Conformations and Chain Dimensions of Poly(ethylene oxide) in Aqueous Solution: A Molecular Dynamics Simulation Study

Abstract

We have performed a molecular dynamics (MD) simulation study of the conformations and chain dimensions of poly(ethylene oxide) (PEO) in aqueous solution. Local conformations were found to depend on temperature and composition in agreement with spectroscopy; in particular, an increase in the C-C dihedral gauche (g) population with decreasing temperature and polymer concentration was observed. In concentrated solution chains were compact relative to the melt due to a decrease in the C-C g dihedral angle and an increase in C-C g population. With dilution chains became more extended. A rotational isomeric state (RIS) model was utilized to examine the influence of local conformations on the dimensions of ideal chains. The RIS chains did not extend with dilution, indicating that this effect is not attributable to changes in local conformations. Additionally, the dimensions of solution chains were found to depend only weakly on temperature despite changes in local conformations that significantly influence RIS chain dimensions. These differences between solution and ideal chains can be attributed to excluded volume and other chain extensional effects in solution. Finally, in contrast to previous simulations and interpretation of some experiments, no tendency for extended helical conformations of the PEO chains was observed despite the large O-C-C-O tgt conformer population. Its wide use, prototypical behavior and simple chemical structure make PEO an excellent candidate for experimental and simulation studies aimed at gaining a better understanding of polymer-water interactions. Our previous simulations revealed that the conformations of glyme and diglyme depend strongly upon temperature and solution composition. In order to determine if the same behavior holds for longer PEO chains and to investigate the influence of local conformations on PEO chain dimensions we have performed MD simulations of H—[ CH2–O–CH2— ] 12 H (PEO-530) using quantum chemistry based atomistic potentials