Binary n-Alkane Mixtures from Total Miscibility to Phase Separation in Microcapsules: Enrichment of Shorter Component in Surface Freezing and Enhanced Stability of Rotator Phases

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• 作者：Dongsheng Fu ; Yufeng Liu ; Xia Gao ; Yunlan Su ; Guoming Liu ; Dujin Wang
• 刊名：The Journal of Physical Chemistry B
• 出版年：2012
• 出版时间：March 15, 2012
• 年：2012
• 卷：116
• 期：10
• 页码：3099-3105
• 全文大小：495K
• 年卷期：v.116,no.10(March 15, 2012)
• ISSN：1520-5207

文摘

The crystallization behaviors of binary normal alkane (n-alkane) mixtures with a series of carbon number difference (denoted as 螖n), both in the bulk state and in nearly monodisperse microcapsules, have been investigated by the combination of differential scanning calorimetry (DSC) and temperature-dependent X-ray diffraction (XRD). As revealed by the DSC data, the surface freezing temperature (denoted as T_s) of spatially confined binary n-alkane mixtures with large 螖n is lower than the calculated value due to the enrichment of shorter component in the surface freezing phase. More alkane molecules with shorter carbon chain are located on the interface between the inner shell of microcapsules and the bulk mixture, thus leading to the decrease of the average chain length of the surface freezing phase and corresponding lower T_s. Furthermore, XRD results have proved that the enhanced surface freezing phenomenon can contribute to the stabilization of the rotator phases in n-alkane mixtures and even induce the crossover of some certain rotator phase (RII) from transient to metastable. However, the decisive reason for such stabilization or crossover is attributed to the suppression of the orienting movement of alkane molecules toward their next-nearest neighbors within the layer of rotator phases.