Nonaqueous colloid applications

This paper is intended to review characterization methods of nonaqueous colloids, their physical properties and technological applications. 

The description of a colloid should include particle size, mobility, charge and their distributions, charge/mass ratio, electrical conductivity of the media, concentration and mobility of ionic species, the extent of a double layer, particle-particle and particle-substrate interaction forces and complete interfacial analysis. The application of classical characterization methods to nonaqueous colloids is limited and, for this reason, the techniques best suited to these systems will be reviewed. Characteristic results obtained with nonaqueous dispersions will be summarized. Physical aspects, such as space charge effects and electrohydrodynamics, will receive special attention while the relationships between chemical and physical properties will not be addressed. An application of nonaqueous colloids, the electrophoretic development of latent images, will also be discussed. 

The AC impedance technique is compatible with both conventional and microfabrication technologies, allowing production of rugged devices for applications in the harsh, highly resistive, chemically complex, and often aggressive media of industrial lubricants and colloids [25]. EIS presents an opportunity to resolve complicated nonaqueous colloidal system both spatially and chemically, and can be applied to monitoring lubricant s degradation process. 

In this chapter I have attempted to show in a broad sense how the application of the basic principles of colloid science can be applied to develop our understanding of the various mechanisms involv in the stabilization of polymer latices. In the space availaUe, it was not possible to go into veiy specific details of the many systems that have been investigated nor to deal with nonaqueous polymer latices. The latter, however, have been discussed in the recent comprehensive book by Barrett (1975). The literature on polymer colloids appears to be growing exponentially and to the authors of the many excellent papers which I have not quoted, I offer my sincere apologies. 

Emulsion polymerization typically refers to the polymerization of a nonaqueous material in water. The polymerization of a water-soluble material in a nonaqueous continuum has been called inverse emulsion polymerization. The inverse emulsion polymerization technique is used to synthesize a wide range of polymers for a variety of applications such as wall paper adhesive, waste water fiocculant, additives for oil recovery fluids, and retention aids. The emulsion polymerization technique involves water-soluble polymer, usually in aqueous solution, emulsified in continuous oil phase using water in oil emulsifier. The inverse emulsion is polymerized using an oil- or water-soluble initiator. The product is a colloidal dispersion of sub-microscopic particles with particle size ranging from 0.05 to 0.3 pm. The typical water-soluble monomers used are sodium p-vinyl benzene sulfonate, sodium vinyl sulfonate, 2-sulfo ethyl acrylate, acrylic acid, and acrylamide. The preferred emulsifiers are Sorbitan monostearate and the oil phase is xylene. The proposed kinetics involve initiation in polymer swollen micelles, which results in the production of high molecular weight colloidal dispersion of water-swollen polymer particles in oil. 

Dispersion stabilization with nanoparticles is also known. A recent example of a dispersion stabilized by nanoparticles was published by Tohver et al. This group used zirconia particles to stabilize an aqueous colloidal system of larger silica particles. The dispersion was stabilized by electrostatic stabilization and thus is essentially applicable only to aqueous systems. Surface modification of the particles changes the stabilization mechanism to steric stabilization, and dispersions in both aqueous and nonaqueous systems have been demonstrated. 

Two effects which may be encountered during nonaqueous electrophoresis are space charge conditions and electrohydrodynamics (EHD). When an electric field is applied across a uniformly dispersed colloid the macroscopic charge density is zero and the field is uniform at the time of application. As the separation of opposite polarity charges occurs, a net internal... 

To this point, our discussion of the protective action of nonionic stabilizing molecules has been concerned exclusively with hydrosols. Realization that stabilization could similarly be imparted to colloidal particles in nonaqueous media was somewhat later in coming. This comment disregards, of course, the pragmatic technological application of the phenomenon in such products as paints, etc. 

The second application area of interest is organosols. Organosols involve the use of nonaqueous systems, for example, in making magnetic colloids and recording media, high-technology ceramic composites, and catalyst... 

There are some potential applications in which the external phase is nonaqueous. Florence and co-workers (79, 80) and Albert et al. (81) described systems in which the aqueous suspension of vesicles are dispersed in the continuous oil phase. The technique was exercised both for the study of its use in drug-delivery systems and as immunological adjuvants, as well as an intrinsically interesting colloidal system. The system is an emulsion prepared from a dispersion of niosomes in water, re-emulsified in an oil using a surfactant mixture of low HUB to achieve a stable W/0 emul-... 

The sol-gel process - either aqueous or nonaqueous - is one of the most important processes for the preparation of oxidic nanopartides. For silica particles, the sol-gel-based Stober process is definitely the most used wet chemical preparation route. Particularly, the mild reaction conditions combined with the excellent control over nanopartides properties malce it a universal method for the production of colloids for various applications. In recent years, the metal oxide routes have also become more and more sophisticated. Another reason for the attractiveness of the preparation route is the activity of the derived particles toward surface functionalization. Such modified particles can be easily incorporated into polymer matrices to obtain nanocomposites with extraordinary properties. 

In addition to their high absorptive eapacity hormite clays offer useful thickening properties. When dispersed in water they do not swell, as smectites do. Instead, their needle-like colloidal particles deagglomerate in proportion to the amoimt of shear applied and form a random colloidal lattice. This loosely cohesive structure thickens the water and imparts thixotropy, pseudoplasticity, and yield value. Because of their mechanically-based dispersion and colloidal structure building, hormite cl s are largely insensitive to the types and levels of acids, bases, and salts dissolved in the aqueous systems in which they are used. Since their dispersion is mechanically rather than ionically driven, as with smectites, they can be used in nonaqueous applications in much the same... 

Apart from these applications, ILs also stimulated research in classical colloid and surface chemistry. The formation of amphiphilic association structures in and with ionic liquids, such as micelles, vesicles, microemulsions and liquid crystalline phases has been reviewed three times between 2007 (Hao Zemb 2007) and 2008 (Qiu Texter 2008 Greaves Drummond 2008 a), reflecting the growing interest and progress in this field. In this review we focus on ILs in nonaqueous microemulsions, because significant new work has been reported in this field since these earher reviews have been published. 

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