Charged Suspensions Research Articles

Multifunctional Imidazolidinyl Urea Additive Initiated Complex with PbI2 Toward Efficient and Stable Perovskite Solar Cells.

High-quality perovskite absorption layer is the fundamental basis for efficient and stable perovskite solar cells (PSCs). Due to the ionic nature of perovskite components, plentiful charged defects and suspension bonds remain on the surface of perovskite grains after continuous high-temperature annealing. Here, the complex initiated by the introduction of a multifunctional imidazolidinyl urea (IU) additive into the PbI2 precursor solution could serve as nucleation sites and crystallization templates for perovskite crystals to optimize the growth of high-quality perovskite films. By anchoring at the grain boundaries of perovskite films, IU molecules could passivate various types of defects, improve the hydrophobic properties, and inhibit lead leakage. Attributed to reduced defect density, improved charge transport, and inhibited α-FAPbI3 transition, the PSCs prepared based on IU additives achieved a champion power conversion efficiency of 23.18% (21.51% for the control PSCs) with negligible hysteresis and satisfactory stability.

Electrosteric Control of the Aggregation and Yielding Behavior of Concentrated Portlandite Suspensions.

Portlandite (calcium hydroxide: CH: Ca(OH)2) suspensions aggregate spontaneously and form percolated fractal aggregate networks when dispersed in water. Consequently, the viscosity and yield stress of portlandite suspensions diverge at low particle loadings, adversely affecting their processability. Even though polycarboxylate ether (PCE)-based comb polyelectrolytes are routinely used to alter the particle dispersion state, water demand, and rheology of similar suspensions (e.g., ordinary portland cement suspensions) that feature a high pH and high ionic strength, their use to control portlandite suspension rheology has not been elucidated. This study combines adsorption isotherms and rheological measurements to elucidate the role of PCE composition (i.e., charge density, side chain length, and grafting density) in controlling the extent of PCE adsorption, particle flocculation, suspension yield stress, and thermal response of portlandite suspensions. We show that longer side-chain PCEs are more effective in affecting suspension viscosity and yield stress, in spite of their lower adsorption saturation limit and fractional adsorption. The superior steric hindrance induced by the longer side chain PCEs results in better efficacy in mitigating particle aggregation even at low dosages. However, when dosed at optimal dosages (i.e., a dosage that induces a dynamically equilibrated dispersion state of particle aggregates), different PCE-dosed portlandite suspensions exhibit identical fractal structuring and rheological behavior regardless of the side chain length. Furthermore, it is shown that the unusual evolution of the rheological response of portlandite suspensions with temperature can be tailored by adjusting the PCE dosage. The ability of PCEs to modulate the rheology of aggregating charged particle suspensions can be generally extended to any colloidal suspension with a strong screening of repulsive electrostatic interactions.

Pluronic Induced Interparticle Attraction and Re-entrant Liquid-Liquid Phase Separation in Charged Silica Nanoparticle Suspensions.

Tuning surface properties of nanoparticles by introducing charge, surface functionalization, or polymer grafting is central to their stability and applications. Here, we show that introducing non-DLVO forces like steric and hydrophobic effects in charged silica nanoparticle suspensions through interaction with a nonionic surfactant brings about interesting modulations in their interparticle interaction and phase behavior. The Ludox TM-40 negatively charged silica suspensions thus exhibit liquid-liquid phase separation driven by the onset of interparticle attraction in the system in the presence of the triblock copolymer Pluronic P123. The observed phase separations are thermoresponsive in nature, as they are associated with lower consolute temperatures and a re-entrant behavior as a function of temperature. The nanoparticle-Pluronic system thus undergoes transformation from one-phase to two-phase and then back to one-phase with monotonic increase in temperature. Evolution of the interparticle interaction in the composite system is investigated by dynamic light scattering (DLS), small angle neutron scattering (SANS), zeta potential, rheological, and fluorescence spectroscopy studies. Zeta potential studies show that the charge interaction in the system is partially mitigated through adsorption of a Pluronic micellar layer on the nanoparticle surfaces. Contrast-matching SANS studies suggest that hydrophobic interactions between the adsorbed micellar layer bring about the onset of interparticle attraction in the system. The results are unique and not reported hitherto in charged silica nanoparticle systems.

Porous crystals in charged sphere suspensions by aggregate-driven phase separation.

The kinetics of phase transition processes often governs the resulting material microstructure. Using optical microscopy, we here investigate the formation and stabilization of a porous crystalline microstructure forming in low-salt suspensions of charged colloidal spheres containing aggregates comprising some 5-10 of these colloids. We observe the transformation of an initially crystalline colloidal solid with homogeneously incorporated aggregates to individual, compositionally refined crystallites of perforated morphology coexisting with an aggregate-enriched fluid phase filling the holes and separating individual crystallites. A preliminary kinetic characterization suggests that the involved processes follow power laws. We show that this route to porous materials is neither restricted to nominally single component systems nor to a particular microstructure to start from. However, it necessitates an early rapid solidification stage during which the aggregates become trapped in the bulk of the host-crystals. The thermodynamic stability of the reconstructed crystalline scaffold against melting under increased salinity was found comparable to that of pure phase crystallites grown very slowly from a melt. Future implications of this novel route to porous colloidal crystals are discussed.

Numerical study of intercomponent high-speed sliding in electrically charged and neutral gas suspensions in a two-dimensional non-stationary formulation with a viscous carrier medium

Numerical study of intercomponent high-speed sliding in electrically charged and neutral gas suspensions in a two-dimensional non-stationary formulation with a viscous carrier medium

Numerical study of the velocity distribution of the disperse component in the generation of a gas suspension flow by an electric field

This paper presents a self-consistent mathematical model of the dynamics of an electrically charged dusty medium. The carrier medium was described as a viscous, compressible and heat-conducting gas. The simulated flow is self-consistent, the parameters of each of the mixture components are determined by changing the parameters of other components. The mathematical model took into account intercomponent momentum exchange and heat transfer between the dispersed component of the mixture and the gas. The equations of the mathematical model are supplemented with boundary conditions. The mixture dynamics equations and the Poisson equation describing the electric field were solved by a numerical finite-difference method. The channel is divided into two parts, in one part of the channel there is a homogeneous gas, in the other part of the channel there is a gas containing electrically charged particles. Under the action of an electric field, the particles of the disperse component begin to move, and a gas flow is formed. This paper presents the results of calculations of the physical fields of an electrically charged dispersed suspension.

Tuning the Self-Assembled Morphology of Ti3C2Tx MXene-Based Hybrids for High-Performance Electromagnetic Interference Shielding.

Hybrid materials based on transition metal carbide and nitride (MXene) nanosheets have great potential for electromagnetic interference (EMI) shielding due to their excellent electrical conductivity. However, the performance of final products depends not only on the properties of constituent components but also on the morphology of the assembly. Here, via the controlled diffusion of positively charged poly(allylamine hydrochloride) (PAH) chains into the negatively charged Ti3C2Tx MXene suspension, MXene/PAH hybrids in the forms of thin films, porous structures, and fibers with distinguished internal morphologies are obtained. Our results confirm that PAH chains could effectively enhance the oxidation stability and integrity of wet and dry MXene structures. The flexibility to tune the structures allows for a thorough discussion of the relations between the morphology, electrical conductivity, and EMI shielding mechanism of the hybrids in a wide range of electrical conductivity (2.5 to 3347 S·cm-1) and thickness (7.7 to 1900 μm) values. The analysis of thin films shows the direct impact of the polymer content on the alignment and compactness of MXene nanosheets regulating the films' electrical conductivity/EMI shielding effectiveness. The colloidal behavior of the initial MXene suspension determines the interconnection of MXene nanosheets in MXene/PAH porous assemblies and the final electrical properties. In addition to the internal morphology, examining the laminated MXene/PAH fibers with geometrically different arrangements demonstrates the role of conductive network configuration on EMI shielding performance. These findings provide insights into tuning the EMI shielding effectiveness via the charge-driven bottom-up assembly of electrically conductive MXene/polyelectrolyte hybrids.

Crystallization kinetics of charged PNIPAM microgels dispersions at low volume fractions

This work studies the kinetics of crystallization of charged microgels suspensions of Poly-N-Isopropylacrylamide (PNIPAM) at low ionic strength. The liquid-crystal transition is induced by suddenly decreasing the temperature of the microgel dispersion, and the crystallization process is monitored by measuring the temporal evolution of the static structure factor of the dispersion using light scattering. We find that the crystal growth rate, indicated by the temporal evolution of the crystallinity factor, strongly depends on the quenching temperature.

The influence of charge characteristics of suspension droplets on the ion flow field in different temperatures and humidity

In order to clarify the charging characteristics of suspension droplets in ion flow field under different temperatures and humidity, the effective charging factor used to characterize the charging characteristics of suspension droplets is introduced in this paper, and a calculation method of charging factor is proposed based on the upstream finite element method (FEM). Then, the charging factor under different temperatures and humidity is calculated, and the analytic expression of the charging factor considering the influence of temperature and humidity is obtained by fitting the calculation results. The influence of suspension droplets on the ion flow field is analyzed. The results show that the charging factor is small and increases little with the relative humidity when the relative humidity is less than 60%, and the charging factor is large and increases rapidly with the relative humidity when the relative humidity is more than 60%. At the same relative humidity, the charging factor increases linearly with the temperature. The influence of charged suspension droplets on the ion flow field can be ignored when the relative humidity is less than 60% and must be considered under high temperature and humidity. The calculation method and analytic expression of the charging factor proposed in this paper can be used to model of ion flow field considering the influence of temperature and humidity and provide technical support for the construction of HVDC transmission lines across high temperature and humidity.

Is the SEC captured? Evidence from political connectedness and SEC enforcement actions

AbstractThis study examines the impact of political connectedness (PC) on enforcement actions by the Securities and Exchange Commission (SEC). Our analysis confirms that SEC is not captured and shows that firms or executives with stronger PC are more likely to be criminally charged or face bar or suspension than firms or executives with weaker PC. In addition, we document that imposed fines are relatively higher for prosecuted firms and executives with stronger PC. These findings are robust to inclusions of controls for Republican Congress, Republican President, and recent regulatory reforms and are not driven by endogeneity concerns and sample selection bias.

Numerical study of the effect of the dispersed particles properties on the electrically charged polydisperse gas suspension dynamics in a channel with electrodes on the walls

In this article the flow of an electrically charged gas suspension in a channel is numerically simulated. It is assumed that the solid component of the gas suspension has a polydisperse composition. Solid component fractions may differ in particle size and density. For the velocity components of the mixture components on the channel surfaces, the Dirichlet boundary conditions were specified, thereby taking into account the wall viscosity. The dynamics of the carrier medium was described by the system of equations of a viscous compressible heat-conducting gas motion. Potentials of different signs are applied to the lateral surfaces of the channel. It was found that due to the action of an electric field, positively charged particles are deposited onto the channel wall with a negative potential. The article studies the effect of particle parameters on the deposition rate of fractions of an electrically charged solid component of the mixture.

Численное исследование распространения ударной волны малой интенсивности из чистого газа в электрически заряженную запылённую среду

Данная работа посвящена численному моделированию процесса распространения удар-ной волны малой интенсивности из чистого газа в неоднородную среду представляющеюсобой газовую взвесь твердых частиц. В вычислительных экспериментах рассматривалиськак электрические нейтральные, так и заряженные взвеси твердых частиц. В использо-ванной в работе математической модели сохранение компонент импульса несущей средыописывалось системой уравнений Навье-Стокса для сжимаемого газа в двухмерной поста-новке. При описании взаимодействия несущей и дисперсной фазы газовзвеси учитывалисьсила Стокса, динамическая сила Архимеда, сила присоединённых масс, также учитывал-ся межфазный теплообмен. Для дисперсной компоненты смеси решалась полная гидроди-намическая система уравнений движения, включавшая в себя уравнение неразрывности,сохранений импульса и энергии. Система уравнений математической модели дополненнаяграничными условиями решалась явным конечно-разностным методом второго порядкаточности. Также в численной модели использовался алгоритм подавления численных ос-цилляций. Численное моделирование показало, что наличие электрического заряда в дис-персной компоненте смеси оказывает воздействие на движение дисперсной компонентыи вследствие межфазного взаимодействия на течение газа. В результате численных рас-чётов было выявлено, что увеличение размера частиц приводит к существенному ростумежфазного скоростного скольжения. Было определено, что интенсивность скоростногоскольжения между несущей и дисперсной фазами в электрически заряженной запылён-ной среде возрастает в направлении увеличения удельной силы Кулона, в то время как вэлектрически нейтральной газовзвеси рост скоростного скольжения происходит в направ-лении движения ударной волны.

Understanding charged vesicle suspensions as Wigner glasses: dynamical aspects

Suspensions of charged vesicles in water with added salt are widespread in nature and industrial production. Here we investigate, via Brownian dynamics simulations, a model that grasps the key features of these systems, with bidisperse colloidal beads interacting via a hard-core and an electrostatic double layer potential. Our goal is to focus on a set of interaction parameters that is not generic but measured in recent experiments, and relevant for a class of consumer products, such as liquid fabric softeners. On increasing the volume fraction in a range relevant to real formulation, we show that the dynamics become progressively slower and heterogeneous, displaying the typical signatures of an approaching glass transition. On lowering the salt concentration, which corresponds to increasing the strength and range of the electrostatic repulsion, the emergence of glassy dynamics becomes significantly steeper, and, remarkably, occurs at volume fractions well below the hard-sphere glass transition. The volume fraction dependence of the structural relaxation time at different salt concentration is well described through a functional law inspired by a recently proposed model (Krausser et al 2015 Proc. Natl Acad. Sci. USA 112 13762). According to our results, the investigated system may be thought of as a Wigner glass, i.e. a low-density glassy state stabilized by long-range repulsive interactions. Overall, our study suggests that glassy dynamics plays an important role in controlling the stability of these suspensions.

Non-monotonic concentration dependence of the electro-phoretic mobility of charged spheres in realistic salt free suspensions.

Using super-heterodyne Doppler velocimetry with multiple scattering correction, we extend the optically accessible range of concentrations in experiments on colloidal electro-kinetics. Here, we measured the electro-phoretic mobility and the DC conductivity of aqueous charged sphere suspensions covering about three orders of magnitude in particle concentrations and transmissions as low as 40%. The extended concentration range for the first time allows the demonstration of a non-monotonic concentration dependence of the mobility for a single particle species. Our observations reconcile previous experimental observations made on other species over restricted concentration ranges. We compare our results to the state-of-the-art theoretical calculations using a constant particle charge and the carefully determined experimental boundary conditions as input. In particular, we consider the so-called realistic salt free conditions, i.e., we respect the release of counterions by the particles, the solvent hydrolysis, and the formation of carbonic acid from dissolved neutral CO2. We also compare our results to previous results obtained under similarly well-defined conditions. This allows identification of three distinct regions of differing density dependence. There is an ascent during the build-up of double layer overlap, which is not expected by theory, an extended plateau region in quantitative agreement with theoretical expectation based on a constant effective charge and a sudden decrease, which occurs way before the expected gradual decrease. Our observations suggest a relation of the non-monotonic behavior to a decrease in particle charge, and we tentatively discuss possibly underlying mechanisms.

Diverse Pathway to Obtain Antibacterial and Antifungal Agents Based on Silica Particles Functionalized by Amino and Phenyl Groups with Cu(II) Ion Complexes.

Production of environmentally friendly multitasking materials is among the urgent challenges of chemistry and ecotechnology. The current research paper describes the synthesis of amino–/silica and amino–/phenyl–/silica particles using a one-pot sol–gel technique. CHNS analysis and titration demonstrated a high content of functional groups, while scanning electron microscopy revealed their spherical form and ∼200 nm in size. X-ray photoelectron spectroscopy data testified that hydrophobic groups reduced the number of water molecules and protonated amino groups on the surface, increasing the portion of free amino groups. The complexation with Cu(II) cations was used to analyze the sorption capacity and reactivity of the aminopropyl groups and to enhance the antimicrobial action of the samples. Antibacterial activities of suspensions of aminosilica particles and their derivative forms containing adsorbed copper(II) ions were assayed against Gram-positive (Staphylococcus aureus ATCC 25923) and Gram-negative bacteria (Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 27853). Meanwhile, antifungal activity was tested against fungi (Candida albicans UCM Y-690). According to zeta potential measurements, its value could be depended on the suspension concentration, and it was demonstrated that the positively charged suspension had higher antibacterial efficiency. SiO2/–C6H5/–NH2 + Cu(II) sample’s water suspension (1%) showed complete growth inhibition of the bacterial culture on the solid medium. The antimicrobial activity could be due to occurrence of multiple and nonspecific interactions between the particle surfaces and the surface layers of bacteria or fungi.

Flocculation behavior and mechanisms of block copolymer architectures on silica microparticle and Chlorella vulgaris systems

HypothesisFlocculation performance using polyelectrolytes is influenced by critical design parameters including molecular weight, amount and sign of the ionic charge, and polymer architecture. It is expected that systematic variation of these characteristics will impact not only flocculation efficiency (FE) achieved but that charge density and architecture, specifically, can alter the flocculation mechanism. Therefore, it should be possible to tune these design parameters for a desired flocculation application. ExperimentsCationic-neutral and polyampholytic copolymers, exhibiting a range of molecular weights (103–106 g/mol), varying charge levels (0–100% cationic, neutral and anionic), and random or block copolymer architecture, were applied to dilute suspensions of silica microparticles (control) and Chlorella vulgaris. FE and zeta potential values were determined over a range of flocculant doses to evaluate effectiveness and mechanism achieved. FindingsThese different classes of copolymers provide specific benefits for flocculation, with many achieving >95% flocculation. Block copolymer flocculants exhibit a proposed, dominant bridging mechanism, therefore reducing flocculant dosage required for effective flocculation when compared to analogous random copolymer flocculants. Polyampholytic copolymers applied to C. vulgaris generally exhibited a bridging mechanism and increased FE compared to equivalent cationic-neutral copolymers, indicating a benefit of the anionic component on a more, complex, diversely charged suspension.

ЧИСЛЕННОЕ МОДЕЛИРОВАНИЕ РАСПРОСТРАНЕНИЯ УДАРНОЙ ВОЛНЫ ИЗ ГАЗА В ЭЛЕКТРИЧЕСКИ ЗАРЯЖЕННУЮ И НЕЙТРАЛЬНУЮ ГАЗОВЗВЕСИ В ПЛОСКОМ КАНАЛЕ

In this paper, we consider the propagation of a shock wave from a pure gas into a heterogeneous mixture consisting of solid particles suspended in a gas and having an electric charge. The applied mathematical model takes into account the speed and thermal interaction of the carrier and dispersed components of the mixture. The force interaction of particles and gas was described by the Stokes force. The carrier medium was described as a viscous compressible heat–conducting gas. The equations of the mathematical model were solved by the explicit finite–difference method of the second order of accuracy, using the non–linear correction of the grid function. The system of equations of the mathematical model was supplemented by boundary and initial conditions for the desired functions. As a result of numerical simulation, it was found that in an electrically charged gas suspension there is a difference in gas pressure and velocity, “average density” and velocity of the dispersed component, compared with similar values in a gas suspension with an electrically neutral dispersed component. The revealed differences in the dynamics of neutral and electrically charged dusty media can be explained by the fact that the dispersed component of an electrically charged gas suspension is affected by both aerodynamic drag forces and Coulomb forces. Due to interfacial interaction, the dynamics of the carrier medium changes.

Численное исследование скоростного скольжения несущей и дисперсной фазы при взаимодействии ударной волны с электрически заряженной газовзвесью

In this paper, we consider the propagation of a shock wave from a pure gas into a heterogeneous mixture con-sisting of solid particles suspended in a gas and having an electric charge. The applied mathematical model takes into account the speed and thermal interaction of the carrier and dispersed components of the mixture. The mathematical model assumed a monodisperse composition of the solid component of the mixture, that is, it was assumed that all particles have the same linear size, shape and consist of one material. The force interaction of particles and gas included the Stokes force, the strength of the attached masses, as well as the dynamic force of Archimedes. The carrier medium was described as a viscous compressible heat-conducting gas. The equations of the mathematical model were solved by the explicit finite-difference method of the second order of accuracy, using the non-linear correction of the grid function. The system of equations of the mathematical model was supplemented by boundary and initial conditions for the desired functions: at the boundaries of the computational domain, the Dirichlet boundary conditions were set for the velocity components of the carrier and dispersed phase for the remaining dynamic functions Neumann conditions were set. For the Poisson equation describing the distribution of the internal electric field of a charged gas suspension, homogeneous Dirichlet boundary conditions were specified. As a result of numerical calculations, differences were revealed in the velocity slip of the carrier and dispersed phases, in cases where the shock wave propagates into a neutral and electrically charged dusty medium. It was also revealed the effect of particle size on the speed of sliding of the carrier and dispersed components of a heterogeneous mixture during the propagation of a shock wave into a neutral and electrically charged gas suspension.

МАТЕМАТИЧЕСКОЕ ИССЛЕДОВАНИЕ СКОРОСТНОГО СКОЛЬЖЕНИЯ ФАЗ ПРИ ВЗАИМОДЕЙСТВИИ УДАРНОЙ ВОЛНЫ ПРЕДЕЛЬНО МАЛОЙ ИНТЕНСИВНОСТИ С ЭЛЕКТРИЧЕСКИ ЗАРЯЖЕННОЙ ГАЗОВЗВЕСЬЮ

The paper presents a mathematical model of an electrically charged suspension of particles, as well as numerical calculations related to the dynamics of the dispersed component of a mixture moving both under the influence of aerodynamic forces and under the influence of the Coulomb force. The author used a mathematical model of a nonequilibrium multiphase medium motion to describe the aerodynamics of suspensions. The mathematical model took into account the force interaction of the carrier and dispersed phases and interphase heat transfer, as well as the internal electric field generated by electrically charged solid particles. Using the software implementation of the mathematical model, a numerical study of the velocity slip of phases was carried out.

Gr-Al2O3 Nanoparticles-Based Multifunctional Drilling Fluid

Various chemical additives are used in drilling fluids to improve drilling efficiency and increase oil production. Dispersing nanoparticles as additives in drilling mud is one of the more promising techniques that could help solve many difficulties of drilling operations. However, the existing research in this field is insufficient and suffers from numerous inconsistent outcomes. This study aims to discover and evaluate the impact of graphite-alumina hybrid nanoparticles on the rheology, thermal properties, zeta potential, and electrical conductivity of water-based drilling fluids. This study shows that that the addition of nanoparticles improves the effectiveness of water-based mud (WBM), both in static and dynamic situations due to the establishment of an appropriate gel structure that can be easily broken under low shear stress. Furthermore, these nanoparticles improve the degree and the speed of structural recovery by reducing the relaxation time, which is necessary to avoid the sedimentation of weighting materials and drilled cuttings. Besides, nanoparticle seeded fluid improves the effective thermal conductivity of conventional drilling fluids, and the highly charged suspension resulting from the addition of nanoparticles is desirable for drilling operations. It is also observed that nanoparticles could penetrate through the porous wall of the wellbore and clog the pores, forming a thin and impermeable cake that reduces drilling fluid loss. When properly engineered, nanoparticles could significantly improve the performance of conventional drilling fluids.