Dispersity
In physical and organic 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 chemical dispersion, such as particles in a colloid, droplets in a cloud, crystals in a rock, or polymer molecules in a solvent. Polymers can possess a distribution of molecular mass; particles often possess a wide distribution of size, surface area and mass; and thin films can possess a varied distribution of film thickness. IUPAC has deprecated the use of the term
polydispersity index having replaced it with the term
dispersity, represented by the symbol
Đ which can refer to either molecular mass or degree of polymerization. It can be calculated using the equation
ĐM =
Mw/
Mn, where
Mw is the weight-average molar mass and
Mn is the number-average molar mass.