Colloid

In general, a colloid or colloidal dispersion is a substance with components of one or two phases, a type of mixture intermediate between a homogeneous mixture and a heterogeneous mixture with properties also intermediate between the two. Typical membranes restrict the passage of dispersed colloidial particles more than they restrict the passage of dissolved ions or molecules; i.e. ions or molecules may diffuse through a membrane through which dispersed colloidal particles will not. The dispersed phase particles are largely affected by the surface chemistry existent in the colloid.

Many familiar substances, including butter, milk, cream, aerosols,asphalt, inks, paints, glues, and sea foam are colloids. This field of study was introduced in 1861 by Scottish scientist Thomas Graham.The size of dispersed phase particles in a colloid range from one nanometer to one micrometer. Dispersions where the particle size is in this range are referred to as colloidal aerosols, colloidal emulsions, colloidal foams, or colloidal suspensions or dispersions. Colloids may be colored or translucent because of the Tyndall effect, which is the scattering of light by particles in the colloid.