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By applying helium gas to an aperiodic nanoporous
crystal, researchers of the Groupe Matière Condensée et
Matériaux (Materials and Condensed Matter Group, CNRS – Grenoble,
France) succeeded in creating the first molecular press. This research
opens new possibilities for the study of the physical properties of nano-confined
molecules.
Researchers chose to work on a urea-alkane
composite since urea forms a cylindrical channel, thanks to its hydrogen
bonds, containing long alkane molecules. This compound is a true nanoporous
crystal confined within the channel of a rigid matrix. Researchers conducted
an original selective compression experiment on this molecular crystal.
Using neutron diffraction , they were able to observe the effect of applying
helium gas that creates pressure at each end of the crystal. The two crystalline
parameters are independent: the length of the alkane molecule, on one
hand, and the helix pitch of the urea matrix, on the other. The structure
is aperiodic along the channel, meaning that all of the relative positions
of the alkane and urea molecules exist. As a result, it is possible to
select and compress either one network or the other one.
These results demonstrate that the contraction of the two subnetworks
is different above a given pressure threshold: the "urea" subnetwork
compresses only slightly, whereas the "alkane" subnetwork compresses
significantly. Depending on the pressure applied, it is possible to vary
the distance between the alkane molecules and to observe the consequences
on the different properties of the crystal.
This experiment is the only example of a molecular press where the piston
is made of helium atoms and the cylinder, of urea channels. The possibilities
created by these results are far-reaching since the continuous control
of distances between molecules contained in a matrix provides a unique
opportunity to vary and study the many physical properties of functional
nano-confined molecules.
Reference:
“First One-Dimensional Stress-Strain Experiments inside an Aperiodic
Inclusion Compound: Evidence of Depinning Effects”, Lydie Bourgeois,
Claude Ecolivet, Bertrand Toudic, Philippe Bourges, Tomasz Breczewski,
Physical Review Letters (Vol. 91,/2, 025504, July 11, 2003).
Researcher
contacts:
Bernard Toudic
Tel: +33 2 23 23 67 19
E-mail: toudic@univ-rennes1.fr
CNRS Mathematics and Physical Sciences Department
contact:
Frederique Laubenheimer
Tel: +33 1 44 96 42 63
E-mail: frederique.laubenheimer@cnrs-dir.fr
Press
contact:
Muriel Ilous
Tel: +33 1 44 96 43 09
E-mail: muriel.ilous@cnrs-dir.fr
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