Diffusié

Diffusié is a term used in theoretical and applied contexts to denote a diffusion-like transport process driven predominantly by gradients of chemical potential or concentration. In contrast to classical Fickian diffusion, diffusié is frequently nonlinear and can involve concentration-dependent diffusivity and coupling to other driving forces such as temperature, electric fields, or hydrodynamic flows.

Mathematically, diffusié is described by generalized diffusion equations in which the flux depends on local concentration in a nonlinear way. A common form is ∂C/∂t = ∇·[D(C) ∇C] plus additional terms for advection or cross-diffusion. In many models, D varies with C, leading to phenomena such as shock-like fronts or self-stabilizing profiles. Diffusié can also encompass diffusiophoresis and chemotaxis, where gradients produce movement through interactions with the medium.

Origins and usage: The term is not part of standard, widely adopted terminology and appears mainly in niche theoretical discussions and some experimental models of non-ideal mixtures, porous media, and active matter. It is often used as a shorthand for diffusion under non-ideal or gradient-driven conditions, rather than a separate, universally defined mechanism.

Applications and scope: Diffusié-type models are used to describe transport in porous solids, gels, electrolytes, and polymer networks where interactions modify diffusion, as well as in biological contexts where concentration or chemical potential gradients bias movement of ions or metabolites. Related concepts include classical diffusion, nonlinear diffusion, cross-diffusion, and diffusiophoresis.