Suspensions Of Colloidal Particles Research Articles

Nematic Phase of Plate-like Semicrystalline Block Copolymer Single Crystals in Solution Studied by Small-Angle X-Ray Scattering.

Crystalline block copolymers have been used to prepare plate-like colloidal systems with well-controlled size, shape, and size distribution. The isotropic-to-nematic (I-N) phase transition of the novel plate-like colloidal particle suspensions has been reported previously. In this work, we focus on the characterization of the solution structure of the crystals and the N-phase using small- and ultrasmall-angle X-ray scattering techniques (SAXS/USAXS). The system has polystyrene-block-poly(l-lactide) (PS-b-PLLA) block copolymer single crystals (BCSCs) with different sizes dispersed in p-xylene. These crystals are truncated lozenge in shape and have effective diameters ranging from 550 to 4000 nm with a uniform dry thickness of 18.0 nm. Scattering of the individual crystal in solution can be simplified using a disc model with a core layer of 9-10 nm due to the lower contrast of the tethered PS layer. BCSC suspensions filled in thin quartz capillaries are prepared for monitoring the structural information. SAXS measurements of the isotropic phase show a strong face-to-face correlation, indicating that platelets form small stacked clusters in solutions. The isotropic phase is thus a coexistence of single crystals and the stacked multiple-layered clusters. The face-to-face spacing, d, in the N phases is around 75-90 nm, which increases slightly upon increasing the size of crystals. For a given system, the spacing does not change with increasing concentration under the current experimental conditions. Finally, the possible formation of lamellar domains within the N phase is also discussed due to the lateral attraction of this system. These results demonstrate the importance of the lateral attraction between the polar crystalline PLLA blocks on the formation of the N phase: the BCSCs self-assemble into larger sheets via the lateral attraction, which further enhances the I-N transition.

The Effect of Particle Sizes on the Concentration Dependence of the Surface Tension of Aqueous Suspensions of Bentonite

The paper presents experimental results on the dependence of surface tension on the concentration of a suspension of bentonite (0 - 10% by weight). The isotherms σ of aqueous suspensions of bentonite are characterized by local minima in the concentration range of 3-4 mass% of the solid phase. It has been established that a decrease in the average particle size leads to the disappearance of the extremum on the surface tension isotherms. The data obtained led to the conclusion that the most important factors affecting the nature of the isotherms of the surface tension of bentonite suspensions are the degree of dispersion and the presence in the aqueous suspension of bentonite, both colloidal and coarse particles.

Transient electrophoresis in a suspension of charged particles with arbitrary electric double layers.

The startup of electrophoretic motion in a suspension of spherical colloidal particles, which may be charged with constant zeta potential or constant surface charge density, due to the sudden application of an electric field is analytically examined. The unsteady modified Stokes equation governing the fluid velocity field is solved with unit cell models. Explicit formulas for the transient electrophoretic velocity of the particle in a cell in the Laplace transforms are obtained as functions of relevant parameters. The transient electrophoretic mobility is a monotonic decreasing function of the particle-to-fluid density ratio and in general a decreasing function of the particle volume fraction, but it increases and decreases with a raise in the ratio of the particle radius to the Debye length for the particles with constant zeta potential and constant surface charge density, respectively. On the other hand, the relaxation time in the growth of the electrophoretic mobility increases substantially with an increase in the particle-to-fluid density ratio and with a decrease in the particle volume fraction but is not a sensitive function of the ratio of the particle radius to the Debye length. For specified values of the particle volume fraction and particle-to-fluid density ratio in a suspension, the relaxation times in the growth of the particle mobility in transient electrophoresis and transient sedimentation are equivalent.

Ferromagnetic Ordering Theory of Colloidal Suspension of Magnetic Particles in Liquid Crystal

A molecular-statistical theory of colloidal suspension of spherical ferromagnetic particles in a nematic liquid crystal matrix is considered. A tensor expression of the suspension Hamiltonian is proposed, which contains contributions that make it possible to describe the ferromagnetic state of the studied system. Within the mean-field approximation, a system of equations is obtained that describes various orientational states of the suspension. Phase diagrams of the suspension are plotted. It is shown that depending on temperature and intensity of particles interaction with the liquid crystal matrix, the suspension can be in an ordered state with different magnetic properties, namely, in the ferromagnetic and superparamagnetic nematic phases, in addition to the isotropic phase.

Synthesis and Characterization of Monodisperse Hydrous Colloidal Zirconia Nanoparticles

The suspension of hydrous colloidal zirconia particles (CZPs) was prepared from zirconium oxychloride solutions via thermal hydrolysis at acidic condition and at boiling point of 110 ºC for 72 h. Characterization of the obtained suspension and dried solid ZrO2 was performed by DLS, FESEM, FTIR, XRD and TGA measurements. Purification via dialysis membrane can maintain the monodispersion of the colloidal suspension when stabilized at pH6. The suspension contained almost sheet-like colloidal particles with amorphous structure with size ranges from 70 to 140 nm in wide and about 40-60 nm in thickness. The formula of hydrous CZPs can be expressed as ZrO2.2H2O.

Corrector Equations in Fluid Mechanics: Effective Viscosity of Colloidal Suspensions

Consider a colloidal suspension of rigid particles in a steady Stokes flow. In a celebrated work, Einstein argued that in the regime of dilute particles the system behaves at leading order like a Stokes fluid with some explicit effective viscosity. In the present contribution, we rigorously define a notion of effective viscosity, regardless of the dilute regime assumption. More precisely, we establish a homogenization result when particles are distributed according to a given stationary and ergodic random point process. The main novelty is the introduction and analysis of suitable corrector equations.

Rheological estimation of aggregate size for a colloidal suspension of carbon black particles

Colloidal aggregation is quantitatively characterized by a rheological analysis of the colloidal suspension at various particle concentrations. The rheological analysis is combined with fractal concept to estimate the compactness, size, and size variation with shear stress on colloidal aggregates. The rheological measurement is carried out for a colloidal suspension of 24 nm carbon black particles suspended in ethylene glycol. The particle concentration ranges from 6.0 to 8.5 percent in volume, which is non-dilute regime where colloidal gelation occurs. Elastic modulus behavior with the particle concentration provides fractal dimension of aggregates. With the fractal dimension, concentration-dependent shear stress behavior is used to estimate aggregate size and its variation with shear stress through a rheological modeling. The estimated fractal dimension of aggregate is 2.020 and the average aggregate size exponentially decreases with the shear rate in the range 1152.24 nm at 1 s−1 to 150.00 nm at 1000 s−1. These estimations are compared with those from optical measurement using static small-angle X-ray scattering (SAXS) technique. The SAXS analysis gives the fractal dimension of 2.495 and the average aggregate size is 320.56 nm. It is found that the optical measurement gives slightly higher fractal dimension and the aggregate size is numerically close to that predicted one around the shear rate 68.7 s−1 where steep size reduction turns into being slow.

Jet instability of a shear-thickening concentrated suspension.

We investigate the flow of a concentrated suspension of colloidal particles at deformation rates higher than the discontinuous shear-thickening transition shear rate. We show that, under its own weight, a jet of a concentrated enough colloidal suspension, simultaneously flows while it sustains tensile stress and transmits transverse waves. This results in a new flow instability of jets of shear-thickening suspensions: the jet is submitted to rapid transverse oscillations, that we characterize.

Differences between Colloidal and Crystalline Evaporative Deposits.

Evaporative deposits from drops are widely studied due to their numerous applications in low-effort self-assembly, including for inkjet printing, microscale separations, and sensing/diagnostics. This phenomenon has been broadly explored for drops containing suspended colloidal particles but has been less quantified for drops with dissolved solutes. When a drop of solute/solvent mixture is evaporated on a substrate, nonvolatile solutes become supersaturated as the solvent evaporates, which then leads to crystal nucleation at the substrate-drop contact line. Emerging crystals alter the local wettability and fundamentally alter the dynamics of evaporation, which, in turn, influences the resultant evaporative deposit. Here we investigate the role of interactions between the substrate, crystals, and solution by comparing the evaporative deposition of three different salts as solutes against an evaporating colloidal solution. We show that nucleation effects can cause crystalline deposits to have a temperature relationship that is opposite to that of colloidal deposits and demonstrate how a balance between the contact-line pinning force and nucleation controls the deposit size.

Primary electroviscous effect in a dilute suspension of charged spherical colloidal particles with a slip surface

The theory of Watterson and White (J Chem Soc Faraday Trans II, 77: 1115, 1981) on the primary electroviscous effect in a dilute suspension of charged spherical colloidal particles in an electrolyte solution is extended to cover the case where liquid slip occurs on the particle surface on the basis of the Navier boundary condition suitable for a hydrophobic surface. The general expressions for the effective viscosity and the primary electroviscous coefficient of the suspension as well as their low-zeta potential approximate expressions are derived.

Confined evaporation-induced self-assembly of colloidal lignin particles for anisotropic adhesion

Colloidal lignin particles out of lignocellulosic biorefineries have gained interest due to their improved properties and wide application range compared to standard lignin. In this work, an application as green adhesive was investigated. Solely a suspension of aqueous colloidal lignin particles was used to achieve anisotropic adhesion between two glass slides. The self-assembly of the colloidal lignin particles into macroscopic structures during drying lead to shear strength 8-times higher the tensile strength. Predefined lignin particles are crucial for the adhesion whereas dissolved lignin leads to no practicable adhesion. The high anisotropy of the adhesion and the fact that solely pure lignin is necessary opens new application and research fields and will propagate the application of colloidal lignin particles even more.

Modelling the fate and transport of colloidal particles in association with BPA in river water

A simplified modelling approach for illustrating the fate of emerging pollutants can improve risk assessment of these chemicals. Once released into aquatic environments, these pollutants will interact with various substances including suspended particles, colloidal or nano particles, which will greatly influence their distribution and ultimate fate. Understanding these interactions in aquatic environments continues to be an important issue because of their possible risk. In this study, bisphenol A (BPA) in the water column of Bentong River, Malaysia, was investigated in both its soluble and colloidal phase. A spatially explicit hydrological model was established to illustrate the associated dispersion processes of colloidal-bound BPA. Modelling results demonstrated the significance of spatial detail in predicting hot spots or peak concentrations of colloidal-bound BPA in the sediment and water columns as well. The magnitude and setting of such spots were system based and depended mainly on flow conditions. The results highlighted the effects of colloidal particles' concentration and density on BPA's removal from the water column. It also demonstrated the tendency of colloidal particles to aggregate and the impact all these processes had on BPA's transport potential and fate in a river water. All scenarios showed that after 7.5–10 km mark BPA's concentration started to reach a steady state with very low concentrations which indicated that a downstream transport of colloidal-bound BPA was less likely due to minute BPA levels.

The role of direct asphaltene inhibitors on asphaltene stabilization during gas injection

There are a large number of investigations, which evaluate the impact of the liquid-based inhibitors on the asphaltene stabilization. In those studies, a specific volume of inhibitor was added to the oil sample and the asphaltene precipitation is then studied. However, this method is indirectly applicable to processes like gas injection. For that reason, in this work, the metal oxide nanoparticles (GO, TiO2, SiO2, and MgO) have been considered in the liquid-free mode as direct asphaltene inhibitors (DAIs) on asphaltene stabilization for the duration of miscible CO2 injection. The dissolution of DAIs in CO2 was investigated by measurement of cloud point pressure to evaluate the pressure/temperature conditions, need for certifying that the CO2/DAIs mixtures have the single-phase condition. Afterwards, the impact of DAI was studied on asphaltene precipitation and deposition by static and dynamic approaches. Results show that the total size of asphaltene particles which precipitated during injection of miscible CO2/DAIs mixture is significantly lower than that for immiscible pure CO2 injection. The amount of asphaltene deposition significantly decreased during injection of miscible CO2/DAIs mixtures compared to immiscible pure CO2 injection. Additionally, themetal oxide nanoparticles hinder the phase separation of asphaltenes kinetically and prevent growth. It is conducted by stabilizing the colloidal suspension of the asphaltene particles, which are in sub-micrometre size to significantly slow the asphaltene flocculation onset.

A facile and cost-effective approach for the fabrication Bi0.5Na0.5TiO3 thick films on flexible substrate for energy storage capacitor applications

The current research reports a facile and cost-effective technique for the deposition of functional ceramics Bi0.5Na0.5TiO3 thick films on flexible, low cost, electrically integrateable Ni substrate by using electrophoretic deposition (EPD) technique. EPD is a well-known, eco-friendly process for depositing coatings on a conductive substrate from a colloidal suspension. A reliable approach was adopted for stable colloidal suspension of BNT particles during conventional solid-state synthesis process by using high energy ball milling in acetone medium without the complications of surfactants and expensive platinum substrate. BNT films with thickness ranging from ~55 to 165 μm were successfully obtained by exploring EPD parameters i.e. voltage from 100 to 125 V and coating time from 30 to 240 s. Thick coatings with comparatively better adhesiveness were deposited at 100 and 125 V with coating time up to 90 s. Thick films were densified by sintering at 1150 °C for 30 min. Phase analysis were conducted by using X-Ray diffraction (XRD), Fourier transformed infrared spectroscopy and Raman spectroscopy. XRD analysis revealed the formation of single (111) peak indicating the pure perovskite structure of BNT thick film. Scanning electron microscope studies indicated that dense and uniform microstructure was obtained by EPD coating with the film thickness of ~93 μm. Impedance spectroscopy confirmed two electrically active regions of grain interior and grain boundaries.

ESTUDIO DE LA COAGULACIÓN DE PARTÍCULAS COLOIDALES DE AgI POR INFLUENCIA DE QUITOSANO CON SULFATO DE ALUMINIO

El objetivo del presente trabajo fue determinar las condiciones óptimas de la coagulación de partículas suspendidas de yoduro de plata de carga negativa por la acción de soluciones de quitosano, sulfato de aluminio, así como la acción mixta de ambos coagulantes. La suspensión de partículas coloidales de AgI se obtuvo mediante la mezcla de soluciones diluidas de KI y AgNO3 en exceso de KI. En todos los experimentos el volumen del sistema coloidal fue de 600 mL y pH= 6. Los parámetros óptimos del proceso de coagulación se determinó a base del método de Test de Jarras. Para la solución de quitosano los parámetros óptimos fueron: concentración 0,01 %, pH=4,5 y un volumen de 25 mL; para el sulfato de aluminio: concentración 30 ppm, pH=4,0 y un volumen 25 mL. En el caso de la acción mixta de ambos coagulantes los parámetros óptimos fueron 5 mL de una solución al 30 ppm de sulfato de aluminio a pH 4,0 y 20 mL de una solución de quitosano al 0,01 % a pH=4,5 . A base de estos parámetros, se estudió la cinética del proceso de coagulación de la suspensión de AgI mediante el método de turbidimetría y se determinó que el proceso de coagulación fue rápido y culminó aproximadamente a los 3 minutos de haber empezado el proceso.

Preparation and evaluation of repaglinide nanosuspensions

Diabetes is a chronic disease that is featured by an increase in the blood glucose levels, and at times, . Current drug is a newer drug that is synthesized to control the blood sugar levels post meals. The most tangible problems that are concurrent with the use of is its very low solubility and thereby causing little dose inconsistency. Various methods have been developed through the years to improve the dissolution of the drug. One of those methods is the concept of . These are colloidal suspensions of drugs particles that are stabilized by . are defined as dual systems that contain a pure drug which is dispersed in a polar vehicle with a diameter of the particle, which is less than 1 in size. was adopted to improve the solubility of to enhance its dissolution rate and absorption. As per the results, it can be said that the of were prepared and represented as a promising new formulation for oral delivery. study in pH 1.2 phosphate buffer showed that the prepared formulations have a better drug release when compared to the pure drug.

New insights on boundary layer control using magnetic fluids: A numerical study

This work investigates the effects of an applied magnetic field on the laminar flow of a ferrofluid over a backward-facing step. Both constitutive equation and global magnetization equation for a ferrofluid are considered. The resulting formulation consists in a coupled magnetic-hydrodynamic problem. Computational simulations are carried out in order to explore the physics of the flow and the consistency of theoretical aspects of our formulation. The unidirectional sudden expansion in a ferrofluid flow is investigated numerically under the perspective of Ferrohydrodynamics in a two-dimensional domain using a Finite Volumes Method. The boundary layer detachment induced by the sudden expansion results in a recirculating zone, which has been extensively studied in purely hydrodynamic problems for a wide range of Reynolds numbers. Similar investigations can be found in literature regarding the sudden expansion under the Magnetohydrodynamics framework, but none considering a colloidal suspension of magnetic particles out of the superparamagnetic regime in the framework of Ferrohydrodynamics. The vorticity-stream function formulation is implemented. Our simulations show a clear coupling between the flow vorticity and the magnetization field. We observe a systematic decay on the length of the recirculating zone as we increase the magnetic parameters of the flow, such as the intensity of the applied field and the volume fraction of particles. The results are discussed from a physical perspective in terms of the dynamical non-dimensional parameters. We argue that the reduction of the recirculating region is a direct consequence of the magnetic torque balancing the action of the torque produced by viscous and inertial forces of the flow. For the limiting case of small Reynolds and magnetic Reynolds numbers, the diffusion of vorticity balances the diffusion of the magnetic torque on the flow. This mechanism controls the growth of the recirculating region.

Phase‐Change Materials for Controlled Release and Related Applications

Phase-change materials (PCMs) have emerged as a novel class of thermo-responsive materials for controlled release, where the payloads encapsulated in a solid matrix are released only upon melting the PCM to trigger a solid-to-liquid phase transition. Herein, the advances over the past 10 years in utilizing PCMs as a versatile platform for the encapsulation and release of various types of therapeutic agents and biological effectors are highlighted. A brief introduction to PCMs in the context of desired properties for controlled release and related applications is provided. Among the various types of PCMs, a specific focus is placed on fatty acids and fatty alcohols for their natural availability, low toxicity, biodegradability, diversity, high abundance, and low cost. Then, various methods capable of processing PCMs, and their mixtures with payloads, into stable suspensions of colloidal particles, and the different means for triggering the solid-to-liquid phase transition are discussed. Finally, a range of applications enabled by the controlled release system based on PCMs are presented together with some perspectives on future directions.

Viscoplastic drop impact on thin films

We use high-speed imaging to study the effect of thixotropic aging in drop impact of yield-stress fluids on pre-coated substrates. Our results reveal that drop splashing is suppressed for "aged" compared to "unaged" samples, indicating that thixotropic breakdown timescales during impact are long enough to affect the dynamics. We propose and test several hypotheses for modifying the dimensionless group ${\rm IF}(D/t)$ [1,2] to account for thixotropic aging. The main challenge is that the steady flow properties (Herschel-Bulkley model parameters) used in the current dimensionless group cannot be defined or measured for thixotropically aged samples, because any deformation inherently rejuvenates and breaks down the microstructure. We find the most suitable hypothesis is to only increase the yield stress ($\sigma_{\rm y}$, plastic component) based on the storage modulus of aged samples, while keeping the viscous parameters ($K$ or $\eta_{\infty}$) constant. The work reveals fundamental insight into rarely studied short-timescale flow conditions with thixotropic effects. These results are important for applications such as fire suppression or spray coating that involve complex fluids of varying degrees of thixotropic aging.

Enhanced fabrication of silicon carbide membranes for wastewater treatment: From laboratory to industrial scale

An environmental-friendly procedure has been developed for the fabrication of pure silicon carbide membranes on macroporous SiC support via ceramic processing. Water dispersions of α-SiC powders were used for deposition of membrane layers by dip-coating. The influence of the fine/coarse powder mixing ratio, solid loading, use of α-SiC powders with different particle sizes as well as sintering temperature on the structural morphology of the membranes were investigated in order to obtain uniform, homogeneous, and defect-free SiC membrane layers. The optimized protocol was up-scaled on industrial SiC tubular supports with high reproducibility, reducing the sintering temperature compared to conventional SiC membrane synthesis. The new SiC membranes were used for the treatment of a secondary effluent from Biofos wastewater treatment plant in Avedøre, Denmark, and their performances evaluated in terms of removal of the suspended solids, colloidal particles and reduction of chemical oxygen demand. According to filtration results, the new SiC membranes showed high removal of suspended solids (99.4%) and colloidal particles (96%) along with significant reduction of chemical oxygen demand (83%). The pure SiC membranes developed in this study have a potential to be applied in the wastewater treatment since they combine the robustness of SiC with high selectivity.