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Raman investigation of stable and metastable states of 4-octyl-4 '-cyanobiphenyl confined in porous silica matrices
Auteur(s): Fehr Catherine, Dieudonne-George P., Sauvajol J.-L., Anglaret E.
(Article) Publié:
Physical Review E: Statistical, Nonlinear, And Soft Matter Physics, vol. 67 p.061706 (2003)
Résumé: We study the polymorphism of solid phases of 4-octyl-4'-cyanobiphenyl (8CB) by Raman spectroscopy. For bulk 8CB, the Raman spectrum of the CN stretch is featured by a single peak, which shifts abruptly at the smectic-A-crystal transition. In confinement, the CN peak splits both at high and low temperatures. In the isotropic and liquid crystal phases, the signature of the liquid crystal bulk (LC) coexists with another peak that is assigned to LC molecules interacting with the matrice interface. We find correlations between the volumic fractions of interfacial liquid and the texture of the matrices. At low temperatures, we assign the splitting of the CN peak to the coexistence of different metastable solid phases. For strong confinements, the temperature dependence of the CN stretching frequency extends to that of the liquid, which suggests the existence of frozen-in smecticlike solid phases. We discuss the structure of these metastable solid phases in the light of neutron diffraction measurements. We also report on the peculiar analogy between the effect of quenched disorder due to the porous matrices and the effect of thermal quenching.
Commentaires: Part 1 061706
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Solid state polymorphism of liquid crystals in confined geometries
Auteur(s): Fehr Catherine, Dieudonne-George P., Primera J., Woignier Thierry, Sauvajol J.-L., Anglaret E.
(Article) Publié:
European Physical Journal E, vol. 12 p.S13-S16 (2003)
Résumé: Solid polymorphism of 4-alkyl-4'-cyanobiphenyl (nCB) was studied so far as a function of thermal history. In this paper we show that metastable solid phases of 4-octyl-4'-cyanobiphenyl (8CB) are also formed when the mesogens are confined in porous silica matrices and we study their structure by neutron diffraction and by Raman spectroscopy. Three metastable solid states are identified : one crystalline phase K', two frozen-in smectic-like phases K-s and K'(s). We discuss the relation between the structure of the metastable solid phases and that of the mesomorph phases.
Commentaires: Suppl. 1
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Orientation of single-walled carbon nanotubes by uniaxial pressure
Auteur(s): Bendiab Nicolas, Almairac Robert, Sauvajol J.-L., Rols Stéphane, Elkaim E.
(Article) Publié:
Journal Of Applied Physics, vol. 93 p.1769-1773 (2003)
Résumé: This article presents a very simple process to align macroscopic quantities of single-wall carbon nanotubes (SWNT), the alignment being controlled by x-ray diffraction. A pellet of SWNT is obtained by pressing a raw nanotube powder up. to a pressure of 10 kbars. A detailed study of the most characteristic lines in the diffraction pattern reveals that the tubes have their axis aligned in the plane of the pellet within an out-of-plane spread angle of similar to4degrees. We also show that the intense small-angle signal-which is observed in all SWNT diffraction diagrams-can be assigned to both the form factor of the isolated nanotubes in the sample and the form factor of the bundles with various size and shape. (C) 2003 American Institute of Physics. [DOI: 10.1063/1.1534905].
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About the profile of the tangential modes in single-wall carbon nanotube bundles
Auteur(s): Bendiab Nicolas, Almairac Robert, Paillet M., Sauvajol J.-L.
(Article) Publié:
Chemical Physics Letters, vol. 372 p.210-215 (2003)
Résumé: We perform Raman investigation on two different samples of single-wall carbon nanotube (SWNTs). The first sample (S1) contains a majority of thick bundles, and the second sample (S2) only contains thin bundles and/or isolated SWNT. Our Raman study reports experimental evidences on the vanishing of the Breit-Wigner-Fano (BWF) resonance when the size of the bundle decreases. (C) 2003 Elsevier Science B.V. All rights reserved.
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Interaction, rayonnement matière et processus indostiques.
Auteur(s): Sauvajol J.-L.
Conference: Ecole Nanotubes : Science et Applications. (Aussois, France, FR, 2003-03)
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Neutron scattering on nanostructure.
Auteur(s): Sauvajol J.-L.
Conference: DYnamycal PROperty of SOlid XXIX (Trieste, Italy, FR, 2003-09-21)
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Modélisation du spectre de diffusion inélastique de neutrons d'un oligomère conjugué modèle : x-bithiophène.
Auteur(s): Hermet P., Bantignies J.-L., Sauvajol J.-L., Lere-Porte J.P.
Conference: Journées des Polymères conducteurs. (Dourdan, France, FR, 2003-09-23)
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