Liquid Crystal Phase Transition Research Articles

Isotropic micellar to tilted lamellar phase transition in lyotropic liquid crystals

We extend our previous phenomenological model for the isotropic micellar to lamellar (smectic-A) phase transition to the isotropic micellar to tilted lamellar (smectic-C) (I–Lt) phase transition in lyotropic liquid crystals. We analyze the influence of micellar concentration on the I–Lt phase transition. The conditions for the I–Lt phase transition and the stability conditions of the tilted lamellar phase are calculated. The temperature dependence of the non-linear dielectric effect in the isotropic micellar phase above the I–Lt phase transition is calculated. Within this model the I–Lt phase transition is found to be always first order.

Phase transitions of a monotropic azomethine liquid crystal investigated by ATR–FTIR spectroscopy

The liquid crystalline behavior of an azomethine, namely 4-chlorobenzylidene-4-n-butoxyaniline (M), was investigated by using optical polarized light microscopy, differential scanning calorimetry, thermo-optical analysis and powder X-ray diffraction at temperature. Fourier transform infrared spectroscopy (FTIR), in attenuated total internal reflection configuration, was employed in order to analyze the microstructural changes occurring during the azomethine phase transitions. Specific sensitive absorption bands were used to observe the smectic A (SmA) mesophase. The hexatic smectic B (SmB) mesophase was evidenced by recording the CH2 scissoring domain, belonging to the butoxy tail. It was assumed that the hexagonal ordering of the SmB mesophase was proven by the band evolution at 1468 cm−1. The azomethine linkage – monitored by the CH=N moiety stretching vibration – showed insignificant response to temperature due to its rigidity.

Critical temperature in phase transition of blue phase liquid crystal

A critical temperature is found in the phase transition of blue phase liquid crystal (BPLC), which affects the electro-optical properties and polymer stabilization of polymer stabilized BPLCs (PSBPLCs). The relation between lattice formation process of BPLCs and the temperature is also demonstrated showing that the heterogeneous lattice generation and the homogeneous lattice growth dominate the different temperature ranges in phase transition process. With different cooling rates, the material properties of BPLCs change as the result of different stages of heterogeneous lattice generation and homogeneous lattice growth.

Phase-transition properties of glycerol-monopalmitate lipid bilayers investigated by molecular dynamics simulation: influence of the system size and force-field parameters

Phase-transition properties of glycerol-1-monopalmitate (GMP) bilayers are investigated using explicit-solvent molecular dynamics (MD) simulations, initiated from structures appropriate for the gel (GL) or liquid crystal (LC) phases, and carried out at different hydration levels and temperatures. Building up on a previous study and based on 600 ns simulations, the influence of the system size and of the force field on the equilibrium thermodynamic and dynamic parameters of the bilayers in the GL and LC phases, as well as on the temperature Tm and properties of the GL ↔ LC phase transition, are analysed. Qualitatively speaking, the results agree with the available experimental data for the area per lipid in the two phases and for the phase-transition temperatures at the three hydration levels irrespective of the selected model parameters. They also suggest that the total number of hydrogen bonds formed between a lipid headgroup and its environment is essentially constant, amounting to about four in both the LC and the GL phases. Quantitatively speaking, the dependence of Tm on the hydration level is found to be non-systematic across the different combinations of model parameters. This results in part from a sensitivity of the results on the system size and force-field parameters but also from the limited accuracy of the bracketing approach employed here to estimate Tm. Finally, a simple kinetic model is proposed to account for the timescales of the transitions. This model involves enthalpy and entropy increases of about 26 kJ mol− 1 and 83 J mol− 1 K− 1 per lipid, upon going from the GL to the LC phase. The transition state is associated with activation parameters corresponding to 13% and 11%, respectively, of these values along the GL → LC transition, resulting in an activation free energy of about 0.3 kJ mol− 1 per lipid at Tm.

P.76: Threshold Temperature Effect on Phase Transition of Blue Phase Liquid Crystal

AbstractThe effect of threshold temperature on the phase transition of blue phase liquid crystals (BPLCs) is investigated that the electro‐optical properties can be affected by the threshold temperature. And the relationship between lattice formation process of BPLCs and temperature is also demonstrated that the heterogeneous lattice generation and the homogeneous lattice growth play different roles in phase transition process with different cooling rates.

Anomaly of Pretransitional Behavior at the Nematic–Smectic-A Phase Transition of Amphiphilic Liquid Crystals with a Hydrophilic Group

In order to clarify the origin of the X-ray diffraction peak corresponding to the smectic-like layer ordering appearing even in the nematic phase over a wide temperature range above the nematic-smectic A (NA) phase transition in liquid crystal (LC) molecules with a hydroxy group, we investigated the critical behavior of bend elastic constants and the correlation length of the smectic-like ordering in the N phase. It is found that cybotactic clusters with the transient layer ordering grow up extremely even far above the NA phase transition, and the critical exponent of the correlation length of the cybotactic clusters is estimated anomalously larger than that of conventional LC materials. Furthermore, we measured diffusion constants parallel and perpendicular to the director in the N phase, and concluded that cybotactic clusters with the smectic layer ordering create a finite potential barrier to prevent diffusion of the molecules parallel to the director as well as the true smectic A layer structure.

Mechanism of Photochemical Phase Transition of Single-Component Phototropic Liquid Crystals Studied by Means of Holographic Grating Recording

Phototropic liquid crystals (PtLC) are a new class of materials possessing number of potential applications in photonics devices. However, so far a significant majority of PtLC materials has been r...

Phase transitions of phospholipids as a criterion for assessing the capacity for thermal adaptation in fish

This study examines the crystal-liquid crystal phase transitions of the major phospholipids, phosphatidylcholine (PC) and phosphatidylethanolamine (PE), from muscle tissue of marine fish living at temperatures of 0–4.1°C (the Pacific cod Gadus macrocephalus, banded Irish lord Hemilepidotus gilberti, Pacific halibut Hippoglossus hippoglossus, black edged sculpin Gymnocanthus herzensteini, dark colored flounder Pleuronectes obscurus, and plain sculpin Myoxocephalus jaok), as well as of fish living at 14 and 18°C (Pacific redfin Tribolodon brandti). The PC and PE phase-transition thermograms of all the investigated species displayed specific profiles. The largest share of the thermogram area at temperatures higher than those of the habitat was found for the PC (28–40%) and PE (47–82%) of the black-edged sculpin, dark-colored flounder, and the plain sculpin, which have reduced physiological activity at low temperatures. In the Pacific cod, banded Irish lord, and the Pacific redfin, this parameter was much lower, 0–18% (PC) and 0–39% (PE). The thermotropic behavior PC and PE was symbate in all fish, except for the cod and the plain sculpin. The transition enthalpy of PC in all the investigated species was 2.8 times higher than that of PE. To interpret the varied PC and PE thermogram profiles of fish with similar fatty-acid compositions, the data on the composition of the molecular species of these phospholipids appeared to be the most informative. This study suggests that each fish species has its own strategy for thermal adaptation, which is realized through a certain set of phospholipid molecular species.

Liquid crystal phase transitions in suspensions of mineral colloids: new life from old roots

A review is given of the field of mineral colloidal liquid crystals: liquid crystal phases formed by individual mineral particles within colloidal suspensions. Starting from their discovery in the 1920s, we discuss developments on the levels of both fundamentals and applications. We conclude by highlighting some promising results from recent years, which may point the way towards future developments.

A temperature–concentration (T–X) phase diagram calculated using the mean field theory for liquid crystals

Phase-line equations for smectic-hexatic phase transitions in liquid crystals were derived using the Landau phenomenological theory. In particular, second-order transitions for the smectic-A-smectic-C (SmA-SmC) and hexatic-B-hexatic-F (or HexI) transitions were studied and the tricritical points for these transitions were located. The calculated phase-line equations were fitted (using experimental data for various liquid crystals) to construct a generalized T-X phase diagram. It was shown that the T-X phase diagram calculated from the free energy adequately describes the observed behavior of liquid crystals during smectic-hexatic transitions.

Quantum dot/liquid crystal composite materials: self-assembly driven by liquid crystal phase transition templating

The isotropic to nematic liquid crystal (LC) phase transition is used to create organized assemblies of CdSe/ZnS core/shell quantum dots (QDs). Under controlled conditions, well dispersed QDs are expelled from the ordered domains of nematic LC into the remaining isotropic domains. The final LC phase produces three dimensional QD assemblies that are situated at the defect points in the LC volume. Through the luminescence of the QDs we are able to track the movement of the nanoparticles as the phase is formed as well as spectrally probe the resulting QD assemblies. Forster resonance energy transfer (FRET) measurements, combined with small angle X-ray scattering (SAXS) data reveal that the QD assemblies have a consistent inter-particle spacing of approximately 7.6 nm. Additionally, the location of the assemblies is shown to be controllable by utilizing beads as defect nucleation points.

Isotropic micellar to lamellar phase transition in lyotropic liquid crystals

A phenomenological theory is presented to describe the isotropic micellar to lamellar (I–LD) phase transition in lyotropic liquid crystals. The model free energy is written in terms of the coupled order parameters including the micellar concentration. The conditions for the I–LD phase transition and the stability conditions of the lamellar phase are calculated. On the basis of this model, it is argued that the I–LD phase transition is always first order. The theoretical predictions are found to be in good qualitative agreement with available experimental results.

Phase separation effects and the nematic–isotropic transition in polymer and low molecular weight liquid crystals doped with nanoparticles

Properties of the nematic–isotropic phase transition in polymer and low molecular weight liquid crystals doped with nanoparticles have been studied both experimentally and theoretically in terms of molecular mean-field theory. The variation of the transition temperature and the transition heat with the increasing volume fraction of CdSe quantum dot nanoparticles in copolymer and low molecular weight nematics has been investigated experimentally and the data are interpreted using the results of the molecular theory which accounts for a possibility of phase separation when the system undergoes the nematic–isotropic transition. The theory predicts that the nematic and isotropic phases with different concentrations of nanoparticles may coexist over a broad temperature range, but only if the nanoparticle volume fraction exceeds a certain threshold value which depends on the material parameters. Such unusual phase separation effects are determined by the strong interaction between nanoparticles and mesogenic groups and between nanoparticles themselves.

Spontaneous formation of micrometer-scale liquid crystal droplet patterns on solid surfaces and their sensing applications

In this study, we report spontaneous formation of two characteristic micrometer-scale liquid crystal (LC) droplet patterns on solid surfaces and also demonstrate the application of the designed LC platform to construct new types of LC-based sensors. By simply spreading LCs dissolved in organic solvents on glass microscope slides, we observed one- and two-dimensional LC droplet patterns with distinctive optical textures that represent different orientations of LCs under a polarized microscope. LC droplets supported on surfaces exhibited high stability during temperature-induced phase transitions of LCs. In addition, based on the distinguishable optical appearance of the LC droplet patterns, their applications in monitoring the presence of water vapors, amphiphiles, and vapors of volatile organic compounds (VOCs) were demonstrated. These results indicate that the surface-anchored LC droplets show high promise for the development of simple, robust, and versatile LC pattern-based sensing devices for real-time and label-free detection of chemical and biological events.

Improved analysis of the effect of chain flexibility on the nematic to smectic-A phase transition

Experimental studies have shown that the chain flexibility plays an important role in the properties of the liquid crystal phase transitions. We examine the effect of the chain flexibility on the nematic to smectic-A phase transition within the Landau phenomenological theory. We show how the flexibility of the chains influences the critical behavior of the nematic to smectic-A phase transition. The possibility of the tricritical point at the nematic to smectic-A phase transition is discussed in a phenomenological way. The theoretical predictions are found to be in good qualitative agreement with available experimental results.

A thermodynamic approach to isotropic-nematic phase transitions in liquid crystals

We propose a dynamical model for (non-isothermal) phase transitions in liquid crystals. Macroscopic motions of the liquid crystal (LC) are neglected, while the coupling with the electromagnetic field is considered. The LC is described in terms of the classical order tensor Q, which is split as Q=sN, where N is a normalized tensor; two independent evolution laws are given for s and N. The model includes an evolutive equation for the temperature field obtained from an appropriate form of the energy balance, in which the internal powers associated to the equations for s and N are accounted for. The thermodynamic restrictions in the constitutive relations which ensure the Clausius–Duhem inequality have been pointed out.

Critical behaviour of the smectic A*–C* phase transition and electroclinic effect of ferroelectric liquid crystals with terphenyl rigid core

The SmA*–SmC* phase transition was studied by measuring the temperature and electric field dependences of the optical tilt angle, the electric polarisation and the dielectric spectra collected in a wide frequency range. Critical behaviour of the phase transition was analysed by varying the length of the fluorinated part of the alkyl terminal chain and by differing fluorine substitution in the terphenyl core. Both tilt and polarisation show tricritical mean-field behaviour for all homologues with n > 2. Almost all coefficients that describe the SmA*–SmC* transition in the frame of the Landau theory were derived for homologue series. Double fluorine substitution in the central ring of the core seems to promote the ‘de Vries'-type smectic A*–C* phase transition with a little layer shrinkage. These well correspond with the lower tilt angle and smaller changes of the birefringence at the phase transition compared to the other homologues.

Photostimulated and Photosuppressed Phase Transitions in Liquid Crystals

Photostimulated and Photosuppressed Phase Transitions in Liquid Crystals

PB13 アントラセン光応答性部位を有するキラル剤の合成とキラル液晶相の光誘起相転移(化学・材料,ポスター発表,2012年日本液晶学会討論会)

PB13 アントラセン光応答性部位を有するキラル剤の合成とキラル液晶相の光誘起相転移(化学・材料,ポスター発表,2012年日本液晶学会討論会)

PA11 側方置換基が及ぼすコレステリック液晶の電界誘起相転移への影響(化学・材料,ポスター発表,2012年日本液晶学会討論会)

PA11 側方置換基が及ぼすコレステリック液晶の電界誘起相転移への影響(化学・材料,ポスター発表,2012年日本液晶学会討論会)