Polymer particles colloidal dispersion

The materials we studied are non-aqueous dispersions of polymer particles. Colloidal stability of these particles in hydrocarbon solvents is conferred by a surface covering of a highly swollen polymer (the stabilizer) on a second polymer, insoluble in the medium (the core polymer), which comprises 90 % of the material (11). These particles are prepared by dispersion polymerization polymerization of a monomer soluble in the medium to yield an insoluble polymer, carried out in the presence of a soluble polymer which becomes the stabilizer. In the examples discussed here, the core polymer is formed by free radical polymerization. Hydrogen abstraction from the soluble polymer present in the reaction medium... 

In describing the mechanical response of microstructured fluids, e.g., polymers, emulsions, colloidal dispersions, etc., one needs to determine the pair distribution function - the probability density P(r) for finding a particle at a position r given a particle at the origin in suspensions, or the probability density of the end-to-end vector in polymers, or a measure of the deformation of drops in an emulsion. This probability density satisfies an advection-diffusion or Smoluchowski equation of the following (when suitable approximations have been made) form ... 

Further, the ability to synthesize random copolymers with various hydrocarbon monomers allows the anchor-soluble balance to be tuned while maintaining solubility even with high incorporations of hydrocarbon comonomers [29]. Because of the amphiphilic nature of such copolymers, it was predicted that these materials would selfassemble into micelles consisting of a highly fluorinated corona segregating the lipophilic core from the compressed CO2 continuous phase. Thus, PFOA-F-PS block copolymers were synthesized via controlled free-radical techniques (Fig. 9.3), and it was confirmed (by smaU-angle neutron scattering) that these copolymers spontaneously assemble into multimolecular micelles in solution [40]. In addition to amphiphilic materials, which physically adsorb to the surface of polymer particles in dispersion polymerizations, fluorinated acrylates can be utihzed as polymerizable comonomers in the stabilization of C02-phobic polymer colloids [41]. 

Basic solvents and high temperatures favor the binding of metal carbonyls to polymers. Stable colloidal dispersions are formed on fire tiiermolysis of carbonyls in dilute polymeric solutions. For example, iron dispersion containing 5-10-mn particles have been produced. Nanoparticles of this type are very reactive. Particles smaller than 10 nm are superparamagnetic, while the magnetic hysteresis is observed for particle sizes between 10 and 20 run. 

Given that the shear rate is constant across the gap. the use of cone and plate is very convenient since the shear rate calculation is simple to perform. Apparent viscosity can be calculated straight from Eqs. [37] and [38] (as T/y). no corrections being needed. Houcver, this tool is not convenient for suspen.sion.s and emulsions containing particles or dropleLs larger than the submicrometcr size (see Sec. IV), being more adequate for polymers and colloid dispersions. 

Polyacrylamides are nonionic polymers, usually with much higher molecular weights (MW from 100,000 up to 12 or 15 M). They often are copolymerized with polyacrylates. Depending on the MW ratios employed, they may act as colloidal dispersants, sludge conditioners, or flocculants. Nonionics such as polyacrylamides (and isobutylenes) are particularly useful at dispersing uncharged particles. 

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. 

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. 

In studying the stability of colloidal dispersions it is of considerable advantage if the particles concerned are monodisperse and spherical. For aqueous, charge-stabilised systems polymer latices have proved invaluable in this regard. With non-aqueous systems, steric stabilisation is usually required. In this case it... 

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. 

Stabilizers are usually used during the reduction of metal ions to stabilize the colloidal dispersions of fine metal particles. The coordination interaction is the main factor to stabilize the metal particles. Thus, polymers with coordinating groups are good stabilizers. The choice of coordinating groups should depend on the kind of metal. 

Separate nanometer- to micron-sized colloidal magnetic particles, often dispersed in solutions they are usually stabilized by polyions or polymers. 

Coagulation of colloidal dispersions (Fig. 1.26h) as a function of salt concentration, pH, or temperature of the suspending liquid medium can also be used to obtain information on the interplay of repulsive and attractive forces between particles in pure liquids as well as in surfactant and polymer solutions. 

In Section 3.4a we examine a model for the second virial coefficient that is based on the concept of the excluded volume of the solute particles. A solute-solute interaction arising from the spatial extension of particles is the premise of this model. Therefore the potential exists for learning something about this extension (i.e., particle dimension) for systems for which the model is applicable. In Section 3.4b we consider a model that considers the second virial coefficient in terms of solute-solvent interaction. This approach offers a quantitative measure of such interactions through B. In both instances we only outline the pertinent statistical thermodynamics a somewhat fuller development of these ideas is given in Flory (1953). Finally, we should note that some of the ideas of this section are going to reappear in Chapter 13 in our discussions of polymer-induced forces in colloidal dispersions and of coagulation or steric stabilization (Sections 13.6 and 13.7). 

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