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Syllabus of Unit 3 :-

Coarse dispersion : Suspension, interfacial properties of suspended particles, settling in suspensions, formulation of flocculated and deflocculated suspensions. Emulsions and theories of emulsification, micro emulsion and multiple emulsions; Stability of emulsions, preservation of emulsions, rheological properties of emulsions and emulsion formulation by HLB method.

1. Suspension

A suspension could be a heterogeneous mixture of a fluid that contains solid particles sufficiently large for sedimentation. The particles could also be visible to the oculus, usually must be larger than one micrometer, and can eventually settle, although the mixture is barely classified as a suspension when and while the particles haven't settled out.

2. Flocculated Suspensions

Flocculation refers to the formation of a loose aggregation of discrete particles held together in a very network like structure by physical adsorption of macromolecules when the longer-range van der Walls forces of attraction exceed the shorter-range forces of repulsion.

Particles, therefore, experience attraction at significant inter particle distances (10 – 20 nm) and form an open network of aggregated particles referred to as floccules. Such a suspension is named flocculated suspension.

3. Deflocculated Suspensions

Whether a suspension is flocculated or deflocculated depends on the relative magnitudes of the electrostatic forces of repulsion and therefore the forces of attraction between the particles. At low electrolyte concentration, the electrical repulsion predominates and particle interactions are maximized. The individual particles are dispersed as discrete entities, leading to a smooth-looking suspension, called deflocculated or peptized suspension.

4. Emulsion

An Emulsion could be a mixture of two or more liquids that are normally immiscible (unmixable or unbendable) thanks to liquid-liquid phase separation. Emulsions are a part of a more general class of two-phase systems of matter called colloids. Although the terms colloid and emulsion are sometimes used interchangeably, emulsion should be used when both phases, dispersed and continuous, are liquids. In an emulsion, one liquid (the dispersed phase) is dispersed within the other (the continuous phase). 

Examples of emulsions include vinaigrettes, milk, liquid biomolecular condensates, and a few cutting fluids for metal working.