What is "dispersity"

n. 1 (context uncountable English) The state of being dispersed, of being a dispersion 2 (context countable English) The extent to which something is dispersed

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 (pronounced D-stroke) which can refer to either molecular mass or degree of polymerization. It can be calculated using the equation Đ = M/M, where M is the weight-average molar mass and M is the number-average molar mass. It can also be calculated according to degree of polymerization, where Đ = X/X, where X is the weight-average degree of polymerization and X is the number-average degree of polymerization. In certain limiting cases where Đ = Đ, 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.