Structural relaxation of glass-formers confined to sol-gel-type porous glasses

We combine the results of dielectric relaxation spectroscopy and solvation dynamics measurements for the glass-forming liquid 2-methyltetrahydrofuran spatially confined to the pores of sol-gel glasses with pore diameters phi = 2.5, 5.0, and 7.5 nm. Although both techniques probe the orientational polarization of the polar liquid, a dielectric experiment is bound to sense macroscopic effects, whereas the solvation method probes the molecular dynamics on microscopic scales. When the tmeperature approaches the glass-transition at T-g upon cooling, an interfacial liquid layer with strongly frustrated dynamics grows in thickness and is thus able to block the connectivity among the pores. As a result the structural alpha-process is subject to an enhanced spatial restriction near T-g and a transition from constant pressure to constant volume conditions might occur as the pore connectivity becomes obstructed by immobile liquid.