Transfer characterization of charged particles through charged conductive membrane via dialysis process

In this work the effects of applied electrical charge on mechanism and transfer rate of charged particles through conductive membrane have been elucidated. Another individual parameter which plays a vital role in assigning mechanism and rate of transport is absolute concentration. This is independent from the effect of concentration gradient which is the driving force for mass transfer. In the experimental section, the transfer of sodium dodecyl sulphate (SDS) micelles through charged membrane was investigated. The membrane consisted of a commercial microfiltration (GVHP) membrane as the support coated with a conductive polymer i.e. polypyrrole. A wide range of electrical charges (voltages) were applied on the surface of the conductive membrane. The electrical charge qualitatively and quantitatively influences the mass transfer rate. The difference between transport mechanisms of charged particles at low and high concentrations is more evident in the presence of electrical surface charge. In summary, initial feed concentration, electrical charge and their interactions affect the transport rate and mechanism.     

A hybrid approach to computing electrostatic forces in fluidized beds of charged particles

In particulate flow devices particles acquire electric charge through triboelectric charging, and resulting electrostatic forces can alter hydrodynamics. To capture this effect, the electrostatic force acting on individual particles in the device should be computed accurately. Electrostatic force is calculated using a hybrid approach consisting of: (1) long‐range contributions from an Eulerian electric field solved using the Poisson equation (2) short‐range contributions calculated using a truncated pairwise sum and (3) a correction to avoid double counting. Euler‐Lagrange simulation of flows incorporating this hybrid approach reveals that bed height oscillations in small fluidized beds of particles with monopolar charge decreases with increasing charge level, which is related to lateral segregation of particles. A ring‐like layer of particles, reported in experimental studies, forms at modestly high charge levels. Beds with equal amounts of positively and negatively charged particles are fluidized in a manner similar to uncharged particles. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2282–2295, 2016     

Effect of pH on gelatin self‐association investigated by laser light scattering and atomic force microscopy

The effect of pH on gelatin self‐association in dilute solution has been investigated for the first time to the authors' knowledge by laser light scattering (LLS) and atomic force microscopy (AFM). It shows that, at the isoelectric point (IEP) of gelatin, the ampholyte macromolecules collapse due to electrostatic attraction forces of oppositely charged groups, and self‐association occurs in turn by an intermolecular association process. The soluble aggregates are stabilized by ionic contacts, hydrogen bonds and hydrophobic interactions, and are protected from precipitation by hydrophilic groups on the surface of the particles. For gelatin‐B away from the IEP, pH ≥ 6.0 or pH ≤ 4.0, the molecular chains behave more like random coils. As expected, the association–disassociation based mainly on electrostatic interactions appears reversible to some certain extent. The experimental results indicate that LLS and AFM, especially a combination of the two, play an important role in obtaining integrated and direct information on the structure and properties of this natural biopolymer. © 2002 Society of Chemical Industry     

The influence of shear forces on clay modification with oppositely charged polyelectrolytes

The interaction between the oppositely charged polymers poly(dimethyldiallylammonium chloride) (PDADMAC) and poly(maleic acid‐co‐styrene) in the presence of clay can be used for strong surface modification. Different methods were applied for characterizing each step of the reaction and the properties of the modified material. By characterizing the formation of the pure polyelectrolyte complex in solution as well as the three component system (two polyelectrolytes in presence of clay) with polyelectrolyte titration and comparing these results with the total carbon content, it was shown that a significant quantity of a soluble, positively charged polyelectrolyte complex is formed in the system. The strong cationic surface charge is obtained by precipitation of this complex on clay. It was found that the conditions of reaction (type of stirrer, time) strongly influence the particle properties like particle size and adsorption behavior/surface charge. The higher surface charge and the greater diameter of particles was obtained with an anchor stirrer, whereas the formation of larger particles and the precipitation of the complex is prevented by the stronger shear forces of the leaf stirrer.     

Electrical Enhancement of Filters with Randomly Oriented Fibers

A model is given for the interception deposition of an electrified filter whose fibers are randomly oriented to the mean direction of flow. A derivation is given for the field resulting from the fiber polarization when an external electrical field is present and when there is charge on a fiber. Analytical solutions are given for the single-fiber effective deposition rates and filter efficiencies in the case of no external forces and in the case of interaction of a charged particle (but no particle polarization) with a polarized or charged fiber. When the particle is polarized by a charged or polarized fiber, a fast numerical method for computing the efficiencies is presented. In the case of no electrical forces, the effective deposition rates due to interception and the corresponding filter efficiencies over a range of fiber orientations are computed. An average value is computed, assuming a uniform distribution of orientations. The results of similar computations are presented for cases when electrical forces are present.     

面向生物能源的酶固定化的计算机模拟

利用酶固定化技术来对生物质发酵获取生物能源已显得日益重要。酶与表面间的相互作用强烈影响固定化酶的取向,进而影响催化效率。本文采用并行退火蒙特卡洛（PTMC）方法对三种生物能源用酶（脂肪酶、纤维素酶和氢化酶）在不同的带电表面和离子强度下的吸附取向进行了模拟研究。模拟结果发现三种酶的吸附主要由静电吸引力主导,并且很大程度上与蛋白表面带电氨基酸的分布和溶液离子的静电屏蔽有关。脂肪酶和氢化酶在带负电表面上吸附,其活性位和电子转移通道分别为朝向溶液和靠近表面,而纤维素酶则在带正电表面上取得较优的吸附取向。本文研究结果可为工业用酶以合理的取向在载体材料表面固定化提供一定的指导。     

Ion-assisted collection of Nylon-4,6 electrospun nanofibers

In electrospinning, electrostatic interaction between charged fibers and the collection substrate can result in poor and non-uniform coverage, particularly when electrically insulating substrates are used, because they are prone to surface charge accumulation. Charged electrospun Nylon-4,6 nanofiber coatings were deposited onto substrates of varying size, conductivity and morphology. The density and uniformity of the nanofiber coatings were significantly enhanced, both on insulating and on conducting substrates, by a new method based on rapid sequential deposition of charged nanofibers and oppositely charged ions onto substrates that were mounted onto a rotating collecting electrode (mandrel) located between an electrospinning source and a focused ion source. Sequential fiber/ion deposition presumably led to surface charge neutralization or reversed charging, and minimization of electrostatic fiber/substrate interactions. An electrostatics model was developed to interpret the experimental results. It was also theoretically argued that any degree of ion charging will induce continuous fiber accumulation.     

Forces Measured between Zirconia Surfaces in Poly(acrylic acid) Solutions

We have studied the forces between a sphere and a plane surface of yttria-partially-stabilized tetragonal-zirconia immersed in aqueous solutions of low-molecular-weight ( M _w= 10 000) poly(acrylic acid) (PAA) using atomic force microscopy. The measurements are performed at high pH where the adsorbed, highly charged anionic polyelectrolyte extends far into the solution, resulting in a combination of polymeric (steric) and electrostatic interactions. Analysis of the experimental data using scaling theory shows that the polymeric contribution dominates and that the electrostatic contribution is small at relatively high ionic strength (0.01 M NaCl). We find that the measured forces are highly dependent on time and interaction history of the absorbed PAA layer; consecutive compression-decompression cycles result in an increase of the surface coverage and the range of the repulsive polymeric interaction. This buildup of PAA at the interface is strongly related to attractive bridging interactions manifested as strong adhesion during decompression at less than full surface coverage. The force results are compared to rheological observations of zirconia suspensions stabilized by the same dispersant; the poor colloidal stability and high viscosity at low surface coverage of PAA are related to the attractive bridging interactions.     

Electrostatic Map of the SARS-CoV-2 Virion Specifies Binding Sites of the Antiviral Cationic Photosensitizer

Electrostatics is an important part of virus life. Understanding the detailed distribution of charges over the surface of a virus is important to predict its interactions with host cells, antibodies, drugs, and different materials. Using a coarse-grained model of the entire viral envelope developed by D. Korkin and S.-J. Marrink’s scientific groups, we created an electrostatic map of the external surface of SARS-CoV-2 and found a highly heterogeneous distribution of the electrostatic potential field of the viral envelope. Numerous negative patches originate mainly from negatively charged lipid domains in the viral membrane and negatively charged areas on the “stalks” of the spike (S) proteins. Membrane (M) and envelope (E) proteins with the total positive charge tend to colocalize with the negatively charged lipids. In the E protein pentamer exposed to the outer surface, negatively charged glutamate residues and surrounding lipids form a negative electrostatic potential ring around the channel entrance. We simulated the interaction of the antiviral octacationic photosensitizer octakis(cholinyl)zinc phthalocyanine with the surface structures of the entire model virion using the Brownian dynamics computational method implemented in ProKSim software (version r661). All mentioned negatively charged envelope components attracted the photosensitizer molecules and are thus potential targets for reactive oxygen generated in photosensitized reactions.     

Microscopic aspects of the deposition of nanoparticles from the gas phase

The deposition process in a homogeneous electric field, and the subsequent microscopic arrangement of charged, metallic nanoparticles in the size range below $\text{100}\text{nm}$ on flat substrate surfaces is described. The main aspect of the investigation is the transfer of the particles from a three-dimensional distribution in the gas phase into their arrangement on the substrate surface, in dependence on particle–particle interactions and on Brownian motion. For this purpose, a trajectory model has been developed, which takes into account the flow field above the substrate surface, the electric field, the interactions of incoming particles with the substrate surface and with already deposited particles, as well as Brownian motion. The results from the trajectory calculations are compared with experimental results, obtained by scanning electron microscopy investigations of deposition patterns, created by deposition of indium and gold nanoparticles in an electrostatic precipitator. The particle diameter, the particle charge, the substrate material, the electric field strength and the number of particles deposited per unit area have been varied.     

The effect of polycations on early cement paste

This paper studies the possibility for improving the ductility of cement based materials by means of oligocationic additives. Actually, the setting of cement is due to ionic correlation forces between highly negatively charged C-S-H nanoparticles throughout a calcium rich solution. The main drawback of this strong attraction is its very short range that results in low elastic deformation of hydrated cementitious materials. A way to enlarge the attraction range between C-S-H particles would be to add cationic oligomers that would compete with calcium ions modifying the ionic correlation forces via a bridging mechanism of longer range, which could lead to a more ductile material. The studied parameters were the polymerization degree, the separation distance between the charged monomers and the balance between oligocations and monovalent and divalent cations in the solution. The results, both experimental and numerical by Monte Carlo (MC) simulations, demonstrate that cationic oligomers can compete with calcium cations as counterions to the C-S-H surface. The cohesive forces between C-S-H surfaces, calculated by MC simulations, show an interesting behaviour where range and magnitude can be tuned with oligomer concentration, polymerization degree and line charge density. Thus, it seems possible to modulate the ductility and critical strain of cement by addition of cationic oligomers.     

Pulsed Electrical Stimulation and Surface Charge Induced Cell Growth on Multistage Spark Plasma Sintered Hydroxyapatite‐Barium Titanate Piezobiocomposite

The primary purpose of the present work was to illustrate whether cell proliferation can be enhanced on electroactive bioceramic composite, when the cells are cultured in the presence of external electrical stimulation. The two different aspects of the influence of electric field (E‐field) application toward stimulating the growth/proliferation of bone/connective tissue cells in vitro, (a) intermittent delivery of extremely low strength pulsed electrical stimulation (0.5–4 V/cm, 400 μs DC pulse) and (b) surface charge generated by electrical poling (10 kV/cm) of hydroxyapatite (HA)‐BaTiO₃ piezobiocomposite have been demonstrated. The experimental results establish that the cell growth can be enhanced using the new culture protocol of the intermittent delivery of electrical pulses within a narrow range of stimulation parameters. The optimal E‐field strength for enhanced cellular response for mouse fibroblast L929 and osteogenic cells is in the range of 0.5–1 V/cm. The MTT [3‐(4, 5‐dimethylthiazol‐2‐yl)‐2, 5‐diphenyl tetrazolium bromide] assay results suggested the increased viability of E‐field treated cells over 7 d in culture, implicating the positive impact of electrical pulses on proliferation behavior. The alizarin red assay results showed noticeable increase in Ca‐deposition on the E‐field treated samples in comparison to their untreated counterparts. The negatively charged surfaces of developed piezocomposite stimulated the cell growth in a statistically noticeable manner as compared with the uncharged or positively charged surfaces of similar composition.     

Mass Spectrometric and Bio-Computational Binding Strength Analysis of Multiply Charged RNAse S Gas-Phase Complexes Obtained by Electrospray Ionization from Varying In-Solution Equilibrium Conditions

We investigated the influence of a solvent’s composition on the stability of desorbed and multiply charged RNAse S ions by analyzing the non-covalent complex’s gas-phase dissociation processes. RNAse S was dissolved in electrospray ionization-compatible buffers with either increasing organic co-solvent content or different pHs. The direct transition of all the ions and the evaporation of the solvent from all the in-solution components of RNAse S under the respective in-solution conditions by electrospray ionization was followed by a collision-induced dissociation of the surviving non-covalent RNAse S complex ions. Both types of changes of solvent conditions yielded in mass spectrometrically observable differences of the in-solution complexation equilibria. Through quantitative analysis of the dissociation products, i.e., from normalized ion abundances of RNAse S, S-protein, and S-peptide, the apparent kinetic and apparent thermodynamic gas-phase complex properties were deduced. From the experimental data, it is concluded that the stability of RNAse S in the gas phase is independent of its in-solution equilibrium but is sensitive to the complexes’ gas-phase charge states. Bio-computational in-silico studies showed that after desolvation and ionization by electrospray, the remaining binding forces kept the S-peptide and S-protein together in the gas phase predominantly by polar interactions, which indirectly stabilized the in-bulk solution predominating non-polar intermolecular interactions. As polar interactions are sensitive to in-solution protonation, bio-computational results provide an explanation of quantitative experimental data with single amino acid residue resolution.     

Electrostatic and Entropic Interactions between Parallel Interfaces Separated by a Glassy Film

A simple classical density functional model is set up to describe the electrostatic and entropic interactions between two parallel planar charged interfaces separated by a thin film of a phase (the glass) containing a distribution of charged ions. The total charge in the system is zero. Three cases are treated: (1) the two interfaces carry a fixed surface charge; (2) the first interface carries a fixed surface charge, simulating a ceramic, while the second is held at zero potential, simulating a metal; and (3) both interfaces are held at zero potential. A discretized form of the nonlinear Poisson–Boltzmann equation is derived and solved by a Newton–Raphson method. The continuum approximation is compared with a model in which the ions are only allowed to occupy discrete planes. The effect of correlation among the ions is included within the local density approximation. Inserting parameters appropriate to the copper–alumina interface, we find that the attractive image force between the ceramic and metal dominates the entropic (DLVO) repulsive force in the 1–2 nm range.     

Electrostatic phenomena during powder handling

During powder handling operations, particles make frequent contact with surfaces often metallic, and become electrically charged due to the process of contact electrification. It is often more appropriate to describes such a contact electrification process as triboelectrification as sliding/frictional contact is invariably involved. Triboelectrification is a complex process as charge exchange involving insulating surfaces takes place. The concept of work function may be applied to some insulator materials, especially those that charge negatively as many polymeric materials do. Surface charging depends upon surface condition and some materials are sensitive to the presence of oxidising agents in the atmosphere and also to the presence of moisture. To quantify the triboelectrification process, the dynamics of particle surface contact must be fully defined and contact area accurately assessed. The dynamic behaviour of charged particles may be significantly dependent upon charge. Space charge fields which exist in charged powder clouds act upon individual particles whose motion depends upon particle electrical mobility. Even in the absence of space charge fields, charged particles experience attractive forces towards nearby neutral surfaces. Upon contact with surfaces, charged particles may adhere strongly by a combination of electrostatic and van der Waals forces. Particle/surface adhesion is important in powder coating applications and in electrostatic precipitators.     

Cationic latex: Colloidal behavior and interaction with anionic pulp fibers

Styrene–butadiene latexes were prepared in the absence of an emulsifier using a redox initiator Fe(NO₃)₃/H₂O₂. Their positive charge was supplied by comonomer N,N‐diethyl aminoethyl methacrylate. At a given styrene–butadiene ratio (60/40) the particle size depends on the concentration of the comonomer and initiator. The latexes are stabilized by electrostatic repulsion, and remain positively charged and stable up to pH 8. At a higher pH, they acquire a negative charge and restabilize. The positively charged particles deposit readily on negatively charged fibers dispersed in water, thus covering the fiber surface. Upon dewatering and drying, the particles coalesce, and the fibers become covered by a polymeric film, which improves the interfiber bonding and, consequently, the mechanical properties of the fiber assembly. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1677–1682, 2000     

Preparation of anionic ion exchange latex particles via heteroaggregation

To prepare relatively large negatively charged polymer particles in a size range from 0.3 μm to 0.5 μm, having high surface charge densities, the heteroaggregation of small (50–100 nm), highly charged (185 and 421 μeq/g) anionic polystyrene particles onto the surface of larger (317–466 nm) poly(vinylbenzyl choride)‐based cationic (10, 614, and 830 μeq/g) particles was carried out. As a result, particles with different surface charges, having a core‐shell structure, were successfully prepared. First, aggregated particles were formed via heteroaggregation of the lowest surface charge density anionic particles (185 μeq/g) with the lowest surface charge density cationic particles (10 μeq/g). However, the anionic particles in the shell layer desorbed with time owing to the relatively weak interaction between the two particles. Second, aggregated particles comprised of the highest surface charge density cationic (830 μeq/g) and anionic latex particles (421 μeq/g) were formed. However, to prepare a stable system, an excess of the small anionic particles was required, leaving a large number of small particles present in the aqueous phase, which proved difficult to remove. Finally, aggregated particles were formed by heteroaggregation of cationic particles with an intermediate surface charge density (614 μeq/g) with the highest surface charge anionic particles (421 μeq/g). As a result, not only were core‐shell particles formed, but few free small anionic particles remained in the aqueous phase. In this article, the preparation and characterization of each of these aggregates are discussed in terms of particle size, morphology, and extent of incorporation of the functional groups. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

电化学界面处离子分布、静电势和ξ势的研究

Density functional theory is applied to predicting the structures and electrostatic potentials of planar electrochemical surfaces within the framework of the restricted primitive model where small ions are represented by charged hard spheres of equal diameter and the solvent is assumed to be a continuous dielectric medium. The hard-sphere contribution to the excess Helmholtz energy functional is evaluated using the modified fundamentalmeasure theory and the electrostatic contribution is obtained from the quadratic functional Taylor expansion using the second-order direct correlation function from the mean-spherical approximation. Numerical results for the ionic density profiles and the mean electrostatic potentials near a planar surface of various charge densities are in excellent agreement with molecular simulations. In contrast to the modified Gouy-Chapman theory, the present density functional theory correctly predicts the second layer formation and charge inversion of charged surfaces as observed in simulations and in experiments. The theory has also been tested with the zeta potentials of positively charged polystyrene particles in aqueous solutions of KBr. Good agreement is achieved between the calculated and experimental results.     

电化学界面处离子分布、静电势和ζ势的研究

Density functional theory is applied to predicting the structures and electrostatic potentials of planar electrochemical surfaces within the framework of the restricted primitive model where small ions are represented by charged hard spheres of equal diameter and the solvent is assumed to be a continuous dielectric medium. The hard-sphere contribution to the excess Helmholtz energy functional is evaluated using the modified fundamental-measure theory and the electrostatic contribution is obtained from the quadratic functional Taylor expansion using the second-order direct correlation function from the mean-spherical approximation. Numerical results for the ionic density profiles and the mean electrostatic potentials near a planar surface of various charge densities are in excellent