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Structural changes of layered alkylsiloxanes during the reversible melting-solidification process
Kazuko Fujii1, Shigenobu Hayashi, Hideo Hashizume
1National Institute for Materials Science (NIMS), Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan. FUJII.Kazuko@nims.go.jp.
Physical Chemistry Chemical Physics : PCCP
|July 1, 2016
Summary
Layered alkylsiloxanes undergo reversible melting and solidification. Disordering of long alkyl chains causes melting, while their reordering upon cooling restores the original structure.
Area of Science:
- Materials Science
- Solid-State Chemistry
- Polymer Science
Background:
- Layered alkylsiloxanes (CnLSiloxanes) exhibit unique properties due to their structural organization.
- Understanding the phase transitions of these materials is crucial for their application.
Purpose of the Study:
- To investigate the structural changes during the reversible melting-solidification of CnLSiloxanes.
- To elucidate the role of alkyl chain conformation and ordering in these phase transitions.
Main Methods:
- In situ high-resolution solid-state carbon-13 nuclear magnetic resonance (NMR) spectroscopy at controlled temperatures.
- In situ X-ray diffraction (XRD) measurements at controlled temperatures.
- In situ high-resolution solid-state silicon-29 NMR spectroscopy.
Main Results:
- NMR analysis revealed significant conformational changes in alkyl chains during melting and solidification.
- X-ray diffraction showed a transition from ordered to disordered alkyl chain arrangements with increasing temperature.
- Silicon-29 NMR confirmed that the siloxane sheets remain structurally unchanged throughout the process.
Conclusions:
- The melting of CnLSiloxanes is driven by the disordering of their long alkyl chains.
- Reversible solidification occurs as the alkyl chains re-pack into an ordered, all-trans conformation upon cooling.
- The siloxane backbone structure remains intact during these reversible phase transitions.
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