Hydrogen bonding in the Raman O–H stretching band of propylene glycol in nanometre-confined space: surface interactions and finite-size effects

Abstract

The O–H stretching vibration of propylene glycol (PG) has been investigated by Raman spectroscopy in the −15 to +60°C temperature range, in the bulk state and confined to the ∼26 Å pores of a controlled porous glass. By modifying the nature of the substrate (from hydrophilic to hydrophobic), we separated the surface-like and the finite-size contributions to the high-frequency vibrational dynamics of this glass-forming system. The spectra have been fitted by four Gaussian peaks associated with PG molecules exhibiting different H-binding states (i.e. non H-bonded, chain-end and doubly bonded). The T-dependencies of the peak wavenumbers and relative areas of the resolved components furnished a quantitative description of the role played by polymer–surface interactions and topological effects on the connectivity distribution of confined PG molecules.