Soft condensed-matter physicists study colloids. These 10 nanometer - 10 micron particles, typically consisting of some plastic like polystyrene or polymethyl methacrylate, are suspended in water or some other solvent. They are small enough that Brownian motion is significant, and large enought to be probed with a light microscope or using light scattering. For these reasons they make an ideal model of of atomic behavior.

The interaction between colloidal particles ranges from "hard sphere" systems, in which the particles are only aware of each other when they are in contact, to highly charged systems with long-range repulsion. Investigations into the dynamics of crystals, as well as glasses and gels have been conducted using colloids.

Colloids come in several varieties:

Sol--solid particles suspended in a liquid

Aerosol--solid particles or liquid droplets suspended in a gas

Emulsion--liquid droplets suspended in a liquid

The former two are related to less fluid mixtures known respectively as gels and aerogels. (Typically formed by linking the suspended particles together into a larger structure)

Another feature of colloids is that unlike suspensions, colloidal particles usually bear electrostatic charges, which (combined with the large surface area to mass ratio of the particles and viscosity of the surrounding fluid) often prevent the suspended particles from settling out.

Colloids are heterogeneous mixtures, as the particles are sufficiently large to scatter visible light.

Col"loid (?), a. [Gr. glue + -oid. Cf. Collodion.]

Resembling glue or jelly; characterized by a jellylike appearance; gelatinous; as, colloid tumors.


© Webster 1913.

Col"loid (?), n.

1. Physiol. Chem.

A substance (as albumin, gum, gelatin, etc.) which is of a gelatinous rather than a crystalline nature, and which diffuses itself through animal membranes or vegetable parchment more slowly than crystalloids do; -- opposed to crystalloid.

2. Med.

A gelatinous substance found in colloid degeneration and colloid cancer.

Styptic colloid Med., a preparation of astringent and antiseptic substances with some colloid material, as collodion, for ready use.


© Webster 1913.

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