Polydisperse
Definition and meaning of Polydisperse in chemistry.
Polydisperse refers to a mixture or sample consisting of particles, droplets, or macromolecules that vary significantly in size, shape, or molar mass.
In more detail
In polymer chemistry and colloidal science, absolute uniformity is quite rare in practice. Most synthetic polymers and natural dispersions contain a broad range of molecular weights or distinct particle sizes. The degree of non-uniformity within a given sample is typically quantified by the dispersity index, which is calculated as the ratio of the weight-average molar mass to the number-average molar mass. A dispersity index strictly equal to one indicates a perfectly uniform, monodisperse system.
Key facts
| Field | Physical Chemistry |
|---|---|
| Measurement | Dispersity index |
| Formula Example | (C2H4)n |
A typical synthetic batch of polyethylene is highly polydisperse because the individual polymer chains terminate at different times during synthesis, resulting in varying chain lengths and differing molecular weights.
Frequently asked questions
How does polydispersity affect material properties?
A broader distribution of molecular weights can lead to lower tensile strength but better processability compared to highly uniform polymers.
What analytical technique measures polydispersity?
Size-exclusion chromatography or gel permeation chromatography is commonly used.