The glass transition of organic liquids confined to small pores

Abstract

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 Å. 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, ΔT g, of benzyl alcohol in 40 Å and 85 Å pores was 7.2 K and 3.1 K, respectively. The magnitude of ΔT g also depends on the material; e.g. for o-terphenyl in the 85 Å pores, ΔT g was 8.8 K versus 3.1 K for benzyl alcohol. In general, it was noted that ΔT g was considerably less than for the depression of the crystalline melting point, ΔT m, studied in related work. For example, for benzyl alcohol in the 85 Å pores, ΔT m was ∼ 25 K and ΔT g was ∼ 3 K.