Dispersiteetti

Dispersiteetti is a term used in polymer and colloid science to describe the breadth or width of a distribution of sizes or molecular weights within a sample. It provides a measure of how uniform or heterogeneous the sample is, and it depends on what is being distributed (molecular weight, particle size, etc.).

In polymer science, dispersiteetti is commonly expressed by the dispersity (Đ), often defined as the ratio of weight-average molecular weight to number-average molecular weight (Đ = Mw/Mn). Mn represents the average molecular weight of the polymer chains, while Mw gives more weight to heavier chains. A perfectly uniform, monodisperse sample has Đ = 1.0; real polymers have Đ greater than 1.0. Typical synthetic polymers exhibit Đ values above 1.0, with higher Đ indicating broader molecular-weight distributions. Materials made by controlled or living polymerization aim for Đ closer to 1.0, whereas conventional processes tend to produce broader distributions.

In colloidal systems, dispersiteetti relates to the width of the particle size distribution within the suspension. It is often discussed in terms of the polydispersity or the polydispersity index (PDI) obtained from measurements such as dynamic light scattering, nanoparticle tracking analysis, or electron microscopy. A low PDI indicates a narrow size distribution, while a high PDI indicates a broad distribution. Measurements and definitions can vary with the technique used.

Measurement and interpretation: molecular-weight distributions are commonly determined by gel permeation chromatography (GPC/SEC), giving Mn, Mw, and Đ. Particle size distributions are derived from imaging or light-scattering techniques, and are influenced by sample preparation and measurement method. Dispersiteetti affects material properties such as rheology, mechanical strength, stability, and processing behavior, making it a key parameter in polymer and colloid design.