Atomistic solvation structure of calcium ion in poly(vinyl alcohol) as studied by Molecular Dynamics simulation and X-ray Absorption Spectroscopy

Abstract

Molecular Dynamics (MD) simulation and the extended X-ray absorption fine structure (EXAFS) spectroscopy were employed to obtain the atomistic solvation structure of calcium (Ca2+) ion in poly(vinyl alcohol) (PVA). From MD simulation results, it is obvious that there is only one dominant shell from oxygen atoms around calcium ion. The distance between the calcium ion and oxygen atoms in the first shell is in good agreement with experiment within 0.1Å. For the Ca K-edge EXAFS spectrum of CaCl2/PVA sample, there is no evidence for the formation of significant numbers of Ca2+–Cl− contact ion pairs. Ca2+ ion can induce the conformational changes of PVA backbone compared to those of neat PVA. The MD and EXAFS technique is a powerful method to elucidate the detailed solvation structure of the probed ion in polymer matrix at the atomistic scale.