Effect of penetrant size and shape on its transport through a thermoset adhesive: I. n-alkanes

The diffusion behaviors of a series of n-alkanes, ranging from C6 to C17, through a polyamide-type polymeric matrix have been investigated by means of mass uptake measurements. Since n-alkanes are known to display negligible interactions with the polymer matrix, this study serves to isolate the effects of penetrant size and shape on the transport process without undue interference from polymer–penetrant interactions. It is established that the diffusion of the n-alkanes through the polymer matrix studied is Fickian and proceeds via a Henryʹs law-type mechanism. The diffusion coefficients, D, are evaluated based on a thin-film approximation of the Fickian equation. The activation energies of diffusion, Ed, are determined from the temperature dependence of D, using the Arrhenius equation. Correlations between the Arrhenius terms, Ed and D0, are also established which enable the prediction of diffusion coefficients for similar polymer–penetrant systems. It is also demonstrated by means of activation energy calculations and molecular simulations that the n-alkanes assume a linear geometry within the polymer matrix and diffuse along their long axes.