Europhys. Lett.
Volume 66, Number 3, May 2004
Page(s) 378 - 384
Section Condensed matter: structure, mechanical and thermal properties
Published online 01 April 2004
Europhys. Lett., 66 (3) , pp. 378-384 (2004)
DOI: 10.1209/epl/i2003-10221-1

Controlling and measuring conformational properties of n-alkane ultraconfined in urea: A high-pressure $\chem{{}^2H}$ NMR study

C. Odin and J. C. Ameline

Groupe Matière Condensée et Matériaux, UMR6626 au CNRS, Université Rennes I Campus de Beaulieu, 35042 Rennes Cedex, France

(Received 24 November 2003; accepted in final form 2 March 2004)

$\chem{{}^2H}$ high-resolution solid-state NMR experiments were performed on the intergrowth compound $\chem{C_{19}D_{40}}$/urea at ambient temperature and helium pressure up to 4500 $\un{bars}$ in a home-made NMR probe. These experiments show that the populations of chain ends gauche conformers can be reversibly modified with pressure. The trans-gauche volume change $\sim 10\pm
2$ $\un{\AA^3}$, free-energy change $\Delta F_{gt}=5\pm
0.7$ $\un{kJ/mol}$ as well as the contribution of the conformational defects to the chain spring constant $C_{gt}\sim 8\mbox{--}4$ $\un{N/m}$ were estimated for the first time for an ultraconfined n-alkane.

68.65.-k - Low-dimensional, mesoscopic, and nanoscale systems: structure and nonelectronic properties.
76.60.-k - Nuclear magnetic resonance and relaxation.
36.20.Ey - Conformation (statistics and dynamics).

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