Nonaqueous dispersions, charge

Recently, great strides have been made in developing electrical and optical transient methods for measuring particle charge and mobility in these nonaqueous dispersions. It has been possible to obtain particle charge/mass ratios as well as the field dependence of particle mobility. 

Surfactants are employed in emulsion polymerizations to facilitate emulsification and impart electrostatic and steric stabilization to the polymer particles. Sicric stabilization was described earlier in connection with nonaqueous dispersion polymerization the same mechanism applies in aqueous emulsion systems. Electrostatic stabilizers are usually anionic surfactants, i.e., salts of organic acids, which provide colloidal stability by electrostatic repulsion of charges on the particle surfaces and their associated double layers. (Cationic surfactants are not commonly used in emulsion polymerizations.)... 

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. 

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... 

Electrostatic Properties in Nonaqueous Media. Although suspensions most commonly comprise particles dispersed in aqueous media, the petroleum industry contains many examples of particles dispersed in nonaqueous media. Examples include precipitated asphaltenes in oil (see Chapter 8) and mineral solids dispersed in diluted froth in oil sands processing (see Chapter 13). Particles can be electrostatically stabilized in nonaqueous media, although the charging mechanism is different (7, 34). In a recent review Morrison (34) emphasized that many models are... 

Surface Charge and Conductance in Dispersions of Titania in Nonaqueous and Mixed Solvents... 

In the normal-phase extraction, compounds with polar functional groups are extracted from a nonaqueous sample. Retention is based on polar interactions such as charge-based interactions, hydrogen bonding, dipole-dipole interactions, and dispersion interactions between the sorbent and the analyte. Charge-based interactions are often not required in the normal phase, since they are very strong and difficult to disrupt (Figure 9.4). 

Figure 14 Commonly used charging agents or dispersants in nonaqueous system.

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