Reversal of charge

Some manufacturers use the principle of the adsorption of a gas by a porous material such as silica gel or charcoal. Since the adsorbent is a solid and cannot migrate from the phial, these valves cannot suffer reversal of charge. 

Matijevic, E., Janauer, G. E. and Kerker, M. J. Coll. Sci. 19 (1964) 333. Reversal of charge of hydro-phobic colloids by hydrolyzed metal ions, I. Aluminium nitrate. 

Similarities between reversal of charge spectra for colloids with solubility sequences of salts in bulk solution have been indicated (7, 37)— for example, for salts possessing different cations but the same anion, the solubility sequence of the phosphates is K+ > Na+ > Li+, while it is the reverse for the sulfates (7, 30). In view of this similarity, it is natural to introduce this fact as another possible link to explain the reversal of the specific cation effect in tt-A isotherms, though the precise relationship to monolayers is not clear at this time. 

Comparison of Figures 2 and 5 shows that at the pH range 6.5 to 7.5 where increased adsorption occurs, simultaneous reversal of charge and equivalent coagulation are both observed. This suggests that strong adsorption of a cationic cobalt (II) species is occurring. The principal... 

Here, Co(OH)2 represents the solid hydroxide. The solution data show that at pH values of 7.5 and 6.5 the dominant cobalt (II) species is the free (aquo) ion by factors of 100 and 1000 respectively. It is therefore highly unlikely that the coagulation at pH 6.5-7.5 and 10"4Af Co (II) and the reversal of charge can be caused by the free CoOH+ species. If it is caused by polynuclear charged species then the log-linear relationship (9) between the critical coagulation concentration and the valence of the coagulating ion would require a polynuclear species to have a charge of +5 or +6. Such a species has not been identified. (It is of interest to note that if this species did exist it would have to be a compact ion,... 

Coagulation Effects. Matijevic and co-workers have shown that in optimum cases the effect of hydrolyzed metal ions upon the coagulation and reversal of charge of lyophobic colloids can be useful in identifying... 

In both types of membrane systems, the current-potential curves corresponding to the first and second scans must be mirror images, which indicates that the ion transfer processes taking place at both the outer and inner interfaces are reversible. Thus, CSWV can be used as an excellent tool for analyzing the reversibility of charge transfer processes. 

Surfaces which are already charged (e.g. by ionisation) usually show a preferential tendency to adsorb counter-ions, especially those with a high charge number. It is possible for counter-ion adsorption to cause a reversal of charge. 

Figure 7.3 (a) Reversal of charge due to the adsorption of surface-active or polyvalent counter-ions, (b) Adsorption of surface-active co-ions... 

Charge recombination Reverse of charge separation. In using this term it is important to specify the resulting electronic state of the donor and acceptor. 

Reversal of Charge Shift Directions Through Competing TICT... 

The assembly of multilayers on SBH particles was observed by measurements of electrophoretic mobility (Fig. 1). Z-potential measurements were taken after each adsorption step. The reversal of charge showed the growth of nanofilms onto surface of SBH microparticles. 

Figure 6 is a graphic representation of the zeta potential data as a function of log molar concentration of different cationic surfactants. At lower concentration, zeta potential is high while on addition of additive it decreases slowly. This decrease is sharp at higher concentrations. On continuous addition of surfactant, the values first become zero and then reversal of charge takes place. 

Van Itallie CM, Fanning AS, Anderson JM (2003) Reversal of charge selectivity in cation or anion-selective epithelial fines by expression of different claudins. Am J Physiol Renal Physiol 285(6) F1078-F1084... 

All chemical bonds, except for symmetrically substituted ones, are inherently dissymmetric in two respects charge dissymmetry and hard-soft dissymmetry. The reversal of charge dissymmetry by modifying the structural unit (umpolung) has been well documented and has become one of the important principles in synthetic organic chemistry (16). On the other hand,... 

The effect of pH on the electrophoretic mobility of COM in systems containing fixed amounts of the four macromolecules is shown in Figure 2. In general, higher pH values led to more negative values of the electrophoretic mobility. The most marked effect was with serum albumin, where a reversal of charge occurred near pH 5.5. 

The chemical behavior of Mo should be similar to that of chromium (Cr) in wastewater treatment systems. The two elements can exist in the +3 oxidation state as cations under reducing conditions and tend to form oxides and hydroxides with very low solubilities. In aerated environments, the dominant species are the molybdate, MoO , the oxidized form of [Mo(Vl)] and chromate [Cr(Vl)], which are anions, in contrast to the cationic forms in reducing environments (Magyar et al, 1993 Beaubien et al, 1993). The reversal of charge as a function of oxidation state is expected to change the adsorption characteristics and precipitation reactions of Mo in wastewater systems compared to As and Se. 

The majority of LbL systems employ oppositely charged polyelectrolytes for the adsorption of polymer layers driven by electrostatic forces (Fig. 1). The assembly relies on the sequential reversal of charge upon the adsorption of oppositely charged polyelectrolytes. Polyelectrolytes may be classified as either strong or weak, with the former maintaining its charge independent of the pH, while the latter exhibits pH-dependent charge due to the presence of ionizable moieties. One of the most... 

Rather high characteristics of PsCs with ECPs have by now been obtained, primarily on the basis of various PT derivatives. One should point out the very high discharge efficiency (i.e., efficiency by capacitance) for such electrodes because of reversibility of charging-discharge processes. 

Chapter ix, entitled Reversal of Charge phenomena, Equivalent Weight, and Specific properties of the ionised groups, not only concerns the phase boundary of coacervates, but also the boundary of floccules and even the boundary of adsorbed colloid films on particles (e.g., on SiOe). 

In the part of this chapter in which the viscosity is treated and in Chapter IX (on reversal of charge), we sihall see that besides this dissociation of the specific groups... 

Ordinates and abscissae as in Fig. 16. A = KCl, B = BaCla, C = Co(NH3)eCl3 and D = [Pt(en)3] (NOa)4 fit completely with the behaviour in Fig. 16. E = hexol nitrate (composition, see note 1 on page 208) gives a curve with a minimum. At this minimum reversal of charge of the sol takes place from negative to positive. Flocculation does not take place with any of the salts, even not around the minimum of the hexol nitrate curve. 

By electrophoresis it could indeed be shown that reversal of charge takes place. Further flocculation nowhere occurs (as also neither with the other salts). But as was to be expected, with an appropriate amount of added alcohol maximum flocculation... 

Though the underlying mechanism of the reversal of charge with proteins by charing the pH is quite different, the minimum of the well known viscosity-pH curve is comparable to the minimum discussed for soluble starch with hexol nitrate. This minimum, occurring at the I,E,P.y is here quite easily detectable, because of the still low values of x. 

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