Latex critical flocculation temperatures

As another criterion of stability, a critical flocculation temperature(OFT) was measured. The measurement of CFT was carried out as follows the bare latex suspension was mixed with the polymer solution of various concentrations at 1+8 °C by the same procedure as in the adsorption experiments. Then, the mixture in a Pyrex tube(8 ml, U.0 wt %) was warmed slowly in a water bath and the critical temperature at which the dispersion becomes suddenly cloudy was measured with the naked eye. 

Figure 8. Relationship between critical flocculation temperature(CFT) and concentration of HPC for polystyrene latex.

Figure 2 The upper critical flocculation temperature is shown plotted against the applied pressure. refers to the PMMA latex while, o refers to the PVAc latex. The solid line represents 9 conditions for a solution of PIB + 2-methylbutane while the dashed line represents the theoretically calculated UCFT as a function of pressure.

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)... 

VI Flocculation Studies, Critical flocculation temperatures were measured using suspensions of 0.6% v/v latex containing the appropriate amount of sodium chloride. Differing degrees of neutralisation were produced by the addition of NaOH to stock solutions and checked by conductometric titration with base in the absence and presence of added HC1. Flocculation temperatures (CFT) were determined by visual observation at a cooling/heating rate of M).5 C s. The flocculation was generally reversible provided that the latices had not been left in the flocculated state for more than a few minutes or so. 

Figure 6. Critical flocculation temperatures (CFVs) for a latex as a function of the degree of neutralization (a) in 0.83M, 1.1 OM, and 1.38M NaCl on heating (, A, M) and on cooling (O, A, Q), respectively.

Neville and Hunter [6] studied the flocculation of poly(methylmethacrylate) (PMMA) latex stabilised with poly(ethylene oxide) (PEO). Flocculation was induced by the addition of electrolyte and/or an increase in temperature. Figure 21.12 shows the variation of with increase of temperature at constant electrolyte concentration. In the figure, it can be seen that increased with increases of temperature, reaching a maximum at the critical flocculation temperature (CFT), and then decreased with further increase in temperature. The initial increase was due to the flocculation of the latex with increase of temperature, as the result of a reduction in solvency of the PEO chains with the increase in temperature. The... 

It is important to note that the UCSD above is for the actual finite molecular weight stabilizer, not an infinite molecular weight stabilizer (theta density). Many experimental stability studies of emulsions and latexes in liquid solvents indicate a correlation between the critical flocculation temperature and the theta temperature, 7 0.[68]. However, the difference between Tq and the UCST is often only a few degrees... 

The principal consideration in selecting an appropriate soluble polymeric component for the steric barrier is that it should be freely soluble in the dispersion medium to be usedo This had been recognised empirically for some years before Napper (4) undertook quantitative studies which showed that sterically stabilised latexes flocculated at or around the theta point for the soliible polymer in the dispersion medium. Later studies have shown that both upper and lower critical flocculation temperatures may occur in organic solventso... 

Figure 9.15 Critical flocculation temperature values and 9 temj>eratures of polyethylene oxide (PEO) for polystyrene latex systems stabilized by adsorbed Pluronic in the presence of varying concentrations of KCl. Pluronic concentration, 200 ppm. From Tadros and Vincent [35]. 

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