Colloid particles, polymer-bearing

We conclude that provided the anchor polymer is attached sufficiently strongly to the colloidal particles, its chemical nature has no significant bearing on the observed CFPT. This conclusion is buttressed by the studies of Clarke and Vincent (1981a) who covalently grafted polystyrene chains on to silica particles and so obviated the need for an anchor polymer. The pattern of incipient flocculation observed for these systems conforms with that detailed in this chapter for stabilizing moieties anchored by polymer chains. 

Cationic Polymers., The relation between zeta potential and flocculation by a polymer has been studied by Rjes (3IS), who pointed out that as soon as a colloidal particle is coated with polymer it bears the same charge as the polymer and is redispersed. Similar studies by Ries and Meyers (316) involved the use of microphoresis and electron microscope observations of model colloids and polymeric flocculants. Polyamine type flocculants appeared to extend out from the particle surface for a distance of 20-300 A. Flocculation occurs simultaneously through charge neutralization and bridging of polymer chains from particle to particle then excess polymer reverses the potential and redispersion occurs. Adsorption of poly [(1,2-dimethylvinylpyridinium) methylsulfate] on silica was similarly studied by Shyluk (317), who concluded that the polymer chains lay flat along the surface when no excess polymer was present. 

In many colloidal systems, both in practice and in model studies, soluble polymers are used to control the particle interactions and the suspension stability. Here we distinguish tliree scenarios interactions between particles bearing a grafted polymer layer, forces due to the presence of non-adsorbing polymers in solution, and finally the interactions due to adsorbing polymer chains. Although these cases are discussed separately here, in practice more than one mechanism may be in operation for a given sample. 

As Morawetz puts the matter, an acceptance of the validity of the laws governing colligative properties (i.e., properties such as osmotic pressure) for polymer solutions had no bearing on the question whether the osmotically active particle is a molecule or a molecular aggregate . The colloid chemists, as we have seen, in regard to polymer solutions came to favour the second alternative, and hence created the standoff with the proponents of macromolecular status outlined above. 

Another family of polyols is the filled polyols.llb There are several types, but die polymer polyols are die most common. These are standard polyether polyols in which have been polymerized styrene, acrylonitrile, or a copolymer thereof. The resultant colloidal dispersions of micrometer-size particles are phase stable and usually contain 20-50% solids by weight. The primary application for these polyols is in dexible foams where the polymer filler serves to increase foam hardness and load-bearing capacity. Other filled polyol types diat have been developed and used commercially (mainly to compete with die preeminent polymer polyols) include the polyurea-based PEID (polyhamstoff dispersion) polyols and the urethane-based PIPA (poly isocyanate polyaddition) polyols. 

Emulsion polymerization refers to a unique process employed for some radical chain polymerizations. It involves the polymerization of monomers in the form of emulsions (i.e., colloidal dispersions). The process bears a superficial resemblance to suspension polymerization (Sec. 3-13c) but is quite different in mechanism and reaction characteristics. Emulsion polymerization differs from suspension polymerization in the type and smaller size of the particles in which polymerization occurs, in the kind of initiator employed, and in the dependence of polymer molecular weight on reaction parameters. 

The main objective of this chapter is to report on the preparation and characterization of thermally sensitive particles, and the pertinent aspects that should be considered before their utilization as a polymer support in the biomedical field. This is followed by an examination of the preparation of such hydrophilic thermally sensitive latex particles bearing reactive groups. Subsequently, the colloidal characterizations that are to be taken into consideration are presented. Finally, the chapter concludes by presenting and illustrating recent applications of thermally sensitive polymer colloids as solid supports in the biomedical field. 

The typical nucleation mechanism coupled with high colloidal stability is achieved by the use of the stabilizing substances. The result is polymer particles with size comparable to nanoreactor precursors of the polymerization process, as shown in Fig. 8.4. Bearing this characteristic in mind, there is a need for optimal conditions of operation, mechanisms, and dispersion stability. These characteristics play a vital role on the particle morphology of the polymers obtained at the end of the process [26,34]. 

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