Melting of alkane nanocrystals: towards a representation of polyethylene

ABSTRACT

To simulate macroscopic properties at the molecular level, interfaces must be represented the most efficiently. In the study reported in this article, we use molecular dynamics (MD) simulation to reveal the impact of the environment around nanocrystals constituted of alkane chains on the melting temperature. The Gibbs-Thomson law was used to compare different simulated systems and experimental data. Based on thermodynamics argument, this law discloses the linear relationships between the melting, or crystallisation, temperature and the inverse of the crystal thickness. The crystal edges of simulated nanocrystals and the alkane chain length have been varied. For each nanocrystal, a simulated melting temperature (T_m) was obtained and reported with respect to the crystal thickness. The simulated enthalpy of fusion (Δh_m), surface (σ_e) and lateral (σ) free energies were thus extracted. All these properties have been compared to experimental data, and to properties stemming from nanocrystals in empty space. It is shown that nanocrystals surrounded by amorphous chains lead to values that agree better experimental data showing the great improvement in the model.

KEYWORDS:

• Polyethylene
• surface tension
• molecular dynamics
• nanocrystals
• Gibbs–Thomson law

Acknowledgements

The computational resources were provided by Calcul Québec and Compute Canada, through the financial support of the Canadian Foundation Innovation (CFI).and the Natural Sciences and Engineering Research Council of Canada (NSERC).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the Université de Sherbrooke, the Fonds Québécois de la Recherche sur la Nature et les Technologies (FRQNT) and Natural Sciences and Engineering Research Council of Canada.