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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,[1] 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).
Since the definition of a colloid is so ambiguous, the International Union of Pure and Applied Chemistry (IUPAC) formalized a modern definition of colloids: "The term colloidal refers to a state of subdivision, implying that the molecules or polymolecular particles dispersed in a medium have at least in one direction a dimension roughly between 1 nanometre and 1 micrometre, or that in a system discontinuities are found at distances of that order. It is not necessary for all three dimensions to be in the colloidal range…Nor is it necessary for the units of a colloidal system to be discrete…The size limits given above are not rigid since they will depend to some extent on the properties under consideration.”[2] This IUPAC definition is particularly important because it highlights the flexibility inherent in colloidal systems. However, much of the confusion surrounding colloids arises from oversimplifications. IUPAC makes it clear that exceptions exist, and the definition should not be viewed as a rigid rule. D.H. Everett—the scientist who wrote the IUPAC definition—emphasized that colloids are often better understood through examples rather than strict definitions.[3]
Some colloids are translucent because of the Tyndall effect, which is the scattering of light by particles in the colloid. Other colloids may be opaque or have a slight color.
Colloidal suspensions are the subject of interface and colloid science. This field of study began in 1845 by Francesco Selmi,[4][5][6][7] who called them pseudosolutions, and expanded by Michael Faraday[8] and Thomas Graham, who coined the term colloid in 1861.[9]
Colloid: Short synonym for colloidal system.[10][11]
Colloidal: State of subdivision such that the molecules or polymolecular particles dispersed in a medium have at least one dimension between approximately 1 nm and 1 μm, or that in a system discontinuities are found at distances of that order.[10][11][12]
- ^ Israelachvili, Jacob N. (2011). Intermolecular and surface forces (4rd ed.). Burlington, MA: Academic Press. ISBN 978-0-08-092363-5. OCLC 706803091.
- ^ International Union of Pure and Applied Chemistry. Subcommittee on Polymer Terminology; Jones, Richard G. (2009). Compendium of polymer terminology and nomenclature : IUPAC recommendations, 2008. Cambridge: Royal Society of Chemistry. ISBN 978-1-84755-942-5. OCLC 406528399.
- ^ Everett, Dogulas H. (1988). Basic Principles of Colloid Science. London: The Royal Society of Chemistry. ISBN 978-0-85186-443-3.
- ^ Selmi, Francesco "Studi sulla dimulsione di cloruro d'argento". Nuovi Annali delle Scienze Naturali di Bologna, 1845.
- ^ Selmi, Francesco, Studio intorno alle pseudo-soluzioni degli azzurri di Prussia ed alla influenza dei sali nel guastarle, Bologna: Tipi Sassi, 1847
- ^ Hatschek, Emil, The Foundations of Colloid Chemistry, A selection of early papers bearing on the subject, The British Association Committee on Colloid Chemistry, London, 1925
- ^ Selmi, Francesco - Sur le soufre pseudosoluble, sa pseudosolution e le soufre mou, Journal de Pharmacie et de Chimie, tome 21, 1852, Paris
- ^ Tweney, Ryan D. (2006). "Discovering Discovery: How Faraday Found the First Metallic Colloid". Perspectives on Science. 14: 97–121. doi:10.1162/posc.2006.14.1.97. S2CID 55882753.
- ^ "X. Liquid diffusion applied to analysis". Philosophical Transactions of the Royal Society of London. 151: 183–224. 1861. doi:10.1098/rstl.1861.0011. S2CID 186208563.. Page 183: "As gelatine appears to be its type, it is proposed to designate substances of the class as colloids, and to speak of their peculiar form of aggregation as the colloidal condition of matter."
- ^ a b Richard G. Jones; Edward S. Wilks; W. Val Metanomski; Jaroslav Kahovec; Michael Hess; Robert Stepto; Tatsuki Kitayama, eds. (2009). Compendium of Polymer Terminology and Nomenclature (IUPAC Recommendations 2008) (2nd ed.). RSC Publ. p. 464. ISBN 978-0-85404-491-7.
- ^ a b Stepto, Robert F. T. (2009). "Dispersity in polymer science (IUPAC Recommendations 2009)" (PDF). Pure and Applied Chemistry. 81 (2): 351–353. doi:10.1351/PAC-REC-08-05-02. S2CID 95122531. Archived (PDF) from the original on 9 October 2022.
- ^ Slomkowski, Stanislaw; Alemán, José V.; Gilbert, Robert G.; Hess, Michael; Horie, Kazuyuki; Jones, Richard G.; Kubisa, Przemyslaw; Meisel, Ingrid; Mormann, Werner; Penczek, Stanisław; Stepto, Robert F. T. (2011). "Terminology of polymers
and polymerization processes in dispersed systems (IUPAC Recommendations 2011)" (PDF). Pure and Applied Chemistry. 83 (12): 2229–2259. doi:10.1351/PAC-REC-10-06-03. S2CID 96812603. Archived (PDF) from the original on 9 October 2022.