЕРСТІ ОРТАЛАРДЫҢ ОПТИКАЛЫҚ ҚАСИЕТТЕРІ

The aim of the study is to study light scattering, one of the optical properties of dispersed media. A number of optical methods for determining the size, shape and concentration of colloidal particles and macromolecules are based on the Tyndall effect. A ray of light passing through a colloidal solution is visible as a result of scattering, this type of scattering is called opalescence. Scientific discovery new data on optical effects occurring on magnetic colloids under the influence of magnetic and hydrodynamic fields have been obtained. To create neutral light filters controlled by a magnetic field, it is possible to use established diffraction scattering models with a small angle. The article defines the correspondence and errors of the J.W. Rayleigh or Clausius equations of light scattering intensity for a collide sulfur solution obtained experimentally to solve the problem.

Prediction of the thermo-physical properties of FGPM aerogels, regarding the development of the Sierpinski carpet model

The Sierpinski carpet is mainly used to model the structure and properties of homogeneous media because of the unique characteristics of fractal materials (self-similarity) and the reduction of calculations complexity. Later, the unit cell of the Sierpinski carpet was modified once with a binomial distribution function to model the functionally gradient aerogels synthesized by the layering method. In this work, the structure and thermal properties of functionally gradient Novolac aerogels are introduced and synthesized by the thermal gradient device (a monolithic, continuous, and controllable method). The structural parameters of the proposed model are determined due to the changes in the sample concentration and gyration radius of colloid particles caused by the thermodiffusion effect. The appropriate range of structural parameters is 0.1 <C/L< 0.93, t = 0, and n = 1. The accuracy of the proposed model is reviewed by experimental samples, which showed suitable matches and reasonable agreement. The main challenge of this study is to involve the effect of the synthesis method (thermal gradient device) in modeling the structure and properties of the Sierpinski carpet in a functionally graded heterogeneous structure.

Co-Transport of Aniline and TNT with Loess Colloid Particles in Saturated Loess Columns: Mechanism and Processes

The transport of mobile colloidal particles with organic pollutants in porous media has attracted considerable attention. Aniline and 2,4,6-trinitrotoluene (TNT), as aromatic compounds and key components of energetic materials, are continuously released into the environment. This study compared the co-transport of loess colloidal particles with aniline and TNT, aiming to investigate the influence of structural and physicochemical properties of the pollutants. The colloids were prepared and characterized, and static adsorption and dynamic column experiments were conducted. The results indicate that the adsorption processes of aniline and TNT both conformed to the quasi-second-order kinetic and the intra-particle diffusion models, with aniline exhibiting higher rate constants than TNT. The main adsorption mechanism involved van der Waals force, hydrogen bonding, and electrostatic interaction. Response surface experiments indicated that the adsorption capacity increased with higher initial concentration of organic compound but decreased with larger particle size and higher Na+ concentration. In column experiments, the adsorption of loess colloid particles on aniline and TNT was strongly correlated with the concentration of loess colloid particles. Loess colloid particles could be used as carriers to enhance the co-transport, with aniline exhibiting a faster transport rate due to the differences in polarity and molecular structure compared to TNT. In summary, loess colloidal particles enhanced the transport behavior of aniline and TNT in saturated loess columns. The differences in polarity and molecular structure of aniline and TNT further affect their co-transport mechanism in loess.

Evaluation of the Anti-Fouling Effects of Micro-Nano Bubbles on the Performance of Reverse Osmosis Membrane

Colloidal fouling on a brackish water reverse osmosis (BWRO) membrane was simulated by a lab-scale plate-and-frame module in the presence and absence of air micro-nano bubbles (AMNBs). Synthetic feed water samples with the same physical and chemical properties, but various concentrations of colloidal silica (50, 100, 200, and 300 mg/L), were used for experiments. The results illustrate that colloidal fouling caused a severe decrease in permeate flux (24%–56%) and salt rejection (1.25% to 4.18%) in the absence of AMNBs. This reduction in membrane performance was attributed to the high hydraulic resistance and the cake-enhanced osmotic pressure (CEOP) of a fouled gel layer that were intensified with increase in the colloidal concentration. On the other hand, presence of AMNBs decreased the deposition rate of colloidal particles significantly and increased the porosity of fouling layer. Thus, an improvement in the membrane permeate flux (21%–40%) and salt rejection (1.2%–2.6%) were seen in the different concentrations of colloidal particles. The SEM images also confirmed the formation of loose fouling layers which were easily removed from the membrane surface by a clean-in-place (CIP) process. This research introduces AMNBs technology as an effective in-line method to control the adverse effects of colloidal fouling in reverse osmosis (RO) systems.

Effects of ionic valence on aggregation kinetics of colloidal particles with and without a mixing flow

Hypothesis: The classical Schulze-Hardy rule states that the critical coagulation concentration (CCC) of colloidal particles is inversely proportional to the counter-ionic valence at powers ranging from 2 to 6. However, the inverse Schulze-Hardy rule has recently been proposed, suggesting that the CCC can also be inversely proportional to the co-ionic valence. Previous studies on these rules did not consider the effect of flow on aggregation kinetics and the CCC. This study aims to investigate the effect of multivalent counter-ions and co-ions on aggregation kinetics and the CCCs in systems with and without a mixing flow.Experiments: We measured the aggregation rate coefficients of polystyrene sulfate latex particles as a function of the salt concentration with different ionic species. Furthermore, we analyzed these measurements using theoretical models based on hydrodynamic pair-diffusion in a random flow and trajectory analysis in two steady flows. The analysis was conducted using zeta potentials determined through electrophoretic measurements.Findings: Although the trajectory analysis underestimates the CCCs, the hydrodynamic pair-diffusion model can capture the shift of critical coagulation concentrations in the mixing flow to higher values than those in Brownian aggregation and also shows a better agreement with the experimental results. This result suggests that combining random flow and Brownian diffusion is crucial for developing a consistent framework for predicting both Brownian aggregation and aggregation in a mixing flow.

Kinetics-driven coagulation treatment of petroleum refinery effluent using land snail shells: An empirical approach to Environmental sustainability

Petroleum refinery effluent (PRE) containing a high concentration of colloidal particles causing turbidity is a point source pollutant. There is currently no baseline for the residual concentration of colloids in industrial effluent. In the present study, the performance of land snail shells (LSS) characterized using FTIR and XRD techniques used for the treatment of PRE was investigated. The effluent collected from the outlet train of the industrial facility contains 220 NTU of turbidity corresponding to 520 mg/L of colloidal particles. Analysis of the industrial effluent yielded a COD to BOD ratio > 3.5 eliminating the option of a biological method of treatment. Coagulation-flocculation treatment of the PRE was carried-out following a standard nephelometric test. To clarify the applicability of LSS beyond removal efficiency, machine learning (ML), adsorption, and coag-flocculation kinetics were applied to investigate the treatment process. The predictive capacities of the ML models were compared using statistical metrics. The synergetic effects of operating variables were equally studied. The predicted optimum operating conditions of the treatment process were pH 6, dosage of 0.1 g/L, and a settling time of 30 minutes. The pseudo-second-order and coag-flocculation kinetics result confirmed the reduction of the colloidal particles that occurred via adsorption and inter-particle bridging mechanism. The flocculation outcome proved that the mixing regime 20 s−1≤ G≤120 s−1 promoted aggregation rate over breakage coefficient transcending to 90% removal efficiency. The finding shows that the stability of the finished water corresponds to the 23 mg/L threshold of residual colloidal particles, and 10NTU, which satisfied the EPA guideline for environmentally sustainable recovery.

Online colloidal particle monitoring for controlled coagulation pretreatment to lower microfiltration membrane fouling at a potable water reuse facility

Fouling of microfiltration (MF)) membranes during water/wastewater treatment is predominantly caused by colloidal particles (size <1 µm) in the feed water. Until recently no online technology was available to directly measure the occurrence of colloidal particles in these waters. This study evaluated the viability of a novel online light scattering technology (Nanoparticle Tracking Analysis) to continuously monitor colloidal particles in the membrane feed water (a secondary-treated wastewater) for targeted removal by injecting coagulant at a dosage proportional to the measured concentration of colloidal particles. A diurnal variation was observed in the colloidal particle concentration in the feed water with the lowest concentration occurring at approximately 6 am and the highest concentration occurring after mid-day. The peak colloidal particle concentrations were 4 to 6 times higher than the lowest concentrations measured on the same day. Bench-scale studies were performed to develop a relationship between colloidal particle concentration and the optimum coagulant dosage required for their removal. Subsequently, a pilot-scale study was performed using two MF pilot units operated in parallel, one receiving targeted coagulant dosing and the other with no coagulant dosing, to demonstrate the effectiveness of targeted coagulant dosing in preventing membrane fouling. The pilot unit that received targeted coagulant dose experienced only 4 to 20% of the transmembrane pressure increase of the increase experienced by the pilot unit that received no coagulant. Evaluation of fouling resistance indicated that targeted coagulation improved flux by predominantly lowering the irreversible fouling. The filtrate water quality measured by colloidal particle concentration, chemical oxygen demand (COD), and turbidity were very similar for the two pilot units. This suggests that although the efficiency of particle and organic materials removal does not change with coagulant addition, the particles filtered by the membrane in the control unit contributed to membrane irreversible fouling, while in the coagulant-treated unit, the coagulated colloidal particles were removed away from the membrane into the backwash stream during the frequent backwash/air scour procedures.

Influence of fluid flows on electric double layers in evaporating colloidal sessile droplets.

A model is developed for describing the transport of charged colloidal particles in an evaporating sessile droplet on the electrified metal substrate in the presence of a solvent flow. The model takes into account the electric charge of colloidal particles and small ions produced by electrolytic dissociation of the active groups on the colloidal particles and solvent molecules. We employ a system of self-consistent Poisson and Nernst-Planck equations for electric potential and average concentrations of colloidal particles and ions with the appropriate boundary conditions. The fluid dynamics, temperature distribution and evaporation process are described with the Navier-Stokes equations, equations of heat conduction and vapor diffusion in air, respectively. The developed model is used to carry out a first-principles numerical simulation of charged silica colloidal particle transport in an evaporating aqueous droplet. We find that electric double layers can be destroyed by a sufficiently strong fluid flow.

Влияние ионной подсистемы на термоэлектрический эффект в коллоидных растворах

The thermoelectric effect is investigated in mixtures of colloidal solutions with ionic electrolytes in the initial state, when the formation of concentration gradients under the influence of an inhomogeneous temperature field can be neglected. Based on experimental measurements in mixtures with different concentrations of colloidal particles and ions, the conditions under with the coefficient of thermoelectric EMF is determined by the ion subsystem and under which the main contribution to the value of the thermoelectric force is made by colloidal particles are determined.

Influence of the ionic subsystem on the thermoelectric effect in colloidal solutions

The thermoelectric effect is investigated in mixtures of colloidal solutions with ionic electrolytes in the initial state, when the formation of concentration gradients under the influence of an inhomogeneous temperature field can be neglected. Based on experimental measurements in mixtures with different concentrations of colloidal particles and ions, the conditions under with the coefficient of thermoelectric EMF is determined by the ion subsystem and under which the main contribution to the value of the thermoelectric force is made by colloidal particles are determined. Keywords: colloidal solution, thermoelectric effect, ionic subsystem.

Impulsively-Laser Excitation and Propagation of Ultrasonic Waves through Nanomagnetic Fluid

Magnetic fluids belong to the class of nanomaterials with a high gain of light absorption, aggregative and sedimentation stability as well as controllability by external fields, which is of interest to use in the field of optoacoustics. The purpose of the work was to experimentally study the effect of the optoacoustic transformation in a magnetic fluid, depending on the concentration of magnetic colloidal particles, boundary conditions, intensity of the laser as well as to identify the possibilities of using the magnetic fluid as an element of the optoacoustic transformation in a number of applications.A brief analysis of the optoacoustic transformation mechanism in a magnetic fluid was carried out and a technique and an installation that implements the shadow measurement variant developed. A Lotis type laser was used as a source of ultrasonic pulse-laser excitation in magnetic fluids. A quartz and air were used as a material transmitting the energy of laser radiation in a magnetic fluid. Receiving of ultrasound signals was made by a piezoelectric probe at a working frequency of 5 MHz. In the measurement process, the concentration of the dispersed phase in tmagnetic fluid was varied from zero to 8 % and the energy in the impulse – from zero to 10 mJ.For the first time, it was established that: a) an amplitude of the function of the optoacoustic transformation in a magnetic fluid, depending on the concentration of the dispersed phase, has a maximum determined by the fluid physical properties and boundary conditions; b) for all samples within the measurement error, a quasilinear dependence of the specified amplitude of energy in the laser pulse in the range of 0–8 MJ has been established.A number ways of the optoacoustic effects in magnetic fluids to use in ultrasonic testing, measuring the intensity of the laser radiation had been suggested.

Irreversibility analysis of nanofluid flow induced by peristaltic waves in the presence of concentration‐dependent viscosity

AbstractThe present study employs irreversibility analysis for the peristaltic movement of a nanofluid. The viscosity of the nanofluid is assumed to vary with the local concentration of colloidal particles. Impacts of thermophoresis, magnetic field, Brownian motion, Ohmic heating, viscous dissipation, and buoyant forces are considered in the flow analysis. Equations representing the flow and heat/mass transfer are prepared by employing Buongiorno's model for nanofluids. The lubrication approach is used to simplify the governing equations. The resulting system of differential equations is numerically solved with the aid of NDSolve in Mathematica. Results for entropy generation, Bejan number, velocity, temperature, and concentration are graphically presented. Outcomes show that entropy generation and temperature reduce by increasing the values of viscosity parameter. By increasing buoyancy forces due to temperature difference, the entropy generation increases, whereas the concentration profile shows a decreasing behavior. Maximum velocity reduces with an increment in the Hartman number.

Measurement of the colloidal particle concentration and size within a drop using the time-shift technique

Liquid drops containing particles of nano to micron size are omnipresent in the chemical, pharmaceutical and process industries. In order to optimize such processes, there is a need to characterize these drops in terms of size and colloidal particle concentration. This study is devoted to estimating the colloidal nanoparticle concentration within such drops by using the time-shift technique. The estimation is achieved using two different approaches. The first utilizes the signal strength generated by light scattering from the particles in the drop relative to reflective scattering from the undisturbed drop surface. The second approach monitors the attenuation of the portion of the time-shift signal generated by second-order refractive scattering, i.e. light which has passed twice through the drop. These methods have been simulated using previously developed light scattering codes based on Monte Carlo ray tracing. Corresponding experiments have been implemented to validate these two estimation methods. For this, colloidal drops were generated by mixing water with the polystyrene latex nanoparticles and varying the volume concentration. Good agreement between the experimental and simulation results has been achieved, indicating that the time-shift technique can be further developed to meet this measurement task.

Evaluating the impact of pretreatment processes on fouling of reverse osmosis membrane by secondary wastewater

Pretreatment of secondary effluents, containing relatively high concentrations of colloidal particles, suspended solids, dissolved organics and high level of biological activity, is required to reduce fouling of reverse osmosis (RO) membranes treating these effluents. Various indices are used to evaluate pretreatment efficacy. The effect of two different pretreatments for secondary effluent (BCMF - biofiltration, coagulation and microfiber filtration) vs. ultrafiltration (UF) were evaluated for their effect in reducing the fouling potential of the effluent as expressed by the indices of BOD (biofouling), TOC (organic and biofouling), and MFI0.45 (colloidal fouling). Actual RO fouling tests were conducted using identical RO flow cells at constant flux conditions. Fouled membrane autopsies were subsequently carried out at the end of each test run. The actual fouling based on real-time performance and post-operation autopsies were then correlated to the fouling indices.The results showed that BCMF pretreatment significantly reduced the fouling potential as reflected in all three indices, but UF pretreatment process reduced BOD and MFI0.45 to a significantly greater extent. RO membranes were in general fouled more severely by BCMF treated effluents as reflected in increased transmembrane pressure (TMP). This correlated with BOD and MFI0.45 analyses of the treated effluents and with membrane autopsies at the end of the run. For both treatments, the calculated biofilm porosity dropped as the experiments were carried out for longer periods. As expected, the hydraulic resistance of the fouling layer was found to contribute significantly more to deterioration of RO performance than biofilm-enhanced osmotic pressure for both BCMF-RO and UF-RO.

Effective fields in magnetic colloids and features of their magnetization kinetics.

We present results of magnetization and magnetic susceptibility dependence investigations performed for undecane-based ferrofluids with dominant of Brownian relaxation for particles. A robust and effective method of fine particle size characterization is presented. It is based on the core-shell model and the analysis of the dependence of saturation magnetization on particle concentration. A novel advantage method has been used as a straightforward way to determine the concentration dependence of the effective field related to particle interaction that was calculated from the experimentally obtained concentration dependence of low field susceptibility. The computed relationship is compared with the concentration dependences of effective fields derived from several well-known theoretical models. We present some peculiarities of the real part of dynamic magnetic susceptibility on temperature. Investigated features are defined both by the magnetic state of fine particles and by crystallization of carrier at the liquid to a solid phase transition. For the first time, the dependence of the magnetization relaxation time on the colloidal particle concentration and the magnitude of bias DC magnetic field was investigated experimentally. Results are in good agreement with theoretical predictions for moderate concentration and significantly differs for concentration greater 7 vol%. It is concluded that this effect can be related either to the enhanced particle interaction or to the transition of some particles from superparamagnetic to a ferromagnetic state. These predictions are verified through the calculation in terms of Cole-Cole diagrams methods.

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.

Real-Time Monitoring of Colloidal Crystallization in Electrostatically-Levitated Drops.

Colloidal crystallization is analogous to the crystallization in bulk atomic systems in various aspects, which has been explored as a model system. However, a real-time probing of the phenomenon still remains challenging. Here, a levitation system for a study of colloidal crystallization is demonstrated. Colloidal particles in a levitated droplet are gradually concentrated by isotropic evaporation of water from the surface of the droplet, resulting in crystallization. The structural change of the colloidal array during crystallization is investigated by simultaneously measuring the volume and reflectance spectra of the droplet. The crystal nucleates from the surface of the droplet at which the volume fraction exceeds the threshold and then the growth proceeds. The crystal growth behavior depends on the initial concentrations of colloidal particles and salts which determine the overall direction of crystal growth and interparticle spacing, respectively. The results show that a levitating bulk droplet has a great potential as a tool for in situ investigation of colloidal crystallization.

Simulation of light scattering from a colloidal droplet using a polarized Monte Carlo method: application to the time-shift technique.

This study is devoted to the development and application of a Monte Carlo ray-tracing model to simulate light scattering when a colloid suspension droplet passes through a highly focused Gaussian laser sheet. Within this study, a colloidal suspension droplet refers to a spherical droplet containing multiple spherical inclusions. Such scattering scenarios arise when using the time-shift measurement technique for particle sizing. The incident laser sheet is treated as a large number of polarized light rays: the Stokes vector of each light ray is tracked, achieved by multiplication of the rotation matrix and the Mueller matrix after each scattering event. For the Monte Carlo simulation of light scattering, a very important issue is to generate the deflection angle and azimuthal angle after each scattering event. The scattering from embedded inclusions is computed using the Lorenz-Mie theory and by employing the rejection sampling technique to update the new propagation direction. Multi-reflection and refraction within the droplet is accounted for, as is total reflection at the drop interface. For this, the Mueller matrix formulation is invoked at the drop surface to update the Stokes vector. To validate this simulation code, the scattering diagram from a nanoparticle is computed with this Monte Carlo method and compared with the scattering diagram computed with the Lorenz-Mie theory, the agreement is excellent. This Monte Carlo code is then applied to simulate signals arising from a time-shift device, when a colloid suspension droplet passes through a focused polarized laser sheet, with the objective of measuring the concentration of colloidal particles in the droplet. Measurements verify the ability of the code to properly simulate this light scattering scenario.

Dissipation of chlortetracycline in the aquatic environment: Characterization in terms of a generalized multiphase pseudo–zero‐order rate law

AbstractThe kinetics of the dissipation of chlortetracycline in the aquatic environment was studied over a period of 90 days using microcosm experiments and distilled water controls. The distilled water control experiments, carried out under dark conditions as well as exposed to natural sunlight, exhibited biphasic linear rates of dissipation. The microcosm experiments exhibited triphasic linear rates of degradation both in the water phase (2.7 × 10−2, 7 × 10−3, 1.3 × 10−3 μg g−1 day–1) and the sediment phase (3.4 × 10−2, 6 × 10−3, 1 × 10−3 μg g−1 day–1). The initial slow rate of dissipation in the dark control (3 × 10−3 μg g−1 day–1) was attributed to a combination of evaporation and hydrolysis, whereas the subsequent fast rate (1.8 × 10−3 μg g−1 day–1) was attributed to a combination of evaporation, hydrolysis, and microbial degradation. For the sunlight‐exposed control, the initial slow rate of dissipation (1.5 × 10−3 μg g−1 day–1) was attributed to a combination of evaporation, hydrolysis, and photolysis, whereas the subsequent fast rate was attributed to a combination of evaporation, hydrolysis, photolysis, and microbial degradation (5.1 × 10−3 μg g−1 day–1). The initial fast rate of dissipation in the water phase of the microcosm experiment is attributed to a combination of evaporation, hydrolysis, photolysis, and microbial degradation, whereas all subsequent slow rates in the water phase and all rates of degradation in the sediment phase are attributed to microbial degradation of the colloidal and sediment particle adsorbed antibiotic. A multiphase zero‐order kinetic model is presented that takes into account (a) dissipation of the antibiotic via evaporation, hydrolysis, photolysis, microbial degradation, and adsorption by colloidal and sediment particles and (b) the dependence of the dissipation rate on the concentration of the antibiotic, type and count of microorganisms, and type and concentration of colloidal particles and sediment particle adsorption sites within a given aquatic environment.