Critical total ionic strength

In agreement with the statements made regarding the influence of hydrodynamic forces in the previous section, Khilar et al. (18, 36) have found at best a weak dependence of CSC on the superficial velocity (for 3 to 568 cm/h). Because in practise one deals with solutions of mixed salts, Khilar et al. (18) have introduced the critical total ionic strength (CTIS) to improve the predictions for solutions containing multivalent ions such as calcium. A number of studies have shown that where freshwater flooding of sandstones may drastically decrease permeability due to fines migration, suitable adjustment of the flooding solution composition to above the CSC or CTIS can decrease or eliminate the permeability reduction (12, 18, 36). In these cases the solution compositions are adjusted so as to reduce the Zeta potential at the particle surfaces, which reduces the repulsive colloidal forces. Thus the same factors that... 

Wright (1953) has shown that the acid-binding capacity of horn is almost identical with that of wool, but insufficient data are available, particularly with respect to amide content, to permit this value to be related to the amino acid composition of hom (Table XIV). Harrold and Pethica (1958) have observed that normal callus absorbs a little more than 1 meq of dodecyl sodium sulfate per gram in the absence of salt at pH 6.6 and almost 3 meq per gram at a total ionic strength of 0.2. Binding continues to a maximum at a concentration above the critical micelle point of dodecyl sodium sulfate. There appears to be no relationship between the large absorption in the presence of salt and the amino acid composition of callus (Table XVI). 

Equations (2)-(4) show that the total potential energy of interaction between two colloidal spherical particles depends on the surface potential of the particles, the effective Hamaker constant, and the ionic strength of the suspending medium. It is known that the addition of an indifferent electrolyte can cause a colloid to undergo aggregation. Furthermore, for a particular salt, a fairly sharply defined concentration, called critical aggregation concentration (CAC), is needed to induce aggregation. 

The mobile phase is a critical factor in SEC because it must eliminate all solute-support interactions. This is effected by adjustment of pH (usually to neutrality), ionic strength (0.05M-0.2M), and/or addition of 5 -10% organic solvent or stabilizing agents. The ionic and hydrophobic properties of proteins and their attraction to the stationary phase must be totally removed. 

Here, d is the micelle hydrodynamic diameter (usually measured by dynamic light scattering) as before, CMC stands for the critical micellization concentration, C, is the total concentration of ionic surfactant 4 is the ionic strength due to added inorganic electrolyte (if any), and is the degree of ionization of the micelle surface ionizable groups (non-neutralized by bound counterions). 

The reaction rate constant k is not truly a constant it is merely independent of the concentrations of the species involved in the reaction. The quantity k is referred to as either the specific reaction rale or the rale constant. It is almost always strongly dependent on temperature. It depends on whether or not a catalyst is present, and in gas-phase reactions, it may be a function of total pressure, in liquid systems it can also be a function of other parameters, such as ionic strength and choice of solvent. These other variables normally exhibit much less effect on the specific reaction rate than temperature does with the exception of supercritical solvents, such as super critical water. 

DLVO theory was applied (63,64) for the description of spontaneous and forced thinning of the liquid film separating the droplets. These experimental results and DLVO theory were used (63) for the interpretation of the reported visual study of coalescence of oil droplets 70—140 pm in diameter in water over a wide pH interval. A comparison based on DLVO theory and these expermental data led the authors to condlue (63) that if the total interaction energy is close to zero or has a positive slope in the critical thickness range, i.e., between 30 and 50 nm, flie oil drops should be expected to coalesce. In the second paper (64), where both ionic strength and pH effects were studied, coalescence was observed at constant pH values of 5.7 and 10.9, when the Debye thickness was less than 5 nm. The main trend in our experiments and in Refs 63 and 64 were in accordance, because it was difficult to establish the decrease in t.d.c at NaCl concentrations lower than 5 x 10 M, i.e., double-layer (DL) thicknesses larger than 5 nm. An almost quantitative coincidence in the double-layer influence on... 

Fig. 18 Phase diagram for ionic strength versus total protein concentration as a function of the temperature (I). Data points circles) were obtained by determining the critical salt concentration and the data point marked by a cross was determined using light scattering (see [82] for more Information). Reprinted from [82] with permission. Copyright 2006, American Chemical Society...

The critical association concentration between a polymer and a surfactant is defined as the free surfactant concentration at which the cooperative adsorption is initiated [16]. This concentration, that depends on ionic strength [3, 27] and polyelectrolyte concentration [28] can be determined from e.g. the adsorption isotherm. For the polyelectrolyte-surfactant mixtures studied here we have not yet determined the adsorption isotherm but instead we estimate an upper limit of the critical association concentration in bulk solution (caCb) as the total (i.e. bound -t- free) surfactant concentration needed to give a significant increase in turbidity due to formation of large floes in the polyelectrolyte-surfactant solution. The values obtained for the 100%, 30% and 10% charged polyelectrolyte (20 ppm polyelectrolyte solution, 0.1 mMKBr as background electrolyte) were about 0.005, 0.01 and 0.01 cmc. The free surfactant concentration at caCb is thus lower than these values. 

---