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Formulations, measurements and solutions for industry

What is a "Colloid"?

A colloid is a dispersion of one material in another, where the dispersed component has a size in the range 1nm - 1mm[i].  In general, colloidal “particles” (the dispersed phase) are aggregates of numerous atoms or molecules whose dimensions are below the limits of resolution of simple optical microscopes.  As a result of the size of the particles/molecules, a colloid will neither dissolve nor precipitate.  However, the size is not the dominant factor, rather the total surface area.  From a thermodynamic perspective, colloidal dispersions are inherently unstable, but kinetically stable.

The term colloid is used to describe a broad array of such two-phase systems.  However the variety of different two-phase combinations has led to a more distinct classification.  For example a “dispersion” is the name given to a solution of solid particles within a liquid whereas a liquid within a liquid is termed an “emulsion” and a liquid within a gas is a “liquid aerosol”.

In more simple terms, colloids are systems comprising at least two distinct phases, at least one of which is very small. Examples of colloids include: blood, skin creams, hair sprays, inks, paints, detergents, mayonnaise, ice-cream, ceramics etc.



[i] Everett, D.H., Basic Principles of Colloid Science, Royal Society of Chemistry, (1988).

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