Liquid Crystal Solvent Research Articles

The Missing Relationship between the Miscibility of Chiral Dopants and the Microscopic Dynamics of Solvent Liquid Crystals: A Molecular Dynamics Study

Nematic liquid crystals (LCs) are known to undergo a phase transition to chiral nematic LCs possessing helices upon doping with enantiomeric molecules known as chiral dopants. The relationship between the helical pitch (p), the molar fraction (x), and the power of the chiral dopant to induce a helix in a nematic solvent (βM) is expressed as p=1/(x·βM). The helical pitch is easily controlled by the concentration of the chiral dopant when the dopant molecule is miscible with the host nematic LC. However, it has not yet been clarified what the miscibility of the chiral dopant molecules with the nematic LCs depends. Therefore, we performed all-atom molecular dynamics (MD) simulations for the system composed of both Δ and Λ isomers of a chiral dopant molecule dispersed in a nematic LC and investigated the relationship between the microdynamics of the chiral molecules and their miscibility with the nematic solvent. The miscibility of the chiral dopant molecules with the LC solvent was found to correlate with the diffusion coefficient of the LC solvent. In the system where the chiral dopant molecules with high miscibility were added, the diffusion coefficient of the LC solvents was comparable to that of the system in which the chiral molecule was not doped. Furthermore, it was confirmed that more elongated chiral dopants were more miscible with the nematic solvent consisting of calamitic molecules, and that these dopant molecules did not have a significant effect on the diffusion behavior of the LC molecules.

Preparation of polyaniline in organic liquid crystal solvent

Polyaniline (PANI) is generally prepared in a water medium. However, a new method for the synthesis of PANI in an organic solvent was developed in this study. PANI was successfully synthesized in an organic cholesteric liquid crystal (CLC) matrix using ammonium peroxodisulfate and 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) as two initiators to progress the polymerization. Polymerization in the CLC matrix resulted to PANI with an ordered structure due to secondary doping in the monomer propagation process.

Precipitation polymerization in liquid crystals to prepare uniform epoxy microspheres

In this paper, uniform epoxy resin polymer microspheres (EMs) with controllable diameters and a narrow size distribution were prepared by precipitation polymerization using liquid crystals (LCs) as the solvent. The effects of the LC solvents on the morphologies of the resultant epoxy resin were thoroughly investigated. It was found that the formation of uniform EMs is sensitive to the properties of the LCs solvents. Uniform EMs can be obtained when the solubility parameters (δ) of the used solvent range from 20.59 to 21.29 (cal/cm3)1/2 and its dispersion terms (δd) are in the range of 19.87–20.89 (cal/cm3)1/2. Apart from the effects of solvents, the size of the as-made EMs can be further regulated from 2.6 μm to 10.1 μm by controlling the reactivity of epoxy monomers and the functionality of thiol hardeners. Moreover, we demonstrated that carbonizing the EMs can directly produce uniform carbon microspheres (CMs) with smooth surface. This work enlightens a new way for the preparation of EMs through precipitation polymerization in LCs solvent.

Probing the orientation of porphyrin oligomers in a liquid crystal solvent – a triplet state electron paramagnetic resonance study

ABSTRACTLinear porphyrin oligomers have found various applications as synthetic molecular wires in the context of light harvesting, solar energy conversion and molecular electronics. In many of these applications a partial ordering of the molecules helps to improve the reaction efficiency or device performance. In this work we study the orientational properties of the building blocks of such porphyrin-based molecular wires, namely a porphyrin monomer and the corresponding butadiyne-bridged dimer. The porphyrins have been embedded in the nematic liquid crystal solvent 4-cyano-4'-pentylbiphenyl (5CB) and the anisotropic properties of their photogenerated triplet states were characterised by transient electron paramagnetic resonance (EPR) spectroscopy. When aligned in strong magnetic fields, the liquid crystal molecules impose their orientational anisotropy onto the solute guest molecules whose orientation-dependent magnetic properties can then be explored. The line shape analysis of the porphyrin triplet state EPR spectra – highly sensitive to small conformational changes – confirms the orientation of the zero-field-splitting (ZFS) tensors previously determined for these molecules by magnetophotoselection experiments. A biaxial distribution function is shown to be necessary to simulate the experimental EPR data. The biaxial behaviour, in conjunction with symmetry considerations, allows an unambiguous assignment of the three ZFS tensor axes to the molecular axes. From the determined orientational distributions of the porphyrins in 5CB, the biaxial order parameters for both molecules were calculated.

Process for a Reactive Monomer Alignment Layer for Liquid Crystals Formed on an Azodye Sublayer.

In this work, the detailed studies of surface polymerization stabilizing liquid crystal formed on an azodye sublayer are presented. The surface localized stabilization is obtained by free-radical polymerization of a dilute solution of a bi-functional reactive monomer (RM) in a liquid crystal (LC) solvent. To optimize the process for surface localized stabilization, we investigate the effects of several process parameters including RM concentration in LC hosts, the types of materials (either RM or LC), the photo-initiator (PI) concentration, ultra-violet (UV) polymerization intensity, and the UV curing temperature. The quality of surface localized stabilization is characterized and/or evaluated by optical microscopy, electro-optical behavior (transmission/voltage curve), the life test, and photo-bleaching. Our results show that, by carefully selecting materials, formulating mixtures, and controlling the polymerizing variables, the RM polymerization can be realized either at the surface or through the bulk. Overall, the combination of surface localized stabilization and photo-alignment offers an elegant and dynamic solution for controlling the alignment for LC, which could play a profound role in almost all liquid crystal optical devices.

NMR of orientationally ordered short-chain hydrocarbons

ABSTRACTThe proton NMR spectra of the straight-chain hydrocarbons from methane to -hexane orientationally ordered in nematic liquid-crystal solvents are reviewed. The theory behind reorientation-vibration coupling (that explains the anisotropic splittings observed in the spectrum of methane) is discussed. This coupling is also important for ethane where the torsional motion about the C–C bond becomes an issue. The ratios of propane to ethane dipolar couplings are found to be independent of liquid crystal and of temperature: this demonstrates that the hydrocarbons are ‘magic solutes’, i.e. their orientational order results from a single anisotropic interaction that involves short-range size-and-shape effects. The longer chains -butane, -pentane and -hexane (which give extremely complicated NMR spectra) exist in several symmetry-unrelated conformers. The spectra are analysed with the aid of evolution strategies. The dipolar couplings obtained are used in a model-free analysis (that is based on the constant ratio between ethane and propane dipolar couplings) to explore important information about the intermolecular potential. For example, the orientational order of longer conformers is favoured by the nematic phase.

The effect of concentration and molecular weight of polycarbonate on the elastic constants of a nematic liquid crystal solvent

We utilized the Light Scattering from Anisotropy of Turbidity (LSAT) method and determined the three Frank’s elastic constants of; "splay" (K1), "twist" (K2) and "bend" (K3), in dilute solutions of polycarbonate (PC) in 4-pentyl-4’-cyanobiphenyl (5CB) nematic liquid crystal solvent. Within the limited solubility range of PC/5CB solutions, we determined the elastic constants of 5CB as a function of the concentration and molecular weight of PC. The results showed that K2 increases, K1 and K3 decrease, whereas K1/K3 and <K> ratio remain almost invariant by increasing the PC concentration and molecular weight.In contrast to the theoretical models and experimental data, the values and trends of K1, K2 and K3 moduli indicate that, increase of K2 at the expense of K1 and K3 moduli is due to extended chain conformation PC polymer structure and enhancment of lateral interactions between PC and 5CB moieties.

Structural analysis of benzothienobenzothiophene-based soluble organic semiconducting crystals grown by liquid crystal solvent

In this study, we analyzed organic semiconducting single crystals composed of benzothienobenzothiophene derivatives (2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene, C8-BTBT) grown by nematic-phase liquid crystal (LC) solvent. As a result, we clarified that the crystal b-axis direction of the C8-BTBT single crystals was consistent with the LC alignment direction. By optical evaluation and simulation based on density functional theory, we found that the C8-BTBT single crystals in LC solvent exhibited a novel molecular conformation having alkyl chains oriented toward the b-axis.

Unusual photoresponses in the upper critical solution temperature of polymer solutions mediated by changes in intermolecular interactions in an azo-doped liquid crystalline solvent.

Photoinduced changes in the upper critical solution temperature (UCST) were investigated for polymer solutions in an azobenzene-doped liquid crystal solvent. The UCST of poly(methyl methacrylate) (PMMA) and polystyrene (PS) solutions dropped upon irradiation with UV light, which induces trans-cis photoisomerization of the doped azo dye. In the case of PMMA solutions, the photoinduced drop in UCST was significantly larger than that expected from previous studies using azo-based polymers and common solvents. Moreover, the UCST of PS solutions also decreased under photoirradiation, in a direction opposite to that expected from the contribution of polarity. X-ray diffraction data of the solvent suggest that the decreased intermolecular interaction in the solvent (i.e. larger distance between the solvent molecules) is responsible for the photoresponsive behavior of the UCST. The proposed mechanism is consistent with the Flory-Huggins theory. Using such photoresponses in the UCST, the isothermal transition between 2-phase and 1-phase states by photoirradiation was demonstrated.

Temperature‐Responsive Luminescent Solar Concentrators: Tuning Energy Transfer in a Liquid Crystalline Matrix

AbstractTemperature‐responsive luminescent solar concentrators (LSCs) have been fabricated in which the Förster resonance energy transfer (FRET) between a donor–acceptor pair in a liquid crystalline solvent can be tuned. At room temperatures, the perylene bisimide (PBI) acceptor is aggregated and FRET is inactive; while after heating to a temperature above the isotropic phase of the liquid crystal solvent, the acceptor PBI completely dissolves and FRET is activated. This unusual temperature control over FRET was used to design a color‐tunable LSC. The device has been shown to be highly stable towards consecutive heating and cooling cycles, making it an appealing device for harvesting otherwise unused solar energy.

Temperature-Responsive Luminescent Solar Concentrators: Tuning Energy Transfer in a Liquid Crystalline Matrix.

Temperature‐responsive luminescent solar concentrators (LSCs) have been fabricated in which the Förster resonance energy transfer (FRET) between a donor–acceptor pair in a liquid crystalline solvent can be tuned. At room temperatures, the perylene bisimide (PBI) acceptor is aggregated and FRET is inactive; while after heating to a temperature above the isotropic phase of the liquid crystal solvent, the acceptor PBI completely dissolves and FRET is activated. This unusual temperature control over FRET was used to design a color‐tunable LSC. The device has been shown to be highly stable towards consecutive heating and cooling cycles, making it an appealing device for harvesting otherwise unused solar energy.

Synthesis of Distinct Iron Oxide Nanomaterial Shapes Using Lyotropic Liquid Crystal Solvents.

A room temperature reduction-hydrolysis of Fe(III) precursors such as FeCl3 or Fe(acac)3 in various lyotropic liquid crystal phases (lamellar, hexagonal columnar, or micellar) formed by a range of ionic or neutral surfactants in H2O is shown to be an effective and mild approach for the preparation of iron oxide (IO) nanomaterials with several morphologies (shapes and dimensions), such as extended thin nanosheets with lateral dimensions of several hundred nanometers as well as smaller nanoflakes and nanodiscs in the tens of nanometers size regime. We will discuss the role of the used surfactants and lyotropic liquid crystal phases as well as the shape and size differences depending upon when and how the resulting nanomaterials were isolated from the reaction mixture. The presented synthetic methodology using lyotropic liquid crystal solvents should be widely applicable to several other transition metal oxides for which the described reduction-hydrolysis reaction sequence is a suitable pathway to obtain nanoscale particles.

PA56 キラル液晶溶媒で膨潤したコレステリックゲルのらせん配向特性(ソフトマター,ポスター発表,2015年日本液晶学会討論会)

PA56 キラル液晶溶媒で膨潤したコレステリックゲルのらせん配向特性(ソフトマター,ポスター発表,2015年日本液晶学会討論会)

Single crystalline growth of a soluble organic semiconductor in a parallel aligned liquid crystal solvent using rubbing-treated polyimide films

For directional control of organic single crystals, we propose a crystal growth method using liquid crystal as the solvent. In this study, we examined the formation of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) single crystals using a parallel aligned liquid crystal (LC) cell and rubbing-treated polyimide films in order to clarify the effects of LC alignment on anisotropic C8-BTBT crystal growth. Based on the results, we found that the crystal growth direction of C8-BTBT single crystals was related to the direction of the aligned LC molecules because of rubbing treatment. Moreover, by optical evaluation, we found that the C8-BTBT single crystals have a aligned molecular structure.

Gold Nanoparticles Incorporated Nematic Gel Micropillars Capable of Laser Actuation at Room Temperature

Liquid crystal elastomers (LCEs) capable of rapid reversible shape change and ease of actuation at room temperature are highly desired. In this study, a photothermally actuated system based on LCE gel micropillars incorporated with gold nanoparticles is reported for the first time. The photothermal conversion effects of gold nanoparticles (AuNPs) have been studied with a focus on nanoparticle shape (rods and spheres) and loading content. Upon swelling in low molecular mass liquid crystal solvent, the formation of LCE and LCE/AuNP gel enables the reduction of nematic-to-isotropic phase transition temperature (TNI), which allows the gelled micropillar capable of photothermal actuation at room temperature. It has been demonstrated that the LCE gel micropillar with incorporation of 1.0 wt % of gold nanorods can achieve a rapid 30% change in volume within 3 s when under proper laser irradiation at room temperature. The observed discontinuous volumetric transition of the gel micropillars is in good agreement wi...

Molecular dynamics simulation of single-walled carbon nanotubes inside liquid crystals

Molecular dynamic simulations of systems of single-walled carbon nanotubes (CNTs) in liquid crystalline solvents were performed, in order to investigate the effect of the molecular structure and phase of the liquid crystal (LC) on the interactions between the CNTs. Three different LC molecules (5CB, 8CB and 5CF) were considered in our study. Our results with 5CB and 8CB suggest that increasing the chain length of the hydrophobic part of the LC molecule by three carbon atoms is insufficient to decrease the tendency for the CNTs to aggregate in the LCs. Additionally, varying the phase of the LC is also insufficient to decrease the aggregation tendency of the CNTs. However, simulations with 5CF (which has fluorine atoms in the head group of the LC molecule) suggest that this LC solvent can decrease the tendency of the CNTs to aggregate. This study is relevant to assist experimentalists with the development of high-quality dispersions of large concentrations of CNTs in the LCs.

P-200L:Late-News Poster: Anisotropic Growth and Structural Analysis of Single Crystal Using Liquid Crystal Solvent for Molecular Alignment Controlled Organic Transistors

We have successfully developed the uniaxially-oriented single crystalline film formation technique of the soluble organic semiconductor (benzothienobenzothiophene) which combined liquid crystal solvent with rubbing-treated solution cell. As further study, we revealed that the one of crystal axes in those films was oriented along the direction of liquid crystal alignment.

Competing forces drive ordering

Colloidal Ordering The power and beauty of liquid crystals come from their tendency to order loosely over long length scales. This ordering can be tweaked using external fields, or via tailored boundary conditions, or embedded objects. Mundoor et al. deposited luminescent nanorods into a liquid crystal solvent (see the Perspective by Blanc). This caused a competition between local electrostatic interactions and the elastic ordering of the liquid crystal. The nanorods ordered into a triclinic structure not otherwise attainable. The authors further adjusted the structure using external fields. Science , this issue p. [69][1]; see also p. [40][2] [1]: /lookup/doi/10.1126/science.aaf0801 [2]: /lookup/doi/10.1126/science.aaf4260

Generation of fluorescent nanodroplets of liquid crystal utilizing electrospray deposition

Fluorescent nanodroplets of liquid crystal (LC) were generated by the electrospray deposition of LC solvent containing rhodamine 6G (Rh6G) dye molecules. The shape and density of the nanodroplets strongly depended on the concentration of LC diluted with ethanol solution. The fluorescent spectra from the Rh6G molecules in LC nanodroplets were obviously blue-shifted compared with the LC films of the bulk state. Furthermore, the LC nanodroplets were dispersed on a metallic nanograting formed by optically modifying an azobenzene thin-film layer under the metallic film. The nanodroplets were size-selectively aligned on the metallic nanograting.

Significant Enhancement of the Chiral Correlation Length in Nematic Liquid Crystals by Gold Nanoparticle Surfaces Featuring Axially Chiral Binaphthyl Ligands.

Chirality is a fundamental scientific concept best described by the absence of mirror symmetry and the inability to superimpose an object onto its mirror image by translation and rotation. Chirality is expressed at almost all molecular levels, from single molecules to supramolecular systems, and present virtually everywhere in nature. Here, to explore how chirality propagates from a chiral nanoscale surface, we study gold nanoparticles functionalized with axially chiral binaphthyl molecules. In particular, we synthesized three enantiomeric pairs of chiral ligand-capped gold nanoparticles differing in size, curvature, and ligand density to tune the chirality transfer from nanoscale solid surfaces to a bulk anisotropic liquid crystal medium. Ultimately, we are examining how far the chirality from a nanoparticle surface reaches into a bulk material. Circular dichroism spectra of the gold nanoparticles decorated with binaphthyl thiols confirmed that the binaphthyl moieties form a cisoid conformation in isotropic organic solvents. In the chiral nematic liquid crystal phase, induced by dispersing the gold nanoparticles into an achiral anisotropic nematic liquid crystal solvent, the binaphthyl moieties on the nanoparticle surface form a transoid conformation as determined by imaging the helical twist direction of the induced cholesteric phase. This suggests that the ligand density on the nanoscale metal surfaces provides a dynamic space to alter and adjust the helicity of binaphthyl derivatives in response to the ordering of the surrounding medium. The helical pitch values of the induced chiral nematic phase were determined, and the helical twisting power (HTP) of the chiral gold nanoparticles calculated to elucidate the chirality transfer efficiency of the binaphthyl ligand capped gold nanoparticles. Remarkably, the HTP increases with increasing diameter of the particles, that is, the efficiency of the chirality transfer of the binaphthyl units bound to the nanoparticle surface is diminished as the size of the particle is reduced. However, in comparison to the free ligands, per chiral molecule all tested gold nanoparticles induce helical distortions in a 10- to 50-fold larger number of liquid crystal host molecules surrounding each particle, indicating a significantly enhanced chiral correlation length. We propose that both the helicity and the chirality transfer efficiency of axially chiral binaphthyl derivatives can be controlled at metal nanoparticle surfaces by adjusting the particle size and curvature as well as the number and density of the chiral ligands to ultimately measure and tune the chiral correlation length.