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Unusual Interfacial Freezing Phenomena in Hexacontane/Silica Composites
Xia Gao1,2, Yunlan Su1,2, Weiwei Zhao1,2
1Beijing National Laboratory for Molecular Sciences, Key Laboratory of Engineering Plastics, Institute of Chemistry, Chinese Academy of Sciences , Beijing 100190, China.
The Journal of Physical Chemistry. B
|June 21, 2017
Summary
n-hexacontane molecules in silica composites exhibit unique interfacial freezing behavior. This phenomenon, driven by molecular attraction and increased interfacial molecules, differs from bulk crystallization.
Area of Science:
- Materials Science
- Physical Chemistry
- Polymer Science
Background:
- Understanding the behavior of long-chain alkanes confined within porous materials is crucial for designing advanced materials.
- The interaction between organic molecules and inorganic surfaces influences material properties and self-assembly.
Purpose of the Study:
- To investigate the crystallization behavior of n-hexacontane (C60H122) within Stöber silica (SiO2) composites.
- To elucidate the role of the silica interface on the phase transitions and molecular ordering of n-hexacontane.
Main Methods:
- Differential scanning calorimetry (DSC) to detect phase transitions.
- Solid-state 13C nuclear magnetic resonance (NMR) to probe molecular structure and dynamics.
- Proton NMR relaxation experiments to study molecular mobility.
- Grazing incidence X-ray diffraction (GIXRD) to determine molecular orientation.
Main Results:
- n-Hexacontane in silica composites displayed interfacial freezing, a phenomenon absent in bulk n-hexacontane.
- Grazing incidence X-ray diffraction confirmed preferential orientation of n-hexacontane molecules normal to the silica surface.
- Solid-state 13C NMR data indicated the interfacial monolayer exists in an orthorhombic phase with some chain disorder.
Conclusions:
- The observed "interfacial freezing" is attributed to strong intermolecular attraction and a higher concentration of molecules at the silica interface.
- Silica surfaces significantly influence the crystallization behavior and molecular ordering of n-hexacontane.
- These findings provide insights into the molecular-level interactions governing composite material properties.
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