A colloid is a heterogeneous mixture composed of two or more particles whose sizes range within 1 to 1000 nm in diameter. Such particles are small enough to completely mix without any variation throughout the mixture, but differ from molecules in that it cannot be separated by any type of filtration or gravity.

Whether emulsions are mixtures of two immiscible liquids, they can be categorized as colloids in which both the dispersed phase and the dispersion medium are liquids.

Colloid is a uniform dispersion of fine solid particles in a liquid medium. An emulsion is a uniform dispersion of one liquid in another liquid which are not miscible.

A colloid is a heterogeneous mixture composed of two or more particles whose sizes range within 1 to 1000 nm in diameter. Such particles are small enough to completely mix without any variation throughout the mixture, but differ from molecules in that it cannot be separated by any type of filtration or gravity.

Whether emulsions are mixtures of two immiscible liquids, they can be categorized as colloids in which both the dispersed phase and the dispersion medium are liquids.

Also emulsions are colloidal systems, only, as said before, here the dispersed phase is a liquid, dispersed in a liquid.

Most welcome............

Tatiana, I think I agree with all the above definitions. I would also point out that hydrogel nanoparticles, proteins, and other very small and very "nanoporous" have also been considered colloidal for over half a century. One may have colloidal solutions (such as micellar solutions) and colloidal suspensions (such as nano ZnSe dispersed in an organic solvent. The length scale can also extend to many microns, as in various types of emulsions. In the case of colloidal solutions we refer to the "disperse" phase as a pseudophase; this means that the solvated colloidal "particles" behave as particles or as networks with at lest one nanoscopic dimension on some time scale in some kind of experiment, such as in photon correlation spectroscopy (dynamic light scattering). Best wishes, John

Ms.Tatiana, I think Interesting answer given by Mr. Texter from nanotech. point of view

An emulsion is a mixture of two or more liquids that are normally immiscible (nonmixable or unblendable).

Emulsions are part of a more general class of two-phase systems of matter called colloids. Although the terms colloid and emulsion are sometimes used interchangeably, emulsion should be used when both the dispersed and the continuous phase are liquids.

In an emulsion, one liquid (the dispersed phase) is dispersed in the other (the continuous phase).

The word "emulsion" comes from the Latin word for "to milk", as milk is an emulsion of milk fat and water, among other components.

Two liquids can form different types of emulsions. As an example, oil and water can form, firstly, an oil-in-water emulsion, where the oil is the dispersed phase, and water is the dispersion medium. Secondly, they can form a water-in-oil emulsion, where water is the dispersed phase and oil is the external phase. Multiple emulsions are also possible, including a "water-in-oil-in-water" emulsion and an "oil-in-water-in-oil" emulsion.

Emulsions, being liquids, do not exhibit a static internal structure. The droplets dispersed in the liquid matrix (called the “dispersion medium”) are usually assumed to be statistically distributed.

A colloid is a substance microscopically dispersed throughout another substance.

The dispersed-phase particles have a diameter of between approximately 2 and 500 nanometers. Such particles are normally invisible in an optical microscope, though their presence can be confirmed with the use of an ultramicroscope or an electron microscope. Homogeneous mixtures with a dispersed phase in this size range may be called colloidal aerosols, colloidal emulsions, colloidal foams, colloidal dispersions, or hydrosols.

References:

IUPAC (1997). Compendium of Chemical Terminology (The "Gold Book"). Oxford: Blackwell Scientific Publications.

"Colloid". Britannica Online Encyclopedia. Retrieved 31 August 2009.

Levine, Ira N. (2001). Physical Chemistry (5th ed.). Boston: McGraw-Hill.

ISBN 0-07-231808-2., p. 955