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Titolo:
A multinuclear magnetic resonance study of pivalic acid in porous silica
Autore:
Aksnes, DW; Gjerdaker, L; Kimtys, L;
Indirizzi:
Univ Bergen, Dept Chem, N-5007 Bergen, Norway Univ Bergen Bergen Norway N-5007 ergen, Dept Chem, N-5007 Bergen, Norway Vilnius State Univ, Dept Phys, LT-2734 Vilnius, Lithuania Vilnius State Univ Vilnius Lithuania LT-2734 LT-2734 Vilnius, Lithuania
Titolo Testata:
JOURNAL OF MOLECULAR STRUCTURE
, volume: 522, anno: 2000,
pagine: 209 - 218
SICI:
0022-2860(20000411)522:<209:AMMRSO>2.0.ZU;2-P
Fonte:
ISI
Lingua:
ENG
Soggetto:
MOLECULAR-MOTION; SELF-DIFFUSION; PROPANOIC ACID; PLASTIC PHASE; RELAXATION; GRADIENTS; MEDIA;
Keywords:
porous silica; confined pivalic acid; dynamic NMR; relaxation; diffusion;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
28
Recensione:
Indirizzi per estratti:
Indirizzo: Aksnes, DW Univ Bergen, Dept Chem, Allegt 41, N-5007 Bergen, Norway Univ Bergen Allegt 41 Bergen Norway N-5007 5007 Bergen, Norway
Citazione:
D.W. Aksnes et al., "A multinuclear magnetic resonance study of pivalic acid in porous silica", J MOL STRUC, 522, 2000, pp. 209-218

Abstract

In this work, the molecular dynamics of pivalic acid ((CH3)(3)C2O2H) (PA) confined in silica pores of nominal diameter 6 and 20 nm were studied in the temperature range 145-360 K using high field (9.4 T) NMR. The H-1, H-2 and C-13 line-widths, relaxation times (T-1,T-2) and self-diffusion coefficients are reported as a function of temperature, and the results are comparedto old and new data obtained for the bulk material. The confinement in thepores gives rise to substantial changes in the phase behaviour and molecular dynamics. The H-1 line shape and line width observations of PA confined in the 20 and 6 nm pores clearly reveal a narrow-line component superimposed on a broad resonance at temperatures well below the transition point of bulk PA. We suggest that the narrow-line component largely originates from the surface layer and the undercooled plastic phase in the smaller pores, while the broad-line component is attributed to the ordered solid in the larger pores. The persistent surface layer does not appear to crystallise at all. Indeed, a high diffusion rate of the liquid-like molecules at the pore walls is observed over a wide temperature range, even 20 K below the transition point of the bulk material. (C) 2000 Elsevier Science B.V. All rights reserved.

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Documento generato il 30/09/20 alle ore 12:25:03