Small polyethylene systems: On the ground state of single chains and few chain aggregates

T. Shakirov, W. Paul

Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, D-06099 Halle (Saale), Germany

The phase behavior of polyethylene has been under investigation for the last six decades. Investigation of single-chain crystallization in solution is a technically difficult problem, because in molecular dynamics simulations as well as in experiments, it is not so easy to distinguish kinetic and thermodynamic effects on chain folding. The general picture, however, is, that single polyethylene chains in solution fold into lamellar crystals. We present results of a Stochastic Approximation Monte Carlo (SAMC) simulation, which gives a possibility to analyze thermodynamical equilibrium properties of a system. Our simulation study of relatively short polyethylene chains is based on a chemically realistic united atom model [1]. Simulational results for low-energy states of single chains of different lengths demonstrate a set of various ground-state configurations: from stretched and hairpin-like configurations of short chains to a helix-like structure reeled round one of the chain’s ends. Aggregates of a few short polyethylene chains exhibit another set of ground states, depending on chain length and number of aggregated chains. However, with increasing chain length, single chain and aggregate morphologies become more similar.

[1] W. Paul, D.Y. Yoon, and G.D. Smith, J. Chem. Phys. 103, (1995) 1702 – 1709. (link)