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首页> 外文期刊>Crystal growth & design >The role of superheated water on the crystallization of N,N '-1,2-ethanediyl-bis(6-hydroxy-hexanamide): Implications on crystallography and phase transitions
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The role of superheated water on the crystallization of N,N '-1,2-ethanediyl-bis(6-hydroxy-hexanamide): Implications on crystallography and phase transitions

机译：过热水在N，N'-1,2-乙二基双（6-羟基己酰胺）结晶中的作用：对晶体学和相变的影响

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摘要

A symmetrical, hydrogen bonded low molecular weight molecule N,N'-1,2-ethanediyl-bis(6-hydroxy-hexanamide), crystallized from melt or from the superheated state of water, is examined. Thermodynamic and structural changes during phase transitions are followed by DSC, time-resolved X-ray techniques and polarized optical microscopy. Considering the hydrogen bonding motifs present in this bisamide-diol, it is selected as a model compound for crystalline domains present in semicrystalline polyamides. By studying this model Compound it was moreover aimed to elucidate the specific role of water molecules that are likely to reside in the crystals obtained from the superheated state of water. On heating the melt crystallized sample, the observed crystalline transitions are not the same as observed in polyamides. However, similar to polyamides the origin of the transition is due to the electron. exchange between the hydrogen bonding moieties and conformational changes in the aliphatic sequences. At low temperatures (below 22 degrees C) non-trans conformations in the central diamine methylene moieties induce a different triclinic structure, having unit cell parameters close to monoclinic, with potential existence of intersheet hydrogen bonding. Crystallization from superheated water entails remarkable differences in the physical behavior. A metastable crystalline structure, obtained from the superheated state of water and having relatively large interchain and intersheet distances, transforms into another hydrogen bonded crystal via sequential temperature cycles. When compared with the melt crystallized sample the crystal obtained after sequential temperature cycles show considerable difference in the crystal-to-crystal phase transition while melting remains the same. In combination with the increased crystal-to-crystal transition temperature, an expansion along the c-axis suggests a stabilizing effect of rigid hydroxylic protons that contribute to the unit cell pararneters.
机译：对对称的，氢键合的低分子量分子N，N'-1,2-乙二基-双（6-羟基-己酰胺）进行了研究，该分子从水的熔融态或过热态结晶。 DSC，时间分辨X射线技术和偏振光学显微镜观察相变过程中的热力学和结构变化。考虑到该双酰胺二醇中存在的氢键基序，选择它作为存在于半结晶聚酰胺中的结晶域的模型化合物。通过研究该模型化合物，其目的还在于阐明水分子的特定作用，这些水分子可能存在于从水的过热状态获得的晶体中。在加热熔融结晶的样品时，观察到的结晶转变与在聚酰胺中观察到的不同。然而，类似于聚酰胺，转变的起源是由于电子。氢键部分之间的交换和脂族序列的构象变化。在低温（低于22℃）下，中央二胺亚甲基部分中的非反式构象诱导了不同的三斜晶结构，其晶胞参数接近单斜晶，并且可能存在片间氢键。从过热水中结晶会导致物理行为发生显着差异。从水的过热状态获得的亚稳态晶体结构，具有较大的链间和片间距离，并通过连续的温度循环转变为另一种氢键结合的晶体。当与熔融结晶的样品相比时，在连续的温度循环后获得的晶体在晶体到晶体的相变中显示出相当大的差异，而熔融保持不变。结合增加的晶体到晶体的转变温度，沿c轴的扩展表明，刚性羟基质子的稳定作用有助于单位晶胞准直器。

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