Determining limonene diffusion in molten polyethylene from within 0.1 mu s molecular dynamics trajectories

• Molecular dynamics simulations of the diffusion of limonene into molten polyethylene were performed in order to explore the possibility of using atomistic simulations to predict the diffusion of larger solute molecules in polymers. The system contained 6000 anisotropic united atom methylene units with a molar mass of 84 000 g mol(-1). A united atom limonene molecule (C10H16) was introduced into the polyethylene matrix. Limonene trajectories were generated for 2-100. ns at 77-227 degreesC. The simulated diffusivities were compared with experimental zero-concentration diffusivities of limonene in natural rubber and ultrahigh molar mass polyethylene, obtained from desorption measurements in the same temperature range. The simulated diffusivities and activation energy were within 30%. and 16% of the experimental thermodynamic diffusivities and activation energies, respectively. The simulated average diffusivities, obtained from 10 trajectories, changed by only 33% when the simulation time was shortened from 100 ns to 500 ps. The limonene molecule vibrated in a cagelike fashion on a 1-2 ps scale, whereas on a larger time scale the jumping was liquidlike. The limonene molecule showed tumbling during its motion through the polyethylene matrix.

Nyckelord

penetrant diffusion

amorphous polymers

simulation

polypropylene

coefficients

desorption

mechanism

sorption

melts

films

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