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HRTEM, TSC and broadband dielectric spectroscopy of a discotic liquid crystal

HRTEM, TSC and broadband dielectric spectroscopy of a discotic liquid crystal

Introduction The literature concerning the dielectric properties of polymeric liquid crystals is vast. 1–4 And yet, the relationships between intrinsic dielectric properties and physical state for DLCs remain obscure. Discotic liquid crystals (DLCs) are good models for the study of self-organising systems. Since their discovery in the 1970s, 5 DLC materials have held our atten- tion 6,7 due to their various mesophases. Their anisotropic properties are induced by the conformation of the disk-shaped molecules and the specific intermolecular interactions. Most of the future applications are influenced by the mesomorphic properties of this molecular system. One of the major applica- tion domain for DLCs is electronic devices. 8 Since the late
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Liquid crystal ionic self-assembly and anion-selective photoluminescence in discotic azatriphenylenes

Liquid crystal ionic self-assembly and anion-selective photoluminescence in discotic azatriphenylenes

and aromatic cores. 17 iLCs therefore possess tremendous potential applications such as ordered reaction media, 16 aniso- tropic ionic 24–26 and electronic 27,28 conductions, and transport media, 29 media for alignment of single wall carbon nanotubes (triphenylene-based ionic discogens show Col hex and bicontinuous cubic mesophases), 27,30,31 applied in biological field as siRNA transfection vectors. 29 Essentially most iLCs so far reported, possess one or two alkyl tails connected to either a small ionic moiety or a rod-like core, and for most of them, show smectic phases, 17,32–37 with only a few cases displaying columnar phases. 38,39 In contrast, studies of ionic discotic liquid crystals (iDLCs) with a discotic core and displaying columnar mesophases, 40–42 are however only just emerging, and only few examples have been reported so far. DLCs with polycyclic aromatic hydrocarbon (PAH) cores 5–8,10,12–15 are indeed of interest since they spontaneously self-organize into columnar mesophases, and possess one-dimensional electronic charge hopping pathway along the molecular columns with fast charge carrier drift mobility. DLC semiconductors are studied as active materials in organic thin film devices, such as photovoltaic solar cells, organic light- emitting diodes, and field-effect transistors. Up to now, the design of iDLCs consists mainly in the peripheral decoration of the neutral triphenylene discotic core by pending pyridinium, ammonium, guanidinium or the emblematic imidazolium units, connected to the discotic unit through soft alkyl spacers. 18,19,43–53 They usually show columnar mesophases near room temperature and over large temperature ranges. Inversely, imidazolium or other suitable cations may be used as connectors between triphenylene units to yield dimeric systems. 48,50 Other systems include bis-triphenylene derivatives connected through crown ethers whose mesophases’ stabilities are enhanced upon the host–guest complexation to various cations. 54 Ionic tapered 55–57 and dendronized 58 molecular systems have also been reported with various types of counterions and found to self-organize into columnar (and cubic) mesophases. Overall, few examples of conjugated core-charged iDLCs with heterocyclic cores containing oxygen, nitrogen or sulfur atoms have been reported. 40–42
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HRTEM, TSC and broadband dielectric spectroscopy of a discotic liquid crystal

HRTEM, TSC and broadband dielectric spectroscopy of a discotic liquid crystal

Introduction The literature concerning the dielectric properties of polymeric liquid crystals is vast. 1–4 And yet, the relationships between intrinsic dielectric properties and physical state for DLCs remain obscure. Discotic liquid crystals (DLCs) are good models for the study of self-organising systems. Since their discovery in the 1970s, 5 DLC materials have held our atten- tion 6,7 due to their various mesophases. Their anisotropic properties are induced by the conformation of the disk-shaped molecules and the specific intermolecular interactions. Most of the future applications are influenced by the mesomorphic properties of this molecular system. One of the major applica- tion domain for DLCs is electronic devices. 8 Since the late
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Rigid $\tau $-crystals

Rigid $\tau $-crystals

is a significant additional information: For example, for the punctured open unit disc, all vector bundles with Frobenius structure are trivial [8]. 3. Formal τ -crystals In the analogy between F -crystals and τ -crystals, the right replacement of the Witt vectors W (A) is the ring A[[t]] of formal power series: Both are adic rings with residue ring A whose projection map has a multiplica- tive section. In this chapter, we will show that F -crystals have a natural analogue over A[[t]], which we call formal τ -crystals. For these much of the

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Classical Time Crystals

Classical Time Crystals

General considerations.—When a physical solution of a set of equations displays less symmetry than the equations themselves, we say the symmetry is spontaneously broken by that solution. Here the meaning of ‘‘physical solution’’ can be interpreted differently in different contexts, but one interesting case that will concern us here is of the lowest- energy solutions of a time-independent, conservative, clas- sical dynamical system. If such a solution exhibits motion, we will have broken time-translation symmetry spontane- ously. If the dynamical variable is an angular variable, then the motion will be periodic in time, so the time-translation symmetry is not entirely lost, but only reduced to a discrete subgroup. Spatial periodicity is, of course, associated with formation of ordinary crystals, so it is natural and sugges- tive to refer to the formation of time crystals.
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Demazure Crystals, Kirillov-Reshetikhin Crystals, and the Energy Function

Demazure Crystals, Kirillov-Reshetikhin Crystals, and the Energy Function

6 Perfect KR crystals and Demazure crystals We now state a precise relationship between KR crystals and Demazure crystals (see Theorem 6.1 ). This was proven by Fourier, Schilling, and Shimozono [ 12 ], under a few additional assumptions on the KR crystals since at the time the existence and combi- natorial models for KR crystals did not yet exist. Here we point out that most of the assumptions in [ 12 ] follow from the later results of [ 49 , 50 , 10 , 11 ] showing that the relevant KR crystals exist, have certain symmetries related to Dynkin diagram automorphisms, and are perfect. In the special cases of type A (2) 2n and the exceptional nodes in type D n (1) ,
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Tubular ice crystals

Tubular ice crystals

Tubular ice crystals Krausz, A. S.; Harron, B.; Litvan, G. G. https://publications-cnrc.canada.ca/fra/droits L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB.

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Cylindrical photonic crystals

Cylindrical photonic crystals

The reflective cladding of the photonic crystal waveguide is unique in that it allows one to confine light in a low index of refraction region, and to work with gui[r]

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fluids Exploring "Dormant" Opto-Mechanical Properties of the Isotropic Phase of Liquid Crystals and Revealing Hidden Elasticity of (Ordinary) Liquids

fluids Exploring "Dormant" Opto-Mechanical Properties of the Isotropic Phase of Liquid Crystals and Revealing Hidden Elasticity of (Ordinary) Liquids

Fluids 2018, 3, 43 2 of 20 The search for hidden elastic properties in the isotropic phase of liquid crystals was primary motivated by non-elucidated observations in steady-state flow conditions of non-linear stress behaviors, and of the emergence of flow birefringence above a critical shear rate. Systems as varied as wormlike micellar solutions [ 3 – 5 ], rigid-rod suspensions [ 6 , 7 ], and isotropic phases of thermotropic liquid crystal polymers (shear-induced isotropic to nematic [ 8 – 10 ] or isotropic to smectic phase transitions [ 11 ]) exhibit abrupt shear-induced transitions. These spectacular non-linear effects cannot be explained on the basis of flow coupling to a molecular relaxation time or a pretransitional lifetime [ 12 – 15 ] since, for example, the flow birefringence of LCPs is observed before reaching shear rates corresponding to the pretransitional lifetimes and the viscoelastic relaxation times [ 8 – 10 , 16 – 18 ]. Theoretical predictions based on a coupling with molecular dynamics can neither account for non-extensive parameters like the dimensionality (shear-induced phase transitions have been found to be thickness-dependent) nor for external conditions (boundary conditions such as surface wetting, surface curvature) [ 19 ]. These spectacular flow effects hide a different mechanism. Since the time scales are much larger than individual relaxation times, long-range collective processes are involved. The present work gathers some experimental results and theoretical developments, indicating that intermolecular interactions might play an important role in the dynamic response of the liquid to a flow field or a mechanical strain field. As a result, upon low-frequency excitation, the intermolecular forces act as a weak elastic network in which liquid molecules do behave not dynamically freely, but elastically (at the submillimeter scale). The identification of elastic properties of the isotropic phase is of prime importance. Static shear
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Study of the dynamic formation of transmission gratings recorded in photopolymers and holographic polymer-dispersed liquid crystals

Study of the dynamic formation of transmission gratings recorded in photopolymers and holographic polymer-dispersed liquid crystals

H-PDLCs are attractive materials as they have the advantages of photopolymers cited previously, and the presence of liquid crystals 共LCs兲 provides them with a switchable behavior. During the exposure to an interference pattern 关see Fig. 1共a兲兴, a phase sepa- ration occurs between the monomer and the LC drop- lets owing to the diffusion process. Polymerization occurs in bright regions, the monomer diffuses from dark to bright regions, and the LC diffuses in the opposite direction. So, after the exposure, the H-PDLC system consists of alternating layers of poly- mer planes and LC-rich droplet planes as shown on Fig. 1 共b兲.
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Multiplexed holographic transmission gratings recorded in holographic polymer-dispersed liquid crystals: static and
dynamic studies

Multiplexed holographic transmission gratings recorded in holographic polymer-dispersed liquid crystals: static and dynamic studies

The optimization of the experimental parameters of two multiplexed holographic transmission gratings recorded in holographic polymer-dispersed liquid crystals is investigated. Two methods are used to record the holograms: simultaneous and sequential multiplexing. These two processes are optimized to produce two multiplexed Bragg gratings that have the same and the highest possible diffraction efficiencies in the first order. The two methods show similar results when suitable recording parameters are used. The parameters of the recorded gratings (mainly the refractive-index modulation) are retrieved by use of an extension of the rigorous coupled-wave theory to multiplexed gratings. Finally, the response of the holograms to an electric field is studied. We demonstrate few coupling effects between the behavior of both gratings, and we expect a possibility of switching from one grating to the other.
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Biaxiality in the asymptotic analysis of a 2D Landau-de Gennes model for liquid crystals

Biaxiality in the asymptotic analysis of a 2D Landau-de Gennes model for liquid crystals

∗ ) 2 tr Q 2 − b tr Q 3 + c tr Q 2  2 . The parameters α, b and c depend on the material, T is the absolute temperature, which we assume to be constant, and T ∗ is a characteristic temperature of the liquid crystal. We work here in the low temperature regime, that is, T < T ∗ . It can be proved (see [1, Proposition 9]) that f attains its minimum on a manifold N , termed the vacuum manifold, whose elements are exactly the matrices having s = s ∗ , r = 0 in the representation formula (1.1) (s ∗ is a parameter depending only on α, b, c, T ). The potential energy ε −2 f (Q) can be regarded as a penalization
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From metallic cluster-based ceramics to nematic hybrid liquid crystals: a double supramolecular approach.

From metallic cluster-based ceramics to nematic hybrid liquid crystals: a double supramolecular approach.

Conclusions In conclusion, we describe in this work, a new and straightforward approach to develop new hybrid materials merging the functionalities of nanometric inorganic anionic entities with the self-assembling abilities of organic liquid crystals. Our strategy combines host guest complex formation between Cs + cations and diazacrown derivatives, with

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Liquid-liquid phase transitions in silicon

Liquid-liquid phase transitions in silicon

near 2k F in a metallic fluid (as in l-Si), then concerted scattering across the Fermi surface causes a giant Kohn anomaly that translates into tr-cb with lifetimes typical of phonon vibrations [3] . That is the “Fermi liquid” picture of tr-cb formation. The presence of tr-cb splits the main peak of SðkÞ and causes a peak in the PDF close to the Si-Si bond distance r b .

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Photomechanical effect in ionic crystals

Photomechanical effect in ionic crystals

L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB.. Technical T[r]

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ELLE & IL : enantioselective liquid-liquid extraction and ionic liquids

ELLE & IL : enantioselective liquid-liquid extraction and ionic liquids

12 ELLE & IL: Enantioselective liquid-liquid extraction and ionic liquids Viacheslav Zgonnik, PhD thesis, Université Toulouse III - Paul Sabatier, 19 July 2011 contre, l’utilisation de liquides en grande échelle ne pose aucun problème pour l’industrie chimique. Par conséquent, il existe un besoin continu de chercher les stratégies alternatives générales pour le dédoublement des mélanges racémiques d’une manière peu chère, rapide et écologique. Une méthode prometteuse repose sur la capacité d'un sélecteur chiral de distinguer les deux énantiomères d'un racémique, ce qui rend la séparation énantiomérique de mélanges racémiques possible. Par exemple, par l’extraction liquide-liquide avec un hôte chiral. Nous retrouvons l’idée de la reconnaissance chirale dans la mythologie grecque (Figure 2-3). La nymphe Echo (hôte chiral) veut se réunir avec Narcisse (énantiomère 1) qui, de son coté, veut partir dans la phase aqueuse pour se retrouver avec son image en miroir (énantiomère 2) pour former un racémique. Dans notre travail l’hôte chiral a été capable de séparer (au moins partiellement) un énantiomère de l’autre, à la différence du mythe original où l’hôte chiral se laissa dépérir en n’étant pas capable de séparer l’énantiomère 1 de son image en miroir.
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Defects in Self Assembled Colloidal Crystals

Defects in Self Assembled Colloidal Crystals

suspended in a fluid medium. They have been experimentally observed to form a homogenous crystal at a volume fraction 0.536. [1] These colloidal crystals have close-packed structure and theoretical considerations have shown that the stable structure is the FCC structure. Colloidal crystals exhibit interesting optical properties like photonic bandgap. Yablonovitch first suggested that it is possible to localize light in a material that has a periodically modulating dielectric constant. [2] These ordered structures have a photonic bandgap (PBG) which prevents light of certain frequency from propagating through the material. Monodispersed colloids will assemble themselves into the FCC crystal structure under the right conditions. This natural process of self assembly makes colloidal crystal an attractive method of fabricating
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Importance of interfacial interactions to access shear elasticity of liquids and understand flow induced birefringence from liquid crystals to worm-like micellar solutions

Importance of interfacial interactions to access shear elasticity of liquids and understand flow induced birefringence from liquid crystals to worm-like micellar solutions

Figure 7 By improving the interactions to the surface, the dynamic measurement reveals a solid-like response (G 0 (red ♦) > G 00 ( e)) in: a) thermotropic liquid crystal: the liquid phase (here at 14 °C above the isotropic-nematic transition and at 0.150 mm thickness) of a liquid-crystal polymer. The inset displays for comparison the conventional flow behavior [as predicted for uncross-linked polymers (Maxwell model)] [ 21 , 25 ]. Thermotropic liquid crystal I(isotropic) – 119 °C – N(nematic) – 30 °C – Glassy state. b) CTAB: Phase diagram from reference [22]. Lyotropic liquid crystal: the liquid phase of salt-free CTAB-water (dilution 18%) measured at 33 °C at 0.2% strain amplitude, 0.3 mm gap thickness. The shear modulus and the viscous modulus are independent of the frequency with G 0 > G 00 indicating a solid-like behavior. Similar responses are obtained by scanning from low to high G 0 (Pa): red d, G 00 (Pa): blue & and from high to low frequency G 0 (Pa): red e, G 00 (Pa): blue h.
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Ultrasound to Enhance a Liquid–Liquid Reaction

Ultrasound to Enhance a Liquid–Liquid Reaction

been carried out in such systems. In the present work, the apparent kinetics of a liq- uid–liquid reaction is investigated in presence of ultra- sound, and the enhancement of the mass transfer volu- metric coefficient k L a is evaluated for different values of operating parameters. The ultrasound frequency of 20 kHz has been chosen because it is known to result in high mechanical effects.

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Cyclic deformation of FCC crystals

Cyclic deformation of FCC crystals

4-8 Comparison of the saturation stress level between uniaxial and non-proportional 900 out-of-phase cyclic test with the same equivalent strain amplitude... List of Tabl[r]

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