STRUCTURAL RELAXATION OF GLASS-FORMERS CONFINED TO SOL-GEL-TYPE POROUS GLASSES

We combine the results of dielectric relaxation spectroscopy and solva tion dynamics measurements for the glass-forming liquid 2-methyltetrah ydrofuran 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 exper iment is bound to sense macroscopic effects, whereas the solvation met hod probes the molecular dynamics on microscopic scales. When the tmep erature approaches the glass-transition at T-g upon cooling, an interf acial liquid layer with strongly frustrated dynamics grows in thicknes s and is thus able to block the connectivity among the pores. As a res ult the structural alpha-process is subject to an enhanced spatial res triction near T-g and a transition from constant pressure to constant volume conditions might occur as the pore connectivity becomes obstruc ted by immobile liquid.