Diffuuttinen

Diffuuttinen is a term used in Finnish to describe phenomena or processes governed primarily by diffusion—the net movement of particles from regions of high concentration to regions of lower concentration as a result of random thermal motion. In this sense, a system is considered diffuuttinen when diffusion is the dominant transport mechanism, rather than advection or bulk flow.

Fundamental principles governing diffuuttinen processes include Fick's laws. Fick's first law states that the diffusion flux J is proportional to the negative gradient of concentration: J = -D ∇C, where D is the diffusion coefficient and ∇C is the concentration gradient. In a homogeneous, isotropic medium, the time evolution of concentration C is described by Fick's second law: ∂C/∂t = D ∇^2 C. The rate and extent of diffusion depend on temperature, the nature of the medium, and the size and properties of the diffusing species.

Applications and examples span multiple fields. Diffusion occurs in gases (gas diffusion and mixing), liquids (solute diffusion in solvents), and solids (diffusion of atoms in metals and ceramics). In biology, diffusion underpins nutrient uptake and gas exchange, as well as the spread of substances such as neurotransmitters in the synaptic cleft. In materials science, diffusion controls processes including alloying, annealing, and polymer swelling.

Measurement and modeling typically involve determining D through tracer experiments or diffusion cells, and using numerical solutions of the diffusion equation to predict concentration profiles in porous media, tissues, or composite materials. Related concepts include advection, diffusion-limited processes, and Brownian motion.