In-situ observation of heterogeneous nucleation of organic crystals induced by templates with Synchrotron radiation X-ray techniques

本研究项目的主要目的是阐明模板的存在诱导有机晶体异相成核的机理。所考察的生长体系是以物理气相沉积制备的薄膜为模板的本体溶液和添加高熔点疏水表面活性剂的水包油(0/W)乳状液。用同步辐射X射线束对和差示扫描量热仪对同一样品进行了形核过程的原位观察。本工作中使用的有机物质是不同碳数的正构烷烃、三酰甘油和植物脂肪。结果表明：1)在由正构烷烃组成的O/W乳状液中，在没有模板添加剂的情况下，三斜晶成核。然而，伪六方正交晶核先于三斜晶型形核。这归因于添加剂的模板膜在正构烷烃成核之前优先结晶。2)在三酰基甘油制成的O/W乳状液中，没有添加剂的情况下，α晶体成核。然而，添加剂的添加诱导了β-原晶的形核。3)在溶液中，模板薄膜的存在改变了晶核的取向、多晶性和成核速率，并用模板膜诱导异相成核的理论对上述结果进行了讨论。通过冻结高熔点疏水链，揭示了乳液中的模板效应。大块溶液中的模板效应显示了模板与新形成的晶体的外延关系

The principal aim of this research project was to clarify the mechanisms of heterogeneous nucleation of organic crystals that were induced by the presence of templates. The growth systems examined were bulk solution in which thin films prepared by physical vapor deposition were put as the template, and oil-in-water (0/W) emulsion in which hydrophobic surfactants with high-melting points were added. The in-situ observation of the nucleation processes were done by using Synchrotron radiation X-ray beam couples with DSC, both were analyzed at the same time for the same sample. The organic substances employed in the present work were n-alkanes with different carbon numbers, triacylglycerols and vegetable fats. The following results were obtained1) In the O/W emulsion made of n-alkanes, triclinic crystals were nucleated without the template additives. However, pseudo-hexagonal-orthorhombic crystal was nucleated prior to triclinic polymorph. This is ascribed to the template films of the additives that were preferentially crystallized before the nucleation of n-alkanes2) In the O/W emulsion made of triacylglycerols, alpha crystals were nucleated without the additives. The addition of the additives, however, induced the nucleation of beta-prime crystals. This result was also interpreted with the help of the template films formed at the oil-in-water interface3) In the bulk solution, orientation, polymorphism and rate of nucleation were modified by the presence of the template thin filmsThe above results were discussed in a theory of heterogeneous nucleation Induced by the template films. The template effect in the emulsion was revealed by the freezing of the hydrophobic chains with high-melting points. The template effects in the bulk solution showed epitaxial relationships of the template and newly-formed crystals