Observation of shear-induced nematic–isotropic transition in side-chain liquid crystal polymers

Pujolle-Robic, Caroline; Noirez, Laurence

doi:10.1038/35051537

Cited by 114 publications

(108 citation statements)

References 22 publications

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“…A proper understanding of the mesogenebackbone interaction is one of the key issues in order to develop the SCPLCs into useful materials. Experimentally the determination of this interaction is an open question [20], and only recently neutron scattering experiments [10,21,22] have shown that the polymeric backbone configuration can indeed be correlated to the local mesogene director.…”

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confidence: 99%

“…This aligned material is technologically interesting because of its strong birefringence and forms an ideal target for further scientific studies like x-ray or neutron scattering experiments. In comparison with other alignment techniques [7][8][9][10][11], magnetic alignment has several advantages, since the field exerts a well-defined, contact free, torque force on all molecules, and can therefore be used for thin films as well as bulk samples.…”

mentioning

confidence: 99%

“…Their current limiting factor is the lack of a reliable method to control the SCPLCs molecular alignment at a macroscopic scale. A large number of techniques are used for alignment, such as surface fields [7], electric fields [8], mechanical fields [9], flow fields [10], or polarized ultraviolet light [11], but only with relative success.…”

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confidence: 99%

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Mesogene-Polymer Backbone Coupling in Side-Chain Polymer Liquid Crystals, Studied by High Magnetic-Field-Induced Alignment

et al. 2003

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We show that cooling side chain polymer liquid crystals in a magnetic field, from the isotropic to nematic and subsequently to the glass phase, results in a macroscopically ordered, transparent, and strongly birefringent material. The aligned samples retain their properties after the field is removed and can be dealigned only by heating them to the isotropic phase. To induce alignment, a threshold field B th is necessary, which strongly depends on the chemical structure details. B th reflects the strength of mesogene-polymer backbone coupling, and we will show that this interaction is responsible for the stability of the induced alignment at zero field.

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confidence: 99%

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Mesogene-Polymer Backbone Coupling in Side-Chain Polymer Liquid Crystals, Studied by High Magnetic-Field-Induced Alignment

et al. 2003

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“…A simple closure condition for passive hard rods [46] is Q ∼ (PP) + , where A + with components A + ij = (A ij + A ji − δ ij A kk )/2 denotes the symmetric traceless part of tensor A in 2D. However, this commonly used closure condition does not account for the fact that active microswimmers permanently impose stress on the ambient fluid which feeds back into the orientational order, analogous to the shear-induced isotropicnematic transition in liquid crystals [47][48][49][50]. To derive a selfconsistent closure condition, we multiply Eq.…”

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Hydrodynamic length-scale selection in microswimmer suspensions

et al. 2016

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A universal characteristic of mesoscale turbulence in active suspensions is the emergence of a typical vortex length scale, distinctly different from the scale invariance of turbulent high-Reynolds number flows. Collective length-scale selection has been observed in bacterial fluids, endothelial tissue, and active colloids, yet the physical origins of this phenomenon remain elusive. Here, we systematically derive an effective fourth-order field theory from a generic microscopic model that allows us to predict the typical vortex size in microswimmer suspensions. Building on a self-consistent closure condition, the derivation shows that the vortex length scale is determined by the competition between local alignment forces, rotational diffusion, and intermediate-range hydrodynamic interactions. Vortex structures found in simulations of the theory agree with recent measurements in Bacillus subtilis suspensions. Moreover, our approach yields an effective viscosity enhancement (reduction), as reported experimentally for puller (pusher) microorganisms. DOI: 10.1103/PhysRevE.94.020601 A universal feature shared by many living systems is the emergence of characteristic length and time scales that arise from the nonequilibrium dynamics of their microscopic constituents. Examples range from circadian oscillations in individual cells [1] to multicellular gene-expression patterns in embryos [2] and vortex structures in microbial suspensions, endothelial tissue, and active colloids [3][4][5][6]. Yet, despite their broad biological relevance, it has proved difficult to predict quantitatively how such emergent scales arise from the underlying chemical or physical parameters. In the past decade, bacterial and other active suspensions [4,5,7] have emerged as important biophysical model systems that can help bridge the gap between large-scale spatiotemporal pattern formation and microscopic nonequilibrium dynamics [8]. At high densities, bacterial fluids form coherent vortex structures, spanning several cell lengths in diameter [5,7,9] and persisting for several seconds [9] or even minutes [10][11][12]. Although a number of insightful theoretical models have been proposed [13][14][15][16][17][18], a theory connecting microswimmer properties to the experimentally observed vortex patterns has been lacking.Here, we present such a theory by drawing guidance from the recent observation [5,9] that an effective fourth-order continuum model can provide a quantitative phenomenological description of dense bacterial suspensions [19]. This model, which combines the seminal Toner-Tu description of flocking [20] with the Swift-Hohenberg equation from pattern formation [21], describes the effective bacterial velocity field w(t,x) bywhere the bacterial pressure field q(t,x) accounts for incompressibility, ∇ · w = 0. Although a direct fit of Eq. (1) (1) directly from a generic model for polar microswimmers. The derivation specifies each parameter in the continuum theory in terms of microscopic swimmer parameters and yields direct theoretical ...

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“…Les régimes de relaxation après élongation comme la reptation sont profondément modifiés par l'état cristal liquide [1 ]. Une phase nématique différente, induite par le cisaillement, a été observée par rhéo-DNPA [12] (bas de la Figure 19). 6.…”

Section: Autres Architectures Copolymeres Polymeres Cristaux Liquidesunclassified

Les polymères comme matériaux désordonnés : l'apport de la diffusion de neutrons

Boué

2003

J. Phys. IV France

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Résumé: Les polymères à l'état amorphe, liquide ou vitreux forment des matériaux désordonnés aux propriétés spécifiques. Les larges gammes de distance impliquées, locale, semi-locale, intermédiaire, globale, de t à 500 nm font de la Diffusion de Neutrons aux Petits Angles (DNPA°, mais aussi de la diffusion inélastique par temps de vol et écho de spin, et de la réflectivité des outils d'étude privilégiés. Nous détaillerons le cas de la chaîne gaussienne dans le fondu, sa statique et sa dynamique à l'état libre puis le cas de la chaîne vermiforme. Nous considérerons ensuite les solutions en bon solvant, en statique et dynamique, les solutions de polyélectrolytes, l'enchevêtrement et la reptation, les réseaux et gels de chaînes réticulées. Ce qui nous amènera à des exemples de diffusion par des objets déformés, ou sous écoulement (rhéo-DNPA). Nous décrirons brièvement le cas de systèmes mixtes et les avantages de la variation de contraste, ainsi que l'étude des interfaces par DNPA ou par réflectivité. Il est évident pour tous que les polymères ont une grande importance en tant que matériaux, structuraux ou à haute valeur ajoutée, dans la vie quotidienne (construction, transport, sport) ou dans les applications biologiques et médicales, en masse-c'est-à-dire sans solvant, comme dans les « matières plastiques », ou en solution, dans l'eau en particulier.Les polymères sont constitués de séquences d'éléments chimiquement identiques (Figure 1). En masse ils peuvent, lorsque leur enchaînement est suffisamment régulier (isotactique, ou syndiotactique), former des zones cristallisées coexistant avec des zones amorphes (à cause des réarrangements complexes des chaînes impliqués dans le processus de cristallisation) dans une structure semi-cristalline. Cela concerne de nombreux matériaux industriels, mais nous ne considérerons ici que le cas amorphe, illustré par le cas simple des non stéréoréguliers. 2 Polymères amorphes un matériau désordonnéLes polymères amorphes sont un exemple particulier de matériaux désordonnés : ils présentent un état liquide et un état vitreux selon la température, avec dans les deux cas une structure identique à celle des liquides ou des verres moléculaires, d'un certain point de vue lié à l'échelle locale essentiellement. D'un autre point de vue, lié à des tailles plus grandes que les polymères impliquent, les chaînes présentent une conformation et arrangement

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Observation of shear-induced nematic–isotropic transition in side-chain liquid crystal polymers

Cited by 114 publications

References 22 publications

Mesogene-Polymer Backbone Coupling in Side-Chain Polymer Liquid Crystals, Studied by High Magnetic-Field-Induced Alignment

Mesogene-Polymer Backbone Coupling in Side-Chain Polymer Liquid Crystals, Studied by High Magnetic-Field-Induced Alignment

Hydrodynamic length-scale selection in microswimmer suspensions

Les polymères comme matériaux désordonnés : l'apport de la diffusion de neutrons

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