Editing Dispersity (section)

{{Short description|Measure of heterogeneity of particle or molecular sizes}}
{{Distinguish|Dispersal (disambiguation)|Dispersion (disambiguation)}}
{{Quote box
|title= IUPAC definition
|quote= <big>''Đ''<sub>M</sub> = ''M''<sub>w</sub>/''M''<sub>n</sub></big><br />where ''M''<sub>w</sub> is the mass-average molar mass (or molecular weight) and<br />''M''<sub>n</sub> is the number-average molar mass (or molecular weight).
|source= [https://doi.org/10.1351/PAC-REC-08-05-02 ''Pure Appl. Chem.'', '''2009''', 81(2), 351-353]
|align= right
}}[[File:Monodisperse Collection.svg|thumb|A uniform (monodisperse) collection]][[File:Polydisperse Collection.jpg|thumb|A non-uniform (polydisperse) collection]]

In [[chemistry]], the '''dispersity''' is a measure of the heterogeneity of sizes of molecules or particles in a mixture. A collection of objects is called '''uniform''' if the objects have the same size, shape, or mass. A sample of objects that have an inconsistent size, shape and mass distribution is called '''non-uniform'''. The objects can be in any form of [[dispersion (chemistry)|chemical dispersion]], such as particles in a [[colloid]], droplets in a cloud,<ref>{{Cite journal |last1= Martins |first1= J. A. |last2= Silva Dias |first2= M. A. F. |doi= 10.1088/1748-9326/4/1/015002 |title= The impact of smoke from forest fires on the spectral dispersion of cloud droplet size distributions in the Amazonian region |journal= Environmental Research Letters |volume= 4 |pages= 015002 |year= 2009 |issue= 1 |bibcode= 2009ERL.....4a5002M |url= http://mtc-m16c.sid.inpe.br/col/sid.inpe.br/mtc-m18@80/2009/04.06.13.52/doc/C__DOCUMENTS%20AND%20SETTINGS_DEICY_DADOS%20DE%20APLICATIVOS_Mozilla_Profiles_default_fupviiyp.pdf|doi-access= free }}</ref> crystals in a rock,<ref>{{cite journal
|url= http://www.uqac.ca/mhiggins/am_min_2000.pdf
|archive-url= https://web.archive.org/web/20170808215935/http://www.uqac.ca/mhiggins/am_min_2000.pdf
|url-status= dead
|archive-date= 2017-08-08
|title= Measurement of crystal size distributions
|last= Higgins
|first= Michael D.
|journal= American Mineralogist
|volume= 85
|year= 2000
|issue= 9
|pages= 1105–1116
|doi= 10.2138/am-2000-8-901
|bibcode= 2000AmMin..85.1105H
|s2cid= 101422067
}}</ref>
or polymer macromolecules in a solution or a solid polymer mass.<ref>{{Cite journal |last1= Okita |first1= K. |last2= Teramoto |first2= A. |last3= Kawahara |first3= K. |last4= Fujita |first4= H. |title= Light scattering and refractometry of a monodisperse polymer in binary mixed solvents |doi= 10.1021/j100847a053 |journal= The Journal of Physical Chemistry |volume= 72 |pages= 278–285 |year= 1968 }}</ref> Polymers can be described by [[molecular mass]] distribution; a population of particles can be described by size, surface area, and/or mass distribution; and thin films can be described by film thickness distribution.{{Citation needed|date=February 2012}}

[[IUPAC]] has [[deprecation|deprecated]] the use of the term '''''polydispersity index''''', having replaced it with the term ''dispersity'', represented by the symbol [[Đ#Chemistry|Đ]] (pronounced D-stroke<ref name="Stepto">Stepto, R. F. T.; Gilbert, R. G.; Hess, M.; Jenkins, A. D.; Jones, R. G.; Kratochvíl P. (2009). "[http://media.iupac.org/publications/pac/2009/pdf/8102x0351.pdf Dispersity in Polymer Science]" ''Pure Appl. Chem.'' '''81''' (2): 351–353. DOI:10.1351/PAC-REC-08-05-02.</ref>) which can refer to either molecular mass or degree of polymerization. It can be calculated using the equation ''Đ''<sub>M</sub> = ''M''<sub>w</sub>/''M''<sub>n</sub>, where ''M''<sub>w</sub> is the weight-average molar mass and ''M''<sub>n</sub> is the number-average molar mass. It can also be calculated according to degree of polymerization, where ''Đ''<sub>X</sub> = ''X''<sub>w</sub>/''X''<sub>n</sub>, where ''X''<sub>w</sub> is the weight-average degree of polymerization and ''X''<sub>n</sub> is the number-average degree of polymerization. In certain limiting cases where ''Đ''<sub>M</sub> = ''Đ''<sub>X</sub>, it is simply referred to as ''Đ''. IUPAC has also deprecated the terms ''monodisperse'', which is considered to be self-contradictory, and ''polydisperse'', which is considered redundant, preferring the terms ''uniform'' and ''non-uniform'' instead. The terms monodisperse and polydisperse are however still preferentially used to describe particles in an [[aerosol]].