Thermotropic Smectic Research Articles

Micro-scale viscosity measurements of different thermotropic and lyotropic classes of liquid crystals by using ferrofluid inclusions

Dispersing micro- and nanoparticles in liquid crystals (LCs) is utilised to tune liquid crystal properties, to add functionality or to exploit the self-organization of the liquid crystals to transfer order onto dispersed particles. Dispersing ferrofluid droplets in LCs produces a system similar to LC-microparticle dispersions, because the ferrofluid droplets behave in first approximation as non-compressible, only slightly deformable particles. Such a LC-ferrofluid system adds a magnetic functionality, which can be exploited to measure the viscosity and its anisotropy on a microscopic scale when moving the ferrofluid inclusions through various liquid crystals of the thermotropic, lyotropic or colloidal kind. Effective viscosities can be determined as a function of changing environment, such as temperature or concentration, and for variation of other factors such as the pitch of chiral phases for instance. The viscosities are calculated using Stokes’ Law together with the introduction of a boundary layer at the liquid crystal – ferrofluid interface. We present results for a variety of different liquid crystalline systems; thermotropic nematics, chiral nematics, smectics, lyotropic phases and chromonic systems, as well as colloidal LCs such as cellulose nanocrystals (CNC) and graphene oxide (GO) varying the viscosity over more than three orders of magnitude. The results are discussed in terms of the structures of respective phases.

Elastic response of colloidal smectic liquid crystals: Insights from microscopic theory.

Elongated colloidal rods at sufficient packing conditions are known to form stable lamellar or smectic phases. Using a simplified volume-exclusion model, we propose a generic equationof state for hard-rod smectics that is robust against simulation results and is independent of the rod aspect ratio. We then extend our theory by exploring the elastic properties of a hard-rod smectic, including the layer compressibility (B) and bending modulus (K_{1}). By introducing weak backbone flexibility we are able to compare our predictions with experimental results on smectics of filamentous virus rods (fd) and find quantitative agreement between the smectic layer spacing, the out-of-plane fluctuation strength, as well as the smectic penetration length λ=sqrt[K_{1}/B]. We demonstrate that the layer bending modulus is dominated by director splay and depends sensitively on lamellar out-of-plane fluctuations that we account for on the single-rod level. We find that the ratio between the smectic penetration length and the lamellar spacing is about two orders of magnitude smaller than typical values reported for thermotropic smectics. We attribute this to the fact that colloidal smectics are considerably softer in terms of layer compression than their thermotropic counterparts while the cost of layer bending is of comparable magnitude.

Preparation and proton conduction in liquid crystals containing sulfonic acid moiety

A series of novel biphenyl benzoate based liquid crystals (1) containing terminal sulfonic acid moieties have been prepared through the etherification reaction for anhydrous proton conduction. The chemical structures of 1 were characterized by nuclear magnetic resonance, Fourier transform infrared spectroscopy and high-resolution mass spectrometry. Differential scanning calorimetry measurements and polarizing optical microscopic observations indicated that 1 exhibited a thermotropic smectic A phase in a temperature range of 188–226°C. X-ray diffraction measurements suggested that the molecules of 1 in the smectic phase formed bilayer nanostructures, wherein the sulfonic acid moieties were lamellar aggregated within the layers to form two-dimensional pathways for proton conduction. Electrochemical impedance spectroscopy measurements suggested that the lamellar assembly of the sulfonic acid moieties in the smectic phase benefited the anhydrous proton conduction of the sulfonic acid derivatives, and proton conductivities on the order of 10−4 S/cm were achieved. The proton conductivity of 1 in the smectic A phase is higher than that in the crystal state and isotropic liquid state.

Macroscopic photocontrol of ion-transporting pathways of a nanostructured imidazolium-based photoresponsive liquid crystal.

The photocontrol of the macroscopic alignment of nanostructured 2D ion-transporting pathways is described. The uniplanar homogeneous alignment of the thermotropic smectic (Sm) liquid-crystalline (LC) phase has been successfully achieved via photoinduced reorientation of the azobenzene groups of the imidazolium-based LC material. The ionic layers of the Sm LC phase are macroscopically oriented perpendicular to the surface of the glass substrate. The oriented films show anisotropic ion conduction in the Sm phase. This is the first example of the macroscopic photoalignment of ion-conductive LC arrays. Reversible switching of homeotropic and homogeneous alignments has also been achieved for the LC material. These materials and the alignment methodology may be useful in the development of ion-based circuits and memory devices.

Myelin Structures Formed by Thermotropic Smectic Liquid Crystals

We report on transient structures, formed by thermotropic smectic-A liquid crystals, resembling the myelin figures of lyotropic lamellar liquid crystals. The thermotropic myelin structures form during the solubilization of a smectic-A droplet in an aqueous phase containing a cationic surfactant at concentrations above the critical micelle concentration. Similar to the lyotropic myelin figures, the thermotropic myelins appear in an optical microscope as flexible tubelike structures growing at the smectic/aqueous interface. Polarizing microscopy and confocal fluorescence microscopy show that the smectic layers are parallel to the tube surface and form a cylindrically bent arrangement around a central line defect in the tube. We study the growth behavior of this new type of myelins and discuss similarities to and differences from the classical lyotropic myelin figures.

棒状硫氰液晶的合成与表征

Rod-shaped thiocyanic compounds based on a 4-benzoyloxy-biphenyl mesogen were prepared by nucleophilic substitution with a thiocyanic salt.The number of carbon atoms in one terminal alkyloxy chain was 6,8 and 10.The mesomorphic properties of the synthesized compounds were characterized by means of polarized optical microscopy and differential scanning calorimeter.The results demonstrated that the thiocyanic compounds exhibited thermotropic smectic A and nematic phases.The isotropic point of the liquid crystals decreased with the increase in length of the terminal alkyloxy chain.

Synthesis and thermotropic liquid crystalline properties of heterogemini surfactants containing a quaternary ammonium and a hydroxyl group

A homologous series of novel heterogemini surfactants, ( N , N -dimethyl- N-[3-(alkyloxy)-2-hydroxypropyl]-alkylammonium bromide (referred to as C m OhpNC n ; m, n = 10 , 8; 12, 8; 14, 8; 16, 8; 14, 10; 12, 12 and 10, 14) were synthesized. Their thermotropic phase behavior was investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), infrared spectroscopy (IR) and X-ray diffraction (XRD). All the compounds showed high thermal stability and formed enantiotropic thermotropic smectic A liquid crystals. The mesophase region was sensitive to the overall length ( m + n ) of the two hydrophobic tails and was widened with increasing ( m + n ). When fixing the overall length of the two hydrophobic tails ( m + n = 24 ), the liquid crystal region was affected little by the dissymmetry of the two hydrophobic chains. The combination of IR and XRD results suggested the cis-configuration of the alkyl chain and the alkoxy chain with respect to the extended N–CH 2–CH(OH) skeleton in both crystal lattice and liquid crystal mesophase. The folding of the alkoxy chain at the carbon atom connecting the hydroxyl group led to the hydrogen bonding between the hydroxyl and the Br − counterion, which is beneficial to stabilizing the liquid crystal phase.

Uniaxially Parallel Alignment of a Smectic A Liquid-Crystalline Rod−Coil Molecule and Its Lithium Salt Complexes Using Rubbed Polyimides

The alignment behavior of thermotropic smectic A liquid-crystalline molecule 1 and its complexes with lithium triflate on the thin films of rubbed polyimides has been examined. Compound 1 has a rod−coil block structure consisting of a tetra(ethylene oxide) chain that is polar and a phenylcyclohexyl mesogen that is nonpolar. The use of a rubbed polyimide having a linear and rigid molecular structure prepared from pyromellitic dianhydride and 1,4-phenylenediamine induces the uniaxially parallel alignment of 1 and its lithium triflate complexes. The lithium salt complexes of compound 1 that exhibit smectic A phases function as two-dimensional ion conductors. The ionic conductivities of the aligned complexes of 1 on the rubbed polyimides were measured by an ac impedance method. Anisotropic ionic conductivities have been observed for the aligned liquid-crystalline lithium salt complexes.

Shape Dependence in the Formation of Condensed Phases Exhibited by Disubstituted Sucrose Esters

We report on the self-organizing properties of sucrose esters that are di-(1',6', 1',6, and 6,6')-substituted with aliphatic chains of identical or different chain lengths and levels of saturation. For the materials possessing two saturated aliphatic chains, the compounds exhibited thermotropic lamellar smectic A phases. A remarkable new phase transition was observed for the di-octadecanoyl homologue in which one smectic A phase transformed into another with a continuous change in layer spacing, but with a discontinuous change in the correlation length. The incorporation of long cis-unsaturated chains led to increased cross-sectional areas of the chains relative to the sucrose head groups and, hence, columnar phases were observed.

Orientational order in smectic liquid-crystalline phases of amphiphilic diols

The thermotropic smectic phases of amphiphilic 2-(trans-4-n-alkylcyclohexyl)-propane-1,3-diols were investigated by means of small- and wide-angle x-ray scattering and values of the smectic (bi-)layer spacing, the orientational order parameters P(2) and P(4), the orientational distribution function as well as the intralayer correlation length were extracted from the scattering profiles. The results for the octyl homolog indicate that these smectic phases combine a very high degree of smectic one-dimensional-translational order with remarkably low orientational order, the order parameter of which (P(2) approximately 0.56) is far below those values typically found in nonamphiphilic smectics. This combination, quite exceptional in thermotropic smectics, most likely originates from the intermolecular hydrogen bonding between the terminal diol groups which seems to be the specific driving force in the formation of the thermotropic smectic structure in these amphiphiles and leads to a type of microphase segregation. Even in the absence of a solvent, the liquid-crystalline ordering of the amphiphilic mesogens comes close to the structure of the so-called neat soaps, found in lyotropic liquid crystals.

Synthesis and mesomorphic properties of glycosyl dialkyl- and diacyl-glycerols bearing saturated, unsaturated and methyl branched fatty acid and fatty alcohol chains: Part II. Mesomorphic properties

The biophysical properties of a series of glycosyl dialkyl- and diacyl-glycerols bearing unsaturated or chiral methyl branched chains in the tail, and di- and trisaccharide carbohydrate headgroups are described. Thermotropism was investigated by polarising microscopy, the lyotropism was investigated by small angle X-ray diffraction and by the contact preparation method, and the gel to liquid crystalline phase transition by FT-IR-spectroscopy. The compounds displayed thermotropic Smectic A (SmA), cubic and columnar phases, whereas in the lyotropic phase diagram lamellar, hexagonal and cubic phases are found. The introduction of unsaturated or methyl branched chains leads to liquid crystallinity at ambient temperature. The difference between the 1,3-oleyl-glycerol maltoside and the corresponding 1,2-oleoyl-glycerol maltoside is small.

Halogen bonding: a new interaction for liquid crystal formation.

It is shown for the first time that liquid crystal behavior can be induced through halogen bonding. Thus, mixing the nonmesomorphic components 4-alkoxystilbazole with pentafluoroiodobenzene leads to a 1:1 halogen-bonded complex whose integrity is shown by X-ray single-crystal analysis and which shows thermotropic smectic A and nematic phases.

Crystal architecture and mesophase structure of long-chain N-alkylpyridinium tetrachlorometallates

The N-hexadecylpyridinium derivatives [C16Py] 2[MCl 4] (M=Cd ( 1), Zn ( 2)) were prepared and structurally characterized by X-ray diffraction methods. The crystal structure of 1 reveals a layered arrangement with alternation of monolayers of interdigitated cations with layers of isolated [CdCl 4] 2− anions. CH⋯ClCd interactions reinforce the association between anions and cations in the polar region of the supramolecular structure. Both 1 and 2 display a thermotropic smectic A phase in addition to some high-temperature crystalline modifications. The thermal polymorphism of the salts was studied by X-ray powder diffraction, differential scanning calorimetry (DSC), and thermal optical microscopy. The structural and mesomorphic characteristics of 1 and 2 are compared with those of the analogous salts along the series [C16Py] 2[MCl 4] (M=Co, Ni, Cu, Zn, Pd, Cd).

Hairpin turn dislocations in two-dimensional smectic phases of long semiflexible polymers.

We elucidate hairpin turn dislocations in two-dimensional smectic phases of long semi-flexible polymers. We discuss hairpin shapes, sizes, and free energies. We find that hairpin dislocation core may be, under some circumstances, substantially bigger than the smectic period size. Such hairpin dislocations are accompanied by large voids that are stable equilibrium structures with sizes determined by a competition of the polymer bending elasticity and smectic bulk elasticity. The large size of hairpin voids is associated with a low hairpin energy, much smaller than anticipated before. The actual hairpin shape, size, and energy are all qualitatively sensitive to the detailed nature of smectics. We document this by considering hairpin dislocations in lyotropic smectics (systems stabilized by repulsion between polymers, with a positive osmotic pressure) and in thermotropic smectics (systems stable even at zero osmotic pressure, with a preferred distance between semiflexible molecules). We discuss in detail hairpin dislocations in lyotropic sterically stabilized Smectics as well as in DNA-cationic lipid complexes. We elucidate the extinction of hairpin dislocations by annihilations with polymer end points. In lyotropic smectics, rates of these processes are shown to be limited by sluggish reptation of semiflexible molecules, as well as by substantial energy barriers.

Thermal and Liquid Crystalline Properties of a Polymer with Amphiphilic-Mesogenic Side-Chains

ABSTRACTA low-molecular-weight liquid crystalline amphiphilic compound (Az6Bu) and a liquid crystalline polymethacrylate [P(Az6Bu)] with amphiphilic-mesogenic side-chains are reported in this present paper. A polyethyleneimine chain with 2-hydroxyethyl side-groups was used as the water-soluble spacer. Az6Bu exhibited a lyotropic columnar phase and no thermotropic mesophase. P(Az6Bu) showed thermotropic and lyotropic liquid crystalline properties. P(Az6Bu) formed thermotropic smectic A and C mesophases on the heating and cooling processes. The lyotropic systems consisting of P(Az6Bu) and water exhibited a smectic C lyomesophase with oilystreak and schlieren textures. The layered structures formed in the thermotropic and lyotropic mesophases are composed of a sublayer produced by the anisotropic alignment of aromatic-mesogenic groups and a sublayer of hydrophilic groups.

Static and Dynamic Observations of Dislocations and Other Defects in Smectic Cano Wedges

We study the role of defects in the flow properties of a thermotropic smectic (in Cano wedge geometry) by in situ deformation experiments in an optical polarizing microscope. The motion of the edge dislocation array is studied for imposed strain rates and their climb velocity is measured. At a stress close to 3000 dyn/ cm2 a jerky climb of edges is observed implying the existence of screw dislocations which hinder the free motion of the former. At a stress close to 5000 dyn/ cm2a viscous motion of edges is evidenced for which we confirm the validity of the Orowan relation, established for solid crystals.

Liquid Crystalline Properties and Orientational Structure of Binary Systems Built from Poly(Vinylalcohol) and Amphiphilic Compound

Liquid crystalline binary systems, consisting of poly(vinylalcohol) and an amphiphilic compound with hydrophobic nitroazobenzene and hydrophilic ethyleneimine units, were prepared, and their thermal and liquid crystalline properties were estimated. The amphiphilic compound exhibited a smectic A phase with a focal conic fan texture. The liquid crystalline binary systems showed a thermotropic smectic A mesophase. In the smectic A phase, a smectic layer structure with hydrophobic and hydrophilic sublayers was formed.

Thermal and liquid crystalline properties of liquid crystalline polymethacrylates with ammonium units and their non-ionic family

Ionic and non-ionic liquid crystalline polymethacrylates were synthesized, and their thermal and liquid crystalline properties were compared. Both the ionic and non-ionic liquid crystalline polymethacrylates exhibited a thermotropic smectic A phase. An isotropization temperature of the ionic liquid crystalline polymethacrylate was higher than for the non-ionic liquid crystalline polymethacrylate. Moreover, the ionic liquid crystalline polymethacrylate showed a higher glass transition temperature when compared to the non-ionic liquid crystalline polymethacrylate. The ionic and non-ionic liquid crystalline polymethacrylates formed a partial bilayer structure in the smectic A phase. Copyright © 2000 John Wiley & Sons, Ltd.

Liquid Crystalline and Surfactant Properties of Alkyl Pyridinium Salts

Several new alkyl pyridinium salts, namely 1-n-alkyl-4-cyanopyridinium bromides with alkyl chains containing 14, 16, and 18 carbon atoms, were synthesized, and their mesomorphic and micellar properties were studied. For compounds with 16 and 18 carbons in the alkyl chain, a thermotropic smectic A phase is present. The compounds also behave as surfactants in dilute aqueous solutions, and the Krafft temperature and the critical micelle concentration of each compound were determined.

Chiral Fluctuations and Structures

Abstract Chiral molecules form a number of non-chiral structures, the simplest being an isotropic fluid phase. In a mesophase of achiral molecules the fluctuations will on an average be achiral as well: left-handed twists and right-handed twists will occur with the same probability. In a system composed of chiral molecules, however, the fluctuations will be biased in one direction or the other, and there will be optical effects such as a non-zero fluctuation induced rotary power in addition to the molecular rotary power of the individual molecules. We discuss this effect in a number of contexts, including lyotropic lamellar phases. When the tendency to twist is strong enough or the line energy of having an exposed edge is small enough, a new, defect riddled ground state of a lyotropic lamella, akin to the Renn-Lubensky twist-grain-boundary phase of thermotropic smectics, can occur.