References of "Lagerwall, Jan 50002154"
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See detailEffects of chain branching and chirality on liquid crystalline phases of bent-core molecules: blue phases, de Vries transitions and switching of diastereomeric states
Ocak, Hale; Bilgin-Eran, Belkiz; Prehm, Marko et al

in Soft Matter (2011), 7(18), 8266-8280

Bent-core molecules based on a resorcinol bisbenzoate core with a series of distinct substituents in different positions at the central resorcinol core have been synthesized and characterized. The focus ... [more ▼]

Bent-core molecules based on a resorcinol bisbenzoate core with a series of distinct substituents in different positions at the central resorcinol core have been synthesized and characterized. The focus is on the effect of branched terminal groups in the racemic and chiral forms on the mesomorphic properties. These were investigated by differential scanning calorimetry, optical polarizing microscopy, X-ray diffraction, electro-optic and dielectric methods. Only bent-core mesogens derived from 4- cyanoresorcinol exhibit liquid crystalline phases and the mesophases of these compounds are strongly influenced by the branching and enantiomeric composition of the terminal chains. Depending on the structure of the rod-like wings and the enantiomeric composition, cybotactic nematic phases (NcybC), BPIII-like isotropic mesophases (BPIIIcybC*) and various polar and apolar smectic phases (SmA, SmC, SmC*, SmCsPA, SmCsPA*) are formed. For one compound, a de Vries type smectic phase is observed and it appears that with decreasing temperature, order develops in two steps. First, at the SmA to SmC transition, the tilt direction becomes long range ordered and in a second step a long range ordering in bend direction takes place. Hence, for the optically active compound a transition from chirality induced polar switching to bend induced (shape induced) antiferroelectricity takes place. In this SmCsPA* phase a homogeneous layer chirality is induced under an applied electric field which interacts with the fixed molecular chirality leading to the energetically favoured diastereomeric state and giving rise to a field direction dependent uniform tilt director orientation. Field reversal induces a flipping of the layer chirality, which first leads to the less favorable diastereomeric state, and then this slowly relaxes to the more stable one by a spontaneous reversal of the tilt direction. [less ▲]

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See detailNematic-smectic transition under confinement in liquid crystalline colloidal shells
Liang, Hsin-Ling; Schymura, Stefan; Rudquist, Per et al

in Physical Review Letters (2011), 106(24), 247801

We carry out the first study of smectic liquid crystalline colloidal shells and investigate how their complex internal structure depends on the director configuration in the nematic phase, preceding the ... [more ▼]

We carry out the first study of smectic liquid crystalline colloidal shells and investigate how their complex internal structure depends on the director configuration in the nematic phase, preceding the smectic phase on cooling. Differences in the free energy cost of director bend and splay give an initial skewed distribution of topological defects in the nematic phase. In the smectic phase, the topological and geometrical constraints of the spherical shell imposed on the developing 1D quasi-long-range order create a conflict that triggers a series of buckling instabilities. Two different characteristic defect patterns arise, one driven by the curvature of the shell, the other by the strong nonuniformities in the director field in the vicinity of the topological defects. [less ▲]

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See detailLiquid Crystals in Novel Geometries prepared by Microfluidics and Electrospinning
Liang, Hsin-Ling; Enz, Eva; Scalia, Giusy et al

in Molecular Crystals & Liquid Crystals (2011), 549

We describe two new techniques of preparing liquid crystal samples and discuss their potential for novel research and applications. Very thin polymer composite fibers func- tionalized by a liquid ... [more ▼]

We describe two new techniques of preparing liquid crystal samples and discuss their potential for novel research and applications. Very thin polymer composite fibers func- tionalized by a liquid crystalline core are realized by coaxial electrospinning of a polymer solution surrounding the liquid crystal during the spinning process. The re- sulting fiber mats exhibit the special properties and responsiveness of the liquid crystal core, e.g. temperature dependent selective reflection when a short-pitch cholesteric is encapsulated. In the second approach an axisymmetric nested capillary microfluidics set-up is used to prepare liquid crystalline shells suspended in an aqueous continuous phase. The spherical geometry of the shell imposes specific defect configurations, the exact result depending on the prevailing liquid crystal phase, the director anchoring conditions at the inner and outer surfaces, and the homogeneity of the shell thickness. With planar director anchoring a variety of defect configurations are possible but for topological reasons the defects must always sum up to a total defect strength of s = +2. Homeotropic anchoring instead gives a defect-free shell, in contrast to a droplet with homeotropic boundary conditions, which must have a defect at its core. By varying the inner and outer fluids as well as the liquid crystal material and temperature, the defect configuration can be tuned in a way that makes the shells interesting e.g. as a versatile colloid crystal building block. [less ▲]

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See detailFilament formation in carbon nanotube-doped lyotropic liquid crystals
Schymura, Stefan; Dölle, Sarah; Yamamoto, Jun et al

in Soft Matter (2011), 7(6), 2663-2667

By introducing carbon nanotubes (CNTs) into lyotropic nematic liquid crystals, strongly enhanced viscoelastic behaviour results, allowing the extraction of very thin and long filaments in which the CNTs ... [more ▼]

By introducing carbon nanotubes (CNTs) into lyotropic nematic liquid crystals, strongly enhanced viscoelastic behaviour results, allowing the extraction of very thin and long filaments in which the CNTs are uniformly aligned. The filament formation requires the liquid crystallinity of the host phase and it does not take place for coarsely dispersed nanotubes or if their concentration is below a threshold value. The type of nanotube plays only a small role, single- as well as multiwall CNTs both trigger the filament formation, but spherical C60 fullerenes do not give rise to the phenomenon. We argue that individualized CNTs stiffen the rod-shaped micelles of the liquid crystal host and that the elongational flow then increases the nematic long-range order as well as the micelle length. If the CNTs are present at a sufficient concentration to connect in continuous linear chains of arbitrary extension, the micelle stiffening is ensured regardless of length, taking the system into a positive feedback loop between increasing orientational order and diverging micelle length. It is this percolation-like transition to aligned and quasi-infinite micelles stabilized by chains of nanotubes that makes the filament formation possible. [less ▲]

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See detailComplex chirality at the nanoscale
Lagerwall, Jan UL; Giesselmann, F.

in Chemphyschem : A European Journal of Chemical Physics and Physical Chemistry (2010), 11(5), 975-977

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See detailElectrospun Microfibres With Temperature Sensitive Iridescence From Encapsulated Cholesteric Liquid Crystal
Enz, Eva; Lagerwall, Jan UL

in Journal of Materials Chemistry (2010), 20(33), 6866-6872

We apply coaxial electrospinning to produce core-sheath polymer composite fibres with encapsulated short-pitch cholesteric liquid crystal, giving the fibres iridescent colours due to selective reflection ... [more ▼]

We apply coaxial electrospinning to produce core-sheath polymer composite fibres with encapsulated short-pitch cholesteric liquid crystal, giving the fibres iridescent colours due to selective reflection within a narrow band of the visible wavelength spectrum. By modifying the feed rate of the liquid crystal during spinning we can tune the fibre diameter from the sub-micron range to about 7 mm, other ranges being accessible via further modifications of the spinning parameters. We demonstrate that the thinnest fibres display quantised colours, determined primarily by the core diameter, whereas the thicker fibres allow a quasi-continuous change in colour if the cholesteric helix pitch changes. Because of the strong response function of liquid crystals, phases as well as structures changing in response to small changes in the environment, the resulting non-woven fibre mats have potential for smart textiles, in particular in sensing applications. [less ▲]

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See detailTowards efficient dispersion of carbon nanotubes in thermotropic liquid crystals
Schymura, Stefan; Kühnast, Martin; Lutz, Vanessa et al

in Advanced Functional Materials (2010), 20(19), 3350-3357

Motivated by numerous recent reports indicating attractive properties of composite materials of carbon nanotubes (CNTs) and liquid crystals (LCs) and a lack of research aimed at optimizing such composites ... [more ▼]

Motivated by numerous recent reports indicating attractive properties of composite materials of carbon nanotubes (CNTs) and liquid crystals (LCs) and a lack of research aimed at optimizing such composites, the process of dispersing CNTs in thermotropic LCs is systematically studied. LC hosts can perform comparably or even better than the best known organic solvents for CNTs such as N-methyl pyrrolidone (NMP), provided that the dispersion process and choice of LC material are optimized. The chemical structure of the molecules in the LC is very important; variations in core as well as in terminal alkyl chain influence the result. Several observations moreover indicate that the anisotropic nematic phase, aligning the nanotubes in the matrix, per se stabilizes the dispersion compared to a host that is isotropic and thus yields random tube orientation. The chemical and physical phenomena governing the preparation of the dispersion and its stability are identified, taking into account enthalpic, entropic, as well as kinetic factors. This allows a guideline on how to best design and prepare CNT–LC composites to be sketched, following which tailored development of new LCs may take the advanced functional material that CNT–LC composites comprise to the stage of commercial application. [less ▲]

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See detailTailor-designed polyphilic promotors for stabilizing dispersions of carbon nanotubes in liquid crystals
Kühnast, Martin; Tschierske, Carsten; Lagerwall, Jan UL

in Chemical Communications (2010), (46), 6989-6991

We present a potent multifunctional molecular design concept for promoting the dispersion of carbon nanotubes (CNTs) in thermotropic liquid crystals (LCs), making CNT-in-LC dispersions of unprecedented ... [more ▼]

We present a potent multifunctional molecular design concept for promoting the dispersion of carbon nanotubes (CNTs) in thermotropic liquid crystals (LCs), making CNT-in-LC dispersions of unprecedented stability possible and broadening the scope of potential applications. [less ▲]

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See detailSelf-assembled ordered structures in thin films of HAT5 discotic liquid crystal
Morales, Piero; Lagerwall, Jan UL; Vacca, Paolo et al

in Beilstein Journal of Organic Chemistry (2010), 6(51), 103762651

Thin films of the discotic liquid crystal hexapentyloxytriphenylene (HAT5), prepared from solution via casting or spin-coating, were investigated by atomic force microscopy and polarizing optical ... [more ▼]

Thin films of the discotic liquid crystal hexapentyloxytriphenylene (HAT5), prepared from solution via casting or spin-coating, were investigated by atomic force microscopy and polarizing optical microscopy, revealing large-scale ordered structures substan- tially different from those typically observed in standard samples of the same material. Thin and very long fibrils of planar-aligned liquid crystal were found, possibly formed as a result of an intermediate lyotropic nematic state arising during the solvent evapor- ation process. Moreover, in sufficiently thin films the crystallization seems to be suppressed, extending the uniform order of the liquid crystal phase down to room temperature. This should be compared to the bulk situation, where the same material crystallizes into a polymorphic structure at 68 °C. [less ▲]

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See detailMacroscopic-scale carbon nanotube alignment via self-assembly in lyotropic liquid crystals
Schymura, Stefan; Enz, Eva; Roth, Siegmar et al

in Synthetic Metals (2009), 159(21-22), 2177-2179

By dispersing carbon nanotubes (CNTs) in a lyotropic liquid crystalline matrix, uniaxial alignment of the nanotubes can easily be achieved over macroscopic areas. We briefly describe the principles behind ... [more ▼]

By dispersing carbon nanotubes (CNTs) in a lyotropic liquid crystalline matrix, uniaxial alignment of the nanotubes can easily be achieved over macroscopic areas. We briefly describe the principles behind the technique and then show that it can be applied to multiwall as well as single-wall nanotubes and that a variety of different dispersing materials can be used, from industrial surfactants to DNA. We also present a new microfluidics-based method for transferring the liquid crystal-dispersed CNTs to a substrate, maintaining a fair control of tube direction. (C) 2009 Elsevier B.V. All rights reserved. [less ▲]

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See detailOn the balance between syn- and anticlinicity in smectic phases formed by achiral hockey-stick mesogens with and without chiral dopants
Enz, Eva; Findeisen-Tandel, Sonja; Dabrowski, Roman et al

in Journal of Materials Chemistry (2009), 19(19), 2950-2957

A series of achiral hockey-stick-shaped mesogens forming tilted smectic liquid crystal phases of synclinic SmC- as well as anticlinic SmCa-type was prepared and characterized. While all homologues exhibit ... [more ▼]

A series of achiral hockey-stick-shaped mesogens forming tilted smectic liquid crystal phases of synclinic SmC- as well as anticlinic SmCa-type was prepared and characterized. While all homologues exhibit both phases, the balance shifts from anticlinic to synclinic order upon elongation of the terminal chain at the meta-position, defining the hockey-stick shape. The elongation also leads to an increased kinetic hindrance of the transition between syn- and anticlinic phases and a decreased transition enthalpy. These observations indicate that a well-defined kink (short meta-substituted chain) promotes the anticlinic structure while a higher flexibility between kinked and rod-shape (long meta-substituted chain) promotes synclinic order. An intermediate chain-length homologue was selected as host material for doping with syn- and anticlinic rod-shaped chiral dopants, respectively, at varying concentrations. Opposite of what might be expected the balance between syn- and anticlinic order was not simply dictated by the choice of dopant. Instead, both types of tilting order prevailed with roughly the same strength as in the achiral host regardless of which chiral material was added, up to concentrations well beyond normal doping conditions. Thus, at least with hockey-stick-shaped achiral hosts, syn- as well as anticlinic chiral compounds can be used effectively as chiral dopants without necessarily having an important impact on the clinicity of the resulting mixture. The hockey-stick design concept should be useful in producing achiral anticlinic-forming mesogens for low-polarization, long-pitch antiferroelectric liquid crystal mixtures. Finally, we point out that a mixture study like the one carried out here yields a conclusive means of establishing the clinicity of achiral tilted smectics, an endeavour that can sometimes be far from trivial. [less ▲]

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See detailElectrolyte effects on the stability of nematic and lamellar lyotropic liquid crystal phases – colligative and ion-specific aspects
Dawin, Ute; Lagerwall, Jan UL; Giesselmann, Frank

in Journal of Physical Chemistry B (2009), 113(33), 11414-11420

We investigated the electrolyte effects on the stability of nematic and lamellar lyotropic liquid crystalline (LLC) phases formed by the simple anionic surfactant cesium pentadecafluorooctanoate (CsPFO ... [more ▼]

We investigated the electrolyte effects on the stability of nematic and lamellar lyotropic liquid crystalline (LLC) phases formed by the simple anionic surfactant cesium pentadecafluorooctanoate (CsPFO) in water. To the lyotropic guest phase, at the constant CsPFO-mass fraction of 0.55, the series of electrolytes LiCl, NaCl, KCl, CsCl, CsI, and Cs2SO4, respectively, was added at concentrations ranging from 0.5 to 2.5 mol %. With increasing electrolyte concentration two substantially different effects were observed. At low concentrations all added electrolytes caused an increase of the thermal stability of the LLC phases, favoring the lamellar phase over the nematic phase. This behavior is, at least qualitatively, understood within the packing parameter model. The extent of the stabilization clearly depends on the chemical nature of the added cation. For a given cation, however, the effect is colligative, i.e., independent of the chemical nature of the added anion. At higher salt concentrations a salting-out-like phase separation was induced. This effect is clearly ion-specific as the salting-out concentration varied for each cation following the order of the Hofmeister series for cations. [less ▲]

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See detailCoaxial Electrospinning of Liquid Crystal-containing Poly(vinyl Pyrrolidone) Microfibers
Enz, Eva; Baumeister, Ute; Lagerwall, Jan UL

in Beilstein Journal of Organic Chemistry (2009), 5(58), 103762558

With the relatively new technique of coaxial electrospinning, composite fibres of poly(vinylpyrrolidone) with the liquid crystal 4-cyano-4′-octylbiphenyl in its smectic phase as core material could be ... [more ▼]

With the relatively new technique of coaxial electrospinning, composite fibres of poly(vinylpyrrolidone) with the liquid crystal 4-cyano-4′-octylbiphenyl in its smectic phase as core material could be produced. The encapsulation leads to remarkable confine- ment effects on the liquid crystal, inducing changes in its phase sequence. We conducted a series of experiments to determine the effect of varying the relative flow rates of inner and outer fluid as well as of the applied voltage during electrospinning on these composite fibres. From X-ray diffraction patterns of oriented fibres we could also establish the orientation of the liquid crystal molecules to be parallel to the fibre axis, a result unexpected when considering the viscosity anisotropy of the liquid crystal kept in its smectic phase during electrospinning. [less ▲]

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See detailCarbon nanotubes in liquid crystals
Lagerwall, Jan UL; Scalia, Giusy

in Journal of Materials Chemistry (2008), 18(25), 2890-2898

We review the research on carbon nanotube (CNT) dispersion in liquid crystals (LCs), focusing mainly on the approaches where the aim is to align CNTs along the LC director field, but also covering briefly ... [more ▼]

We review the research on carbon nanotube (CNT) dispersion in liquid crystals (LCs), focusing mainly on the approaches where the aim is to align CNTs along the LC director field, but also covering briefly the proposed possibility to enhance thermotropic LCs by CNT doping. All relevant LC types are considered: thermotropic LC hosts allowing dynamic CNT realignment, lyotropic LC hosts allowing very high concentration of CNTs uniformly aligned over macroscopic areas and consequent removal of the LC, and LC phases formed by CNTs themselves, used in spinning high-quality carbon nanotube fibres. We also discuss the issue of CNT dispersion in some detail, since successful nanotube separation is imperative for success in this field regardless of the type of LC that is considered. We end by defining a few major challenges for the development of the field over the next few years, critical for reaching the stage where industrially viable protocols for LC-based CNT alignment can be defined. [less ▲]

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See detailSpontaneous macroscopic carbon nanotube alignment via colloidal suspension in hexagonal columnar lyotropic liquid crystals
Scalia, Giusy; von Bühler, Clemens; Hägele, Constanze et al

in Soft Matter (2008), 4(3), 570-576

The self-assembly of amphiphilic molecules in aqueous solution into lyotropic liquid crystals (LCs), characterised by soft yet long-range ordered nanoscale structures, constitutes a fascinating phenomenon ... [more ▼]

The self-assembly of amphiphilic molecules in aqueous solution into lyotropic liquid crystals (LCs), characterised by soft yet long-range ordered nanoscale structures, constitutes a fascinating phenomenon at the heart of soft matter science which can be employed in a manifold of creative ways. Particularly interesting structures may arise as a result of functionalisation of the LC with appropriate guest molecules, adopting the order of their host. Here we combine cat- and anionic surfactants to form a liquid-crystalline colloidal suspension of carbon nanotubes (CNTs), which by virtue of the spontaneously formed hexagonal columnar LC structure are uniaxially aligned over macroscopic areas. The nanotube concentration can be so high, with sufficiently uniform alignment, that the mixture becomes a fluid linear polariser, the anisotropic optical properties of CNTs having been transferred to macroscopic scale by the LC. Moreover, thin and highly aligned filaments can be drawn and deposited in selected directions on arbitrary surfaces, after which the LC template can be rinsed away. Combined with recently developed methods for CNT fractionation according to chirality, the technique would yield an unprecedented degree of control in the practical realisation of carbon nanotube-based devices and materials. [less ▲]

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See detailCoaxial Electrospinning of Microfibres With Liquid Crystal in the Core
Lagerwall, Jan UL; McCann, J. T.; Formo, Eric et al

in Chemical Communications (2008), 42

Liquid crystal containing composite fibres were produced via coaxial electrospinning, demonstrating that this technique can be used for producing new functional fibres and/or to study the impact of ... [more ▼]

Liquid crystal containing composite fibres were produced via coaxial electrospinning, demonstrating that this technique can be used for producing new functional fibres and/or to study the impact of extreme confinement on liquid crystal phases. [less ▲]

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See detailOrder-disorder molecular model of the smectic-A-smectic-C phase transition in materials with conventional and anomalously weak layer contraction
Gorkunov, M. V.; Osipov, M. A.; Lagerwall, Jan UL et al

in Physical Review. E : Statistical, Nonlinear, and Soft Matter Physics (2007), 76(5), 051706

We develop a molecular-statistical theory of the smectic-A-smectic-C transition which is described as a transition of the order-disorder type. The theory is based on a general expansion of the effective ... [more ▼]

We develop a molecular-statistical theory of the smectic-A-smectic-C transition which is described as a transition of the order-disorder type. The theory is based on a general expansion of the effective interaction potential and employs a complete set of orientational order parameters. All the order parameters of the smectic-C phase including the tilt angle are calculated numerically as functions of temperature for a number of systems which correspond to different transition scenario. The effective interaction potential and the parameters of the transition are also calculated for specific molecular models based on electrostatic and induction interaction between molecular dipoles. The theory successfully reproduces the main properties of both conventional and so-called ``de Vries-type'' smectic liquid crystals, clarifies the origin of the anomalously weak layer contraction and describes the tricritical behavior at the smectic-A-smectic-C transition. The ``de Vries behavior,'' i.e., anomalously weak layer contraction is also obtained for a particular molecular model based on interaction between longitudinal molecular dipoles. A simple phenomenological model is presented enabling one to obtain explicit expressions for the layer spacing and the tilt angle which are used to fit the experimental data for a number of materials. [less ▲]

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See detailNanotube alignment using lyotropic liquid crystals
Lagerwall, Jan UL; Scalia, G.; Haluska, Miroslav et al

in Advanced Materials (2007), 19(3), 359-364

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See detailCarbon nanotubes in liquid crystals as versatile functional materials
Scalia, Giusy; Lagerwall, Jan UL; Schymura, Stefan et al

in Physica Status Solidi B. Basic Research (2007), 244(11), 4212-4217

Liquid crystals can be easily aligned in desired directions by treated surfaces or by external fields. The least ordered liquid crystal phase, the nematic, exhibits orientational order that can be easily ... [more ▼]

Liquid crystals can be easily aligned in desired directions by treated surfaces or by external fields. The least ordered liquid crystal phase, the nematic, exhibits orientational order that can be easily transferred onto carbon nanotubes dispersed in it. The alignment of the carbon nanotubes can be demonstrated by po- larized Raman spectroscopy. Carbon nanotubes not only well integrate in the matrix but also, even at very low concentration, have a detectable effect on the liquid crystal properties that can be very attractive for display applications. The presence of big aggregates of carbon nanotubes, on the other hand, interfere strongly with the switching behaviour of the liquid crystal, as we can show following the local switching of liquid crystal molecules with Raman spectroscopy. [less ▲]

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See detailAntiferroelectric liquid crystals with induced intermediate polar phases and the effects of doping with carbon nanotubes
Lagerwall, Jan UL; Dabrowski, R.; Scalia, G.

in Journal of Non-Crystalline Solids (2007), 353(47-51), 4411-4417

By mixing a commercial broad-temperature-range nematic liquid crystal mixture with a single-component antiferroelectric chiral smectic exhibiting two different chiral smectic-C-type phases as only ... [more ▼]

By mixing a commercial broad-temperature-range nematic liquid crystal mixture with a single-component antiferroelectric chiral smectic exhibiting two different chiral smectic-C-type phases as only mesophases, we have induced three phases which appear in neither of the two components; the paraelectric SmA* phase and the so-called intermediate phases SmC􏰀b and SmC􏰀c, antiferroelectric and heli- electric in nature, respectively. The generation of the two latter phases in mixtures where one component is an essentially non-chiral nematic is highly unexpected, since these phases are generally linked to high degree of smectic order and/or strong chiral interactions. It is probably made possible through microphase segregation driven by the incompatibility of the fluorinated tail of the smectic compo- nent with the non-fluorinated constituents of the nematic mixture. We also doped the nematic with single-wall carbon nanotubes (SWCNTs) before adding it to the smectic at the same concentration, allowing us to study the effect of SWCNTs on antiferroelectric liquid crystals. Although the final SWCNT concentration was very small (0.002 wt%) the phase sequence was radically altered, the ordin- ary SmC* phase now being present all the way between SmA* and crystallization, while all other variations of smectic-C-type order were suppressed. [less ▲]

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