The Basics of Diffusion

Diffusion is so important to so many activities and applications that it is unfortunate that it is so little understood. This guide takes you from beginner to expert in just a few pages. Whether you are interested in food packaging (migration of bad things in or good things out), glove safety, skin permeation for cosmetics and pharma, environmental membranes or any other application where diffusion is important, you will find that four basic principles are all you need to master the subject:

  1. Fickian Diffusion
  2. Concentration Dependent Diffusion Coefficients
  3. Surface Resistance
  4. Diffusion Coefficients

Click on the Basics link to get started then carry on clicking to each in turn to grow your own understanding - you never get lost as the links are always there at the top and bottom.

One key aspect of diffusion is that a solvent that is highly compatible with a polymer will have a higher concentration in the outer few nm and therefore gives a larger concentration gradient to drive diffusion and will also, as we see in the Concentration Dependent app, give a larger diffusion coefficient. And because HSP are a good way to know how good a match there is between solvents and polymers, the HSP section in Practical Solubility is a good starting point. For a fuller understanding visit where you will find in-depth papers on diffusion theory and the HSPiP software, dataset and eBook package which includes a very powerful Diffusion modeller on which these apps are based.

About the Diffusion Apps

The Diffusion apps are written by Prof Steven Abbott and Dr Charles Hansen. The models have been verified against an extensive list of challenging diffusion cases across many academic and industrial applications.

YouTube Videos

Here are 9 videos that give a quick guide to the key themes of the book and this site. The app for the 5th is found in Practical Coatings.

Diffusion Basics

Fickian Diffusion

Concentration-Dependent Diffusion

Diffusion Coefficients