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Influence of a dispersion of magnetic and nonmagnetic nanoparticles on the magnetic Fredericksz transition of the liquid crystal 5CB

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hal.structure.identifierLaboratoire de Physique de la Matiere Molle et de la Modélisation Electromagnétique [Tunis] [LP3ME]
dc.contributor.authorMOUHLI, Ahmed
hal.structure.identifierLaboratoire de Physique de la Matiere Molle et de la Modélisation Electromagnétique [Tunis] [LP3ME]
dc.contributor.authorAYEB, Habib
hal.structure.identifierLaboratoire de Physique de la Matiere Molle et de la Modélisation Electromagnétique [Tunis] [LP3ME]
dc.contributor.authorOTHMAN, Tahar
hal.structure.identifierPHysicochimie des Electrolytes et Nanosystèmes InterfaciauX [PHENIX]
dc.contributor.authorFRESNAIS, Jérôme
hal.structure.identifierPHysicochimie des Electrolytes et Nanosystèmes InterfaciauX [PHENIX]
dc.contributor.authorDUPUIS, Vincent
hal.structure.identifierCase Western Reserve University [Cleveland]
dc.contributor.authorNEMITZ, Ian
hal.structure.identifierCase Western Reserve University [Cleveland]
dc.contributor.authorPENDERY, Joel
hal.structure.identifierCase Western Reserve University [Cleveland]
dc.contributor.authorROSENBLATT, Charles
hal.structure.identifierLaboratoire de Chimie des Polymères Organiques [LCPO]
hal.structure.identifierTeam 3 LCPO : Polymer Self-Assembly & Life Sciences
dc.contributor.authorSANDRE, Olivier
hal.structure.identifierInstitut des Nanosciences de Paris [INSP]
dc.contributor.authorLACAZE, Emmanuelle
dc.date.accessioned2020
dc.date.available2020
dc.date.issued2017
dc.identifier.issn2470-0053
dc.identifier.urihttps://oskar-bordeaux.fr/handle/20.500.12278/20105
dc.description.abstractEnA long time ago, Brochard and de Gennes predicted the possibility of significantly decreasing the critical magnetic field of the Fredericksz transition (the magnetic Fredericksz threshold) in a mixture of nematic liquid crystals and ferromagnetic particles, the so-called ferronematics. This phenomenon is rarely measured to be large, due to soft homeotropic anchoring induced at the nanoparticle surface. Here we present an optical study of the magnetic Fredericksz transition combined with a light scattering study of the classical nematic liquid crystal: the pentylcyanobiphenyl (5CB), doped with 6 nm diameter magnetic and nonmagnetic nanoparticles. Surprisingly, for both nanoparticles, we observe at room temperature a net decrease of the threshold field of the Fredericksz transition at low nanoparticle concentrations, which appears associated with a coating of the nanoparticles by a brush of polydimethylsiloxane copolymer chains inducing planar anchoring of the director on the nanoparticle surface. Moreover, the magnetic Fredericksz threshold exhibits nonmonotonic behavior as a function of the nanoparticle concentration for both types of nanoparticles, first decreasing down to a value from 23% to 31% below that of pure 5CB, then increasing with a further increase of nanoparticle concentration. This is interpreted as an aggregation starting at around 0.02 weight fraction that consumes more isolated nanoparticles than those introduced when the concentration is increased above c = 0.05 weight fraction (volume fraction 3.5 × 10 −2). This shows the larger effect of isolated nanoparticles on the threshold with respect to aggregates. From dynamic light scattering measurements we deduced that, if the decrease of the magnetic threshold when the nanoparticle concentration increases is similar for both kinds of nanoparticles, the origin of this decrease is different for magnetic and nonmagnetic nanoparticles. For nonmagnetic nanoparticles, the behavior may be associated with a decrease of the elastic constant due to weak planar anchoring. For magnetic nanoparticles there are non-negligible local magnetic interactions between liquid crystal molecules and magnetic nanoparticles, leading to an increase of the average order parameter. This magnetic interaction thus favors an easier liquid crystal director rotation in the presence of external magnetic field, able to reorient the magnetic moments of the nanoparticles along with the molecules.
dc.language.isoen
dc.publisherAmerican Physical Society (APS)
dc.rights.urihttp://creativecommons.org/licenses/by-nc-nd/
dc.title.enInfluence of a dispersion of magnetic and nonmagnetic nanoparticles on the magnetic Fredericksz transition of the liquid crystal 5CB
dc.typeArticle de revue
dc.identifier.doi10.1103/PhysRevE.96.012706
dc.subject.halPhysique [physics]/Matière Condensée [cond-mat]/Matière Molle [cond-mat.soft]
dc.subject.halChimie/Matériaux
dc.identifier.arxiv1708.00286
bordeaux.journalPhysical Review E
bordeaux.page012706
bordeaux.volume96
bordeaux.hal.laboratoriesLaboratoire de Chimie des Polymères Organiques (LCPO) - UMR 5629*
bordeaux.issue1
bordeaux.institutionBordeaux INP
bordeaux.institutionUniversité de Bordeaux
bordeaux.peerReviewedoui
hal.identifierhal-01569599
hal.version1
hal.origin.linkhttps://hal.archives-ouvertes.fr//hal-01569599v1
bordeaux.COinSctx_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:journal&rft.jtitle=Physical%20Review%20E&rft.date=2017&rft.volume=96&rft.issue=1&rft.spage=012706&rft.epage=012706&rft.eissn=2470-0053&rft.issn=2470-0053&rft.au=MOUHLI,%20Ahmed&AYEB,%20Habib&OTHMAN,%20Tahar&FRESNAIS,%20J%C3%A9r%C3%B4me&DUPUIS,%20Vincent&rft.genre=article


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