Diffusioesteet

Diffusioesteet, or diffusion barriers, refer to physical, chemical, or electrostatic features that impede the diffusion of molecules or ions within a system. They modify transport by lowering effective diffusivity, altering selectivity, or changing the pathways available for diffusing species.

Mechanisms of diffusion barriers can be categorized into several types. Physical barriers slow diffusion through limited porosity, increased thickness, or tortuous pathways that lengthen diffusion routes. Chemical barriers arise when diffusing species adsorb to surfaces or react with materials at interfaces, effectively trapping or retarding them. Electrostatic barriers occur at charged interfaces where Coulombic forces repel or attract certain ions, creating energetic hurdles to diffusion. Phase or interfacial barriers exist at boundaries where adjacent materials have markedly different diffusivities or affinities, producing a separation effect.

Diffusioesteet appear in diverse fields. In biology and medicine, cell membranes and intercellular junctions regulate paracellular and transcellular transport, while mucus layers act as viscous diffusion barriers. In materials engineering and electronics, diffusion barriers are deliberately employed to prevent interdiffusion between layers, for example in microelectronic stacks where materials such as titanium nitride (TiN), tantalum nitride (TaN), or aluminum oxide serve to block copper diffusion into silicon or dielectrics. In filtration and membrane science, polymer or inorganic barriers control gas or solvent permeation. In environmental science, soil layers and mineral boundaries can slow the spread of contaminants.

Assessment of diffusion barriers uses parameters like effective diffusivity and permeability, measured through tracer experiments, impedance methods, or time-lag analyses, and modeled with adaptations of Fick’s laws to account for interfaces and adsorption.