Diffusion Coefficients

The chief difficulty with any diffusion scenario is finding the diffusion coefficient, D. One approach is to follow a method approved by US and European regulatory bodies which provides a set of standard polymers and estimates D from the MWt of the molecule and the temperature, T (°K), for the specific scenario. The formula is:

D=10⁴exp(A-C₁MWt^0.666+C₂MWt-C₃/T) cm²/s

C₁=0.135, C₂=0.003, C₃=10454. A in turn depends on T and two polymer specific terms, A* and τ:

A=A*-τ/T

When you choose a polymer the A* and τ values are shown and from your given MWt and T, D is calculated

Although this formula is often used in food packaging applications, be aware that this app carries no guarantees that the calculated D values are correct. For example, the linear, branched and cyclic versions of a molecule with the same molecular weight will each have different D values; branched and cyclic molecules have lower D values than linear ones.