Diffusion in polymers |

Posted by K.S.Rajan on

Hi All,

I need to calculate the diffusion of a two component mixture, being liquefied butane and propane through a carbon reinforced polyethylene vessel. I have heard that for multicomponent diffusion, Fick's law is not suitable and that the Maxwell-Stefan equation must be used, including the free volume theory for inclusion of plasticizing of the polyethylene matrix material. How does this work? How do I determine the chemical potential of butane and propane in the liquid phase and in the polyethyelene. The temperature is 40 degr. C and the pressure is 10 bar. Why can Fick's law not be used for diffusion calculations of butane and propane, which is almost an ideal mixture? Will butane and propane diffuse as one front or seperately, I hope the Maxwell-Stefan equation gives clear insight in this problem!

Thanks for your help.