| Autor: |
Cadars, Sylvian, Mifsud, Nicolas, Lesage, Anne, Dirk Epping, Jan, Hedin, Niklas, F. Chmelka, Bradley, Emsley, Lyndon |
| Zdroj: |
The Journal of Physical Chemistry - Part C; May 2008, Vol. 112 Issue: 25 p9145-9154, 10p |
| Abstrakt: |
Surfactant-templated layered silicates are shown to possess complex compositional, structural, and dynamic features that manifest rich and interrelated order and disorder at molecular length scales. Temperature-dependent 1D and 2D solid-state 29Si NMR measurements reveal a chemical-exchange process involving the surfactant headgroups that is concomitant with reversible broadening of 29Si NMR line shapes under magic-angle-spinning (MAS) conditions at temperatures in the range 205−330 K. Specifically, the temperature-dependent changes in the 29Si transverse dephasing times T2′ can be quantitatively accounted for by 2-fold reorientational dynamics of the surfactant headgroups. Variable-temperature analyses demonstrate that the temperature-dependent 29Si shifts, peak broadening, and 2D 29Si{ 29Si} correlation NMR line shapes are directly related to the freezing of the surfactant headgroup dynamics, which results in local structural disorder within the silicate framework. |
| Databáze: |
Supplemental Index |
| Externí odkaz: |
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