Mini-Encyclopedia of Papermaking Wet-End
Part Two: Definitions and Concepts
An emulsion is a colloidal dispersion of droplets of one liquid within another liquid. Milk is a familiar example of an oil-in-water emulsion. Rosin size emulsions are also of the oil-in-water type. We call rosin emulsions "emulsions" even though the droplets become solid when the mixture is cooled. Retention aids are commonly delivered to paper mills in the form of water-in-oil emulsions. This form of delivery makes it possible to ship retention aid at between 25 and 50% actives. The same polyelectrolytes would have to be diluted to about 2% solids in order to ship them as highly viscous solutions. Emulsions are thermodynamically unstable and the droplets tend to coalesce over sufficiently long periods of time. The stability of emulsions can be greatly increased by the use of suitable surface-active agents to decrease the free energy content of the interfacial area. Highly stable emulsions require the use of steric stabilizers, i.e., polyelectrolytes that cover all the surfaces with loops and tails extending into solution.
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