The role of superheated water on the crystallization of N,N′-1,2-ethanediyl-bis(6-hydroxy-hexanamide): Implications on crystallography and phase transitions

Jules A.W. Harings, Otto Van Asselen, Robert Graf, Rene Broos, Sanjay Rastogi

Research output: Contribution to journalArticlepeer-review

10 Scopus citations

Abstract

A symmetrical, hydrogen bonded low molecular weight molecule N,N′-1,2-etrianediyl-bis(6-riydroxy-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 °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 parameters. © 2008 American Chemical Society.
Original languageEnglish (US)
Pages (from-to)2469-2477
Number of pages9
JournalCrystal Growth and Design
Volume8
Issue number7
DOIs
StatePublished - Jul 1 2008
Externally publishedYes

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