Monodispersity refers to the amount of uniformity in the size and shape of a set of objects. This can apply to a number of relevant systems in soft matter including polymer molecules and multi-phase systems. For instance, drops of oil emulsified in a continuous water phase can be either monodisperse, having the same volume, or polydisperse, having a range of different volumes.
The polydispersity index of a set of objects can be measured by examining the quantity of interest and taking the ratio of its standard deviation to its mean. The lower the polydispersity index, the higher the monodispersity of the objects. Identical objects or perfectly monodisperse objects will have a polydispersity index of zero percent.
An example of monodispersity is shown on the right. Each of these bubbles has the same size, composition, and dimensions so the bubbles can be called monodisperse.
- Garstecki, P., Gitlin, I. DiLuzio, W., Kumacheva, E., Whitesides, G.M., & Stone, H.A. "Formation of monodisperse bubbles in a microfluidic flow-focusing device." Appl. Phys. Lett. (2004). Vol. 85(13), pp. 2649-2652.