Thermal and vibrational investigation of crystal nucleation and growth from a physically confined and supercooled liquid

Differential scanning calorimetry and temperature-dependent Raman-scattering investigation of 2,4,6 trinitrotoluene (TNT) confined in four different pore-sized silica hosts have been conducted. The results suggested that (i) nucleation occurs at the pore center rather than at the pore walls; (ii) although the freezing transition of the bulk has a volume reduction of about 10%, the freezing transition of the confined phase maintains its interconnectivity; (iii) that TNT confined in 10-nm pores without bulk on the outer surface shows no freezing transition upon cooling and shows recrystallization and melting transitions upon heating suggests that the characteristic curves of nucleation and growth are modified resulting from the surface and physical confinement effects. In addition, our Raman study suggests that (i) the freezable confined TNT retains the similar solid structure to its bulk; (ii) the TNT physically confined in dₚ{≤}5-nm pores may exist in a cluster form. {} 1996 The American Physical Society.