Binary Liquid Crystalline Systems Research Articles

Critical behavior in the vicinity of nematic to smectic A (N–SmA) phase transition of two polar–polar binary liquid crystalline systems

ABSTRACTPhase diagram, critical behavior and order of the nematic (N)–smectic A (SmA) phase transition of two polar–polar binary systems (i) 4-n-heptyloxy-4′-cyanobiphenyl (7OCB) and 4-n-octyloxy-4′-cyanobiphenyl (8OCB); (ii) 4-n-octyloxy-4′-cyanobiphenyl (8OCB) and 4-n-nonyloxy-4′-cyanobiphenyl (9OCB) by means of a high-resolution temperature scanning measurement of birefringence have been reported in this work. A simple power law analysis has been adopted to extract the specific heat critical exponent (α′) at N–SmA transition from birefringence data. The α′ for N–SmA transition indicates a uniform crossover behavior and has appeared to be non-universal in nature. With increasing concentration of the higher homologues for both the binary systems, the N–SmA transition reveals a strong tendency to be driven towards the tricritical nature. The 3D-XY limit (i.e. α′ = −0.007) for N–SmA transition reaches at the concentration x8OCB = 0.28 corresponding to the McMillan ratio 0.914, whereas the tricritical point has been found to appear near x9OCB = 1.0 corresponding to McMillan ratio 0.992.

PA22 非晶高分子と極性分子からなる二成分系液晶における秩序構造の形成(液晶化学材料,ポスター発表,2015年日本液晶学会討論会)

PA22 非晶高分子と極性分子からなる二成分系液晶における秩序構造の形成(液晶化学材料,ポスター発表,2015年日本液晶学会討論会)

Effect of the hockey-shaped mesogen as an additive on the critical behaviour at the smectic A to nematic phase transition

We present systematic experimental data on high resolution measurements of temperature dependence of optical birefringence (Δn) in a binary liquid crystalline system comprising calamitic 4-cyano-4′-octyloxybiphenyl (8OCB) and a hockey stick-shaped compound, 4-(3-decyloxyphenyliminomethyl) phenyl 4-decyloxycinnamate (SF7). The hockey stick-shaped mesogen shows a smectic A (SmA) phase in addition to two polymorphic tilted smectic phases. From an analysis of the Δn data, a quotient Q(T) has been derived which exhibits power law divergences both above and below the smectic A-nematic (SmA-N) phase transition. A noticeable shrinkage in width of the nematic range has been observed for a small increase in concentration of the angular mesogenic dopant. In the vicinity of the SmA-N phase transition, the values of effective critical exponent (α′), characterizing the critical fluctuation at this transition, have appeared to be in between those predicted by the 3D-XY and tricritical hypothesis. Furthermore, with increasing hockey stick-shaped molecular concentration, the SmA-N transition shows a tendency to be driven towards a first order nature.

Structure and optical properties of glasses in binary liquid crystalline systems based on cobalt octanoate

The effect of composition and aggregative state (melt, mesophase, glass) on the coordination state of Co (II) ions in an octanoate ligand field has been studied for binary liquid crystalline systems based on cobalt (II) octanoate by the analysis of electronic absorption spectra. It has been shown that several coordination forms of Co (II) ions: octahedral, tetrahedral and dodecahedral ones can coexist in cobalt octanoate based systems. It has been found by positron annihilation lifetime spectroscopy and small-angle X-ray scattering that glasses of cobalt octanoate based systems have a bilayer and nanoporous structure. The thickness of cation–anion bilayers in mesophases and glasses of binary systems depends on the polarizing power of cations: it is the smaller, the higher the polarizing power of cations.

Liquid-Crystalline Binary Systems with Nonmesomorphic Comb-Shaped Polymer Component

Binary liquid-crystalline systems were prepared by mixing a nonmesomorphic comb-shaped polymer (CSP) and low-molecular-weight liquid crystal. CSP exhibited a glass-isotropic phase transition. The binary liquid-crystalline systems consisting of CSP and polar molecule formed smectic A and smectic B phases. The induction of liquid crystalline phases is due to interactions between the side chain of CSP and low-molecular-weight liquid crystals.

Phase diagrams and optical properties of binary liquid crystalline systems of cobalt (II) caprylate with lithium and lead caplylates

The concentration and temperature ranges of liquid crystal and glass formation in binary systems of cobalt (II) caprylate with either lithium or lead caplylates have been studied by differential thermal analysis and optical polarization microscopy. Absorption spectra of Co(II) cations in mesophases and glasses of these binary caprylate systems have been analyzed as a function of temperature and composition to get information on the coordination of Co(II) ions. For the binary system of lead–cobalt caprylate, we found that the Co(II) ions are octahedrally coordinated over the range of temperatures and compositions studied, whereas in the binary lithium–lead caprylate system, the Co(II) ions can exist in both octahedral and tetrahedral coordination depending on composition and temperature. Thermochromic behavior was observed for all compositions studied here, from blue to violet and pink, depending on the composition and temperature of the system studied. An unusual increase of optical density with decreased Co(II) ion concentration has been observed for the Co–Li caprylate binary system up to 50 mol%. An increasingly ionic Co(II) coordination environment as Li ion concentration increases facilitates a concomitant increase in the proportion of more optically dense tetrahedrally coordinated Co(II) ions.

Thermodynamics of Sorption in the Binary Liquid Crystalline System Composed of the Poly(propyleneimine) Dendrimer and p-n-Pentyloxy-p′-cyanobyphenyl by Inverse Gas Chromatography

A binary system composed of the liquid crystalline poly(propyleneimine) dendrimer and nematic p-n-pentyloxy-p'-cyanobyphenyl has been studied by thermomicroscopy, scanning calorimetry, and inverse gas chromatography. In this system, there is the columnar phase being stable within broad ranges of temperature and component ratio. Dependences of the retention volumes of various solutes, namely, hydrocarbons, alcohols, and amines, on composition of the sorbents are revealed to exhibit the maximum. Thermodynamic functions of sorption of n-alkanes and n-alcohols on the binary sorbents composed of the said liquid crystals have been calculated specifically. Thermodynamic solute-sorbent compatibility characterized by the activity coefficients of the solutes is dependent on the sorbent composition; namely, it is controlled by counterbalancing of the enthalpy or entropy factors. The nonadditive mode of the solute-sorbent interaction is explained by arising of the microdomain nematic structure enclosed in the columnar structure of the dendrimer.

First Observation of a Photo-Induced Transition to a More Ordered Phase in a System Exhibiting Reentrant Nematic - Smectic A Phase Sequence

Materials composed of photoactive molecules like azobenzenes are known to show photo-induced isothermal phase transitions. However, in all the cases investigated so far, the trans-cis conversion brought about by photoisomerization always leads to an order to disorder transition, i.e., the ordering decreases in the process. In this paper we report observation of the reverse behavior, namely, a photo-induced disorder to order transition. Experiments have been done on a binary liquid crystalline system doped with a photoactive azo molecule, showing a reentrant nematic-smectic A phase transition. In the reentrant nematic phase UV illumination of the sample and the consequent photoisomerization leads to the transformation to the smectic A phase. A possible explanation for this behavior is suggested on the basis of the recently proposed photo controlled nanophase segregation mechanism.

Phase Equilibria in Binary Liquid Crystalline Systems under High Pressure.

The effect of pressure on the crystal-nematic and nematic-isotropic transition temperatures, TCN and TNI, was investigated for MBBA (n- (4-methoxybenzylidene) -4-n- butylaniline), EBBA (n- (4-ethoxybenzylidene) -4-n-butylaniline), and binary mixtures containing these compounds such as (MBBA+EBBA), and (MBBA, EBBA + C6H6, C6H12) at temperatures from 263 to 363 K and pressures up to 30 MPa. The measurements were performed using a high-pressure optical vessel designed for direct visual observation with the aid of a video microscope, and a three-terminal cylindrical capacitor for dielectric study.

Phase diagrams and mixing enthalpies of binary liquid‐crystalline systems exhibiting a semectic A phase

AbstractThe induced smectic A phase which appears in binary liquid crystalline systems has been investigated. Phase diagrams, clearing enthalpies, heat capacities and mixing enthalpies of two binary mixtures of a terminal polar component and of a weakly polar one are presented. The influence of the alkyl chain length, steric and EDA‐type interactions on the formation of induced smectic A phase are discussed.

A small angle neutron scattering study of the lamellar and nematic phases of caesium pentadecafluoro-octanoate (CsPFO)/2H2O and CsPFO/CsCl/2H2O

The binary lyotropic liquid crystalline system caesium pentadecafluoro-octanoate (CsPFO)/water ( 2 H 2 O) exhibits an isotropic micellar phase, a lyotropic nematic phase and a positionally ordered, lamellar phase whose planes contain substantial water filled defects. It has been suggested that the structural unit in all three phases is a disk shaped micelle which, as temperature is lowered, first become orientationally ordered and then positionally ordered onto planes. Increasing the surfactant concentration apparently causes the micelles to first increase in size and then decrease, explained by invoking an attractive inter-micellar interaction. In this small angle neutron scattering study, we present further results on the strucutre of the binary and the ternary systems, the latter containing added electrolyte. Our results call into question the previously prposed model of the lamellar phase and show that the form of the temperature dependence of the aggregate dimensions depends on the structural model that has been adopted. We show that a much more satisfactory picture of the lamellar phase is obtained if the shape of the aggregates is assumed to consist of continuous amphiphile layers pierced by irregular water filled holes; increasing the CsPFO concentration then causes the amphiphile aggregates to grow. This structure is confirmed by the effect of adding electrolyte (CsCl) to the lamellar phase. Here, scattering shows explicitly that the water filled holes anneal out. The addition of electrolyte is also shown to cause changes of aggregate shape in the nematic phase. These changes in both binary and ternary systems are shown to be attributable to modifications of the intra-aggregate electrostatic head-group interactions

Phase diagram exhibiting a smectic-A-smectic-C-smectic-F meeting point.

We report an observation of a smectic-A--smectic-C--smectic-F (A-C-F) meeting point in a binary liquid-crystalline system. Detailed high-precision x-ray measurements enabled us to characterize the meeting point as a triple point, a point at which the three phases coexist. A direct consequence of this result is the existence of a tricritical point (TCP) on the A-C boundary. Contrary to the known results, the TCP appears despite a large temperature range for the A phase and the occurrence of a nematic phase at a higher temperature. Bearing in mind that F is a tilted hexatic phase, it is suggested that a possible reason for this behavior is the molecular-tilt field arising from the coupling between the tilt and the bond-orientational-order parameters.

Filled smectic A phases in binary liquid-crystalline systems of terminal-nonpolar compounds. V. Smectic A phases with unusually high ratio of the layer spacing and the average molecular length

Abstract The phase diagrams of four binary systems are presented in which one component is a bi-swallow tailed compound and the second is a nematogenic rod-like compound. In all of the phase diagrams studied an induced smectic A phase occurs. According to X-ray measurements the layer spacing d of the smectic A phase is considerably higher than the average molecular length L . Depending on the binary system and the concentration d/L ratios between 1·17 and 2·13 were found. We propose an interpretation of the results on the basis of a simple packing model.

Binary Phase Studies of 4-4'-N-Pentylcyanobiphenyl

The phase behavior for three binary liquid crystalline systems has been explored. All three contained the room-temperature nematic, 4-4'-n-pentylcyanobiphenyl (K15), as one of their components. K15 has a T KN of 22.3 o C and a T NI of 35.1 o C. The second component for each system is a member of the homologous series 4-[4-alkylcyclohexyl]cyanophenyl. The n-ethyl (S1236), n-butyl (S1188) and n-heptyl (S1115) members of this series were chosen. The eutectic composition of all three systems was found to occur at ≃60 mole % K15. The nematic range of the eutectic composition for the S1236/K15, S1188/K15 and the S1115/K15 system is 16, 27 and >40 o C, respectively. The Schroder-van Laar (S-vL) equation was found to be useful in predicting the eutectic composition for each binary system. The K15/S1236 phase diagram shows a new phase between 10 and 62 mole % K15. This phase is believed to be a co-smectic

Filled SAphases in binary liquid crystalline systems of terminal‐nonpolar compounds (III). The role of the molecule length of the rod‐like component

AbstractThe phase diagrams of 8 binary systems of liquid crystals are presented whereby one component is a “biswallow tailed” compound and the second component is a member of the homologous series of 4,4′‐bis‐n‐alkyloxy‐azoxybenzenes. In all phase diagrams studied induced smectic A phases occur. X‐ray investigations give evidence that in the binary systems of short‐chain homologues the layer spacing d of the smectic A phase is clearly greater than the average molecular length L̄, whereas in the systems of long‐chain homologoues d is found to be somewhat smaller than L̄. The results are interpreted on the basis of a simple packing model.

Filled smectic A phases in binary liquid-crystalline systems of terminal-nonpolar compounds

Abstract We present five phase diagrams of binary systems in which one component is a bi-swallow tailed compound and the second component is a compound with pronounced nematogenic properties. The common feature of these binary systems is the induction of smectic A phases which have been investigated using X-ray. The smectic A induction seems largely to be the result of specific steric interactions between the components.

Equal G analysis of ternary liquid-crystalline systems

Abstract The equal Gibbs energy analysis of binary liquid-crystalline systems can predict, to a high degree of accuracy, the phase diagram of the binary system. We extend this analysis to ternary systems. Two systems of homologous dialkyloxy-azoxybenzenes were studied. In particular we studied the mixtures 6-1-5 and 6-4-5, where the number denotes the number of carbon atoms in the terminal alkyl chain. The experimental temperature-composition phase diagrams were determined by differential scanning calorimetry and by optical microscopy using a ternary contact method as well as individual compositions. Both the crystal-nematic and nematic-isotropic phase regions were studied. The first mixture is highly non-ideal, whereas the second is almost ideal. The form used for the excess Gibbs energy was This particular form, where x, y and (1 - x - y) are the molar fractions of the three components and Aijk are the interaction parameters, either binary or ternary, looks at the origins of the excess Gibbs energies fr...

New Nematic Phase in Lyotropic Binary Liquid Crystals Detected by Positron Annihilation Techniquest

Abstract A new nematic phase in lyotropic binary liquid crystalline systems consisting of sodium dodecyl sulfate-water was detected, for the first time, in the absence of additives by utilizing positron annihilation techniques. Lyotropic and thermotropic phase transitions were also investigated by the same methods. The positron annihilation parameters have also indicated a better definition of the concentration ranges at which each phase exists in the system studied. Crossed polarized light microscopy was applied to substantiate these results.

EDA complex stability constants and formation enthalpies in a binary liquid crystalline system with induced smectic phase

AbstractIn the binary system 4,4′‐bis‐[n‐butylamino]‐biphenyl/‐(2,2‐dicyano‐ethenyl)‐phenyl 4‐n‐nonyloxybenzoate which due to EDA complex formation exhibits an induced SA phase, measurements of the charge transfer band, the molar volumina and transition enthalpies were done. By the concentration and temperature dependence, resp., of the charge transfer absorption and the strongly negative excess volumina we estimated the stability constant and the formation enthalpy of the complex.The data obtained by the two independent methods agree sufficiently.

Intermediate Phases in Binary Liquid Crystalline Systems

Intermediate Phases in Binary Liquid Crystalline Systems