Colloids

thumb|Solid and melted butter Butter is a dairy product made from the fat and protein components of churned cream. It is a semi-solid emulsion at room temperature, consisting of approximately 81% butterfat. It is used at room temperature as a spread, melted as a condiment, and used as a fat in baking, sauce-making, pan frying, and other cooking procedures.

thumb|upright=1.4|Mist and [[fog are aerosols|alt=photograph of heavy mist]]

thumb|Top of a foamy drink Foam is a two-phase material systems where a gas is dispersed in a second, non-gaseous material, specifically, in which gas cells are enclosed by a distinct liquid or solid material. Foam "may contain more or less liquid [or solid] according to circumstances", although in the case of gas-liquid foams, the gas occupies most of the volume.

A colloid is a mixture in which one substance, consisting of microscopically dispersed insoluble particles, is suspended throughout another substance. Some definitions specify that the particles must be dispersed in a liquid, while others extend the definition to include substances like aerosols and gels. The term colloidal suspension refers unambiguously to the overall mixture (although a narrower sense of the word suspension is distinguished from colloids by larger particle size). A colloid has a dispersed phase (the suspended particles) and a continuous phase (the medium of suspension). thu

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thumb|An upturned vial of hair gel|241x241px thumb|Silica gel A gel is a semi-solid that can have properties ranging from soft and weak to hard and tough. Gels are defined as a substantially dilute cross-linked system, which exhibits no flow when in the steady state, although the liquid phase may still diffuse through this system.

thumb|Turbidity standards of 5, 50, and 500 NTU

colloidal suspension of very small solid particles in a continuous liquid medium

suspension of gold particles in another medium

thumb|200px|Chemical structures of two synthetic polyelectrolytes, as examples. To the left is sodium polystyrene sulfonate|poly(sodium styrene sulfonate) (PSS), and to the right is [[polyacrylic acid (PAA). Both are negatively charged polyelectrolytes when dissociated. PSS is a 'strong' polyelectrolyte (fully charged in solution), whereas PAA is 'weak' (partially charged).]]

Imbibition is a special type of diffusion that takes place when liquid is absorbed by solids-colloids causing an increase in volume. Water surface potential movement takes place along a concentration gradient; some dry materials absorb water. A gradient between the absorbent and the liquid is essential for imbibition. For a substance to imbibe a liquid, there must first be some attraction between them. Imbibition occurs when a wetting fluid displaces a non-wetting fluid, the opposite of drainage in which a non-wetting phase displaces the wetting fluid. The two processes are governed by differe

thumb|210px|right|A nephelometer at the Kosan, Cheju Island, South Korea NOAA facility

thumb|A uniform (monodisperse) collectionthumb|A non-uniform (polydisperse) collection

extraction or expulsion of a liquid from a gel

The peptization of a liquid mixture is the process of converting the mixture into a colloid by shaking it with a suitable electrolyte called a peptizing agent. That is, the insoluble solid particles which have settled out of the mixture (i.e. the precipitate) are reformed into microscopic particles suspended in the mixture. Peptization is the reverse of flocculation, the aggregation of colloidal particles into precipitate; as such, it is also known as deflocculation.

thumb|Polymers prior (no gel) and after crosslinking (gel)

thumb|upright=2.0|Freeze-cast alumina that has been partially sintered. The freezing direction in the image is up.