Potential distribution around a polyelectrolyte-coated spherical particle in a salt-free medium

Simple analytic approximate expressions for the solution to the Poisson-Boltzmann equation around a spherical particle coated with an ion-penetrable polyelectrolyte layer in a salt-free medium containing counterions only are derived. The results of the calculation of the potential distribution using the approximate solution are found to be in good agreement with exact numerical results. It is shown that as in the case of a charged rigid particle, there is a certain critical value of the particle charge, separating two cases, that is, the low-particle-charge case and the high-particle-charge case. In the low-charge case the potential is essentially the same as if counterions were absent and thus the potential is proportional to the particle charge. In the high-charge case counterion condensation occurs in the polyelectrolyte layer region, so that the dependence of the potential on the particle charge is considerably suppressed.     

The reactivity of TiO2 with different preparation histories in solid-state reactions in CaSO2-TiO2 systems

Influences of the preparation histories of TiO₂ on its reactivity in solid-state reactions in CaSO₂-TiO₂ systems were studied by means of TG, DTA and isothermal kinetic experiments.In order to estimate the reactivities of solids, it was necessary to note the behaviors in the initial reaction step in the selected reaction system. It was concluded that the reactivity of TiO₂ was dependent on the structure difference due to the different preparation histories, and the greater the stability of the anatase form, up to higher temperature, the higher the reactivity of TiO₂.

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Zusammenfassung Der Einfluß der Herstellungsgeschichten von TiO₂ auf seine Reaktivität bei der Festphasenreaktion im System CaSO₄-TiO₂ wurde durch TG, DTA und isotherme kinetische Versuche untersucht.Zur Abschätzung der Reaktivität der Festkörper mußte ihr Verhalten während des Anfangsschrittes der Reaktion im gewählten System beobachtet werden. Es wurde gefolgert, daß die Reaktivität des TiO₂ von den durch verschiedene Herstellungsgeschichten verursachten Strukturdifferenzen abhängt und bis zu höheren Temperaturen umso stabiler in der Anatas-Form ist, je höher die Reaktivität des TiO₂ ist.

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Résumé On a étudié par TG, ATD et expériences cinétiques isothermes l'influence du mode de préparation de TiO₂ sur sa réactivité lors de la réaction en phase solide des systèmes CaSO₄-TiO₂.Afin d'estimer la réactivité des solides, il a été nécessaire d'observer leurs comportements lors de l'étape initiale de la réaction dans le système réactionnel choisi. On en a conclu que la réactivité de TiO₂ dépend des différences de structure dues aux différents modes de préparation et que ce composé est d'autant plus stable, à températures élevées, sous la forme d'anatase, que la réactivité de TiO₂ est forte.

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C , TiO₂ CaSO₄-TiO₂. , . , TiO₂ , TiO₂.

     

Zeta potential and surface charge density of polystyrene-latex; comparison with synaptic vesicle and brush border membrane vesicle

The electrophoretic mobility of polystyrene — latex (PSL) of diameter 870 Å was determined using a Laser Zee System 3000. This instrument enables automatic measurement of the electrophoretic mobility of fine particles. Effect of pH and ionic strengthI on the PSL mobility was analyzed. It was found that the mobility as a function of pH has a minimum around pH 3–4 atI=0.1, showing no isoelectric point, and that the mobility decreases with increasing ionic strength up toI=0.1 but is almost constant forI=0.1–0.2 at pH=7.34. From the mobility date, we estimated the zeta potential of PSL. We used an approximate mobility formula derived by Ohshima, Healy and White, which is considerably more accurate than Smolchowski's and Henry's formula and is applicable for fine particles with small a ( a10), where is the Debye-Hückel parameter anda is the particle radius. Further, we calculated the surface charge density of PSL using an approximate relationship. It was found that there are 2000–4000 negative charges on the PSL surface at pH=7.34. Comparison is made with the results on synaptic vesicles (SV) from brain cerebrum cortex and brush-border-membrane vesicles (BBMV) from the small intestine.     

Change in electrophoretic mobility of HL-60RG cells by apoptosis

We measured the electrophoretic mobilities of HL-60RG cells and their apoptotic cells triggered by Actinomycin D as a function of the ionic strength of the suspending medium at pH 7.4. Both types of cells showed negative mobilities. The apoptotic HL-60RG cells exhibited larger mobility values in magnitude than intact HL-60RG cells in the whole range of the electrolyte concentration measured. The obtained data were analyzed via a mobility expression for soft particles, that is, colloidal particles with ionpenetrable surface layers. The observed mobility difference between the intact and apoptotic HL-60RG cells was found to be due mainly to the difference in friction exerted by the cell surface layers on the liquid flow around the cells between these two types of cells rather than the difference in charge density in their surface layers. A possible explanation for this mobility change by apoptosis is given.     

Electrostatic interaction of ion-penetrable membranes. Effects of ionic solubility

An analytic, approximate expression for the electrostatic interaction between two membranes immersed in an electrolyte solution is derived on the basis of a simple membrane model. This model assumes that the membrane has a surface layer in which charged groups are uniformly distributed and that electrolyte ions can penetrate into the surface layer. The partition coefficients of cations and anions between the solution and the surface layer, which are related to their solubilities in the surface layer, may be different from unity.The electrostatic interaction depends on the ionic partition coefficients between the solution and the surface layer, and the relative permittivity of the surface layer, as well as on the membrane-fixed charges, the electrolyte concentration in the solution, and the surface layer thickness. It is shown, in particular, that even where the charge layer has no fixed charges, the electrostatic interaction force can be produced if the solubilities of cations and anions are different in the surface layer.     

Electrophoresis of soft particles with hydrophobic inner core grafted with pH-regulated and highly charged polyelectrolyte layer

Electrophoresis of core–shell composite soft particles possessing hydrophobic inner core grafted with highly charged polyelectrolyte layer (PEL) has been studied analytically. The PEL bears pH-dependent charge properties due to the presence of zwitterionic functional groups. The dielectric permittivity of the PEL and bulk aqueous medium were taken to be different, which resulted in the ion-partitioning effect. Objective of this study was to provide a simple expression for the mobility of such core–shell soft particles under Donnan limit where the thickness of the PEL well exceeds the electric double layer thickness. Going beyond the widely used Debye–Hückel linearization, the nonlinear Poisson–Boltzmann equation coupled with Stokes–Darcy–Brinkman equations was solved to determine the electrophoretic mobility. The derived expression further recovers all the existing results for the electrophoretic mobility under various simplified cases. The graphical presentation of the results illustrated the impact of pertinent parameters on the electrophoretic mobility of such a soft particle.     

Synthesis of networked polystyrene endowed with nucleophilic reaction sites by the living anionic polymerization technique

The living anionic copolymerization of styrene with 1,2‐bis(4′‐ethenylphenyl)ethane (1) or p‐divinylbenzene (PDVB) with sec‐butyllithium in benzene was carried out. The copolymerizations of styrene with more than 20 mol % of 1 gave insoluble polymers in quantitative yields, whereas the yield showed the maximum (97%) for PDVB at 15 mol %. The content of unreacted double bonds of the network polymer formed by the copolymerization with PDVB was four times as large as that formed with 1. Gas chromatographic analyses of the copolymerization suggested close reactivities of the double bonds between styrene and 1, whereas a rapid consumption of PDVB compared with styrene was observed in their copolymerization. The r₁, r₂,and r₁r₂ values for the copolymerization of styrene with 1 were determined to be 1.00, 1.09, and 1.09, respectively, which suggests that a more homogeneous network structure can be attained with 1. The living chain end of the produced living gel initiated the polymerization of tert‐butyl methacrylate to give an insoluble block copolymer in a good yield. The hydrolysis of the ester group of the block copolymer led to an amphiphilic copolymer that exhibited a characteristic property of a hydrogel. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2543–2547, 2000     

Chemical reaction concerns of gate metal with gate dielectric in Tagate MOS devices: an effect of self-sealing barrier configurationinterposed between Ta and SiO2

Chemical reaction of gate metal with gate dielectric for Ta gate MOS devices has been experimentally investigated both by electrical and physical measurements: capacitance-voltage (C-V), current-voltage (I-V), transmission electron microscopy (TEM), energy dispersive X-ray (EDX), electron diffraction measurements. In spite of the chemical reaction of Ta with SiO₂ consuming ~1-nm-thick in gate oxide, the interface trap densities of ~2×10¹⁰ cm^-2 eV ^-1 at midgap and ideal channel mobility characteristics have been observed in the Ta gate MOS devices with 5.5-nm-thick thermal oxide gate dielectric. Considering the experimental data with theoretical calculation based on thermodynamics together, a barrier layer model has been developed for the Ta gate MOS systems. The physical mechanism involved is probably self-sealing barrier layer formation resulting from the chemical reaction kinetics in the free-energy change of Ta-Si-O system     

Pulsed Power Applications for Protein Conformational Change and the Permeabilization of Agricultural Products

Pulsed electric fields (PEFs), which are generated by pulsed power technologies, are being tested for their applicability in food processing through protein conformational change and the poration of cell membranes. In this article, enzyme activity change and the permeabilization of agricultural products using pulsed power technologies are reviewed as novel, nonthermal food processes. Compact pulsed power systems have been developed with repetitive operation and moderate output power for application in food processing. Firstly, the compact pulsed power systems for the enzyme activity change and permeabilization are outlined. Exposure to electric fields affects hydrogen bonds in the secondary and tertiary structures of proteins; as a result, the protein conformation is induced to be changed. The conformational change induces an activity change in enzymes such as α-amylase and peroxidase. Secondly, the conformational change in proteins and the induced protein functional change are reviewed. The permeabilization of agricultural products is caused through the poration of cell membranes by applying PEFs produced by pulsed discharges. The permeabilization of cell membranes can be used for the extraction of nutrients and health-promoting agents such as polyphenols and vitamins. The electrical poration can also be used as a pre-treatment for food drying and blanching processes. Finally, the permeabilization of cell membranes and its applications in food processing are reviewed.