Binary Liquid Crystal Mixtures Research Articles

Induced blue phase and twist grain boundary phase in binary mixtures of chiral calamitic and achiral hockey stick-shaped liquid crystals

Frustrated phases in chiral liquid crystalline systems, such as the blue phase (BP) and the twist grain boundary (TGB) phase, can create new opportunities in liquid crystal research. These frustrated phases have unique optical properties which can be used for specific applications. A new binary mixture system composed of a chiral rod-like ferroelectric liquid crystal and an achiral hockey stick-shaped compound was designed. This binary system exhibits induced frustration, resulting in the emergence of the BP-III and TGB*A phases in addition to the chiral ferroelectric Smectic-C* phase. We report a comprehensive study on several binary mixtures (xH-22.5= 0.162, 0.25, 0.396, 0.562) designed of a chiral ferroelectric liquid crystal derived from the lactic acid, namely 4-(octyloxy)phenyl 3-methoxy-4-((4-((2-(pentyloxy)­propanoyl)­oxy)benzoyl)oxybenzoate and achiral hockey stick-shaped compound, namely (E)-4-((E-((3-(decyloxy)-2-methylphenyl)imino)methyl)-phenyl 3-(4-(dodecyloxy)phenyl)acrylate. These mixtures induced the blue phase (BP-III, ~2.5–6.2K) and the twist grain boundary Smectic-A*phase (TGB*A  ~1.8–6K). Polarizing optical microscopy, birefringence, and dielectric spectroscopy were employed to investigate the BP-III and  phases, as those techniques provide insights into their structural and dynamic properties. The ferroelectric behaviour of the SmC* mesophase was investigated by electro-optics. The obtained results are discussed in relation to the molecular structures of the used materials.

Optical and thermodynamic studies of binary mixtures of nematic liquid crystals from homologous members of alkyloxybenzoic acid

Optical and thermodynamic studies of binary mixtures of nematic liquid crystals from homologous members of alkyloxybenzoic acid

Investigations of axioms of twist grain boundary phases (TGBPs) in binary mixture of liquid crystals

In this paper, the investigated mixture of liquid crystals shows a spacious range of twist grain boundary phases (TGBPs). Thermo dynamical, optical and dielectric measurements confirmed the presence of TGBPs in the mixtures of nematic and cholesteric liquid crystals. In the heating cycle, differential scanning calorimetry (DSC) thermogram shows the mixed different TGBPs at the high scanning rate. Cylindrical and cone-like textures with brushes of TGBA* is observed under the optical investigation. The grain boundaries and blocks of smectic phases are twisting two times around an axis. Wide-ranging dielectric investigation of nematic and cholesteric liquid crystal mixture have been performed in the 50 Hz–10 MHz range of frequency for the homogeneous conditions. In the absence of direct bias, TGBA* phase exhibits two dielectric relaxation processes, soft mode (SM) and process in the grain boundaries (PGBs). In the presence of electric field, grain boundaries steadily demolished the phases. Whereas the weak dielectric relaxation processes have been distinguished in the presence of the electric field in the TGBPs.

Binary mixtures of double hydrogen bond liquid crystals: chemical, optical, thermal investigations

Binary mixtures of double hydrogen bond liquid crystals are investigated by chemical, optical and thermal studies. These binaries exhibiting rich phase polymorphism, in which hydrogen bond is formed between Methyl Malonic acid (MM), heptyloxy benzoic acid (7BOA), and decyloxy benzoic acid (10BOA) abbreviated as MM + 7BOA and MM + 10BOA. MM + 7BOA (X) is considered as one of the variants while MM + 10BOA (Y) is considered as other variant. Appropriate molar ratio (0.1X to 0.9X and 0.1Y to 0.9Y) variation in the precursors leads to formation of nine binary mixtures.

Statement of Retraction: Formation of Lyotropic Micellar Nematic Phase in Binary Mixture of Liquid Crystals

This article refers to:Formation of Lyotropic Micellar Nematic Phase in Binary Mixture of Liquid Crystals

Statement of Retraction: Induced Reentrant Smectic-A Phase in Binary Mixtures of Liquid Crystals

Statement of Retraction: Induced Reentrant Smectic-A Phase in Binary Mixtures of Liquid Crystals

Statement of Retraction: Phase Transition Behavior of Smectic Phases in Binary Mixture of Liquid Crystals

This article refers to:Phase Transition Behavior of Smectic Phases in Binary Mixture of Liquid Crystals

Statement of Retraction: Optical and Thermal Characterization of Binary Mixtures of Liquid Crystals

Statement of Retraction: Optical and Thermal Characterization of Binary Mixtures of Liquid Crystals

Statement of Retraction: Twisted Grain Boundary Phase in Binary Mixture of Liquid Crystals

Statement of Retraction: Twisted Grain Boundary Phase in Binary Mixture of Liquid Crystals

Beyond Bulk Gay-Berne fluids: An outlook on mesogenic mixtures with molecular dynamics simulations

In this review, we focus on heterogeneous, thermotropic liquid crystal (LC) mixtures our group has studied with molecular dynamics (MD) simulations. Systems considered include: (1) binary LC mixtures, (2) colloidal inclusions in a mesogenic solvent, and (3) confined mesogenic samples. An extension of the Gay-Berne model is provided to treat the mixtures investigated. Our findings are contextualized to calamitic and discotic LC systems. Structural properties of the mesogenic solvent are probed using the Maier-Saupe (nematic) order parameter. Representative snapshots from MD simulations are used to corroborate phase phenomenology. Topological defects are treated in the presence of colloidal inclusions and in confined samples. The effect of solvent flow on the behavior of topological defects is also assessed. These LC mixtures are of interest in the area of applied materials: aside from their rich mesophase behavior, these systems provide a promising platform for molecular self-assembly and organization.

A second-order time accurate and fully-decoupled numerical scheme of the Darcy-Newtonian-Nematic model for two-phase complex fluids confined in the Hele-Shaw cell

We consider the numerical approximation of the binary immiscible mixture of nematic liquid crystals and viscous Newtonian fluids confined in a Hele-Shaw cell, where the free interface motion is simulated by using the phase-field approach via the energy variational method. The governing system is highly complicated nonlinear and coupled, consisting of the Darcy equations for the flow field, the Cahn-Hilliard equations for the free moving interface, and the constitutive equation for the nematic liquid crystal. The numerical scheme developed in this paper is the first “ideal” scheme, namely, it not only has the following characteristics: linearity, second-order time accuracy, unconditional energy stability, and decoupling structure, but also at each time step, only needs to solve a few elliptic equations with constant coefficients. We strictly prove that the scheme satisfies the unconditional energy stability and give a detailed implementation process. Various numerical experiments are further carried out to prove the effectiveness of the scheme, in which the influence of the initial orientations and anchoring elastic energy of the liquid crystal on the Saffman-Taylor fingering instability are studied.

Effect of size and concentration of magnetic nanoparticles on blue phase stabilization and electro-optical properties in blue phase liquid crystalline nanocomposites

Blue phase liquid crystal material having a wide blue phase range of 7 °C was prepared in a binary mixture of nematic and chiral nematic liquid crystals with optimization of chiral dopant concentration. Magnetic nanoparticles of size 20 nm, 40 nm in varying concentrations (<0.5 wt %) could successfully stabilize the blue phase temperature range. Interestingly, the BP stability increases approximately 7.8 °C with an increase in nanoparticles concentration up to a critical concentration (0.1 wt %) and then gradually decreases at higher concentrations of nickel nanoparticles. A detailed comparative electro-optical study of pure blue phase liquid crystal and size dependent nickel nanoparticles doped blue phase liquid crystals is accomplished. The transmission of light increases up to 42–45% for nickel nanoparticles doped blue phase liquid crystal samples than pure blue phase liquid crystal with negligible residual birefringence. An increase in isotropic temperature was noticed in 40 nm nickel nanoparticles doped sample. Also an improvement in threshold voltage, induced birefringence, contrast ratio and Kerr constant with doping of nickel nanoparticles was observed. The present study is a synergistic correlation of size and concentration of nickel nanoparticles with blue phase liquid crystals and sufficiently productive for developing nanoparticles doped blue phase liquid crystal optical devices in future. • Size and concentration dependent magnetic nanoparticles stabilised blue phase liquid crystals are prepared and studied. • 7.8 °C wide BP range was observed using Ni NPs in BPLCs. • Variation in phase transition temperatures and BP range was noticed with variation in concentration and size of NPs. • An improvement in switching voltage, contrast ratio, birefringence and Kerr constant was observed by stabilization of BPLCs through Ni NPs.

High-resolution investigation by Peltier-element-based adiabatic scanning calorimetry of binary liquid crystal mixtures with enhanced nematic ranges

High-resolution Peltier-element-based adiabatic scanning calorimetry (pASC) has been used to investigate the temperature dependence of the specific heat capacity and specific enthalpy of two mixture systems of the liquid crystal smectic A1 compound 5-n-nonyl-2-(4′-isothiocyanatophenyl)dioxane-1.3 (9DBT), and one of the smectic Ad compounds 4-n-octyloxy-4′-cyanobiphenyl (8OCB) and 4-nonyloxy-4′cyanobiphenyl (9OCB). For both mixture systems, measurements have been carried out over a large temperature range, from the crystalline solid phase over the smectic and nematic phases into the isotropic liquid phase. Both systems exhibit substantial, mixing-induced, enhanced nematic ranges and large changes in the composition dependence of the transition temperatures between the different phases. In both systems, eutectic melting points have been located and, for the different mixtures, the melting and eutectic transition heats have been obtained. The nematic to isotropic (NI) transitions are weakly first order with latent heat values in the range usually observed for this transition in other liquid crystals. The critical behavior of the specific heat capacity at the NI transition is described by exponent values near the tricritical one of 0.5. Along the smectic A to nematic (AN) transition lines, strong composition dependence was observed for the latent heat, from almost zero to values comparable to those observed at the nematic to isotropic transition. The concentration dependence of these AN latent heats was adequately fitted with a crossover function consistent with a mean-field free-energy expression that has a nonzero cubic term; the latter is induced by the Halperin-Lubensky-Ma coupling between the smectic A order parameter and orientational order director fluctuations. The fitting analysis resulted in the location of a Landau-tricritical point along one branch of the transition line in the system 9DBT-8OCB and one in each branch (for low and high 9OCB mole fractions) of the NA transition line of the 9DBT-9OCB system. The effective critical exponent values for the specific heat capacity of the AN transitions follow the McMillan ratio-dependence observed for other liquid crystal mixtures.

Optical and thermal studies on binary liquid crystal mixture

The novel binaryliquid crystal mixture is designed and synthesized from 4-methoxycinnamic acid (MCA) and 4-ethoxycinnamic acid&#x0D; (ECA). Quantum chemical (DFT) calculation for MCA+ECA geometry is optimized by DFT/B3LYP with 6-311G (d, p) basis set and its&#x0D; results are good agreement with experimental data. Fourier-transform infrared spectroscopic(FT-IR) study confirm the presence of&#x0D; intermolecular hydrogen bond in the liquid crystal mixture .The paramorphic changes in nematic phase and thermo-optic properties&#x0D; of binary liquid crystal mixture isanalyzed using polarizing optical microscope (POM) and differential scanning calorimetry (DSC)&#x0D; techniques. A noteworthy observation in the present liquid crystal mixture possesses smectic A phase along with nematic phases.&#x0D; Intermolecular hydrogen bond interaction and it’s stabilization energy of present mixture is studied by natural bond orbital (NBO)&#x0D; analysis. Due to the transition,the presen tliquid crystal mixtur einduces smecticA phase. The molecular properties of presen t binary liquid crystal mixtureis analyzed by HOMO-LUMO and experimental UV-Visible studies. Thermal spanwidth, stability factor and quantum chemical properties of the liquid crystal mixture are calculated.Molecular electrostatic potential, mulliken atomic&#x0D; charge distribution of the optimized MCA+ECA geometry is also reported.

Second-order accurate and energy stable numerical scheme for an immiscible binary mixture of nematic liquid crystals and viscous fluids with strong anchoring potentials

We consider in this paper numerical approximations of the immiscible binary mixture of nematic liquid crystals (LCs) and viscous fluids. We develop a second-order time marching scheme by adopting the recently developed stabilized-SAV (scalar auxiliary variable) approach where several critical stabilization terms are added to enhance the stability; thus, large time steps are allowed in computations. The scheme is highly efficient and one only needs to solve several decoupled linear equations with constant coefficients at each time step. The energy stability of the scheme is proved, and various 2D and 3D numerical experiments including the drop deformations and phase separations are then performed to validate the accuracy and energy stability of the proposed scheme.

Studies on binary mixtures of nematic liquid crystals made of strongly polar molecules with identical cores and antagonistic orientation of permanent dipoles

We report experimental studies on optical (birefringence, Δn), dielectric (Δε) and bend-splay elastic anisotropies (ΔK = K33 − K11) of a few mixtures of two nematic liquid crystals, namely CCH-7 and CCN-47, made of highly polar molecules with identical cores and antagonistic orientation of permanent dipoles. In particular, the polar group (-CN) attached to the bicyclohexane core of CCH-7 is oriented along the longitudinal direction whereas, in CCN-47, it is oriented along the transverse direction. We show that apart from the significant contribution to the optical and dielectric anisotropies, the antagonistic orientation of strongly polar groups plays a crucial role in determining the bend-splay elastic anisotropy. The elastic properties are explained based on a model proposed by Priest, considering the effect of intermolecular association and the resulting length-to-width ratio of the molecules.

Binary Liquid Crystal Mixtures Based on Schiff Base Derivatives with Oriented Lateral Substituents

Binary mixtures of the laterally substituted Schiff base/ester derivatives, namely 4-((2- or 3-) substituted phenyl imino methyl) phenyl-4”-alkoxy benzoates, Ia–d, were prepared and mesomorphically studied by differential scanning calorimetry (DSC) and their mesophases identified by polarized optical microscopy (POM). The lateral group (1-naphthyl, 2-F, 2-Br, 3-F in Ia–d, respectively) is attached to different positions of the phenyl Schiff moiety. The mixtures investigated were made from two differently shaped compounds that differ from each other in the polarity, size, orientation, and relative positions of the lateral group. The results revealed that the binary mixture Ia/Ib (bearing the naphthyl and 2-flouro substituents) exhibited the SmA phase, which covered the whole composition range. For the mixtures Ib/Id (2-F and 2-Br), the isomeric lateral F-group in compound Ib distributed the SmA arrangement of Id. In the Ic/Id mixture bearing two positionally and structurally different substituents, the addition of Ic to Id resulted in solid binary mixtures where its behavior may be attributed to the negligible steric effect of the small electronegative fluorine atom compared to the Br atom. Density functional theory (DFT) theoretical calculations were carried out to estimate the geometrical parameters of individual components and to show the effect of these parameters in the mesophase behavior of the binary system, where the higher dipole moment of Id (6 Debye) may be the reason for its high π–π molecular stacking, which influences its mesophase range and stability.

Influence of gold nanorods on the structure and photonic bandgap in a twist grain boundary phase with smectic C* blocks

We describe the first report of the influence of gold nanorods (GNR) on the induced twist grain boundary smectic C* (TGBC*) phase in a binary mixture of achiral bent-core and chiral linear liquid crystals. The GNR concentration-dependent phase diagram of these nanocomposites shows that the thermal range of this twist grain boundary phase having smectic C* blocks phase increases by 50% for an intermediate composition compared to that for the host binary mixture without nanorods. The inclusion of the nanorods is seen to have substantial effect on the structural and photonic bandgap features of the TGBC* phase. For example, the helical periodicity gets altered in all the three dimensions: while those within the block undergo a huge increase, the one which is orthogonal to the blocks, shrinks. The spacing of the square grid pattern arising normal to the TGB helix direction increases for the nanocomposites getting even doubled for a certain composition, a feature evidenced by optical microscopy as well as optical diffraction. Xray diffraction clearly brings out the feature that the presence of GNR alters the thermal character of the transition between the TGBC* and the cholesteric phase. Quantitative analysis of the data indicates that the system would remain in the vicinity of a possible tricritical point, a behavior having wider ramifications to understand the underlying critical phenomenon. Based on the experimental observations, and capturing the essence of the reported adaptive defect core targeting mechanism we propose a model wherein GNRs get confined in the grain boundary region. This feature offers a potential to have periodic and anisotropic plasmonic structure arising out of the synergetic interactions between the metal nanorod and the twisted grain boundary structure.

Dielectric investigation on some binary mixtures of hockey-stick-shaped liquid crystal and octyloxy-cyanobiphenyl

ABSTRACTWe report the measurement of temperature-dependent dielectric parameters in some binary liquid crystal mixtures comprising of a hockey-stick-shaped mesogen 4-(3-decyloxyphenyliminomethyl) phenyl-4-decyloxycinnamate (SF7) and calamitic compound 4′-octyloxy-4-cyanobiphenyl (8OCB). All the investigated mixtures possess a large positive dielectric anisotropy (Δε), although a noticeable reduction has been found by increasing the diverse-shaped dopant concentration. Investigation on the pretransitional behavior in the vicinity of isotropic to nematic (I–N) phase transition suggesting a tricritical character for all the studied mixtures. Parameterization of dielectric permittivity close to the nematic to smectic-A (N–Sm-A) phase transition exhibits non-universal values of the critical exponents describing a second-order nature of the transition. Systematic variation of critical exponents against dopant concentration and McMillan ratio reveals a well consistency with those obtained from the high-resolution optical birefringence measurements.

The formation of biaxial nematic phases in binary mixtures of thermotropic liquid-crystals composed of uniaxial molecules

ABSTRACTMonte Carlo simulations in the isothermal-isobaric ensemble are used to investigate the formation of an ordered, biaxial nematic phase in a binary mixture of thermotropic liquid crystals. The orientational dependence of the interaction between molecules of each pure component is the same as in the well-known Maier-Saupe model; each pure component of the mixture is therefore capable of forming a uniaxial nematic phase. For the interaction between molecules of different components, we use the same Maier-Saupe model but change the sign of the coupling constant. As a consequence a T-shaped arrangement of these molecules is energetically favoured. The formation of the biaxial phase occurs in two steps. At higher temperatures T, one of the components forms a uniaxial nematic phase whereas the other is in a quasi two-dimensional restricted isotropic liquid state. We develop a simple theoretical model to understand the high degree of (ostensible) nematic order in the latter. At lower T, the second component becomes nematic and then the entire mixture of the two compounds has biaxial symmetry. The biaxial nematic phase does not demix into domains rich in molecules of one or the other species.