Dielectric Studies of the Glass Transition in Porous Media

Dynamic processes in liquid propylene glycol and two of its oligomers inside the ≅ 100 Å pores of controlled porous glasses have been investigated as a function of temperature by dielectric spectroscopy. We find that geometrical restriction results in retardation and broadening of the inherent $\alpha$ relaxation. This retardation is most pronounced for the monomer liquid and gives rise to an increase in the glass transition temperature by $\Delta T_G=+4.5\mathrm{}$ K. We also observe a second slower relaxation process for all liquids, ascribed to the hindered dynamics of molecules affected by the surface.