Polymeric surfactants with nonionic polymers

The interaction between ionic polymers and nonionic surfactants has not received as much attention as the other cases discussed in the preceding sections. Much of the earlier research in this area has been focused on the interaction of anionic polymeric acids with nonionic surfactants of polyethylene oxide. The polyethylene oxide has shown the ability to form hydrogen bonds with polymeric acid like polycarboxylic acid in water. This canses a redaction in the solution viscosity as the polymer chains tend to shrink. Saito and Taniguchi (1973) studied the interaction of polyacrylic acid with a series of nonionic surfactants (EO) RE in which EO is ethylene oxide, R is hydrocarbon group, and E represents ether. They reported that the interaction in this system is a function of the nature of the hydrophobic moiety (R) and the length of the hydrophilic tail (EO). 

PTFE aqueous dispersions are made by the polymerization process used to make fine powders. Raw dispersions are polymerized to different particle sizes.24 The optimum particle size for most applications is about 0.2 pm. The dispersion from the autoclave is stabilized by the addition of nonionic or anionic surfactants, followed by concentration to a solids content of 60 to 65% by electrodecantation, evaporation, or thermal concentration.25 After further modification with chemical additives, the commercial product is sold with a polymer content of about 60% by weight, viscosity of several centipoise, and specific gravity around 1.5. The processing characteristics of the dispersion depends on the conditions for the polymerization and the type and amounts of the chemical additives contained in it. 

Mention has been made of the fact that the polar character of polymer surfaces is strongly affected by the ionic polymer end groups that are residues of initiator-derived ion radicals, when persulfates are used in emulsion polymerizations. Variation of the initiator type between those that yield ionic and nonionic end groups is an effective way to control particle stability and avoid complications due to migration of surfactant from one polymer surface to another [25]. This method can also be supplemented by copolymerization with polar monomers to affect surface hydrophilicity. 

The condensation method begins with molecular units, and the particles are built-up by a process of nucleation typical example is the preparation of polymer lattices, in which case the monomer (e.g., styrene or methylmethacrylate) is emulsified in water using an anionic or nonionic surfactant (e.g., sodium dodecyl sulphate or alcohol ethoxylate). A polymeric surfactant is also added to ensure the long-term colloid stabiHty of the resulting latex. An initiator such as potassium persulphate is then added and, when the temperature of the system has increased, initiation occurs that results in formation of the latex [polystyrene or poly(methylmethacrylate)]. 

Nonionic surfactants and both natural and synthetic polymers (which are collectively referred to as polymeric surfactants), when used to stabilise soHd/hquid (suspensions) andliquid/liquid (emulsions) disperse systems, play important roles in many industrial applications including paints, cosmetics, agrochemicals, and ceramics. Nonionic surfactants and polymers are particularly important for the preparation of concentrated dispersions - that is, with a high volume fraction

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Polymers are also essential for the stabilisation of nonaqueous dispersions, since in this case electrostatic stabilisation is not possible (due to the low dielectric constant of the medium). In order to understand the role of nonionic surfactants and polymers in dispersion stability, it is essential to consider the adsorption and conformation of the surfactant and macromolecule at the solid/liquid interface (this point was discussed in detail in Chapters 5 and 6). With nonionic surfactants of the alcohol ethoxylate-type (which may be represented as A-B stmctures), the hydrophobic chain B (the alkyl group) becomes adsorbed onto the hydrophobic particle or droplet surface so as to leave the strongly hydrated poly(ethylene oxide) (PEO) chain A dangling in solution The latter provides not only the steric repulsion but also a hydrodynamic thickness 5 that is determined by the number of ethylene oxide (EO) units present. The polymeric surfactants used for steric stabilisation are mostly of the A-B-A type, with the hydrophobic B chain [e.g., poly (propylene oxide)] forming the anchor as a result of its being strongly adsorbed onto the hydrophobic particle or oil droplet The A chains consist of hydrophilic components (e.g., EO groups), and these provide the effective steric repulsion. 

Wang I, Schork FJ. Miniemulsion polymerization of vinyl acetate with nonionic surfactant. J Appl Polym Sci 1994 54 2157-2164. 

Polymers with which we will deal throughout this chapter are water soluble. They can be either ionic or nonionic. Some of them are synthetic, others are of biological origin (proteins, for instance). Both homopolymers and heteropolymers exist. Some polymers own amphiphilic monomers that induce surface-active properties to the whole polymeric structure. Water plays a very important role in determining the polymer properties in solution. The properties are also greatly modified by the addition of salts or by a pH modification. Frequently encountered nonionic polymers in polymer-surfactant interactions and their subsequent adsorption behavior at solid surfaces are poly(ethylene oxide) (PEO), poly(vinyl pyrrolidone) (PVP), polyacrylamide, and poly(vinyl alcohol). 

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