Solids in Liquids

Solution

Solvents are liquids, which are able to dissolve gaseous, liquid or solid substances. During that process, neither the solvent nor the dissolved substance becomes chemically altered.

Colloid

A substance is a colloid when microscopic particles of this substance are dissolved in a fluid in a way that they do not fuse with the solvent or precipitate. The particles are so small (10 – 100 nm), that they do not sink to the ground, due to the Brownian movement and the resulting collisions with other molecules. The dissolved particles (clouding particles) are larger than molecules, but still smaller than particles in suspensions.

Examples of ‘solid in liquid’ colloidal systems are varnish, paint, ink, and latex suspensions.

Suspensions

A suspension is material that has been stirred up, which is (in contrast to colloidal solutions) present as “coarse” particles in a carrier fluid. Because of gravity, this material sinks to the ground. In an attempt to avoid this negative effect, suspension-stabilising substances are used. Margarine, for example, is a suspension of very fine fat droplets dispersed in water.

Examples:

Blood

Blood is a suspension of erythrocytes in the plasma. The major component of blood is water, in which proteins, amino acids, carbohydrates, hormones, blood salts, blood fats, vitamins and several products of the metabolism are dissolved.

Ink and paint consist of pigments that are dissolved in water or oil.

Besides the colouring pigments, other major components of paint include solvents, vehicles, extenders and additives like thickening agents or preservatives.

Vehicles merge the components - especially the pigments and the extenders - and are responsible for the characteristics of the paint. Solvents affect the flowing properties and the workability and greatly influence the drying process. Emulsion paints are called this because the binding agents are dispersed in water. These binding agents are not water-soluble and form a plastic-like surface once the water has evaporated.

Very often, suntan lotion is not an emulsion, but a suspension. That’s why suntan lotions do not separate. However, they have to be shaken before use so that the components of the suspension become evenly distributed.