The melting and clearing processes of the Schiff base nematogens, p-ethoxybenzylidene-p'-aminobenzonitrile (PEBAB) and p-pentyloxybenzylidene-p'-aminophenylbutanoate (PBAPB) were studied by DSC and hot-stage microscopy. The temps., heats and entropies of melting and transition were determine The melting enthalpy of mixture of the two compounds is 12.36 ?0.17 kJ/mol. It is independent of the heating rates which ranged from 1.25 to 20.00 K/min. According to the mean field theory, there is a relationship between the clearing enthalpies and the clearing points of the nematic materials, i.e. DH1/DH2 = T1/T2. The clearing entropies are close to those of most nematic materials. In the case of PBAPB, a solid-solid transition and others were observed in some samples heated doubly and kept at room temperature The enthalpy of solid-solid transition is equal to 13.96?.35 kJ/mol.

Key words: BENZENEBUTANOIC ACID P, THERMODYNAMIC PROPERTIES, ELECTRON-MICROSCOPIC ANALYSIS, LIQUID CRYSTAL, CARBOXYLIC ACID ESTER, PHASE TRANSFORMATION, ENTROPY, ENTHALPY, DIFFERENTIAL SCANNING CALORIMETRY, SCHIFF BASE