THE MELTING BEHAVIOR OF ORGANIC MATERIALS CONFINED IN POROUS SOLIDS

The solid-liquid phase transition temperatures and heats of fusion DELTA-H(f) 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 angstrom 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 DELTA-H(f) 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 (DELTA-T(m)) and the reciprocal diameter, as predicted by theories of solidification in a capillary. The calculated values of the solid-liquid interfacial energy sigma(sl) were in reasonable agreement with values reported in the literature based on other methods of measurement.