Two-Dimensional Subnanometer Confinement of Ethylene Glycol and Poly(ethylene oxide) by Neutron Spectroscopy: Molecular Size Effects

We explore the effects of chain size on the structure and dynamics of ethylene glycol (EG) and poly(ethylene oxide) (PEO) intercalated in graphite oxide (GO). To this end, EG as well as a PEO series of increasing chain length have been studied by means of high-resolution inelastic neutron spectroscopy. The neutron experiments are complemented by X-ray diffraction, differential scanning calorirnetry, Fourier-transform infrared spectroscopy, and Raman scattering. We find that EG is accommodated in a layer of thickness similar to 3 angstrom within the GO substrate and adopts a preferential, yet largely disordered, gauche conformation. Longer PEO chains give rise to a layer thickness in the range similar to 3.0-3.4 angstrom characterized by planar zigzag (trans trans trans) conformations. Moreover, we observe a strong reduction of vibrational motions for the confined EG and polymer phases, as clearly evidenced by the disappearance, shift, and/or broadening of mode-specific inelastic neutron scattering spectral features, as well as by the complete suppression of crystallization. All of these effects are surprisingly insensitive to the length of the PEO chains.