jp7b00603_si_001.pdf (315.86 kB)
Unusual Interfacial Freezing Phenomena in Hexacontane/Silica Composites
journal contribution
posted on 2017-06-19, 00:00 authored by Xia Gao, Yunlan Su, Weiwei Zhao, Qingyun Qian, Xin Chen, Robert Wittenbrink, Dujin WangThe
crystallization behaviors of n-hexacontane (C60H122)/Stöber silica (SiO2) composites
with various compositions were investigated by a combination of differential
scanning calorimetry (DSC), solid-state 13C nuclear magnetic
resonance (solid-state 13C NMR), and proton NMR relaxation
experiments. By means of DSC, C60H122 molecules
in C60H122/silica composites were observed to
be involved in the interfacial freezing not present in the free bulk
C60H122. The orientation of C60H122 molecules, being preferentially normal to silica surface,
was confirmed by grazing incidence X-ray diffraction experiments on
thin n-hexacontane film adsorbed on the silicon wafer
with a native SiO2 layer. Inferred from the solid 13C NMR data, the interfacial monolayer is in orthorhombic
phase with certain chain disorders. It is speculated that the “interfacial
freezing” of C60H122 formed in the presence
of silica particles is driven by the combination of the strong attraction
between the molecules and the enhanced number of interfacial molecules
on the silica surface.