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题名: Two-Step Freezing in Alkane Monolayers on Colloidal Silica Nanoparticles: From a Stretched-Liquid to an Interface-Frozen State
作者: Gao, Xia1; Huber, Patrick2; Su, Yunlan1; Zhao, Weiwei1; Wang, Dujin1
刊名: JOURNAL OF PHYSICAL CHEMISTRY B
发表日期: 2016-08-04
卷: 120, 期:30, 页:7522-7528
收录类别: SCI
英文摘要: The crystallization behavior of an archetypical soft/hard hybrid nanocomposite, that is, an n-octadecane C-18/SiO2-nanoparticle composite, was investigated by a combination of differential scanning calorimetry (DSC) and variable-temperature solid-state C-13 nuclear magnetic resonance (VT solid-state C-13 NMR) as a function of silica nanoparticles loading. Two latent heat peaks prior to bulk freezing, observed for composites with high silica loading, indicate that a sizable fraction of C-18 molecules involve two phase transitions unknown from the bulk C-18. Combined with the NMR measurements as well as experiments on alkanes and alkanols at planar amorphous silica surfaces reported in the literature, this phase behavior can be attributed to a transition toward a 2D liquid-like monolayer and subsequently a disorder-to-order transition upon cooling. The second transition results in the formation of a interface-frozen monolayer of alkane molecules with their molecular long axis parallel to the nanoparticles' surface normal. Upon heating, the inverse phase sequence was observed, however, with a sizable thermal hysteresis in accord with the characteristics of the first-order phase transition. A thermodynamic model considering a balance of interfacial bonding, chain stretching elasticity, and entropic effects quantitatively accounts for the observed behavior. Complementary synchrotron-based wide-angle X-ray diffraction (WARD) experiments allow us to document the strong influence of this peculiar interfacial freezing behavior on the surrounding alkane melts and in particular the nucleation of a rotator phase absent in the bulk C-18.
语种: 英语
内容类型: 期刊论文
URI标识: http://ir.iccas.ac.cn/handle/121111/35238
Appears in Collections:工程塑料实验室_期刊论文

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作者单位: 1.Chinese Acad Sci, Beijing Natl Lab Mol Sci, Inst Chem, Key Lab Engn Plast, Beijing 100190, Peoples R China
2.Hamburg Univ Technol TUHH, Inst Mat Phys & Technol, Eissendorfer Str 42, D-21073 Hamburg, Germany
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