EFFECTS OF CONFINEMENT ON THE GLASS-TRANSITION TEMPERATURE OF MOLECULAR LIQUIDS

Effects of confinement on the glass transition of several molecular liquids in porous silica glasses were investigated by differential scanning calorimetry. The glass transition temperature, T(g), of liquid isopropylbenzene, glycerol, di-n-butyl phthalate, tert-butylbenzene, and n-butyl acetate confined to sol-gel silica glasses with pore radii in the range 18-152 angstrom was determined. For all liquids the confinement lowers the T(g) observed, and the Kelvin equation and the Ehrenfest relation were used in a phenomenological way to describe the observed trends of the glass transition with the pore size. A linear relationship between T(g) and the inverse of the pore radius, R, was observed. The relative temperature depression of the liquid-glass transition (DELTA-T/T(g)) due to confinement was found to be much smaller than that observed for freezing point depression.