SOLID-PHASE NUCLEATION OF BULK AND DISPERSED 3-METHOXY-4-HYDROXYBENZALDEHYDE

Studies of the solid-phase nucleation of molten 3-methoxy-4-hydroxyben zaldehyde (vanillin) were performed either on bulk (a few cubic millim eters) or on emulsified (cubic microns) samples. The results obtained from macroscopic observations and differential scanning calorimetry ha ve pointed out undercooling phenomena characterized by roughly the sam e order of undercooling degrees Delta T = T-m - T-s (T-m, melting temp erature; T-s, the most probable solidification temperature) for steady cooled (-3 degrees C/min) bulk and emulsified samples, namely, Delta T approximate to 43 degrees C. At a fixed temperature, the solidificat ion of the dispersed droplets can be described by an S-shaped curve th at has been interpreted in terms of a polynuclear mechanism. Finally, the decrease of the undercooling degree exhibited after a solidificati on-melting process has been explained by the formation of nucleating s ites at the liquid-emulsifying medium interface.