Latexes critical coagulation concentration

The stabihty of the latexes was determined by determining the critical coagulation concentration (ccc) using CaClj. Although the CCC was low (0.0175-0.05 mol dm ), it was higher than that for the latex prepared without surfactant The subsequent addition of INUTEC SPl resulted in a large increase in the CCC, as illustrated in Figure 17.2, which shows log W-log C curves (where W is the ratio between the fast flocculation rate constant to the slow flocculation rate constant, referred to as the stability ratio) at various additions of INUTEC SPl . 

The usual result of such variation in the zeta potential with pH and 1 1 electrolyte concentration is that the critical coagulation concentration normally varies with pH as shown schematically by the theory line in Figure 20.4. The critical coagulation concentration increases as the pH is increased above the isoelectric point and peaks at high values as shown. Many examples of these trends are confirmed for oxide and latex colloids for which H ... 

The critical coagulation concentrations (c.c.c.) determined turbidimetrically for latex A-2 with NaCl, CaCl2, AlCl3(pH 3), and AlCl3(pH 7) were 180, 18.5, 0.37, and 0.15 mM, respectively (the values for NaCl and CaCl2 were independent of pH). These results do not follow the inverse sixth-power Schulze-Hardy rule derived by Verwey and Overbeek (18, 22) for the dependence of c.c.c. on valence. Instead, the log c.c.c.-log valence plot has a slope of about 3.3. This could indicate a low C potential for this system, since, in the limiting case of low potentials where the Debye-Hiickel approximation applies, the derived dependence is second-power (22) However, more extensive data are required before it can be concluded that this case deviates from the "normal sixth-power Schulze-Hardy rule. 

The authors acknowledge gratefully the contributions of J. G. Cobler and Miss C. Kleeman for the ultracentrifuge particle size measurements, E. B. Bradford for the electron microscope particle size measurements. Miss D. L. Dickens, A. S. Teot, and N. Sarkar for the critical coagulation concentration experiments, R. D. Van Dell for the SDS adsorption experiments, the East Main Analytical Laboratory for the osmometric molecular weight and nitrogen adsorption measurements, the Chemical Physics Laboratory for the X-ray fluorescence measurements, and J. B. Shaffer in the preparation of the latexes. 

Further studies also deal with the use of the dodecyl moiety of the allylic compound SAAS (already studied by Urquiola [36] in the semibatch polymerization of butyl acrylate. Such surfactant was reported to behave like SDS, with the fraction of chemically incorporated surfactant hurried inside the particles increasing with the size of the particles [60]. A study of the stability of these latexes was recently reported, showing the influence of the shear rate during the polymerization, as well as the critical coagulation concentration (CCC) in the presence of electrolytes [61],... 

In Table 6.3 some values for ti/2 are given, as a function of a (10-1000 nm) and max(0-30 IcT), for aqueous latex dispersions at 20 C the value of calculated from Equation 6.7. It is noteworthy that the timescale for ti/2, for this set of variables, varies from approximately miliseconds to the age of the Universe ( 4.5 x 10 years). In terms of Figure 6.4, one can deduce that 100 run polystyrene latex particles latex at 10 and 10 M NaCl should be indefinitely stable, and that the critical coagulation concentration for this latex is somewhere between 10 and 100 mM with NaCl, as was indeed observed experimentally (Vincent, 1992). Furthermore, in the context of growing latex particles, in an emulsion polymerisation process. Table 6.3 illustrates how the particles become much more stable to coagulation as both their size and their surface charge (and, hence, ijr and therefore V ax) increase. 

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