Polymeric dispersity

Fig. 8. General structures of polymeric dispersants (a) liomopolymer, (b) random copolymer, (c) diblock copolymer, and (d) comb polymer, where A = anchor group, B = soluble repeat unit, and C = repeat unit with solubility different from B. The repeat units may occur in sequences hundreds of...

Adsorption of dispersants at the soHd—Hquid interface from solution is normally measured by changes in the concentration of the dispersant after adsorption has occurred, and plotted as an adsorption isotherm. A classification system of adsorption isotherms has been developed to identify the mechanisms that may be operating, such as monolayer vs multilayer adsorption, and chemisorption vs physical adsorption (8). For moderate to high mol wt polymeric dispersants, the low energy (equiUbrium) configurations of the adsorbed layer are typically about 3—30 nm thick. Normally, the adsorption is monolayer, since the thickness of the first layer significantly reduces attraction for a second layer, unless the polymer is very low mol wt or adsorbs by being nearly immiscible with the solvent. 

Organic Polymeric Dispersants. Table 5 Hsts dispersant materials by types and trademarked names for each class of materials. 

Also, gross organic chemical treatment overdosing or thermal breakdown further adds to deposition risks. For example, many common polymeric dispersants act as flocculants if significantly overdosed. 

NOTE Many common polymeric dispersants typically produce a flocculating effect in a boiler when they are present at levels exceeding 100 to 120 ppm or so of active polymer. BWactives should not exceed 40 to 50ppm. 

Where phosphate is used for internal treatment programs, a variety of insoluble phosphate and hydroxide salts are produced to form sludges. If these sludges are not properly held in a suspension by the use of appropriate polymeric dispersants (and then blown down from the boiler within a certain period), they will deposit on heat exchange surfaces as hard, adherent scales. 

Programs containing lignins as the primary polymeric dispersant are generally formulated to provide 30 to 50 ppm of active lignin product in the BW. 

Tannins may be found bound up with magnetite in waterside tube deposits. Degradation products of amines, glycols, polymeric dispersants, chelants, and other organics may also be found and usually are reported in the deposit analysis as a loss on ignition. 

Apart from metals, ammonium chloride, amine, and diamine salts, and various organic polymeric dispersants and surfactants are employed in fuel treatment additive formulations. 

Hann, W.M. Keller, L.H. Sanders, T.W. Weinstein, B. Towards Field-Friendly Traceable Polymeric Dispersants. 58th International Water Conference, USA, Nov 1-5, 1997. 

An aqueous colloidal polymeric dispersion by definition is a two-phase system comprised of a disperse phase and a dispersion medium. The disperse phase consists of spherical polymer particles, usually with an average diameter of 200-300 nm. According to their method of preparation, aqueous colloidal polymer dispersions can be divided into two categories (true) latices and pseudolatices. True latices are prepared by controlled polymerization of emulsified monomer droplets in aqueous solutions, whereas pseudolatices are prepared starting from already polymerized macromolecules using different emulsification techniques. 

R Bodmeier, P Maincent. Polymeric dispersions as drug carriers. In HA Lieberman, MM Rieger, GS Banker, eds. Pharmaceutical Dosage Forms Disperse Systems, Vol. 3. 2nd ed. New York Marcel Dekker, 1998, pp 87-128. 

Rekhi, G. S., Mendes, R. W., Porter, S. C., and Jambhekar, S. S., Aqueous Polymeric Dispersions for Controlled Drug Delivery - Wurster Process, Pharm. Technol., 13(3) 112-125 (1989)... 

Figure 1. Mechanism of electrostatic charging in oil of particles with acidic sites (AH) by a polymeric dispersant with basic sites (B). Reproduced with permission from Ref. (5).Copyright 1982, American Chemical Society.

New Polymeric Dispersants for Very Fine Calcium Carbonate Slurries... 

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