Knudsen Diffusion

Pore Interaction

Surface area and pore geometry dictate the speed at which gases pass through the material. When the pores are smaller than 50 nanometres, this specific type of diffusion becomes the dominant transport mode.

Permeability Factor

Designers of functional barriers use this principle to calculate the required thickness and density of a coating to block mineral oil migration. Adding mineral fillers can create a more tortuous path, effectively reducing the rate of Knudsen diffusion by forcing the molecules to travel further. The temperature of the environment also plays a role as it increases the velocity of the gas particles.

Measuring the air resistance of a paper grade provides an indirect indication of its pore structure. Successful barrier papers achieve very low diffusion rates even at thin applications. This ensures the safety of the packaged food over its entire shelf life.