The hydrogen-bond network in propylene-glycol studied by Raman spectroscopy

In the present work, we report a polarized Raman study versus temperature of the complex O–H stretching vibrational band (3800–3000 cm−1) performed in a glass forming liquid, namely propylene-glycol (PG), with chemical formula given by H[OCH(CH3)CH2]OH. The spectra were collected in bulk and confined state within a sol–gel controlled porous glass having highly interconnected 25 Å diameter pores and characterized by a huge number of silanol groups (Si–OH), able to interact with PG molecules via hydrogen bond. The goal was to investigate how the hydrophilic nature of the surface influenced the molecular mobility of this hydrogen-bonded system, by monitoring intra- and inter-molecular host–host and host–guest interactions. The analysed O–H spectral region was decomposed into Gaussian symmetrical profiles, each of them associated to a well-defined aggregate, triggered by the presence of H-bond. Passing from the bulk state to the confined one, a clear change of the dynamical properties has been revealed and related to the interactions with the surface. The observed results were discussed on the basis of current models for associated liquids.