Polymorphic trnanformtions during crytallization processes of fatty acid studied with FT-IR spectroscopy

摘要

Polymorphic crystallizaiton processes of fatty acids have been studie dwith FT-IR specroscopy, whcih is highly sensitive to strucural differences in funcional groups of a molecule. It has been found hat sructural changes take place during the crystallizaion of fatty acids. In the soltution crysalliaion of stearic acid, sinle crystals of the E form transofrm to the B form. This transforakmation sars with a heterogeneous nucleation ofhe B form on the {0 0 1} faces of the signle crystal of E, and the B domains spread to the shole region of teh single crystal through a solid-stae phase transition. In addtion, the polytypic transformation from a sinle-laeyr to a double-laeyr tructure takes place during the crystallization of the E form. In the melt crytallization of the β phase of oleic acid, th grwoth mechanism greatly changes with increasing supercooling (ΔT). In the condtion of Δ1.5 deg C, the crystakl edge grwos as β_1, while in the case of ΔT>1.5 deg C, the growth edge bgrew as β_2. initially, then changed gradually to β_1 through a solid-stae pahse transition. It was assumed that the lattice imperfections present in the ingsle crystals and the relaxation rae of structural changes at the grwoing faces are predominant facors for the polymorphic transormations to occur during crysalliation.ΔΔ