Читать книгу Applied Colloid and Surface Chemistry - Richard M. Pashley - Страница 15

The term ‘colloid’ usually refers to particles within the approximate size range of 50 Å to 50 μm, but this, of course, is somewhat arbitrary. For example, blood could be considered as a colloidal solution in which large blood cells are dispersed in water. They are stabilized by their negative charge, and so oppositely charged ions, for example, those produced by an alum stick, will coagulate the cells and hence stop bleeding. Often we are interested in solid dispersions in aqueous solutions, but many other situations are also of interest and industrial importance. Some examples are given in the following table.

The properties of colloidal dispersions are intimately linked to the high surface area of the dispersed phase and the chemistry of these interfaces. This linkage is well illustrated by the titles of two of the main journals in this area: the Journal of Colloid and Interface Science and Colloids and Surfaces. The natural combination of colloid and surface chemistry represents a major area of both research activity and industrial development. It has been estimated that something like 20 per cent of all chemists in industry work in this area. The more recent term nano is also applied to these small scale materials, because of their typical nanometre size.

Table 1.1

Dispersed phase	Dispersion medium	Name	Examples
Liquid	Gas	Liquid aerosol	Fogs, sprays
Solid	Gas	Solid aerosol	Smoke, dust
Gas	Liquid	Foam	Foams
Liquid	Liquid	Emulsion	Milk, mayonnaise
Solid	Liquid	‘Sol’,	Au sol, AgI sol.
		Paste at high	Toothpaste
		concentration
Gas	Solid	Solid foam	Expanded polystyrene
Liquid	Solid	Solid emulsion	Opal, pearl
Solid	Solid	Solid suspension	Pigmented plastics