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 calorimetry, Fourier-transform infrared spectroscopy, and Raman scattering. We find that EG is accommodated in a layer of thickness ∼3 Å 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 ∼3.0–3.4 Å 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