Dispersions, aqueous colloidal

Poly(vinyl chloride) is commercially available in the form of aqueous colloidal dispersions (latices). They are the uncoagulated products of emulsion polymerisation process and are used to coat or impregnate textiles and paper. The individual particles are somewhat less than 1 p,m in diameter. The latex may be coagulated by concentrated acids, polyvalent cations and by dehydration with water-miscible liquids. 

Gilligan, C. A., and Po, A. L. W., Factors affecting Drag Release from a Pellet System Coated with an Aqueous Colloidal Dispersion, Int. J. Pharmaceutics, 73 51-68 (1991)... 

Tachibana T, Nakamura A. A method for preparing an aqueous colloidal dispersion of organic materials by using water-soluble polymers dispersion of beta-carotene by polyvinylpyrrolidone. Kolloid-Z Polym 1965 203 130-133. 

As manufactured, PTFE is of two principal types dispersion polymer, made by suspension polymerization followed by coagulation, and granular PTFE, polymerized and generally comminuted to a desirable particle size. Some details are given by Sperati. We have observed cast films of an aqueous colloidal dispersion and see that it consists of peanut-shaped particles, approximately 0.25 pm in size, which are composed of even finer particles. Electron micrographs of as-polymerized granular particles show three structures bands arranged in parallel, striated humps, and fibrils, some of which have the shish-kebab structure."... 

Zeolite crystallization represents one of the most complex structural chemical problems in crystallization phenomena. Formation under conditions of high metastability leads to a dependence of the specific zeolite phase crystallizing on a large number of variables in addition to the classical ones of reactant composition, temperature, and pressure found under equilibrium phase conditions. These variables (e.g., pH, nature of reactant materials, agitation during reaction, time of reaction, etc.) have been enumerated by previous reviewers (1,2, 22). Crystallization of admixtures of several zeolite phases is common. Reactions involved in zeolite crystallization include polymerization-depolymerization, solution-precipitation, nucleation-crystallization, and complex phenomena encountered in aqueous colloidal dispersions. The large number of known and hypo-... 

The use of natural and synthetic polymers to stabilize aqueous colloidal dispersions is technologically important, with much research in this area being focused on adsorption and steric stabilization [286-291]. Steric stabilization is discussed further in the next section. 

The first step in the manufacture of fine powder resins is to prepare an aqueous colloidal dispersion by polymerization with initiator and emulsifier present.21 Although the polymerization mechanism is not a typical emulsion type, some of the principles of emulsion polymerization apply here. Both the process and the ingredients have significant effects on the product.22 The solids contents of such disper-... 

Micellar aggregates are considered in chapter 3 and a critical concentration is defined on the basis of a change in the shape of the size distribution of aggregates. This is followed by the examination, via a second order perturbation theory, of the phase behavior of a sterically stabilized non-aqueous colloidal dispersion containing free polymer molecules. This chapter is also concerned with the thermodynamic stability of microemulsions, which is treated via a new thermodynamic formalism. In addition, a molecular thermodynamics approach is suggested, which can predict the structural and compositional characteristics of microemulsions. Thermodynamic approaches similar to that used for microemulsions are applied to the phase transition in monolayers of insoluble surfactants and to lamellar liquid crystals. 

TEX-WET colloidal silica is an aqueous colloidal dispersion of silica particles varying in solids content and particle size. 

NYACOL non-aqueous colloidal dispersions are generally used in the plastics, coating, and adhesives industries where one or more of the following criteria are important ... 

Aqueous colloidal dispersions created by template synthesis, principally used for processing polyaniline and poly(ethylenedioxythiophene), PEDOT. 

At high temperature and humidity, polyvinyl acetate phthalate undergoes less hydrolysis than other commonly used enteric coating polymers. In aqueous colloidal dispersions of polyvinyl acetate phthalate, the formation of free phthalic... 

The most commercially successful method of producing processable forms of CEPs has been the aqueous colloidal dispersion route pioneered by Vincent and Armes118 120 (see two recent reviews by Armes121 and Wessling122). Unlike the methods discussed earlier, which all require extensive derivatization of the aniline monomer, dispersions are readily formed from unsubstituted aniline and are readily manufactured in bulk quantities. 

Enzymatically synthesized PANI has been deposited in thin films of controlled thickness by the layer by layer assembly technique. Aniline was first polymerized using a template-free approach, de-doped and dissolved in dimethylacetamide. After filtration, this solution was further diluted with water at pH 2.5 (adjusted with hydrochloric acid) and filtered again, resulting in the formation of a stable ultrafine aqueous colloidal dispersion. This dispersion was used in the layer-by-... 

The amphiphilic compounds used to stabilize aqueous colloidal dispersions of metals, semiconductors, and organic polymer particles are surfactants, broadly defined. The surfactant replaces the high energy of the particle-water interface with two lower energy interfaces of the surfactant with particles and of the surfactant with water. Amphiphilic polymers also stabilize colloidal dispersions by reducing the interfacial free energies of the system. 

Protective agents can act in several ways. They can increase double layer repulsion if they have ionizable groups. The adsorbed layers can lower the effective Hamaker constant. An adsorbed film may necessitate desorption before particles can approach closely enough for van der Waals forces to cause attraction, or approaching particles may simply cause adsorbed molecules to become restricted in their freedom of motion (volume restriction). The use of natural and synthetic polymers to stabilize aqueous colloidal dispersions is technologically important, with research in this area being focused on adsorption and steric stabilization [75-80]. 

Polymer dispersed nematic films are made by one of two distinct processes. In one, the nematic is emulsified in either an aqueous solution of a film-forming polymer (for example, poly vinyl alcohol) or an aqueous colloidal dispersion (for example, a latex). This emulsion is coated onto a conductive substrate and allowed to dry, dming which time the polymer coalesces around the nematic droplets. Laminating a second conductive substrate to the dried film completes the device. Alternatively, the nematic is mixed with a precursor to the polymer to form an isotropic solution. When polymerization is initiated, typically with heat or light, nematic droplets nucleate in situ as the polymer chains grow. 

In Table 16.2, values of ccc s are collected for different aqueous colloidal dispersions. Within a series of counterions having the same valency, a small but systematic influence of the type of ion is observed. This nonelectrostatic and, therefore, specific influence seems to be related to the size of the hydrated ion. The larger the ions, the less they are hydrated and the smaller their hydrated size. These ions can approach the particle surface more closely. In view of the Stem model, presented in Section 9.4.3, a larger value of /j and, hence, a higher ccc is expected. The observation of... 

---