PERMEATION OF WATER AND OTHER SMALL MOLEC ULES THROUGH POLYMERS

Corrosion at the interface of a metal and a polymer coating requires t ransport of water and oxygen through the coating. Permeation of small molecules is determined by their solubility S and their diffusion coef ficient D. Whereas at low contents of the dissolved molecules in the r ubbery state S and D do not depend on concentration c, they do so stro ngly in the glassy state. In this case S decreases with increasing c w hereas D increases such that the product, i.e. the permeability D S, r emains constant. In the present study a model will be presented which explains these experimental findings. Water molecules are an exception as a solute/solute interaction of the dipolar molecules plays already a strong role at low concentrations.