Diffusional and vibrational dynamics of confined ethylene glycol and homologous systems: a light and neutron scattering investigation

Abstract

The understanding of new phenomena arising in confined condensed matter is important for the physics of interfaces and finite systems. This has stimulated intensive research on solids, liquid crystals and liquids confined in different geometries. Experimental techniques and theoretical approaches have shown that a liquid confined to a region that approaches molecular dimension exhibits dynamic and thermodynamic properties strongly changed relatively to the bulk with increasing geometrical confinement. This was interpreted by geometric as well as absorption effects: the first ones are related to the tortuosity of the interconnected channel for diffusion, the second ones take into account the degree of adsorption of molecules on the active inner surface sites. We present a detailed study of the reorientational, vibrational and diffusional dynamics of ethylene glycol (EG: OH–CH 2CH 2OH), ethylene glycol monomethyl ether (EGmE: CH 3–OCH 2CH 2OH) and ethylene glycol dimethyl ether (EGdE: CH 3–OCH 2CH 2OCH 3), in the bulk state and confined in a matrix of sol–gel porous glass with 26 Å interconnected cylindrical pores. This investigation has been performed by means of Rayleigh wing (as far as reorientational dynamics is concerned), Raman (as far as vibrational dynamics is concerned) and Incoherent Quasi Elastic Neutron Scattering (as far as diffusional dynamics is concerned). The clear influence of the confinement on the mobility of the studied liquids, with a dramatic frozen-in effect with respect to the bulk state, is evidenced.