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See detailUltra-long ordered nanowires from the concerted self-assembly of discotic liquid crystal and solvent molecules.
Park, J. H.; Kim, K. H.; Park, Y. W. et al

in Langmuir (2015), 31(34), 9432-9440

The realization of long and aligned molecular wires is a great challenge and different approaches have been proposed. Interestingly, hexapentyloxytriphenylene (HAT5) discotic liquid crystal molecules ... [more ▼]

The realization of long and aligned molecular wires is a great challenge and different approaches have been proposed. Interestingly, hexapentyloxytriphenylene (HAT5) discotic liquid crystal molecules, model system of molecules with flat and aromatic cores, can spontaneously form well aligned, micrometer long yet only tens of nanometers thick nanowires on solid surfaces. We have investigated the formation mechanism of these wires by using different solvents with selected characteristics like chemical structure, boiling point, vapor pressure and surface tension. When casting from toluene and benzene solutions, atomic force microscopy reveals that the discotics spontaneously form very long and thin wires, self-aligning along a common orientation. If instead dodecane or heptane are used, different and in general thicker structures are obtained. The chemical structure of the solvent appears to have a key role, coupling to the liquid crystal self-assembly by allowing solvent molecules to enter in the ordered structure if their design matches the core of HAT5 molecules, thereby guiding the assembly. However, also other aspects are relevant in the assembly, like the nature of the substrate or the rate of solvent evaporation, and these can favor or interfere with the self-assembly into long structures. The use of solvents with aromatic structure is advantageous not only because it affects the geometry of the assembly, promoting long wire formation, but it is also compatible with good quality of the intermolecular order, as suggested by a high anisotropy of the Raman spectra of the nanowires formed from these solvents. Finally, the electrical properties of ordered systems show a clearly higher electrical conductivity compared to the disorganized aggregates. [less ▲]

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See detailA New Era for Liquid Crystal Research: Applications of Liquid Crystals in Soft Matter Nano-, Bio- and Microtechnology
Lagerwall, Jan UL; Scalia, G.

in Current Applied Physics (2012), 12(6), 1387-1412

Liquid crystals constitute a fascinating class of soft condensed matter characterized by the counterin- tuitive combination of fluidity and long-range order. Today they are best known for their ... [more ▼]

Liquid crystals constitute a fascinating class of soft condensed matter characterized by the counterin- tuitive combination of fluidity and long-range order. Today they are best known for their exceptionally successful application in flat panel displays, but they actually exhibit a plethora of unique and attractive properties that offer tremendous potential for fundamental science as well as innovative applications well beyond the realm of displays. Today this full breadth of the liquid crystalline state of matter is becoming increasingly recognized and numerous new and exciting lines of research are being opened up. We review this exciting development, focusing primarily on the physics aspects of the new research thrusts, in which liquid crystals e thermotropic as well as lyotropic e often meet other types of soft matter, such as polymers and colloidal nano- or microparticle dispersions. Because the field is of large interest also for researchers without a liquid crystal background we begin with a concise introduction to the liquid crystalline state of matter and the key concepts of the research field. We then discuss a selection of promising new directions, starting with liquid crystals for organic electronics, followed by nanotemplating and nanoparticle organization using liquid crystals, liquid crystal colloids (where the liquid crystal can constitute either the continuous phase or the disperse phase, as droplets or shells) and their potential in e.g. photonics and metamaterials, liquid crystal-functionalized polymer fibers, liquid crystal elastomer actuators, ending with a brief overview of activities focusing on liquid crystals in biology, food science and pharmacology. [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 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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See detailEffect of phenyl rings in liquid crystal molecules on swcnts studied by raman spectroscopy
Scalia, G.; Lagerwall, Jan UL; Haluska, Miroslav et al

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 ▲]

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See detailSimultaneous alignment and dispersion of carbon nanotubes with lyotropic liquid crystals
Lagerwall, Jan UL; Scalia, G.; Haluska, Miroslav et al

in Physica Status Solidi B. Basic Research (2006), 243(13), 3046-3049

We demonstrate that single-wall carbon nanotubes (SWCNTs) can be macroscopically aligned by means of templating in a lyotropic nematic liquid crystal (LC), a self-assembling anisotropic fluid with orienta ... [more ▼]

We demonstrate that single-wall carbon nanotubes (SWCNTs) can be macroscopically aligned by means of templating in a lyotropic nematic liquid crystal (LC), a self-assembling anisotropic fluid with orienta- tional but no translational order. The CNTs spontaneously adopt the alignment of the host, as we verify by means of resonant Raman spectroscopy. The aqueous LC host, based on the surfactant SDS, simultane- ously keeps the nanotubes well dispersed over time scales of months or longer. The LC can be loaded with CNTs to almost the same extent as the standard isotropic 1% surfactant solutions normally used for dispersing CNTs without any optically visible bundling occurring. [less ▲]

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