diffussivity

Diffusivity is a material property that quantifies the rate at which a substance diffuses through another. It is a measure of how quickly particles spread out from an area of high concentration to an area of low concentration due to random molecular motion. The concept is fundamental in understanding transport phenomena in physics, chemistry, and engineering. Mathematically, diffusivity is often represented by the symbol D and has units of area per time, such as square meters per second (m²/s) or square centimeters per second (cm²/s).

Higher diffusivity indicates a faster rate of diffusion. Factors influencing diffusivity include temperature, the size and shape of the diffusing particles, and the properties of the medium through which diffusion occurs. For example, gases generally have higher diffusivities than liquids, which in turn have higher diffusivities than solids. In the context of Fick's laws of diffusion, diffusivity relates the flux of diffusing particles to the concentration gradient. It plays a crucial role in processes like mass transfer, heat transfer, and the movement of charge carriers in semiconductors.