The melting behavior of organic materials confined in porous solids

The solid–liquid phase transition temperatures and heats of fusion ΔHf of nonpolar organic solids confined in the pores of controlled pore glasses were measured by differential scanning calorimetry. The pore diameters d were in the range of 40–730 Å and the organics studied were cis-decalin, trans-decalin, cyclohexane, benzene, chlorobenzene, naphthalene, and heptane. In accordance with previous reports on studies of primarily inorganic materials, the melting point of the pore solid T(d) decreased with decreasing pore diameter. In addition, a large reduction in the bulk enthalpy of fusion ΔHf of the pore solid was measured, which apparently has not been studied in detail by other workers. A linear correlation was found between the melting point depression (ΔTm) and the reciprocal diameter, as predicted by theories of solidification in a capillary. The calculated values of the solid–liquid interfacial energy σsl were in reasonable agreement with values reported in the literature based on other methods of measurement.