monodispers

Monodispers is an adjective used in materials science and chemistry to describe a population of particles, molecules, or droplets whose sizes or molecular weights are nearly identical, resulting in a very narrow distribution. The term is commonly contrasted with polydisperse systems, which contain a broad range of sizes or weights. Monodispersity is particularly important in contexts where uniform behavior is required, such as in optical materials, self-assembly processes, and drug delivery vehicles.

In polymers, monodispers implies a single or nearly single molecular weight, reflecting a uniform chain length. In practice, true monodispersity is rare and often approximated by living polymerization methods. The more common designation is near-monodisperse, accompanied by a small polydispersity index (PDI). Measurement typically involves dynamic light scattering to assess size distribution, gel permeation chromatography for molecular weight distribution, and electron microscopy for direct sizing. A PDI in the low tens of percent range or below is frequently described as narrowly dispersed, though there is no universal threshold.

Production methods that yield narrowly dispersed populations include seed-mediated growth for nanoparticles (such as gold or silica spheres), controlled precipitation, and refined emulsion or precipitation polymerization. Microfluidic synthesis and other controlled-flow techniques can reduce variability further. Purification steps, such as size-selective precipitation or centrifugation, may also improve dispersity.

Applications of monodisperse or nearly monodisperse systems span catalysis, photonics, sensing, and biomedical delivery, where uniform particle behavior enhances performance and reproducibility. Limitations include the practical difficulty of achieving perfect monodispersity and the sensitivity of measurements to aggregation, aging, and experimental conditions.