Interdiffusion of small molecules into a glassy polymer film via coarse-grained molecular dynamics simulations

Publication date: 21 April 2017
Source:Polymer, Volume 115
Author(s): Enqiang Lin, Xiaorong You, Robert M. Kriegel, Ronald D. Moffitt, Romesh C. Batra
The interdiffusion of the C8, the C9 and the C10 aldehyde molecules into a glassy uncrosslinked polymer film composed of four components is studied by using coarse-grained (CG) molecular dynamics simulations. Effects of the aldehyde molecule size, water and temperature on the interdiffusion processes are probed. It is found that (i) the interdiffusion generally follows the smaller-the faster rule with the smallest C8 aldehydes diffusing fastest into the polymeric film, (ii) the water molecules significantly affect the adsorption and the initial interdiffusion of the aldehyde molecules onto/into the polymer film, (iii) the interdiffusions are strongly temperature dependent as the higher temperature enhances the initial dynamics of the aldehyde-polymer systems, (iv) the computed aldehydes diffusivities are highly concentration-dependent and increase with an increase in the concentration, and (v) the aldehydes density profiles scale as t0.5 in the polymer-rich regions, and are well described by the Fickian diffusion with a constant diffusivity. Here t is the time of diffusion. Even though only relative values of the diffusivity coefficients can be predicted via the CG simulations, this work suggests that this approach is very useful in guiding the design and the selection of polymeric films with a tailored barrier property. Furthermore, it enables one to analyze small molecules-polymer interdiffusions into a polymeric film that is difficult to study experimentally but is of technological importance.

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