Silica dispersions

Jansen J W, de Kruif C G and Vrij A 1986 Attractions in sterically stabilised silica dispersions. I. Theory of phase separation J. Colloid Interface Sc/. 114 471-80... 

Rouw P W and de Kruif C G 1989 Adhesive hard-sphere colloidal dispersions fractal structures and fractal growth in silica dispersions Phys. Rev. A 39 5399-408... 

Chen M and Russel W B 1991 Characteristics of flocculated silica dispersions J. Colloid Interface Sol. 141 564-77... 

Sugar Processing. Dispersants are used in the production of cane and beet sugar to increase the time between evaporator clean outs. Typical scales encountered include calcium sulfate, calcium oxalate, calcium carbonate, and silica. Dispersants are fed at various points in the process to prevent scale buildup, which would interfere with efficient heating of the vessels. Only certain dispersants, conforming to food additive regulations, can be used, since a small amount of the dispersant may be adsorbed on the sugar crystals. 

The silica dispersion showed the smallest retention volume. It should be noted, however, that the authors reported that the silica dispersion required sonicating for 5 hours before the silica was sufficiently dispersed to be used as "pseudo-solute". The retention volume of the silica dispersion gave the value of the kinetic dead volume, /.e., the volume of the moving portion of the mobile phase. It is clear that the difference between the retention volume of sodium nitroprusside and that of the silica dispersion is very small, and so the sodium nitroprusside can be used to measure the kinetic dead volume of a packed column. From such data, the mean kinetic linear velocity and the kinetic capacity ratio can be calculated for use with the Van Deemter equation [12] or the Golay equation [13]. 

Preparation and Stability of Polymer-Grafted Silica Dispersions... 

It may be seen that, within experimental error, the diameters determined by TEH and PCS agree. Moreover, where studied, the PCS diameters are very similar for the silica dispersions in water and DMF, suggesting that the particles do exist as singlets in both solvents. 

The Si02-g-PS systems were prepared by adding the methacy-terminated PS to the silica dispersion in DMF. The mass ratio PS Si02 used in each case is recorded in Table III. The dispersion was then heated at 120°C, under nitrogen, for varying periods up to 45 hr. 

Colloid stability assessments of silica dispersions in CCI4 by sediment volume and coagulation rate are in general concordance and confirm the pattern previously reported by Barron and Howard... 

Poly(methyl methacrylate) provides a level of stabilization even though the solution in CCl is below the 0-temperature. All the copolymers, both random and block, are better stabilizers than PMM, the methacrylate units acting as anchors, with stabilizing sequences of styrene loops, of block copolymers, or mixed loops and tails, of random copolymers, at better than 0-conditions. Higher M.W. polystyrenes give silica dispersions too unstable to measure by our optical method the sediment volumes are between those of poly(methyl methacrylate) solutions and pure solvent. 

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