Debye length, electrolyte effects

Charged interfaces in electrolyte solutions cause counterions to adsorb. A cloud with net opposite charge hovers around the interface, with a characteristic thickness comparable to the Debye length. At distances much larger than the Debye length, the effect of charged interfaces is essentially absent. 

In concentrated NaOH solutions, however, the deviations of the experimental data from the Parsons-Zobel plot are quite noticeable.72 These deviations can be used290 to find the derivative of the chemical potential of a single ion with respect to both the concentration of the given ion and the concentration of the ion of opposite sign. However, in concentrated electrolyte solutions, the deviations of the Parsons-Zobel plot can be caused by other effects,126 279"284 e.g., interferences between the solvent structure and the Debye length. Thus various effects may compensate each other for distances of molecular dimensions, and the Parsons-Zobel plot can appear more straight than it could be for an ideally flat interface. 

In addition, the effect of ionic screening was analyzed [89] using Eqs. (67). The ionic concentrations considered (1.0 M, 0.1 M, 0.01 M) correspond to Debye lengths Ijj = 0.3,1 and 3 nm. The results for /o = 3 nm, the most dilute electrolyte, where ionic screening is least effective, are presented in Table 3. 

By the logic of the capacitor model, salting in is a stabilizing mechanism whereby is lowered and in turn Q/ is elevated. The capacitor model does not explain salting out as easily as does the electrolyte effect of i directly on the Debye length. 

The hydration force is important for distances between plates less than a few nanometers. Since the DLVO potential barrier between spherical particles or droplets is located at separation distances of the order of the Debye length, it is clear that at least at high electrolyte concentrations the hydration force becomes relevant. The qualitative effect of hydration was earlier recognized, regarding the stability of silica colloids at high electrolyte concentrations1 or the stability of amphoteric latex particles at high concentrations of some electrolytes.12... 

To study the self-image effect on the interaction between two plates, we will develop a linear theory with respect to the plasma parameter with kt1 = (SncoPBe2 / e)1/2, where k-1 is the Debye length, and cq is the electrolyte concentration in solution. According to this approximation, all the higher distribution functions (gapy, etc.) are represented via the correlation function as (see, for example, [19])... 

A whole range of cations and anions in different combinations have been explored. The results are surprising. Measurements of coalescence rates for a range of typical electrolytes as a function of electrolyte concentration are shown in Fig. (3.5). There is a correlation between valency of the salt and transition concentration, defined as 50% bubble coalescence, with more highly charged salt effective at lower concentration. The effect is independent of gas flow rate. All the results scale with Debye length (ionic strength). Some salts and acids have no effect at all on bubble coalescence, a situation summarised in Table 3.1. 

Electrostatic repulsion has a limitation. It works only for systems that do not contain large quantities of electrolytes. Indeed, the presence of electrolytes reduces the so-called Debye length, which is basically the distance at which electrostatic repulsion is effective. Electrolytes also compress the electrical double layer. The result is a reduction of the electrostatic repulsion, which may become weaker than van der Waals attraction. 

We next calculate how the electroosmotic flow and potential change in a long capillary for different ratios of Debye length to radius. We shall allow for pressure gradients, but the mean velocity and tube radius are assumed sufficiently small that inertia effects can be neglected. The dilute electrolyte solution in the capillary is taken to be binary. 

---