Colloid
A colloid is a dispersion of very small particles, droplets or bubbles in another material. Its components are called the dispersed phase and the dispersion medium. Emulsions, foams, aerosols and gels are familiar forms. The dispersed units may contain many molecules or consist of individual large polymer molecules.[1]
Size definitions vary between research fields. In environmental research, a commonly used range runs from about one nanometre to one micrometre in at least one dimension. Behaviour, including how long particles remain suspended and how they move through water, also matters to their classification.[2]
Thomas Graham introduced the term in 1861 while studying how substances passed through membranes. It derives from the Greek word for glue.[3]
Forms and preparation
In an emulsion, liquid droplets are dispersed in another liquid; milk and mayonnaise are examples. A sol contains solid particles in a liquid, as in some inks. Fog is an aerosol of liquid droplets in a gas, while whipped cream contains gas bubbles dispersed in liquid. Colloidal particles scatter light, producing the Tyndall effect.[1]
Preparation can involve breaking larger particles into smaller ones, for example by grinding pigments, or building particles from molecules or ions. Condensation of water into droplets illustrates the latter process.[1]
Motion and stability
Particles in a fluid undergo Brownian motion: irregular movement caused by collisions with the surrounding molecules. Their persistence as a dispersion depends on the balance between attractive and repulsive interactions. Van der Waals forces attract particles, while like surface charges can produce repulsion. DLVO theory combines these contributions to describe an energy barrier that can delay particle aggregation. Such a dispersion may remain stable for practical purposes without being at its lowest-energy state.[3]
Coating particles with polymer chains provides another means of stabilisation. When the coatings approach one another, their interaction creates steric repulsion, helping to keep the particles apart.[3]
Hydrocolloids in food
Hydrocolloids are water-dispersible polymers, principally polysaccharides and proteins, used to control food texture and flow. Starch, xanthan gum and guar gum thicken liquids as their polymer chains become entangled. Some hydrocolloids also form gels: linked chains create a three-dimensional network that holds water and resists flow. Pectin, gelatin and agar are examples of gelling agents. These different behaviours allow hydrocolloids to thicken sauces, set jellies and modify the texture of ice cream. Their effects depend on concentration, temperature and the surrounding food mixture.[4]
Environmental transport
Natural colloids include clay minerals, metal oxides, organic macromolecules and microorganisms. Their reactive surfaces can carry nutrients and contaminants through groundwater and surface water. Transport depends partly on whether the particles remain dispersed or attach to surrounding solids. Changes in water chemistry, including pH and ionic strength, can alter particle charges and encourage dispersion or aggregation.[2]
References
- ↑ 1.0 1.1 1.2 Flowers, Paul; Theopold, Klaus; Langley, Richard; Robinson, William R. (2019-02-14). "11.5 Colloids". OpenStax. Retrieved 2026-10-14.
a phenomenon called the Tyndall effect ... the dispersed phase ... breaking down larger particles ... growth from smaller units
- ↑ 2.0 2.1 Spielman-Sun, Eleanor; Boye, Kristin; Dwivedi, Dipankar; Engel, Maya; Thompson, Aaron; Kumar, Naresh; Noël, Vincent (2024-03-22). "A Critical Look at Colloid Generation, Stability, and Transport in Redox-Dynamic Environments: Challenges and Perspectives". ACS Earth and Space Chemistry. 8 (4): 630–653. doi:10.1021/acsearthspacechem.3c00255. Retrieved 2026-10-14.
carriers of critical substances ... a solid particle with at least one dimension between 1 nm and 1 μm
- ↑ 3.0 3.1 3.2 López-Esparza, R.; Balderas Altamirano, M. A.; Pérez, E.; Gama Goicochea, A. (2015-09-09). "Importance of Molecular Interactions in Colloidal Dispersions". Advances in Condensed Matter Physics. 2015 683716. doi:10.1155/2015/683716. Retrieved 2026-10-14.
balance of attractive and repulsive forces ... polymer layer ... results from collisions between the molecules of the solvent
- ↑ Saha, Dipjyoti; Bhattacharya, Suvendu (2010-11-06). "Hydrocolloids as thickening and gelling agents in food: a critical review". Journal of Food Science and Technology. 47 (6): 587–597. doi:10.1007/s13197-010-0162-6. Retrieved 2026-10-14.
modify the rheology of food system ... a three dimensional network that traps or immobilises the water
Attribution
Adapted from English Wikipedia's Colloid, revision 1379556746 (contributors and history), under the Creative Commons Attribution-ShareAlike 4.0 licence. The prose has been rewritten and condensed, and the references replaced with independently checked sources.