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Confined crystallization of binary n-alkane mixtures: stabilization of a new rotator phase by enhanced surface
Dongsheng Fu1, Yufeng Liu, Guoming Liu
1Beijing National Laboratory for Molecular Sciences, Key Laboratory of Engineering Plastics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
Abstract:
The present work reports the confined crystallization behaviours of binary even-even normal alkane (n-alkane) mixtures of n-octadecane (n-C(18)H(38)) and n-eicosane (n-C(20)H(42)), which are microencapsulated in monodisperse microcapsules, using the combination of differential scanning calorimetry (DSC) and temperature-dependent X-ray diffraction (XRD). A new metastable rotator phase (RII) absent in the bulk state, has been detected for the n-alkane mixture in confined geometry under all the investigated compositions. Such a crossover is attributed to the lower interfacial energy due to the same in-planar hexagonal structure of the surface monolayer and RII, as well as the weakened intermolecular interaction in alkane mixtures. This is the first time that RII is found in such a binary even-even n-alkane mixture that neither of the components contains RII phase in the crystallization process. Furthermore, based on the variation of alkane molecule conformation and in-planar structure with temperature, the correlations between the phase transition temperature and composition have been discussed.
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