Effect of Additional Electrolytes

FIGURE 10. Mo72Fe3o A weak acid type of 2.5-nm diameter, Ceo-shaped spherical hydrophilic polyoxometalate molecular cluster formed by Mo-O polyhedrals (blue) and Fe-O polyhedrals (yellow). It can partially deprotonate the water ligands attached to its Fe centers (Reprinted with permission from ref. 21.) 

FIGURE 11. For Mo72Fe3o macroanions in dilute aqueous solution, the degree of association depends on pH. At pH 3.0, blackberries form as the Mo72Fe3o are charged, and the blackberry size decreases with increasing ptf (Reprinted with permission from ref. 21.) 

Counterion association appears to be an important aspect in blackberry formation.Therefore, it is important to understand the effects of adding extra electrolytes to POM solutions (either before or after) the blackberry formation. 

The experiments were performed by adding predetermined amounts (0-50 mM) of chloride salts (e.g., LiCl, NaCl, KCl, RbCl, CaCh, MgCh, BaCl2, and NiCl2) to freshly prepared 0.5-mg/mL Mo72Fe3o aqueous solutions (ones where no blackberries are present). 

If the small counterions are involved in the blackberry formation process as shared counterions between POM macroions, it is possible that the size of the counterions would affect their capability of attracting adjacent POMs. Because Rb is less hydrated, its size is smaller than the other types of cations 

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Effects of additives (electrolytes, surfactants, nonelectrolytes) on the volume fraction and temperature percolation thresholds of a water/AOT/n-heptane system have been investigated [280,281]. 

It was of interest for both fundamental understanding and practical use to examine the effects of additional electrolytes on polyelectrolyte-surfactant interactions. Initial studies investigated the effects of NaCl on cationic cellulosic polymer-SLES interactions. For sample preparation via high-throughput screening, the salt was pre-mixed with the surfactant at a 30 1 SLES NaCI ratio. A representative phase diagram is shown in Figure 8. 

A number of investigations concerning the effect of added electrolytes and change in the solvent polarity have been reported (see ref. 25 pp. 17-19 for a more detailed account). The addition of neutral salts causes a large increase in the rate of reaction in both the one and two-proton mechanisms. In addition, the effect of increasing the water content in a dioxan-water solvent, provided that the concentration of water is above a certain threshold value, also produces a large increase in... 

The effect of swamping electrolytes. The second method of minimizing the junction potential is to employ a swamping electrolyte, S. Addition of a high concentration of ionic electrolyte will greatly increase the ionic strength of the solution and thus all of the activity coefficients (y ) will be decreased to quite small values. 

In this work, the critical micelle activity, cma, which is the activity of the surfactant at the cmc, is introduced and used Instead of the cmc to Investigate the free energy of micelle formation. It is found that upon the addition of an extra methylene group into the hydrocarbon chain, an approximately 3-fold reduction in cma is observed, irrespective of the hydrophilic head group. The effect of added electrolyte on cmc is also examined by the use of cma. 

In general, the effect of additives (supporting electrolyte) to the electroless Co(P) solution results in changes of the coercivity values of the product films. In line with this, coercivity of up to 1000 Oe in electrolessly produced Co(P) films was shown to be possible in Ref. 77. 

It may not be obvious exactly how the addition of excess supporting electrolyte effectively nullifies migration. This will be clearer after reading Sect. 4.6, in which the quantitative effect of additions of supporting electrolyte are assessed. 

In the early work of Schulze ( 0, Linder and Picton (2) and Hardy (3) the sensitivity of colloidal dispersions to the addition of electrolytes was clearly demonstrated. Then in 1900 Hardy (4) showed that the stability of sols was connected with the electrophoretic mobility of the particles and he demonstrated, i) that the valency of the ion opposite in charge to that of the sol particles determined the ability of an electrolyte to coagulate a sol and that, ii) the effectiveness of the electrolyte increased rapidly with increase in valency of the counter-ion. These observations formed the basis of the so-called Schulze-Hardy rule. 

Aqueous suspensions of cellulose microcrystalhtes obtained by acid hydrolysis of native cellulose fibers can also produce a cholesteric mesophase [ 194]. Sulfuric acid, usually employed for the hydrolysis, sulfates the surface of the micro crystallites and therefore they are actually negatively charged. Dong et al. performed some basic studies on the ordered-phase formation in colloidal suspensions of such charged rod-like cellulose crystallites (from cotton filter paper) to evaluate the effects of addition of electrolytes [195,196]. One of their findings was a decrease in the chiral nematic pitch P of the anisotropic phase, with an increase in concentration of the trace electrolyte (KC1, NaCl, or HC1 of < 2.5 mM) added. They assumed that the electric double layer on... 

The effect of other electrolytes is also of interest. Addition of divalent cations, e.g., in the form of calcium and magnesium chloride salts, results in precipitation of the anionic vesicles, which is also observed for micelles in water. There is, however, a significant trend within the alkali metal cations, e.g., from Na+ to Rb+. The larger rubidium ion has a promotional effect on the formation of vesicles, and indeed with Cs+, vesicles are already formed on the addition of trace amounts of salt. The relevant data are shown in Fig. 19.8. 

Arrhenius 6 investigated the effects of addition of non-electrolytes, or very weak electrolytes, small amounts of which (e.g. acetic acid) markedly increase the viscosity of a salt solution, although the pure substance may have a smaller viscosity than water, and the viscosity often reaches a maximum, which becomes flatter with rising temperature. This seems to be confined to aqueous solutions. 

Further evidence to support the above hypothesis on the role of structure in phase separation of aqueous solutions is provided by the effect of additional alcohol. The amount of alcohol was increased from 3.0 to 5.0 gm/dl, the surfactant concentration kept constant, and the salinity varied. The addition of alcohol extended the range of salinity where the aqueous solutions are isotropic to 0.8 gm/dl NaCl. According to the above hypothesis, no phase separation should take place on addition of polymer to the isotropic solutions existing up to 0.8 gm/dl NaCl. Indeed, no phase separation was observed when as much as 1500 ppm Xanthan was added at such compositions. Thus, the addition of alcohol increases the critical electrolyte concentration for phase separation, an effect seen also by others (9). 

Chandra, I., Jeffrey, M. I. (2004).An electrochemical study of the effect of additives and electrolyte on the dissolution of gold in thiosulfate solutions. Hydrometallurgy,73(3-4), 305-312. 

Fig. 16.2 Effect of addition of electrolyte on exhaustion of direct dyes...

The above terminology ( inert vs. specific ) was adopted for studies of the surface charging of colloids. Different experimental methods are used and different quantities are measurable for colloids than for the Hg electrode, but the model of an electrical double layer is analogous. Studies of pH-dependent surface charging of colloids are usually carried out in the presence of an inert electrolyte and an acid or base (used to adjust the pH) with an anion or cation in common with the inert electrolyte. Products of dissolution of the solid are also present in solution at low concentration (we are only interested in sparingly soluble solids), but are ignored in most studies. Sometimes, the concentration of dissolution products is measured, and very occasionally the concentration of dissolution products (which are water-soluble salts) is controlled by addition of these salts to the dispersion. The effect of addition of Al(iii) salt on the potential of alumina was studied in [35]. At the lEP, the solubility of Al species is low thus, the lEP was not very different from that in a 1-1 electrolyte. The solubility problem is discussed in more detail in Section 1.6. 

Fundamental investigation of the system at the molecular level. This requires investigations of the structure of the solid/liquid interface, namely the structure of the electrical double layer (for charge-stabiUsed suspensions), adsorption of surfactants, polymers and polyelectrolytes and conformation of the adsorbed layers (e.g., the adsorbed layer thickness). It is important to know how each of these parameters changes with the conditions, such as temperature, solvency of the medium for the adsorbed layers, and the effect of addition of electrolytes. 

The effect of neutral electrolyte on the aggregation number of micelles of POE nonionics in aqueous solution is somewhat unclear, with both increases and decreases being observed on the addition of electrolyte. In either case, however, the effect appears to be small. 

A commercial CE system and a micropacked capillary was used to separate N—, O—, and S-containing heterocyclic compounds. Migration time reproducibility, linearity, and detector response was found to be comparable to HPLC. A study of the heterocyclic compound s elution order followed that predicted by the octanol-water partition coefficients (354). While chiral CEC provides improved resolution and higher efficiencies, additional work is needed since chiral CEC capillaries are not available commercially. The separation principles and chiral recognition mechanism for the separation of enantiomers have been reviewed (355). Furthermore, a comprehensive collection of drug applications and other compounds of interest has been reported (356). Direct enantiomeric separations by CEC were studied using a capillary packed with alpha-1-acid glycoprotein chiral stationary phase (357). Chiral resolution was achieved for enantiomers of benzoin, hexobarbital, pentobarbital, fosfamide, disopyramide, methoprolol, oxprenolol, and propanolol. The effects of pH, electrolyte concentration, and con-... 

This chapter reviews the effects of additives in the positive active-material of the lead acid battery. Common materials found in the oxide and the positive-plate paste, such as lead oxides, basie lead sulfates, and lead earbonate, are not included. Additives and impurities that derive from grid eorrosion or from the reaction of the plate with the electrolyte are also beyond the seope of this chapter. 

Although the work of Smith and Kennedy only investigates the effect of NaCl on noble gas solubility, they note that the contribution by individual ions should be additive and in dilute brines it should be possible to estimate the salt effect of multi-electrolyte solutions. While no data exists for Mg and Ca ions, data for KI solutions show that kAr is independent of the electrolyte species (Ben-Naim and Egel-Thal 1965), suggesting that an NaCl equivalent concentration provides a reasonable value from which to calculate the Setchenow coefficient. This relationship has been used in multi-ion mixtures such as seawater and for more concentrated solutions such as the Dead Sea brines (Weiss 1970 Weiss and Price 1989). 

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