Polymeric surfactants suspension stabilization

This chapter, will begin with a brief description of polymeric surfactants and their solution properties, followed by a description of the fundamental principles of using polymeric surfactants for stabilization of emulsions (as well as suspensions), starting with a section on the adsorption and conformation of these molecules at the interface. This is followed by a section on stabilization of dispersions by polymeric surfactants. Particular... 

Steric repulsion results from the presence of adsorbed layers of surfactants and/or polymers. The use of natural and synthetic polymers (referred to as polymeric surfactants) for stabilization of suspension concentrates and emulsions (EW s) plays an important role in agrochemical formulations. Polymers are particularly important for preparation of concentrated dispersions, i.e. at high volume fraction ( j of the disperse phase,... 

Instead of low Mw surfactants or in combination with those natural or semisynthetic colloids are used in suspension polymerization of PVC and in emulsion polymerization of vinyl acetate homo- and co-polymers as protective colloids also called suspension stabilizers or suspending agents. 

In suspension polymerization, inorganic solids such as hydroxyapatite [3 Ca3 (P04)2 Ca(OH)2] are often used in conjunction with (polymeric) surfactants. Des-landes [92] reported in 1987 a study in which he investigated the morphology of the beads obtained in the suspension copolymerization of styrene and butadiene. A thin layer composed of very uniformly distributed hydroxyapatite particles was adhered to the surface of the polymer bead, and surrounded by a thicker and flakier layer of loosely packed agglomerates of hydroxyapatite and small polymer beads, which were also covered by a monolayer of inorganic matter. Despite this paper, studies on the use of solid particles in suspension polymerization remained focused on their effective use as stabilizers. 

Understanding the adsorption and conformation of polymeric surfactants at interfaces is key to understanding how these molecules act as stabilizers for suspensions and emulsions. Most basic theories on polymer adsorption and conformation have been developed for the solid/liquid interface (9). The same concepts may be applied for the liquid/liquid interface, with some modifications whereby some part of the molecule may reside within the oil phase, rather than simply staying at the interface. Such modifications do not alter the basic concepts, particularly when one deals with the stabilization by these molecules. 

The foregoing relationships of chain length to extent of reaction would then be expected to apply to such step polymerizations as are involved in the synthesis of poly(alkylene sulfides) from a dihalide and sodium polysulfide (polycondensation) or in the formation of the urethane polymers from glycols and diisocyanates (polyaddition). The polysulfide reaction is actually carried out in a suspension of the dihalide in an aqueous solution of the polysulfide, using a surfactant to stabilize the resulting polymer suspension. 

Another graft copolymer that could be used for stabilization of suspensions is that based on a polyfructose backbone on which several alkyl groups have been grafted (INUTEC SPl), mentioned earlier for stabilization of emulsions. This polymeric surfactant was used to investigate the stability of polystyrene (PS) and PMMA suspensions in the presence of electrolytes [NaCl, CaClj, and Al2(S04)3l [25]. The polystyrene latex was prepared by emulsion polymerization without surfactant, and it was fairly monodisperse, with a diameter of 210 nm. The PMMA latex was prepared... 

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