PERMEATION OF GASES ACROSS THE POLY(CHLORO-P-XYLYLENE) MEMBRANE

Gas permeabilities across poly(chloro-p-xylylene) (parylene C) films a re measured with different thicknesses of 20.2, 10.0, 8.9, 4.6, 3.4, a nd 1.0 mum. Measurements were carried out below 1 atm and between 10 a nd 80-degrees-C, which are under the glass transition temperature. The temperature and pressure dependencies of the permeability and the app arent diffusion coefficients were measured. If the membrane thickness is larger than 8 mum, the gas-transport mechanism is solution-diffusio n, which implies that it is pinhole-free, because the pressure depende ncy of the permeability cannot be found and the apparent activation en ergy of permeation and diffusion are observed. If the membrane thickne ss is less than 8 mum, the gas transport mechanism is pore flow combin ed with solution-diffusion flow because gas may penetrate both the por ous area and the polymer matrix. The thinner the membrane, the higher is the permeability coefficient, since the diameter and number of pore s increase with decrease of the membrane thickness. The gas permeabili ty coefficient has different values at the same pressure or temperatur e. As this film is in the glassy state, it should be explained using t he average ordering parameter (xi), which is a function of temperature , pressure, gas concentration, and time. (C) 1994 John Wiley & Sons, I nc.