Diffuusi

Diffuusi is a term used in Finnish to describe diffusion, the passive spread of particles from regions of higher concentration to regions of lower concentration due to random thermal motion. In scientific contexts, diffusion is formalized by Fick’s laws and the diffusion equation. The first law states that the diffusive flux is proportional to the negative concentration gradient; the second law describes how concentration evolves over time, enabling modeling of diffusion in gases, liquids, and solids.

Diffusion can occur without bulk movement, but it is influenced by temperature, medium properties, and the size of diffusing species. The diffusion coefficient, D, quantifies the ease of diffusion and generally increases with temperature and decreases with viscosity or particle size. In liquids, smaller molecules diffuse faster; in solids, diffusion often proceeds via vacancies or interstitial mechanisms and is typically slower. The Stokes–Einstein relation provides a common estimate of D for small particles in liquids.

Biological and technological relevance is broad. In biology, diffusion drives gas exchange, nutrient uptake, and the passive movement of drugs and signaling molecules across membranes. In materials science, diffusion controls alloying, sintering, and semiconductor doping. In environmental science, diffusion contributes to the initial spread of pollutants when convective transport is limited.

Related concepts include osmosis, the diffusion of water across membranes, and the distinction between diffusion and dispersion, where the latter involves spreading due to velocity variations. In Finnish usage, diffuusi often appears as an adjective describing processes or states that pertain to diffusion or diffusional spreading.