モノグリセリドの多形 (第2報) : 転移の熱力学的考察

概要

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In previous paper, the authors reported that, one exothermic peak was observed in the DTA curves of monolaurin and monomyristin by quenced sample, but such a phenomenon was not observed in monopalmitin and monostearin. In the present work, structure of this exothermic peak was elucidated by DSC and dilatometry using monomyristin. Examinations were also made on the relationship between free energy and temperature in polymorphism by determination of thermodynamic data from DSC. 1) Exothermic phenomenon in DSC is determined apparently by the competitive action of the transition rate from α-type or its fused state to β-type and melting rate to α-type. Therefore, contraction of the specific volume and exothermic peak appear when heating rate is slow. 2) Correlation among the melting point, melting enthalpy (ΔH), and melting entropy (ΔSm) decreases in the order of β>α>sub-α type, and the melting point is proportional to ΔH andΔSm. 3) Specific heat decreases in the order of α<sub-α>β ptype, and this showed the same tendency as well with the order of specific volume of each crystal system. 4) Relationship between free energy of polymorphism and temperature as indicated in Fig.-5, shows that sub-α type is more stable than α-type in temperature ranges below 36°C, and it was found that transition in this temperature range proceeds to β and β type without passing through α-type.