INDUSTRIAL APPLICATIONS OF DISPERSIONS

In this review some industrial applications of dispersions have been d iscussed. After a general introduction, some specific topics have been covered. The preparation of dispersions using condensation and disper sion methods was discussed in terms of the various interfacial process es involved such as nucleation and growth, wetting, breaking of aggreg ates and agglomerates as well as comminution. The process of emulsific ation (for production of liquid/liquid dispersions) was also analyzed in terms of the interfacial processes, such as reduction in interfacia l tension, interfacial elasticity and viscosity. The control of the pr operties of dispersions was described in terms of the interaction forc es between the particles or droplets in the system. These interaction forces are governed by the structure and properties of the interfacial region such as double layers, presence of adsorbed surfactant or poly mer layers. Four main types of interaction forces may be distinguished : hard-sphere, electrostatic, steric and van der Waals. Combination o f these forces lead to three general energy-distance curves that can b e used to describe the state of the dispersion (stable, flocculated or coagulated). The various physical states of suspensions and emulsions produced on standing were schematically presented and they could be e xplained in terms of the energy-distance curves. The flow characterist ics (theology) of dispersions could also be accounted for in terms of the various interaction forces between the particles. Solubilization a nd microemulsions, which produce thermodynamically stable dispersions, could be described in terms of the balance between the interfacial en ergy and entropy of dispersion of the system. The driving force for pr oducing such thermodynamically stable systems was the ultra low interf acial tension which could be achieved by using a combination of surfac tants. The application of microemulsions in various fields such as sol ubilization, enhanced oil recovery and energy production was briefly d escribed. The application of dispersions in microncapsulation and slow release was described in terms of interfacial polymerization, coacerv ation and multiple emulsion formation. These systems find application in medicine, agrochemicals and cosmetics. The application of dispersio ns in pharmacy and medicine was also described by quoting specific exa mples such as liposomes (vesicles), nanoparticles and magnetic microsp heres. These systems have potential use in targeting delivery of drugs .