Diffusion of m‐nitroaniline into polyacylonitrile

The diffusion of nonionic penetrant, m ‐nitroaniline, into polyacrylonitrile was studied in detail on a range of temperature from 50.6°C to 95.0°C. The penetrant distribution in polymer is Fickian, which is different from that of cationic dye, Malachite Green reported earlier. The diffusion coefficient D increases with the rise of temperature. The sharp inflection point (72°C) of the Arrhenius plot, log D versus 1/ T , corresponds to T g of polyacrylonitrile in the presence of water, which is lower than that measured in the dry state by a dynamic mechanical testing method. The activation energy is constant below T g (ca. 10 kcal/mole), suddenly reaches a maximum at T g and then gradually decreases with increasing temperature. General trends of Arrhenius plot for different polymer–penetrant systems are discussed. The temperature dependence of penetrant diffusion above T g can be described by a general form of the WLF equation, log a T = log ( D Tg / D T ) = − C 1 g ( T − T g )/( C 2 g + T − T g ), where the values of C 1 g and C 2 g were calculated to be 4.03 and 24.54, respectively. A comparison was made between m‐ nitroaniline and Malachite Green. The difference in the respective T g and the constants C 1 g and C 2 g of the WLF equation in polyacrylonitrile is attributed to the size of the penetrants and their ionic character. The surface concentration increases below T g and decreases above T g with rise in temperature.