THE GLASS-TRANSITION OF ORGANIC LIQUIDS CONFINED TO SMALL PORES

The glass-transition temperatures, T(g), of organic liquids confined to small pores were studied by differential scanning calorimetry (DSC). The T(g) was measured as a function of pore size in controlled pore glasses (CPG) having pore diameters in the range of 40-730 angstrom. The surface of the glass was treated with hexamethyldisilazane to promote wetting by the organic liquids studied (o-terphenyl and benzyl alcohol). Glasses formed in the pores had a lower T(g) than in the bulk and the reduction in T(g) increased as the pore size decreased. For example, the depression of the glass transition temperature, DELTA-T(g), of benzyl alcohol in 40 angstrom and 85 angstrom pores was 7.2 K and 3.1 K, respectively. The magnitude of DELTA-T(g) also depends on the material; e.g. for o-terphenyl in the 85 angstrom pores, DELTA-T(g) was 8.8 K versus 3.1 K for benzyl alcohol. In general, it was noted that DELTA-T(g) was considerably less than for the depression of the crystalline melting point, DELTA-T(m), studied in related work. For example, for benzyl alcohol in the 85 angstrom pores, DELTA-T(m) was approximately 25 K and DELTA-T(g) was approximately 3 K.