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H-2-solid state NMR and DSC study of isobutyric acid in mesoporous silica materials

Vyalikh, A. and Emmler, T. and Shenderovich, I. and Zeng, Y. and Findenegg, G. H. and Buntkowsky, G. (2007):
H-2-solid state NMR and DSC study of isobutyric acid in mesoporous silica materials.
9, In: Physical Chemistry Chemical Physics, (18), pp. 2249-2257, [Online-Edition: http://apps.webofknowledge.com/full_record.do?product=WOS&se...],
[Article]

Abstract

Solid state deuterium NMR has been used to study the molecular motion of d(6)-isobutyric acid (d(6)-iBA) in the pure (unconfined) state and confined in the cylindrical pores of two periodic mesoporous silica materials (MCM-41, pore size 3.3 nm and SBA-15, pore size 8 nm), and in a controlled pore glass (CPG-10-75, pore size ca. 10 nm). The line shape analysis of the spectra at different temperatures revealed three rotational states of the iBA molecules: liquid (fast anisotropic reorientation of the molecule), solid I (rotation of the methyl group) and solid II (no rotational motion on the time scale of the experiment). Transition temperatures between these states were determined from the temperature dependence of the fraction of molecules in these states. Whereas the solid I-solid II transition temperature is not affected by confinement, a significant lowering of the liquid-solid I transition temperature in the pores relative to the bulk acid was found for the three matrix materials, exhibiting an unusual dependence on pore size and pore morphology. Complementary DSC measurements on the same systems show that the rotational melting (solid I-liquid) of d(6)-iBA in the pores occurs at a temperature 20-45 K below the thermodynamic melting point. This. finding indicated that the decoupling of rotational and translational degrees of freedom in phase transitions in con. ned systems previously found for benzene is not restricted to molecules with non-specifi. c interactions, but represents a more general phenomenon.

Item Type: Article
Erschienen: 2007
Creators: Vyalikh, A. and Emmler, T. and Shenderovich, I. and Zeng, Y. and Findenegg, G. H. and Buntkowsky, G.
Title: H-2-solid state NMR and DSC study of isobutyric acid in mesoporous silica materials
Language: English
Abstract:

Solid state deuterium NMR has been used to study the molecular motion of d(6)-isobutyric acid (d(6)-iBA) in the pure (unconfined) state and confined in the cylindrical pores of two periodic mesoporous silica materials (MCM-41, pore size 3.3 nm and SBA-15, pore size 8 nm), and in a controlled pore glass (CPG-10-75, pore size ca. 10 nm). The line shape analysis of the spectra at different temperatures revealed three rotational states of the iBA molecules: liquid (fast anisotropic reorientation of the molecule), solid I (rotation of the methyl group) and solid II (no rotational motion on the time scale of the experiment). Transition temperatures between these states were determined from the temperature dependence of the fraction of molecules in these states. Whereas the solid I-solid II transition temperature is not affected by confinement, a significant lowering of the liquid-solid I transition temperature in the pores relative to the bulk acid was found for the three matrix materials, exhibiting an unusual dependence on pore size and pore morphology. Complementary DSC measurements on the same systems show that the rotational melting (solid I-liquid) of d(6)-iBA in the pores occurs at a temperature 20-45 K below the thermodynamic melting point. This. finding indicated that the decoupling of rotational and translational degrees of freedom in phase transitions in con. ned systems previously found for benzene is not restricted to molecules with non-specifi. c interactions, but represents a more general phenomenon.

Journal or Publication Title: Physical Chemistry Chemical Physics
Volume: 9
Number: 18
Uncontrolled Keywords: nuclear-magnetic-resonance pore-size distribution molecular-dynamics h-2 nmr neutron-scattering mcm-41 materials water spectroscopy surface diffusion
Divisions: 07 Department of Chemistry
07 Department of Chemistry > Physical Chemistry
Date Deposited: 27 Oct 2014 20:52
Official URL: http://apps.webofknowledge.com/full_record.do?product=WOS&se...
Additional Information:

166HE Times Cited:20 Cited References Count:42

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