Mini-Encyclopedia of Papermaking Wet-End
Part Two: Definitions and Concepts
A colloidal substance has the following attributes: (a) at least two phases, (b) at least one dimension of a liquid or solid phase than is less than one micro-meter, and (c) properties that are dominated by interactions within and between surfaces. Examples of colloids are suspensions, emulsions, foams, and aerosols. Most colloids are thermodynamically unstable. Given enough time, most foam bubbles pop, and most suspensions coagulate or settle. Many colloids can be stabilized by additives that decrease the interfacial tension, i.e. the free energy per unit area of surface. Such substances are known as surface-active agents or surfactants. Aqueous suspensions and emulsions can be further stabilized by addition of suitable water-loving polyelectrolytes to the aqueous phase (see steric stabilization).
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