【摘要】 甘油三酯具有独特的同质多晶现象，其结晶和熔化特性对油脂产品性能及工业应用至关重要。利用正电子湮没寿命谱（PALS）可在原子尺度对结晶态甘油三酯的微观结构变化进行特征化描述。当正电子进入分子材料时，会与周围的电子形成电子偶素（电子-正电子的束缚态），其寿命反映了材料中空洞（自由体积）的大小。该文使用PALS首次研究了5种饱和脂肪酸甘油三酯的多晶性和晶型转变过程，包括甘油三月桂酸酯、甘油三肉豆蔻酸酯、三棕榈酸甘油酯、三硬脂酸甘油酯、花生酸甘油三酯。正电子数据和由其他表征手段得到的晶型变化规律很好符合。用正电子观察到更长分子链甘油三酯固相收缩成更稳定的晶型时有空洞形成，以及α晶在固-固转化过程中形成了2种β晶形态。更多还原

【Abstract】 Polymorphism is a specific feature of the triacylglycerols. The crystallization and melting properties are essential for the characteristics and industrial applications of fats. Positron annihilation lifetime spectroscopy(PALS) allows for the characterization of microstructural changes in triacylglycerol crystals at the atomic scale. When positrons enter molecular materials,they form positronium(electron-positron bound states) with surrounding electrons,whose lifetime reflects the size of molecular-voids(free volumes). In this paper,PALS was used to study the polymorphism and phase transition processes of five saturated monoacid triacylglycerides for the first time,including trilaurin,trimyristin,tripalmitin,tristearin and arachidin. The patterns of crystal phase transitions obtained from the PALS are in good agreement with those from other characterization methods. The positrons experiments revealed the formation of voids during the solid phase contraction of longer-chain triglycerides into more stable crystal forms,as well as the transformation from the α form into two β forms by solid-solid transformations.更多还原