Difusioon

Difusjon, also known as diffusion, is the net movement of particles from regions of higher concentration to regions of lower concentration as a result of their random thermal motion. It occurs in gases, liquids and solids and leads to a gradual mixing and an approach to uniform distribution when barriers are removed. In gases diffusion is typically fast due to high molecular mobility; in liquids it is slower; in solids it proceeds mainly through defects in the crystal lattice and is usually slow.

Two main descriptions are used to quantify diffusion. Fick's laws provide a framework for the rate and distribution of diffusing species. Fick's first law states that the diffusive flux J is proportional to the negative gradient of concentration: J = -D (dC/dx), where D is the diffusion coefficient. Fick's second law describes how concentration changes with time: ∂C/∂t = D ∂^2C/∂x^2 for simple one-dimensional diffusion. The diffusion coefficient D depends on temperature, solvent, and the size and interactions of the diffusing particles; it often follows an Arrhenius-type relation, D = D0 exp(-Ea/RT).

Diffusion plays a central role in chemistry, physics, biology and environmental science. In biology, simple diffusion and facilitated diffusion allow gases and small molecules to cross membranes without energy input, while larger or charged species may require channels or transport proteins. In materials science, diffusion governs alloying, sintering and corrosion processes. Real-world examples include perfume spreading in a room, ink diffusing in water, and oxygen diffusing from alveoli into blood. Diffusion is distinct from active transport and convective transport, as it proceeds due to concentration differences rather than direct energy-driven movement.