The effect of electrophoretic convection for the separation of solute in the chromatography column (I)

A theoretical model has been derived in an electrophoretic packed column where an electric potential is applied to a column in the axial direction. The effect of electrophoretic convection in gel particles packed in the column significantly contributes to the separation of large polyelectrolytes because the conformation of polyelectrolyte quickly orients in the field direction. The dependence of the transport in the gel particle upon field intensity and molecular size aids in understanding the transport of polyelectrolyte in the packed column, since the convective velocity of polyelectrolyte is accelerated inside a porous gel particle. There are few convection studies of large poly-electrolyte in a column packed with porous gel particles under an electric field for the separation. Convective-diffusive transport of a large polyelectrolyte is analyzed using Peclet number described by electrophoretic mobility and diffusion coefficient measured experimentally. The separation of two different polyelectrolytes in the packed column is performed using a value ofPe _f/Pe_g of individual polyelectrolyte by molecular size and an electric field. The purpose of this paper is to study the separation of solute from a mixture in the column using the physicochemical properties in the gel particle which are measured experimentally.     

Adsorption of a weakly charged polymer on an oppositely charged colloidal particle: Monte Carlo simulations investigation

Monte Carlo simulations were used to investigate the conformational and electrical properties of isolated weak polyelectrolytes in the presence of an oppositely charged particle. Titrations curves were calculated to get an insight into the role of pH on the degree of ionization and conformation of isolated chains. The effect of ionic concentration and polyelectrolyte length on the titration curves was also investigated. The complex formation between the isolated polyelectrolyte and the oppositely charged particle was considered at different pH and ionic concentration values. The adsorption/desorption limit was calculated and the effect of the polyelectrolyte adsorption on the titration curves investigated. In particular, it was demonstrated that the presence of an oppositely charged particle clearly increases the degree of ionization of the weak polyelectrolyte and that ionic concentration plays a subtle role by increasing/reducing both the attractive energy between the polyelectrolyte and the particle and the polyelectrolyte degree of ionization.     

Conjugated polyelectrolytes--conformation-sensitive optical probes for staining and characterization of amyloid deposits

Specific markers for diseases associated with protein aggregate depositions are of great interest. Here we report the use of conjugated polyelectrolytes as conformation-sensitive optical probes for histological labeling of amyloid deposits in ex vivo tissue samples-amyloid light chains in primary systemic amyloidosis, islet amyloid polypeptide in human pancreas, and Abeta amyloid in Alzheimer's disease. Under suitable conditions, these probes bind specifically to amyloid deposits, and this is seen as an orange-red emission from the polyelectrolyte. Furthermore, the probes emit light of different colors when bound to different amyloid deposits or other intracellular structures. This phenomenon is most probably due to differences in the protein conformation in these structures. Hence, different protein conformations will generate geometric alterations of the bound polyelectrolyte backbone, affording different emissions from the bound probe. Conformation-sensitive probes thus provide a direct link between spectral signal and protein conformation. Finally, the probes also proved useful for ex vivo fluorescence imaging by multiphoton excitation.     

Interaction of cationic and anionic polyelectrolyte with SiO2 and Al2O3 powders

The adsorption of anionic and cationic polyelectrolytes onto alumina and silica surfaces is studied. The results indicate that the polyelectrolyte-surface interaction is affected by various factors such as (i) polyelectrolyte nature, (ii) distribution and nature of the oxide surface sites, and (iii) medium properties. A strong interaction enhances the formation of a flat conformation of the adsorbed polyelectrolyte onto the surface, whereas a weak interaction leads to a loops conformation. The effect of the adsorbed polyelectrolyte on the electrokinetic behaviour of the two oxides was also investigated using an electrokinetic sonic amplitude analyser.     

The physical chemistry of polyelectrolyte solutions

Some physical properties of aqueous solutions containing linear, flexible, polyelectrolytes are reviewed in order to emphasize the role of charge interactions in these systems which strongly depend on the charge of the macromolecular chain and the concentration of low molar mass electrolyte in solution. Particular emphasis is put on polyelectrolyte solutions containing an excess of added salt, which from a theoretical point of view are easier to understand. Both the dilute and the semi-dilute case will be discussed. In the former the problem of the electrostatic potential around the macromolecular chain is briefly reviewed as well as the use of a wormlike chain model to derive average dimensions of polyelectrolytes in solutions. In the latter the scaling approach to concentration effects in polyelectrolyte solutions is briefly discussed. The pecularities of the semi-dilute regime in polyelectrolyte solutions is illustrated with the help of results obtained with dynamic light scattering and the time dependent decay of electric birefringence.     

Interactions of nitrates with cationic polyelectrolytes in chelation/ultrafiltration systems for water treatment

The interaction between poly(dimethylamine-co-epichlorohydrin-co-ethylene-diamine) with positive charges and nitrate ions in synthetic water was investigated during ultrafiltration (UF). The adsorption behaviour of nitrate onto cationic polyelectrolyte was evaluated with Langmuir and Freundlich isotherms in dilute polyelectrolyte solutions. During UF, ionic strength, Debye–Hückel screening length, average electric potentials at the polyelectrolyte interface, and the amount of nitrates adsorbed per mole of polymeric functional groups were estimated at different concentration factors. The results indicated that polyelectrolyte skeletons tended to coil at a higher concentration factor. It was also discovered that adsorbed nitrate was released from the polyelectrolytes while making their surface charge more positive at high concentration factors. The coiling of polyelectrolyte chains caused negative effects on the lateral interactions of nitrate with the polyelectrolyte.     

Increasing viscosity in entangled polyelectrolyte solutions by the addition of salt

The viscosity of several polyelectrolytes is measured in both salt free solutions and solutions in the high salt limit. At low polymer concentrations, the zero shear rate viscosity decreases as much as 100-fold upon addition of a monovalent salt, namely NaCl. However, as polymer concentration increases, the viscosity difference between polymer in salt free and in monovalent salt solution diminishes. Further, the zero shear rate viscosity becomes independent of added monovalent salt at the critical polyelectrolyte concentration c_D. Above c_D, the addition of monovalent salt increases the zero shear rate viscosity of the entangled polyelectrolyte solutions. The viscosity increase agrees with viscosity scaling theory for polyelectrolytes in the entangled regime. Polyelectrolytes exhibiting an increase in viscosity above c_D in the presence of monovalent salt include three natural anionic polyelectrolytes (xanthan, carrageenan, welan), one synthetic anionic polyelectrolyte (hydrolyzed polyacrylamide), and one natural cationic polyelectrolyte (chitosan). Generally, these polyelectrolytes are relatively high molecular weight (>1 M Dalton), which makes c_D experimentally accessible (e.g., c_D = 0.2 wt% for xanthan). The magnitude of the viscosity increase is as high as 300% for xanthan and nearly independent of monovalent salt concentration in the high salt limit. The increase in viscosity in monovalent salt solution and magnitude of c_D appear to be heavily influenced by the molecular characteristics of the polymers such as monomer weight, molecular structure, and chain conformation.     

Experimental research on piezoelectric ceramics activating micro-sized thermochemical battery

To verify feasibility of piezoelectric ceramic activating micro-sized thermochemical batteries, it is very necessary to disclose shock pressure and electric output performances of piezoelectric ceramic. In order to simulate piezoelectric ceramic activating micro-sized thermochemical batteries in the bore, shock pressure, and electronic output testing systems for piezoelectric ceramic have been established. And the piezoelectric ceramics composite structural targets are impacted using one-stage light gas gun to load projectile, which is used to simulate the overload of the projectile with piezoelectric ceramics during projectile launching process, and combining with the experimental tests of a military 3# electric fuse head as a firing component in series. In experiments, the composite structural targets (front steel substrate-piezoelectric ceramic-rear steel substrate) are vertically impacted by the cylindrical 2A12 aluminum projectiles. The change rules of shock pressure, output voltage, and current peak values for piezoelectric ceramics are obtained at the different experimental parameters, and the firing conditions of piezoelectric ceramic igniting the military 3# electric fuse heads and ignition paper are presented.     

Determination of reversible and irreversible contributions to the polarization and strain response of soft PZT using the partial unloading method

Experimental work is aimed at systematically investigating the non-linear ferroelectric and ferroelastic behavior of a commercially available soft lead zirconate titanate (PZT) material. The fast partial unloading method is used to measure the material properties of unpoled soft PZT under pure electric field and of initially pre-poled soft PZT under compressive stress loading. In the first experiment using unpoled PZT, the evolution of piezoelectric constants and dielectric permittivity is determined as a function of electric field. It is found that the piezoelectric constants and dielectric permittivity depend on the electric field history. The results are used to separate the reversible strain and polarization from the irreversible ones caused by domain switching. In the second experiment using initially pre-poled PZT, it is found that the strain response is significantly dependent on the stress loading rate. The elastic moduli and piezoelectric coefficients are evaluated with respect to the compressive stress history. The measured longitudinal and transverse irreversible strains change significantly during both loading and unloading processes. An attempt is made to discuss the use of irreversible strain and irreversible polarization as internal variables for constitutive modeling. This investigation provides valuable information for modeling to predict the performance and for improving the reliability of piezoelectric devices.     

Gas Phase Reactions in Silent Electric Discharges. Part I: Exact Calculation of the Charge Passed Through the Discharge Chamber and the Electric Field Using the Electrical Parameters of the Circuit

The rate of a chemical reaction occurring in a silent electric discharge is dependent on the electric charge passing through the gas. In the knowledge of the electrical characteristics of the circuit and its elements (i.e., the ohmic resistance and capacitance), the composition and the pressure of the gas, the electric charge involved in the discharge can be calculated. The application of a purely sinusoidal alternating current to the system allows deduction of the time dependence of the voltage drops across various circuit elements and also the time dependence of the current. Experiments were conducted with two reactor types (static and tubular flow) and their electrical characteristics were varied to test the results of the calculations, which were thereby confirmed.     

Tip Deflection and Blocking Force of Soft PZT-Based Cantilever RAINBOW Actuators

A piezoelectric/electrostrictive RAINBOW actuator is a monolithic bending device consisting of an electromechanically active layer and a reduced passive layer formed in a high-temperature reduction treatment. When the piezoelectric or electrostrictive layer is driven under an electric field or when the environmental temperature changes, bending deflection is produced because of the constraint of the reduced inactive layer or because of the thermal expansion coefficient difference of the two layers. In this study, general analytical expressions relating tip deflection, blocking force, and equivalent moment with an applied electric field and temperature change are derived for a cantilevered RAINBOW actuator. It is shown that optimal actuator performance can be achieved in the RAINBOW actuator by choosing a suitable thickness ratio of the reduced layer to the PZT layer. A series of RAINBOW cantilever actuators have been experimentally prepared from high-density, soft, lead zirconate titanate (PZT) ceramics. Different reduction layer thickness is obtained by adjusting the processing parameters, such as reduction temperature and time. The measured results on tip deflection and blocking force agree well with theoretical prediction under a weak electric field. However, when a high driving electric field is used, deviation is observed, which can be attributed to a nonlinear piezoelectric response and a nonlinear elastic behavior associated with soft PZT materials under high driving electric fields.     

An easily recoverable thermo-sensitive polyelectrolyte as draw agent for forward osmosis process

As a potential solution to the crises of energy and resources, forward osmosis(FO) has been limited by the development of draw agents. An ideal draw agent should be able to generate high osmotic pressure and can be easily recovered. In this study, a thermo-sensitive polyelectrolyte of poly(N-isopropylacrylamide-co-acrylic acid)(PNA)is developed as an efficient draw agent, and two easy and simple methods are proposed to effectively recover the polyelectrolytes. After adjusting the pH value of polyelectrolyte solutions to around 6.0, the polyelectrolyte can generate relatively high osmotic pressure, and induce average water fluxes of 2.09 and 2.95 L·m~(-2)·h~(-1) during12 h FO processes when the polyelectrolyte concentrations are 0.20 and 0.38 g·ml~(-1) respectively. After acidifying and heating to 70 °C, the PNA-10 polyelectrolyte can aggregate together because of hydrophobic association and separate from water, so it can be easily recovered by either simple centrifugation or gravitational sedimentation. The recovery ratios of PNA-10 polyelectrolyte in both methods are as high as 89%, and the recovered polyelectrolytes can be reused with almost the same FO performance as fresh ones. The results in this study provide valuable guidance for designing efficient and easily recoverable draw agents for FO processes.     

The Separation of Polyelectrolyte Using an Electric Field in a Packed Column

Abstract

The effect of electrophoretic convection in a packed column is presented. When an electric field is applied, the conformation of polyelectrolyte quickly orients in the field direction. The convective velocity of polyelectrolyte inside a porous gel particle is accelerated. The dependence of the transport in the gel particle upon field intensity and molecular size aids in understanding the transport of polyelectrolyte in the packed column. To date, few dynamic studies of polyelectrolyte in a porous gel particle have been attempted for the separation of polyelectrolyte in a packed column. A large polyelectrolyte like DNA will separate due to conformation changes in the presence of the electric field. Convective-diffusive transport of DNA is analyzed by physical properties measured experimentally, such as the diffusion coefficient, the electrophoretic convection, and the gel porosity. The purpose of this study is to show how the variation of physicochemical properties in the gel particle affects the separation of DNA from a mixture in a packed column. A theoretical model using the characteristic method is used to calculate the separation point in a packed column.     

The effect of anionic polyelectrolytes on the properties of aqueous silicon nitride suspensions

The effect of anionic polyelectrolytes on the electrokinetic and rheological properties of concentrated Si3N4 suspensions was investigated experimentally. We found that polyelectrolyte adsorption and, thus, colloidal stability at pH>pHSi3N4iep is mainly governed by the surface charge density of the solid phase. Comparing anionic methacrylic acid comb copolymer modifications with grafted poly(ethylene oxide) chains (PMMA-PEO), with poly(acrylic acid) (PAA) showed that the grafted PEO chains have a minor influence on the colloidal stability. The common viscosity minimum for all the anionic polyelectrolytes around pH 7 suggests that the suspensions are electrosterically stabilized. The polyacrylic backbone attains an extended conformation perpendicular to the surface. The effect of excess addition of polyelectrolyte was also discussed; we attribute the significant increase in suspension viscosity to the increased ionic strength caused by the release of associated counterions of the polymer functional groups.     

The role of 90° domain wall displacements in forming physical properties of perovskite ferroelectric ceramics

A proposed model which takes into account an elastic interaction between a polydomain grain and a surrounding ceramic matrix under weak external mechanical stresses has been used for evaluating a contribution from 90° domain wall displacements to piezoelectric and elastic constants of the perovskite ferroelectric ceramics. A difference between experimental and averaged constants of BaTiO₃ ceramics can be explained by the estimated contribution.     

In situ measurement of material properties of lead zirconate titanate piezoelectric ceramics during cyclic mechanical loading

To better understand the material properties of lead zirconate titanate (PZT) ceramics, in situ mechanical and electrical properties have been investigated continuously during cyclic mechanical loading. The material properties are demonstrated to change as a function of applied maximum stress, with the effective elastic constant increasing with increase of the stress level. The increase of effective elastic constant is attributed to the domain structure of the PZT. 90° domain switching can occur anywhere in the sample, which makes the strain accumulate and leads to high values of the effective elastic constant. The domain switching characteristics are clearly revealed by electron back scattered diffraction analysis. The changes of the electrical properties (electromechanical coupling coefficient, piezoelectric constant and permittivity) are in the opposite sense because of the material strain (or material damage), caused by the change of domain orientation; the electrical properties are degraded with increasing cycle number and applied stress. Based upon the variation of the material properties, details of the damage characteristics in the PZT ceramics are discussed.     

基于ANSYS的ECT系统传感器的仿真研究

采用ANSYS有限元软件对8电极电容传感器的电场进行模拟仿真计算,比较分析不同介电常 数的介质对电场的影响,计算无径向、有径向以及径向电极插入管壁不同深度的电容值.仿真结果表明,加径向电极使电场趋向均匀,传感器电极之间的干扰降低.     

Study of the stoichiometric polyelectrolyte complex between chitosan and carboxymethyl cellulose

Summary The polyelectrolyte complex (PEC) between chitosan and carboxymethyl cellulose was studied. Turbidimetric measurements revealed that the amount of stoichiometric PEC increased gradually as the solution of one polyelectrolyte was added to the other; the turbidity of the solution reached a maximum for the stoichiometric ratio of the reacting polyelectrolytes in the mixture. At pH 4,0 the composition of the complex is very near to equimolarity. IR spectra and thermal analysis of the PEC exhibited significant differences from those of the 1:1 mixture of the starting polyelectrolytes.     

聚电解质研究进展

介绍了聚电解质的性质及分类;综述了聚电解质作为絮凝剂、分散剂、高吸水树脂、药物缓释等材料,已被广泛应用于能源、生物医药、功能材料等诸多领域;展望了聚电解质今后的研究方向。     

Permeability characteristic of polyelectrolyte complex capsule membranes: Effect of preparation condition on permeability

Because polyelectrolyte complex formation is known to depend on charge densities of polyelectrolytes, influence of pH condition in the preparation of the polyelectrolyte complex capsules on their permeability characteristic for phenylethylene glycol was examined. Partly crosslinked polyelectrolyte complex capsules were prepared by addition of an aqueous poly(acrylic acid) solution into an aqueous poly(ethylenimine) or L-histidine attached poly(ethylenimine) (ethylenimine unit/L-histidine residue: 5/1, mol/mol) solution and subsequent crosslinking under various pH conditions. Although poly(acrylic acid) and poly(ethylenimine) change their charge density depending on pH in an aqueous solution, the resultant capsules prepared at pHs 7, 6, and 5 show similar permeation properties under neutral and acidic conditions. By contrast, when L-histidine-attached poly(ethylenimine) was used instead of the unmodified polymer as the capsule membrane component, the resultant capsules prepared at pHs 8, 7, and 6 revealed remarkable difference in the permeability under neutral and acidic conditions. Because the ionization of an imidazolyl group, whose pKa is 6, on the L-histidine-attached poly(ethylenimine) is influenced significantly by pH near its pKa, such situation might affect density of networks formed by the ionic bonds in the polyelectrolyte complex membrane and resulted in the permeability difference. © 1996 John Wiley & Sons, Inc.