Composition-dependent multicomponent diffusivity of 2,5-lutidine with acetonitrile in polyurethane

Abstract

Evaluation and prediction of multicomponent diffusion in polymers is an important area of research since it occurs in several fields associated with mass transport including membrane separations, preparation of polymer films, and material decontamination. The functional dependence of the diffusivity on the composition in a multicomponent system is critical for accurately predicting transport in these processes. Here, the composition dependent diffusivity of 2,5-lutidine in polyurethane with acetonitrile as a co-penetrant was experimentally determined using Fourier transform infrared spectroscopy (FTIR) to acquire differential sorption curves for lutidine across the composition space and fitting a multicomponent diffusion model to the data. The free volume theory of diffusion was used to develop a mathematical expression for the composition-dependent diffusivity, and shows good agreement with the experimental data for both single and multicomponent cases. The lutidine diffusivity was found to vary up to two orders of magnitude with ACN concentration, and the importance of capturing this dependence quantitatively is highlighted by applying the multicomponent diffusion model with the best-fit values to predict previously published data for lutidine desorption from polyurethane.