Macroscopic-scale carbon nanotube alignment via self-assembly in lyotropic liquid crystals

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 ▲]

Electrolyte effects on the stability of nematic and lamellar lyotropic liquid crystal phases – colligative and ion-specific aspects

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 ▲]

Carbon nanotubes in liquid crystals

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 ▲]

Carbon nanotubes in liquid crystals as versatile functional materials

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 ▲]

Nanotube alignment using lyotropic liquid crystals

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

Partitioning and reorientational dynamics of phenylalcohols in SDS lyotropic liquid crystalline mesophases: An alc-μsr study

in Colloids and Surfaces A : Physicochemical and Engineering Aspects (2007), 309

Avoided level crossing muon spin resonance (ALC-􏰝SR) has been applied to monitor location and reorientational dynamics of two different sets of muoniated cyclohexadienyl radicals derived from 3 ... [more ▼]

Avoided level crossing muon spin resonance (ALC-􏰝SR) has been applied to monitor location and reorientational dynamics of two different sets of muoniated cyclohexadienyl radicals derived from 3-phenylpropan-1-ol and 5-phenylpentan-1-ol as tracer molecules in SDS–water–pentanol ternary mixtures and in SDS–water–pentanol–dodecane quaternary systems. The present results show a dependence of the phenylalcohol partitioning on the environment polarity and on the structure of the SDS dispersions. Both radicals tend to be incorporated within the mesophases at 25◦C. The low polarity sensed by the tracer molecule indicates that among all mesophases these species are immersed the deepest in the sponge phase. Alternatively, the effect could be explained by a dependence of the water gradient in the surfactant layer on the overall water versus hydrocarbon content of a system. The changing amplitudes, widths and shapes of the 􏰰1 resonances reveal a different extent of dynamics of three isomers of the muoniated 3-phenylpropan-1-ol radical in particular mesophases. The most extensive dynamics occurs in the hexagonal phase. The probe molecule chain length and the fractions of pentanol and dodecane are additional factors that affect partitioning. [less ▲]

Effect of phenyl rings in liquid crystal molecules on swcnts studied by raman spectroscopy

in Physica Status Solidi B. Basic Research (2006), 243(13), 3238-3241

Carbon nanotubes can be aligned by dispersing them in a liquid crystalline matrix. To control and opti- mize the obtained alignment it is important to understand the interactions between the molecules of ... [more ▼]

Carbon nanotubes can be aligned by dispersing them in a liquid crystalline matrix. To control and opti- mize the obtained alignment it is important to understand the interactions between the molecules of the liquid crystal host phase and the carbon nanotubes. To this end we have carried out resonant Raman spec- troscopy investigations of dispersions of single-wall carbon nanotubes (SWCNTs) in a liquid crystal com- pound comprising molecules with a biphenyl rigid core structure. We detect a distinct wavenumber shift of the radial breathing modes, confirming that the carbon nanotubes interact with the surrounding liquid crystal molecules, most likely through aromatic interactions (π-stacking). The interactions between liquid crystal host and nanotube guests are also evident from a polarizing microscopy study of the liquid crys- tal – isotropic phase transition in the proximity of bundles of nanotubes. The ordered liquid crystal phase is stable up to higher temperatures around the bundles than in areas without visible signs of CNTs. Con- versely, the transition from the disordered isotropic phase to the liquid crystal phase on cooling always nucleates at the carbon nanotube bundles. [less ▲]

The peculiar optic, dielectric and x-ray diffraction properties of a fluorinated de vries asymmetric-diffuse-cone-model ferroelectric liquid crystal

in Liquid Crystals (2006), 33(1), 17-24

A new semi-fluorinated chiral smectic liquid crystal, W504, is investigated by electro-optic, dielectric and X-ray scattering experiments. It exhibits a huge dielectric soft mode response, strong ... [more ▼]

A new semi-fluorinated chiral smectic liquid crystal, W504, is investigated by electro-optic, dielectric and X-ray scattering experiments. It exhibits a huge dielectric soft mode response, strong electroclinic effect and a birefringence which increases considerably with the director tilt angle theta; typical characteristics of a SmA - SmC transition following the de Vries asymmetric diffuse cone (ADC) model in which the non-zero director tilt in SmC arises through an ordering of tilting directions rather than an actual increase in average molecule tilt <theta(mol)>. In W504 a small increase in <theta(mol)> of about 4 degrees is however detected in the SmC phase. Although the increase in molecule inclination is much less than the increase in director tilt h, saturating close to 30 degrees, it leads to a shrinkage of the smectic layers by about 1 angstrom, a result of the large initial molecule tilt in the SmA phase, <theta(mol)>(SmA) approximate to 30 degrees. The tilting transition in W504 is thus mainly an ADC model disorder - order transition, but it also has a component of a structural transition. The semi- fluorinated molecular structure of W504 leads to a very weak electron density modulation along the layer normal, giving a vanishing form factor in bulk samples which exhibit no (001) X-ray scattering peak. In thin films the (001) peak is however observed, indicating that the electron density modulation is enhanced by the breaking of the head - tail symmetry of the liquid crystal phase at the LC - air interface. [less ▲]

Book review: Crystals that flow

in Technikgeschichte (2006), 73

Ein bekanntes Zitat von Mark Twain lautet "ein Klassiker ist ein Werk, das jeder gelesen ha- ben möchte, aber niemand lesen will". Mit dem ausgezeichneten Buch Crystals that flow - classic papers from the ... [more ▼]

Ein bekanntes Zitat von Mark Twain lautet "ein Klassiker ist ein Werk, das jeder gelesen ha- ben möchte, aber niemand lesen will". Mit dem ausgezeichneten Buch Crystals that flow - classic papers from the history of liquid crystals haben die drei Autoren Timothy J. Sluckin, David A. Dunmur und Horst Stegemeyer, vielen technik- und wissenschaftsinteressierten Le- sern das Klassikerlesen wesentlich erleichtert, da sie in diesem Buch 46 klassische Artikel aus der Geschichte der Erforschung und technischen Anwendung von Flüssigkristalle zu- sammengestellt haben. Sie erzählen damit die Geschichte, wie eine ‚akademische Kuriosität’, entdeckt Ende des neunzehnten Jahrhunderts, erst unsere Vorstellung von den Aggregatzu- ständen kondensierter Materie verändert hat, und danach zu einer Schlüsseltechnologie ent- wickelt wurde, die die Grundlagen der heutigen Multimillionen-Euro-Industrie der Flachbild- schirme liefert (LCD = Liquid Crystal Display, also Flüssigkristallanzeige). ... [less ▲]

Frustration between syn- and anticlinicity in mixtures of chiral and non-chiral tilted smectic-c-type liquid crystals

in European Physical Journal E. Soft Matter (2005), 18(1), 113-121

We study the effects of mixing ferroelectric and antiferroelectric liquid-crystal compounds (FLCs and AFLCs) when the former are strictly synclinic and the latter strictly anticlinic, i.e. one mixture ... [more ▼]

We study the effects of mixing ferroelectric and antiferroelectric liquid-crystal compounds (FLCs and AFLCs) when the former are strictly synclinic and the latter strictly anticlinic, i.e. one mixture component exhibits only SmC* and the other only SmCa* as tilted phase. Three different paths between syn- and anticlinicity were detected: transition directly between SmC* and SmCa*, transition via the SmCβ* and SmCγ* subphases, or by “escaping” the clinicity frustration by reducing the tilt to zero, i.e. the SmA* phase is extended downwards in temperature, separating SmC* from SmCa* in the phase diagram. The most common path is the one via the subphases, demonstrating that these phases appear as a result of frustration between syn- and anticlinic and, consequently, between syn- and antipolar order. For assessing the role of chirality, we also replaced the FLC with non-chiral synclinics. With one of the AFLCs, the route via supbhases was detected even in this case, suggesting that chirality —although necessary— does not have quite the importance that has previously been attributed to the appearance of the subphases. The path chosen in the mixture study seemed to be determined mainly by the synclinic component, the subphase induction occurring only when the SmA*-SmC* transition was second order. [less ▲]