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由模板的存在诱导的有机晶体非均相成核的机制。所研究的生长体系为以物理气相沉积制备的薄膜为模板的体溶液和添加高熔点疏水表面活性剂的水包油（0/W）乳液。采用同步辐射x射线束耦合DSC对同一样品的成核过程进行了原位观察，并对两者进行了同时分析。本研究中使用的有机物有不同碳数的正构烷烃、三酰基甘油和植物脂肪。结果表明：1)在正构烷烃乳液中，不添加模板剂，三斜晶可以成核；然而，在三斜晶形形成之前，伪六方正交晶形先成核。这是由于添加剂的模板膜在正链烷成核之前优先结晶所致。2)在三酰基甘油的O/W乳液中，α晶体在没有添加剂的情况下成核。然而，添加剂的加入诱导了β -原晶的成核。3)在体溶液中，模板薄膜的存在改变了材料的取向、多态和成核速率。上述结果用模板薄膜诱导非均相成核理论进行了讨论。通过高熔点疏水链的冻结，揭示了乳液中的模板效应。块体溶液中的模板效应表现出模板与新形成晶体的外延关系

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