Static Properties of a Simulated Supercooled Polymer Melt: Structure Factors, Monomer Distributions Relative to the Center of Mass, and Triple Correlation Functions

TL;DR

This study investigates the static structural properties of a simulated supercooled polymer melt, revealing that glassy behavior is driven by inter-chain monomer correlations rather than intra-chain or center-of-mass correlations, with detailed analysis of structure factors and triple correlations.

Contribution

It provides a comprehensive analysis of static structure factors and triple correlations in a supercooled polymer melt, highlighting the role of inter-chain correlations in glassy behavior and validating theoretical models like PRISM.

Findings

Center-of-mass structure factor remains unchanged upon cooling.

Inter-chain monomer correlations depend on temperature, influencing glass transition.

Chain connectivity does not significantly affect triple correlations.

Abstract

We analyze structural and conformational properties in a simulated bead-spring model of a non-entangled, supercooled polymer melt. We explore the statics of the model via various structure factors, involving not only the monomers, but also the center of mass (CM). We find that the conformation of the chains and the CM-CM structure factor, which is well described by a recently proposed approximation [Krakoviack et al., Europhys. Lett. 58, 53 (2002)], remain essentially unchanged on cooling toward the critical glass transition temperature of mode-coupling theory. Spatial correlations between monomers on different chains, however, depend on temperature, albeit smoothly. This implies that the glassy behavior of our model cannot result from static intra-chain or CM-CM correlations. It must be related to inter-chain correlations at the monomer level. Additionally, we study the dependence of inter-chain correlation functions on the position of the monomer along the chain backbone. We find that this site-dependence can be well accounted for by a theory based on the polymer reference interaction site model (PRISM). We also analyze triple correlations by means of the three-monomer structure factors for the melt and for the chains. These structure factors are compared with the convolution approximation that factorizes them into a product of two-monomer structure factors. For the chains this factorization works very well, indicating that chain connectivity does not introduce special triple correlations in our model. For the melt deviations are more pronounced, particularly at wave vectors close to the maximum of the static structure factor.