Industrial applications of dispersions

In this review some industrial applications of dispersions have been discussed. After a general introduction, some specific topics have been covered. The preparation of dispersions using condensation and dispersion methods was discussed in terms of the various interfacial processes involved such as nucleation and growth, wetting, breaking of aggregates and agglomerates as well as comminution. The process of emulsification (for production of liquid/liquid dispersions) was also analyzed in terms of the interfacial processes such as reduction in interfacial tension, interfacial elasticity and viscosity. The control of the properties of dispersions was described in terms of the interaction forces 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 polymer layers. Four main types of interaction forces may be distinguished : hard-sphere, electrostatic, steric and van der Waals. Combination of these forces lead to three general energy-distance curves that can be 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 explained in terms of the energy-distance curves. The flow characteristics (rheology) of dispersions could also be accounted for in terms of the various interaction forces between the particles.Solubilization and microemulsions, which produce thermodynamically stable dispersions, could be described in terms of the balance between the interfacial energy and entropy of dispersion of the system. The driving force for producing such thermodynamically stable systems was the ultra low interfacial tension which could be achieved by using a combination of surfactants. The application of microemulsions in various fields such as solubilization, enhanced oil recovery and energy production was briefly described.The application of dispersions in microncapsulation and slow release was described in terms of interfacial polymerization, coacervation and multiple emulsion formation. These systems find application in medicine, agrochemicals and cosmetics. The application of dispersions in pharmacy and medicine was also described by quoting specific examples such as liposomes (vesicles), nanoparticles and magnetic microspheres. These systems have potential use in targeting delivery of drugs.