Critical flocculating concentration

Figure 7 Relationship between critical flocculation concentration(CFC) and concentration of HPC-M for HPC-latex systems.

The crucial question is at what value of <)> is the attraction high enough to induce phase separation De Hek and Vrij (6) assume that the critical flocculation concentration is equivalent to the phase separation condition defined by the spinodal point. From the pair potential between two hard spheres in a polymer solution they calculate the second virial coefficient B2 for the particles, and derive from the spinodal condition that if B2 = 1/2 (where is the volume fraction of particles in the dispersion) phase separation occurs. For a system in thermodynamic equilibrium, two phases coexist if the chemical potential of the hard spheres is the same in the dispersion and in the floe phase (i.e., the binodal condition). 

To (obtained from extrapolation of the ascending part of the flow curve) as a function of C. The shear modulus, GQ, measured using the pulse shearometer, is also shown as a function of C in the same figure. A measurable x and GQ is obtained above a critical value of C, which in both cases is -0.22 mol dm 3. As we will see later, this electrolyte concentration should be taken as the critical flocculation concentration (CFC) for the concentrated dispersion. Above the CFC, xg increases rapidly with increasing C whereas G initially increases gradually with increasing C until C = 0.3 mol dm 3, above which there is a more rapid increase of Gq. 

Critical currents, 23 821-823 in superconducting, 23 819-825 Critical event (CE), 15 462 Critical failure, 26 982 Critical features, in separating nonideal liquid mixtures, 22 307 Critical fields, thermodynamic, 23 809-811 Critical flocculation concentration, 11 631 Critical item evaluation, for reliability, 26 991... 

Panayiotopoulos KP, Barbayiannis N, Papatolios K (2004) Influence of electrolyte concentration, sodium adsorption ratio, and mechanical disturbance on dispersed clay particle size and critical flocculation concentration in alfisols. Comm Soil Sci Plant Anal 35 1415-1434... 

Several major barriers need to be overcome for the development of nonviral gene delivery systems into true therapeutic products for use in humans. These barriers fall into three classes manufacturing, formulation, and stability (extracellular barriers and intracellular barriers) (85). Cationic lipids and cationic polymers self-assemble with DNA to form small particles that are suitable for cellular uptake. At the therapeutic doses positively charged particles readily aggregate as their concentration increases, and are quickly precipitated above their critical flocculation concentration. 

Larpent and Tandros [102] prepared microlatex particles by polymerization of PEO-MA macromonomer with MMA, styrene, and vinyl acetate. The nonionic latexes are very stable, giving no flocculation up to 6 mol dm 3 NaCl or CaCl2 and a critical flocculation concentration (CFC) of 0.6 mol dm 3 for Na2S04 or MgS04 was estimated. Charged latexes are less stable than the nonionic ones. The CFC of all latexes are determined as a function of electrolyte concentration. With the nonionic latexes, however, the critical flocculation temperature (CFT)... 

This is expected since the extrapolation procedure usually overestimates the yield value. The data of Figs. 3 and 4 show a rapid increase in yield value above a critical PEO concentration, 4. This concentration corresponds to the critical flocculation concentration of the free polymer. However, since the rise in Tg did not occur at a sharp value, the latter was taken as the intersection point at which the extrapolated hprizontal and vertical lines meet. This gave values of 4 of 0.02 0.002, O.OItO.001 and O.OOStO.OOl for PEO with of 20,000, 35,000 and 90,000 respectively. Moreover, the 4p values obtained from the two sets of rheological results were almost the scime within the error of locating p. 

When the electrostatic stabilization of the emulsion is considered, the electrolytes (monovalent and divalent) added to the mixture are the major destabilizing species. The zeta potential of the emulsion particles is a function of the concentration and type of electrolytes present. Two types of emulsion particle-electrolyte (ions) interaction are proposed non-specific and specific adsorption.f H non-specific adsorption the ions are bound to the emulsion particle only by electrical double-layer interactions with the charged surface. As the electrolyte concentration is increased, the zeta potential asymptotes to zero. As the electrostatic repulsion decreases, a point can be found where the attractive van der Waals force is equal to the repulsive electrostatic force and flocculation of the emulsion occurs (Fig. 9A). This point is called the critical flocculation concentration (CFC). 

Plots of log W versus log C are shown in Figure 10.28. The condition log W = 0 [W = 1) is the onset of fast flocculation. The electrolyte concentration at this point defines the critical flocculation concentration (CFG). Above the CFG, W<1 (due to the contribution of van der Waals attractions which accelerate the rate above the Smoluchowski value). Below the GFG, W > 1 and it increases with a decrease... 

The effect of the concentration of the potential-determining ions and the counterions on the interface potential of the particles has been discussed earlier in this section. Also, it was stated that the critical flocculation concentrations (CFG) of inorganic electrolytes of different valencies are related to each other in the following manner ... 

CFC Critical flocculation concentration. See Critical Coagulation Concentration. 

Add a little 1 mol dm-- sodium chloride to each of the sols atid observe whether flocculation occurs. In the cast of gold sol flocculation is marked by a change in colour from ruby-red to blue. If the salt solution is added from a burette, the critical flocculation concentration (Chapter 9) can be determined. Repeat using 0.1 mol dm 3 sodium sulphate solution. 

At high potentials y approaches unity, so the theory predicts that the critical flocculating concentration of indifferent electrolytes containing counterions with charge numbers 1, 2, and 3 will be in the ratio 1 2 3 or 100 1.56 0.137. In other words, successively lower concentrations of salts of Na", Ca, AP are needed to cause spontaneous flocculation. Experiment closely bears out the theoretical results given (Shaw 1980, Hiemenz 1986). We also note from these results that the flocculating concentration strongly depends... 

Vincent (7) investigating the effect of non-adsorbing polystyrene on polystyrene microgels reported the critical flocculation concentration (CFC) of polymer increased... 

Critical Flocculation Concentration Schultze-Hardy Rule... 

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