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dc.contributor.author
Buljubasich Gentiletti, Lisandro
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Monti, Gustavo Alberto
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Acosta, Rodolfo Héctor
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Bonin, Claudio Julio
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González, Cecilia Élida
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Zamar, Ricardo César
dc.date.available
2017-09-18T21:13:50Z
dc.date.issued
2009-01
dc.identifier.citation
Buljubasich Gentiletti, Lisandro; Monti, Gustavo Alberto; Acosta, Rodolfo Héctor; Bonin, Claudio Julio; González, Cecilia Élida; et al.; Quasi-equilibrium states in thermotropic liquid crystals studied by multiple quantum NMR; American Institute of Physics; Journal of Chemical Physics; 130; 1-2009; 1-10; 024501
dc.identifier.issn
0021-9606
dc.identifier.uri
http://hdl.handle.net/11336/24535
dc.description.abstract
Previous work showed that by means of the Jeener-Broekaert JB experiment, two quasiequilibrium states can be selectively prepared in the proton spin system of thermotropic nematic liquid crystals LCs in a strong magnetic field. The similarity of the experimental results obtained in a variety of LC in a broad Larmor frequency range, with crystal hydrates, supports the assumption that also in LC the two spin reservoirs, into which the Zeeman order is transferred, originate in the dipolar energy and that they are associated with a separation in energy scales: A constant of motion related to the stronger dipolar interactions S, and a second one W corresponding to the secular part of the weaker dipolar interactions with regard to the Zeeman and the strong dipolar part. We study the nature of these quasi-invariants in nematic 5CB 4-pentyl-4-biphenyl-carbonitrile and measure their relaxation times by encoding the multiple-quantum coherences of the states following the JB pulse pair on two orthogonal bases, Z and X. The experiments were also performed in powder adamantane at 301 K which is used as a reference compound having only one dipolar quasi-invariant. We show that the evolution of the quantum states during the buildup of the quasiequilibrium state in 5CB prepared under the S condition is similar to the case of powder adamantane and that their quasiequilibrium density operators have the same tensor structure. In contrast, the second constant of motion, whose explicit operator form is not known, involves a richer composition of multiple-quantum coherences of even order on the X basis, in consistency with the truncation inherent in its definition. We exploited the exclusive presence of coherences of 4,6,8, besides 0 and 2 under the W condition to measure the spin-lattice relaxation time TW accurately, so avoiding experimental difficulties that usually impair dipolar order relaxation measurement such as Zeeman contamination at high fields and also superposition of the different quasi-invariants. This procedure opens the possibility of measuring the spin-lattice relaxation of a quasi-invariant independent of the Zeeman and S reservoirs, so incorporating a new relaxation parameter useful for studying the complex molecular dynamics in mesophases. In fact, we report the first measurement of TW in a LC at high magnetic fields. Comparison of the obtained value with the one corresponding to a lower field 16 MHz points out that the relaxation of the W-order strongly depends on the intensity of the external magnetic field, similarly to the case of the S reservoir, indicating that the relaxation of the W-quasi-invariant is also governed by the cooperative molecular motions.
dc.format
application/pdf
dc.language.iso
eng
dc.publisher
American Institute of Physics
dc.rights
info:eu-repo/semantics/openAccess
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https://creativecommons.org/licenses/by-nc-sa/2.5/ar/
dc.subject
Magnetic Field Effects
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Molecular Orientation
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Nematic Liquid Crystal
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Nuclear Magnetic Resonance
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Nuclear Spi-Lattice Relaxation
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Otras Ciencias Físicas
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Ciencias Físicas
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CIENCIAS NATURALES Y EXACTAS
dc.title
Quasi-equilibrium states in thermotropic liquid crystals studied by multiple quantum NMR
dc.type
info:eu-repo/semantics/article
dc.type
info:ar-repo/semantics/artículo
dc.type
info:eu-repo/semantics/publishedVersion
dc.date.updated
2017-09-13T16:16:05Z
dc.journal.volume
130
dc.journal.pagination
1-10; 024501
dc.journal.pais
Estados Unidos
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Maryland
dc.description.fil
Fil: Buljubasich Gentiletti, Lisandro. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomia y Física. Sección Física. Grupo de Resonancia Magnética Nuclear; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina
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Fil: Monti, Gustavo Alberto. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomia y Física. Sección Física. Grupo de Resonancia Magnética Nuclear; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina
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Fil: Acosta, Rodolfo Héctor. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomia y Física. Sección Física. Grupo de Resonancia Magnética Nuclear; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina
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Fil: Bonin, Claudio Julio. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina
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Fil: González, Cecilia Élida. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina
dc.description.fil
Fil: Zamar, Ricardo César. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomia y Física. Sección Física. Grupo de Resonancia Magnética Nuclear; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina
dc.journal.title
Journal of Chemical Physics
dc.relation.alternativeid
info:eu-repo/semantics/altIdentifier/doi/http://dx.doi.org/10.1063/1.3042235
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info:eu-repo/semantics/altIdentifier/url/http://aip.scitation.org/doi/10.1063/1.3042235
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