Electrolyte concentration effect

E. Ruckenstein, H. Huang Colloid Restabilization at High Electrolyte Concentrations Effect of Ion Valency, LANGMUIR 19 (2003) 3049-3055. 

Colloid Restabilization at High Electrolyte Concentrations Effect of Ion Valency... 

Electrolyte and Electrolyte Concentration Effects on O2 Diffusion Coefficient 15... 

Avena, M. J., A. W. P. Vermeer, and L. K. Koopal. 1999. Volume and structure of humic acids studied by viscometry pH and electrolyte concentration effects. Colloids and Surfaces A Physicochemical and Engineering Aspects 151, no. 1-2 213-224. 

Fig. VI-5. The effect of electrolyte concentration on the interaction potential energy between two spheres where K is k in cm". (From Ref. 44.)...

The repulsion between oil droplets will be more effective in preventing flocculation Ae greater the thickness of the diffuse layer and the greater the value of 0. the surface potential. These two quantities depend oppositely on the electrolyte concentration, however. The total surface potential should increase with electrolyte concentration, since the absolute excess of anions over cations in the oil phase should increase. On the other hand, the half-thickness of the double layer decreases with increasing electrolyte concentration. The plot of emulsion stability versus electrolyte concentration may thus go through a maximum. 

For example, van den Tempel [35] reports the results shown in Fig. XIV-9 on the effect of electrolyte concentration on flocculation rates of an O/W emulsion. Note that d ln)ldt (equal to k in the simple theory) increases rapidly with ionic strength, presumably due to the decrease in double-layer half-thickness and perhaps also due to some Stem layer adsorption of positive ions. The preexponential factor in Eq. XIV-7, ko = (8kr/3 ), should have the value of about 10 " cm, but at low electrolyte concentration, the values in the figure are smaller by tenfold or a hundredfold. This reduction may be qualitatively ascribed to charged repulsion. 

These results show more clearly than Fq. (8.126)-of which they are special cases-the effect of charge and indifferent electrolyte concentration on the osmotic pressure of the solution. In terms of the determination of molecular weight of a polyelectrolyte by osmometry. ... 

The electrolyte concentration also has an effect on the co-areas. An increase in the ionic strength from 0.01 to 0.04 M causes a considerable decrease in the interfacial tension [56]. 

Equation 46 suggests that, maintaining pi constant, q, must depend linearly on if only a first-order electroviscous effect exists, and an increase in the electrolyte concentration implies a decrease in the thickness, 1/k, of the electrical double layer. 

Table II also shows the effect of electrolyte concentration on Rf and kj. Both effects reflect the fact that at the higher ionic strengths particle/substrate repulsion is decreased, thus effectively increasing the available pore volume at a given particle size. These results are illustrated in Figure 3. Included in this figure are data from work by Nagy (14) with a column set similar in configuration to that employed here.

The trends of behavior described above are found in solutions containing an excess of foreign electrolyte, which by definition is not involved in the electrode reaction. Without this excess of foreign electrolyte, additional effects arise that are most distinct in binary solutions. An appreciable diffusion potential q) arises in the diffusion layer because of the gradient of overall electrolyte concentration that is present there. Moreover, the conductivity of the solution will decrease and an additional ohmic potential drop will arise when an electrolyte ion is the reactant and the overall concentration decreases. Both of these potential differences are associated with the diffusion layer in the solution, and strictly speaking, are not a part of electrode polarization. But in polarization measurements, the potential of the electrode usually is defined relative to a point in the solution which, although not far from the electrode, is outside the diffusion layer. Hence, in addition to the true polarization AE, the overall potential drop across the diffusion layer, 9 = 9 + 9ohm is included in the measured value of polarization, AE. ... 

Using the equation, very strong concentration effects in small systems have been calculated. For instance, if the macroaqueous phase contains 1 M NaCl and 1 /rM NaTPB, the concentration of this electrolyte in the micro-organic phase at partition equilibrium is 1390/rM [14] This approach is valid if the phases in small systems are thick enough (> 1 /rm), in comparison to the Debye screening length, to fulfill the electroneutrality conditions. 

Figure 11 analyzes the effect of the electrolyte concentration in the aqueous phase, for fixed electrolyte concentrations in the organic phase c" = 10 mM and 50 mM, and a Galvani potential difference/= 5. These theoretical results are in agreement with the observations in Ref. 13. Moreover, it is shown that a deerease in the eleetrolyte eoneen-tration in the organic phase has a similar effeet to a deerease in the eleetrolyte eoneentra-tion in the aqueous phase. 

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