Order In Nematic Liquid Crystals Research Articles

Dipole-dipole interactions and the origin of ferroelectric ordering in polar nematics

ABSTRACT A molecular origin of the ferroelectric ordering in the nematic phase is considered in detail considering a model based on electrostatic interaction between permanent molecular dipoles modulated by the anisotropic molecular shape. It is shown that a contribution to the total free energy of the long-range tail of the dipole-dipole interaction potential defines the total electrostatic energy of the system which depends on the sample shape and on the boundary conditions. This contribution may strongly affect the transition into the ferroelectric phase. However, the dipole-dipole interaction itself can hardly be responsible for the ferroelectric ordering in nematic liquid crystals for any reasonable values of the molecular dipole. A more promising model which combines dipole-dipole interaction and short-range orientational-translational correlations is also considered.

Improving the nonlinear electro-optical responses of doped nematic liquid crystals with chiral dopants

Liquid crystals with considerable optical and electro-optical responses play important roles in photonics and optoelectronics. In this research, the electro-optical responses of pure and doped nematic liquid crystal with left-handed S-1011 chiral dopant with different percentages were investigated at different temperatures for the first time. According to the results, nematic liquid crystal with 4 wt% of chiral dopant indicates high electro-optical Kerr constat and third-order nonlinear susceptibility. In this case, various molecular interactions enhance the average order of nematic liquid crystal. By increasing the temperature, gradually the Kerr constant is deecreased, but this decreasing is slow for liquid crystal with 9 wt% of chiral dopant. Moreover, the temperature dependence of Kerr constant was used for calculating the pre-transition temperature. Therefore, these results provide a precise and simple method for improving the electro-optical responses of a nematic liquid crystal, which is an important step in the design of optoelectronic devices.

A new order of liquids: polar order in nematic liquid crystals.

Given the widespread adoption of display technology based on nematic liquid crystals, the discovery of new nematic phases at thermodynamic equilibrium, although extremely rare, generates much excitement. The remarkable discovery polar order and giant ferroelectric polarisation in a nematic fluid is a watershed moment in soft matter research, and is one of the most important discoveries in the 150 year history of liquid crystals. After a brief introduction to this emerging field, we present the current state-of-the art in terms of understanding the molecular origins of this phase, before exploring how molecular structure underpins the incidence of this phase, as well as exploring future directions.

Relationship of pitch length of cholesteric liquid crystals with order parameter and normalized polarizability

It is well-known that a cholesteric liquid crystal (CLC) resembles nematic liquid crystal (NLC) in all physical properties except a tendency to align CLC molecules into a helical structure. Thus, due to these mutual similarities between a CLC and NLC, finding the relationship of pitch length (P) with physical parameters of an NLC can develop the CLC properties. In this work, we introduced the relationship of P with NLC's order parameter, and normalized polarizability as used in CLC. We successfully equationalized the temperature dependence of p with order parameter, and normalized polarizability of NLC. The temperature-dependent p shows linear equational form with order parameter, and normalized polarizability. Based on our results, P decreases at high temperatures, and increases with the order parameter values and molecular normalized extraordinary polarizability parameter. The results exhibit several advantages, such as simplifying the complex experimental works before synthesizing chiral dopants as employed in CLC, developing the selective reflection properties in a CLC with NLCs, and investigating the helical twisting property in CLC with the physical properties of NLCs.

Bioinorganic Membrane Using A New Kurumi Liquid Crystal

The work characterizes develop a single layer bioinorganic membrane using nano-molecule Kurumi C13H20BeLi2SeSi / C13H19BeLi2SeSi, is well characterize computationally. As its scientific name 3-lithio-3-(6-{3-selena-8-beryllatricyclo [3.2.1.02,⁴]oct-6-en-2-yl}hexyl)-1-sila-2-lithacyclopropane. The work was based on a molecular dynamics (MD) of 1ns, using the CHARMM22 force field, with step 0.001 ps. Calculations indicate that the final structure, arrangement have the tendency to form a single layer micellar structure, when molecular dynamics is performed with a single layer. However, when molecular dynamics were carried out in several layers, indicates the behavior of a liotropic nematic liquid crystal order. Kurumi features the structure polar-apolar-polar predominant. Limitations our study has so far been limited to computational simulation via quantum mechanics e molecular mechanics (QM/MM), an applied theory. Our results and calculations are compatible and with the theory of QM/MM, but their physical experimental verification depend on advanced techniques for their synthesis, obtaining laboratory for experimental biochemical. Going beyond imagination, the most innovative and challenging proposal of the work advances the construction of a structure compatible with the formation of a “new DNA”, based now on the kurumi molecule.

Bioinorganic Membrane Using Kurumi, A New Liquid Crystal

The work characterizes develop a single layer bioinorganic membrane using nano-molecule Kurumi C13H20BeLi2SeSi / C13H19BeLi2SeSi, is well characterize computationally. As its scientific name 3-lithio-3-(6-{3-selena-8-beryllatricyclo [3.2.1.02,⁴] oct-6-en-2-yl}hexyl)-1-sila-2-lithacyclopropane. The work was based on a molecular dynamics (MD) of 1ns, using the CHARMM22 force field, with step 0.001 ps. Calculations indicate that the final structure, arrangement have the tendency to form a single layer micellar structure, when molecular dynamics is performed with a single layer. However, when molecular dynamics were carried out in several layers, indicates the behavior of a liotropic nematic liquid crystal order. Kurumi features the structure polar-apolar-polar predominant. Limitations our study has so far been limited to computational simulation via quantum mechanics e molecular mechanics (QM/MM), an applied theory. Our results and calculations are compatible and with the theory of QM/MM, but their physical experimental verification depend on advanced techniques for their synthesis, obtaining laboratory for experimental biochemical. Going beyond imagination, the most innovative and challenging proposal of the work advances the construction of a structure compatible with the formation of a “new DNA”, based now on the kurumi molecule.

Microfluidic control over topological states in channel-confined nematic flows

Compared to isotropic liquids, orientational order of nematic liquid crystals makes their rheological properties more involved, and thus requires fine control of the flow parameters to govern the orientational patterns. In microfluidic channels with perpendicular surface alignment, nematics discontinuously transition from perpendicular structure at low flow rates to flow-aligned structure at high flow rates. Here we show how precise tuning of the driving pressure can be used to stabilize and manipulate a previously unresearched topologically protected chiral intermediate state which arises before the homeotropic to flow-aligned transition. We characterize the mechanisms underlying the transition and construct a phenomenological model to describe the critical behaviour and the phase diagram of the observed chiral flow state, and evaluate the effect of a forced symmetry breaking by introduction of a chiral dopant. Finally, we induce transitions on demand through channel geometry, application of laser tweezers, and careful control of the flow rate.

Induced orientational molecular ordering in nematic liquid crystals with magnetic nanoparticles

Induced orientational molecular ordering in nematic liquid crystals with magnetic nanoparticles

A method to find the initial temperature range of the short-range order in the isotropic phase of nematic liquid crystals based on the electro-optical Kerr effect

It is well-known that orientational order of nematic liquid crystals (NLCs) is converted during phase transition from the long-range order (LRO) in the nematic phase to the short-range order (SRO) in the isotropic state. Finding the initial temperature range of SRO in the isotropic state can be a challenging issue because most of the physical constants disappear after this phase transition. For the first time, to resolve this issue, we introduced a new method based on the electro-optic Kerr (EOK) effect in NLC mixtures. In this method, the coherence length (ξ), which was qualitatively estimated by employing the pre-transitional temperature (T⁎) according to the de Gennes phenomenological theory, and the refractive index (n) were correlated with the Kerr constant (B) at the same temperature in the isotropic phase. Because molecular interaction in the NLCs is one of the essential factors in the investigation of the orientational ordering, we used n and ξ as described intra- and intermolecular interactions, respectively. In other words, n attributes to the polarization and dipole moment as an important parameter of the intramolecular interaction and ξ demonstrates the intermolecular interaction and domains of SRO interaction in the isotropic phase. Finally, the initial temperature range of SRO in the isotropic phase was found from the temperature dependence with B of the normalized values of influential coefficients n and ξ at the similar temperatures. Our proposed method appropriately can provide a suitable approach to distinguish the preservation of the anisotropy effect in the isotropic phase of NLCs.

Induced orientational molecular ordering in nematic liquid crystals with magnetic nanoparticles

Magneto-induced molecular orientational transitions in nematic liquid crystals doped by ferromagnetic nanoparticles have studied. On the basis of a microscopic approach of tensor operators it is sequentially considered the influence of the ferromagnetic dopes on the sensitivity of the orientational structure and the optical activity of the nematic liquid crystals.

The effect of voltage controlled orientation order of liquid crystals in non-acrylic polymer dispersed liquid crystals films

ABSTRACTThe nematic liquid crystals (LCs) are randomly dispersed material with random orientation order in polymer dispersed liquid crystal (PDLC) films. The LCs change their orientation from random to vertical as electric field is applied. This transformation of orientation order of nematic liquid crystals in the PDLC films is controlled by many factors operating simultaneously. For instance, some factors like the internal forces of attractions among the neighboring LC molecules, anchoring with polymeric matrix, ITO glass boundaries, and chemical structures of the materials are less studied. The learning of extent of vertical orientation of liquid crystal droplets in an electric field is essential to attain optimum electro optical properties of PDLCs. In this finding, bipolar and radial LCs droplets with random orientation have been observed in non-acrylic polymeric media. It is learned that with small increase of contents of external material, the extent of vertical orientation has been varied intensely. The extent of vertical orientation of LCs molecules increases as the contents of external non-acrylic polymeric material decreased. For this study, the orientations of LCs with respect to material type/contents, external applied force, and restoration of electric filed as hysteresis have been studied in details.

Determination of the symmetry classes of orientational ordering tensors

The orientational order of nematic liquid crystals is traditionally studied by means of the second-rank ordering tensor . When this is calculated through experiments or simulations, the symmetry group of the phase is not known a priori, but needs to be deduced from the numerical realisation of , which is affected by numerical errors. There is no generally accepted procedure to perform this analysis. Here, we provide a new algorithm suited to identifying the symmetry group of the phase. As a by product, we prove that there are only five phase-symmetry classes of the second-rank ordering tensor and give a canonical representation of for each class. The nearest tensor of the assigned symmetry is determined by group-projection. In order to test our procedure, we generate uniaxial and biaxial phases in a system of interacting particles, endowed with or symmetry, which mimic the outcome of Monte–Carlo simulations. The actual symmetry of the phases is correctly identified, along with the optimal choice of laboratory frame.

Electronic in-plane symmetry breaking at field-tuned quantum criticality in CeRhIn5.

Electronic nematic materials are characterized by a lowered symmetry of the electronic system compared to the underlying lattice, in analogy to the directional alignment without translational order in nematic liquid crystals. Such nematic phases appear in the copper- and iron-based high-temperature superconductors, and their role in establishing superconductivity remains an open question. Nematicity may take an active part, cooperating or competing with superconductivity, or may appear accidentally in such systems. Here we present experimental evidence for a phase of fluctuating nematic character in a heavy-fermion superconductor, CeRhIn5 (ref. 5). We observe a magnetic-field-induced state in the vicinity of a field-tuned antiferromagnetic quantum critical point at Hc ≈ 50 tesla. This phase appears above an out-of-plane critical field H* ≈ 28 tesla and is characterized by a substantial in-plane resistivity anisotropy in the presence of a small in-plane field component. The in-plane symmetry breaking has little apparent connection to the underlying lattice, as evidenced by the small magnitude of the magnetostriction anomaly at H*. Furthermore, no anomalies appear in the magnetic torque, suggesting the absence of metamagnetism in this field range. The appearance of nematic behaviour in a prototypical heavy-fermion superconductor highlights the interrelation of nematicity and unconventional superconductivity, suggesting nematicity to be common among correlated materials.

Fluctuation-induced forces in nematics with a foreign anisotropy in the bulk

Within a linear coupling between orientational order of nematic liquid crystal and anisotropic mesoscopic particles immeresed in the nematic, the pseudo-Casimir effect is investigated. A quenched disorder in the alignment of the particles, which is on average in the direction of the nematic director, induces an inter-substrate force as this composite is confined by two flat parallel surfaces a distance d apart. The disorder-induced force decays as –d−1 in the weak coupling regime. The force magnitude increases with the variance of the disorder and decreases on increasing the correlation length of the disorder. If the disorder is considered to be annealed, the disorder effects are not decoupled from the thermal effects and thus the form of the nematic fluctuation-induced force does not alter. The force is affected by the disorder only through a re-normalization of the mean particles’ pinning strength. The trend for this modified thermal-induced force with respect to the variance and the correlation length of the disorder remains as in the quenched case, where the pseudo-Casimir force was decomposed into two distinct thermal- and disorder-induced components.

Search for microscopic and macroscopic biaxiality in the cybotactic nematic phase of new oxadiazole bent-core mesogens

The possibility of biaxial orientational order in nematic liquid crystals is a subject of intense current interest. We explore the tendencies toward local and global biaxial ordering in the recently synthesized trimethylated oxadiazole-based bent-core mesogens with a pronounced asymmetric (bow-type) shape of molecules. The combination of x-ray diffraction and optical studies suggests that the biaxial order is expressed differently at the short- and long-range scales. Locally, at the scale of a few molecules, x-ray-diffraction data demonstrate biaxial packing. However, above the mesoscopic scale, the global orientational order in all three compounds is uniaxial, as evidenced by uniform homeotropic alignment of the nematic phase which is optically tested over the entire temperature range and by the observations of topological defects induced by individual and aggregated colloidal spheres in the nematic bulk.

Nematic liquid crystal order reconstruction in ultraconfinement, from density-functional theory

ABSTRACTI use the Onsager approximation of density-functional theory with a simple Parsons–Lee re-scaling to study a hybrid-aligned liquid crystal under very strong confinement. The system is modelled as a film of hard Gaussian overlap particles in a slit geometry, where anchoring is planar at one wall and homeotropic at the other. As the film density is increased from the isotropic phase, a planar-disordered layer grows from the planar-anchoring wall, and a homeotropic layer from the homeotropic-anchoring wall. For film thicknesses between 2 and 7 particle lengths, the degree of overall nematic order as measured by the spatial average of (where is the nematic order parameter tensor) is a continuously increasing function of the density, with a pronounced rise around the bulk isotropic-nematic transition. This rise is steeper the thicker the film, and is preceded by a large amount of biaxiality growing from the planar-anchoring wall. Deeper into the nematic phase, most of the film is either planar or homeotropic, but some biaxiality persists in a region of otherwise reduced overall nematic order whose position varies with film thickness. This is similar to the Schopohl–Sluckin scenario of a biaxial defect core.

Tuning phase retardation behaviour of nematic liquid crystal using quantum dot

We here report on the phase retardation behavior of nematic liquid crystal (NLC) doped with CdSe quantum dot (QD). A study of birefringence and relative permittivity in 4-octyl-4′-cyanobiphenyl (8CB) NLC and its variation with doping of QDs has been presented. The study shows improvement of NLC ordering after addition of QDs. The observed higher value of birefringence in QD doped NLC system has been attributed to improved alignment due to additional order in NLC by self assembled QDs. The improved order of NLC system has also been explained by a schematic illustration for pristine and QD doped NLC system. Study of relative permittivity has also revealed the ordering effect in QD dispersed NLC system.

Eight types of symmetrically distinct vectorlike physical quantities.

The Letter draws the attention to the spatiotemporal symmetry of various vectorlike physical quantities. The symmetry is specified by their invariance under the action of symmetry operations of the nonrelativistic space-time rotation group O(3)×(1,1') = O'(3), where 1' is a time-reversal operation, the symbol × stands for the group direct product, and O(3) is a group of proper and improper rotations. It is argued that along with the canonical polar vector, there are another seven symmetrically distinct classes of stationary physical quantities, which can be--and often are--denoted as standard three-component vectors, even though they do not transform as a static polar vector under all operations of O'(3). The octet of symmetrically distinct "directional quantities" can be exemplified by two kinds of polar vectors (electric dipole moment P and magnetic toroidal moment T), two kinds of axial vectors (magnetization M and electric toroidal moment G), two kinds of chiral "bidirectors" C and F (associated with the so-called true and false chirality, respectively) and still another two bidirectors N and L, achiral ones, transforming as the nematic liquid crystal order parameter and as the antiferromagnetic order parameter of the hematite crystal α-Fe(2)O(3), respectively.

Nematic order on a deformable vesicle: theory and simulation

We develop a coarse-grained particle-based model to simulate membranes with nematic liquid-crystal order. The coarse-grained particles form vesicles which, at low temperature, have orientational order in the local tangent plane. As the strength of coupling between the nematic director and the vesicle curvature increases, the vesicles show a morphology transition from spherical to prolate and finally to a tube. We also observe the shape and defect arrangement around the tips of the prolate vesicle.

Orientational order parameter studies in two symmetric dimeric liquid crystals – an optical study

The optical technique developed by [W. Kuczynski, B. Zywucki, and J. Malecki, Determination of orientational order parameter in various liquid-crystalline phases, Mol. Cryst. Liq. Cryst. 381 (2002), pp. 1–19; B.J. Zywucki and W. Kuczynski, IEEE transactions on optical phenomena – The orientational order in nematic liquid crystals from birefringence measurements, Dielectr. Electr. Insul. 8 (2001), pp. 512–515] is fabricated and used to determine the orientational order parameter in two dimeric liquid crystalline compounds nematic and SmA phases of α,ω-bis(4-alkylanilinebenzylidene-4′-oxy)alkane (m.OnO.m) homologous series. The compounds studied are 5.O8O.5 and 5.O10O.5 which exhibit nematic and SmA, and nematic phases, respectively. The orientational order parameter in both the phases of nematic and SmA phases of the compound one and the nematic phase of the compound two are obtained using the principle of Newton's rings which gives directly the birefringence, δn of the liquid crystal dimer. The merits of the technique used are presented over the conventional techniques for the determination of orientational order parameter. The results for the two compounds are compared with those values estimated from n e, n o and density using the two internal field models due to Vuks and Neugebauer applicable to nematic phase.