Short-Range Order in Polyethylene Melts: Identification and Characterization

Abstract

Experimental results by Fisher et al. [Faraday Discuss. Chem. Soc. 1979, 68, 26] showed the existence of local orientational correlations of segments of the n-alkane molecules in the liquid state. Since the estimated correlation volume is below 103 A3, molecular dynamics simulations appear to be a suitable method for their identification and characterization. We used molecular dynamics to fully characterize short-range order in polyethylene melts. The characterization started by identifying sequences of aligned segments in chains, each one having at least one Kuhn monomer in length. Afterward, a search was made for interactions of a tagged aligned chain segment with others fulfilling the same condition, laying within a limiting separation distance (18 A) and making a limiting orientation angle (40°). When, at least, four interactions are counted, a short-range ordered region is defined. Chain placement in these regions has similarities to that of the unit cell at the solid phase, although with different s...