Unusual Glassy Smectic-G Liquid Crystal: Heat Capacity of N-p-n-Pentyloxybenzylidene-p'-n-butylaniline between 11 and 393 K

Abstract

The heat capacities of the title compound (C₃H₁₁,O—C₆H₄,- CH=N—C₆H₄,—C₄H₉, abbreviation 5O ? 4) with a purity of 99.92 mole percent have been measured with an adiabatic-type calorimeter between 11 and 393 K. The transition temperature and the enthalpy and entropy of phase transition for stable crystal → S_G, S_G → N and N → isotropic liquid were T _c = 299.69 K/ΔH = 22.68 kJ mol^?1/ΔS = 75.70 JK^?1 mol^?1, 325.72/7.11/21.79 and 342.48/1.78/5.22, respectively. The crystal which melts at 285.5 K is a metastable modification. The S_A phase hitherto reported in between S_G and N does not exist. The glassy So state was realized by rapid cooling of the specimen from the So phase. The molar enthalpy of the glassy S_G state at 0 K was by (10.1±0.1) kJ mol^?1 higher than that of the stable crystalline state and the residual entropy of the glassy state was (9.40±0.83) JK^?1 mol^?1. The relaxational heat-capacity anomaly was observed from as low as 100 K and double glass transition phenomenon occurred around 200 K; a quite unusual phenomenon which has never been observed for the glassy states of nematic and cholesteric liquid crystals. The present results give a fair evidence that the unusual glass transition phenomenon previously found for the S_G state of 6O?4 (a homologous compound) is not exceptional at all but common to the smectic glasses; at least common to the glassy S_G states. Two possible origins responsible for the double glass transitions have been discussed.     

Effect of the oxygen pressure during annealing on Tc and lattice parameter c of Bi-2212 single crystals

The influence of oxygen partial pressure (p_o2 = 10⁻⁴–1.5 · 10² atm) during annealing on the T_c and lattice parameter c of Bi-2212 single crystals has been investigated. Antibate correlation between non-monotonous alteration of the c parameter and T_c with the increase in oxygen content has been revealed.     

New chiral liquid crystal materials based on menthol: Synthesis and phase behavior

To study structure-mesomorphism relationships of chiral materials based on menthol, a series of chiral compounds containing menthyl group were synthesized. Their chemical structures, formula, and the purity were characterized by Fourier transform infrared (FTIR), proton nuclear magnetic resonance (¹H NMR), and elemental analyses. The corresponding phase behavior was investigated with differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). The effect of the mesogenic core, flexible spacer, and terminal groups on the mesophase formation and type was discussed. The compound 4-menthyloxyacetoxybenzoyloxy-4′- (6-bromohexyloxy)biphenyl showed the smectic A (S_A) and cholesteric phases on heating cycle, and a cubic Blue Phase, chiral smectic C (S_C^*), S_A and cholesteric phases on cooling cycle. However, the compound 4-menthyloxyacetoxybenzoyloxy-4′-(4-bromobutoxy)biphenyl showed enantiotropic S_C^*, S_A and cholesteric phases, moreover, the platelet texture of a cubic Blue Phase was also observed on cooling cycle. The methacrylate monomer with six flexible methylene units and three phenyl rings as mesogenic core only showed cholesteric phase, while the methacrylate monomer with four methylene unit and three phenyl rings showed the S_C^* and cholesteric phases. However, when the terminal methacryloyloxy groups in the monomers were substituted by thiophenylacryloyloxy groups, the corresponding monomers all show no mesophase. With increasing the rigidity of mesogenic core or decreasing the flexible methylene spacer length, the corresponding melting temperature (T_m) or isotropic temperature (T_i) increased.     

The Dielectric Anomaly Near the Transition from the Smectic A* to Smectic C* Phase and Visco-Elastic Properties of Ferroelectric Liquid Crystals

A pyro-electric technique is developed which allows the measurement of the dielectric response near the A*-C* phase transition in ferroelectric liquid crystals. The temperature dependence of the elastic modulus K _θ(T) corresponding to the molecular tilt in smectic layers is calculated from the experimental data. Direct pyro-electric measurements of the relaxation time for the spontaneous polarization P _s and the data on K _θ(T) allow us to calculate the temperature behaviour of the twist-viscosity γ₁(T) for the smectic C* phase. The curves γ₁(T) are compared for the smectic C* and the nematic phase of the same compound and the dependence of the twist viscosity on the molecular tilt angle in the C* phase is investigated. The results of the dielectic measurements are discussed in terms of the mean-field approximation.     

Crystal and molecular structures of trans-bis(acetonitrile)bis(bipyridine)ruthenium(II) perchlorate and trans-diamminebis(bipyridine)ruthenium(II) perchlorate

The structures of trans-[(MeCN)₂(bpy)₂Ru](ClO₄)₂(I) andtrans-[(NH₃)₂(bpy)₂Ru](ClO₄)₂(II) have been determined by single crystal X-ray diffraction methods. (I) forms monoclinic crystals in the space groupP2₁/c witha=8.399(2),b=10.406(2),c=15.590(3) Å,=93.78(2)° andZ=2 atT=293 K. The final refinement gaveR=0.040 for 2448 reflections withF _o ² >3(F _o ² ). (II) crystallizes in the triclinic space groupP¯1 witha=1.702(1),b=8.439(2),c=10.525(2) Å,=107.56(2),=104.63(1), =100.89(2)° andZ=1 atT=293 K. Refinement using 1878 reflections withF _o ² >3(F _o ² ) produced a finalR value of 0.036. Both of these structures have the ruthenium atom located on a crystallographic inversion center. The bipyridine ligands in both structures are in the bowed conformation as a means of circumventing the steric problems associated with the trans arrangement of the bipyridine ligands. The Ru-N(monodentate) distance is longer for the ammonia complex (2.106(3) Å) than for the acetonitrile complex (2.008(4) Å); there are no significant differences in the distances and angles of the two Ru(bpy)₂ frameworks.     

Low-temperature X-ray studies of a [(CH3)2NH2]2 · CuCl4 crystal

The a, b, c lattice parameters of a [(CH₃)₂NH₂]₂ · CuCl₄ crystal have been measured by the X-ray diffraction method within the temperature range of 100–300 K. The temperature dependences of thermal expansion coefficients α_a = f(T), α_b = f(T), and α_c = f(T) along the principal crystallographic axes and thermal expansion coefficient of the unit-cell volume αV = f(T) are determined. It is found that all the three parameters, a, b, and c, vary with temperature in a complicated way and show jumplike anomalies in the a = f(T), b = f(T), and c = f(T) curves at phase-transition temperatures T _c1 = 255 K and T _c2 = 279 K. An incommensurate phase with the modulation wave vector q _i = (1/2 + δ)(a* + c*) is revealed in the temperature range 279–296 K. It is shown that the incommensurability parameter δ increases with an increase in temperature.     

Structural and spectroscopic properties of the 1∶1 complex of Δ2, 2′-bis-1,3-dithiole (TTF) and 1,2,4,5-tetracyanobenzene (TCNB)

{2,2-bis-1,3-dithiole-1,2,4,5-tetracyanobenzene}, (TTF-TCNB), C₆H₄S₄-C₁₀H₂N₄,M=382.3, monoclinic,P2₁/a,a=9.194(3),b=12.342(3),c=7.426(2) Å,=95.12(3)°,Z=2,D _x =1.52 Mg m^–3, (MoK)=0.71069 Å,=0.51 mm^–1,F(000)=776,T=293 K, finalR=0.039 for 1480 unique observed [F _o >4(F _o ² )] reflections. The complex represents a member of the series of crystal structures of molecular complexes containing TTF as an electron donor and TCNB as an electron acceptor. The structure was solved by direct methods and has been refined by full matrix least-squares calculations. The constituent molecules are stacked alternatively in infinite columns along thec axis. The mean separation of the molecular planes, which are inclined at the angle of 4.4°, is 3.48 Å. There are no unusually short intermolecular contacts. Bond lengths and angles in the component molecules agree with values for neutral species; also the infrared and Raman spectra indicate a very slight degree of ionicity.     

Synthesis,structure and photoluminescence of a 3D pillared heterometallic coordination polymer containing 2D inorganic cadmium‐potassium‐oxide layer subunits

Self‐assembly of Cd(NO₃)₂ with o ‐phthalic acid monopotassium salt (KHphth) in the presence of ethylenediamine (en) produced a new heterometallic coordination polymer [CdK₂(phth)₂(en)_0.5(H₂O)]_n ( 1 ). Single‐crystal X‐ray analyses reveal that it crystallizes in a monoclinic space group P 2₁/c. a = 11.6707(6) Å, b = 8.1019(4) Å, c = 20.9503(11) Å, β = 94.6640(10)^o. The complex displays an en‐pillared 3D framework, which is constructed from 2D [CdK₂(phth)₂(H₂O)]_n layers featuring uncommon inorganic cadmium‐potassium‐oxide layers containing potassium‐oxide layers. In the solid state, complex 1 shows photoluminescence with the maximum emission intensities at 355 nm upon excitation at 312 nm. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Interfacial stability and grain diameter of the metal phase of directionally solidified Al-Si-type eutectics

The morphology of the solid-liquid interface and the metal phase grain diameter of Al—Si-type eutectics (Al—Si, Ag—Si, Ag—Ge, Zn—Ge) were investigated in the range of a growth rate R = 0.2 … 20 mm/h and of a temperature gradient at the solid-liquid interface G = 2 … 25 K/mm. Three types of interfacial morphologies depending on the G/R ratios were found out. The G/R ratio of the transition from a planar to a nonplanar solid-liquid interface corresponds to the critical G/R|_c ratio, which can be calculated by the criterion of the constitutional undercooling. The grain diameter of the metal phase depends on growth parameters as follows: d_K ∼ R^—rG^—g with r = 0.33 … 0.43 and g = −0.37 … 0.03.     

Absorption spectrum of Ni2+ doped in NH4Br single crystal

The optical absorption spectrum of Ni²⁺ doped in NH₄Br single crystals has been studied at room and liquid-air temperatures. The observed ambient bands at 6300, 11,600, 13,400, 18,500, and 20,000 cm^–1 have been assigned, respectively, to the transitions³ A ₂(F) ³ T ₂(F),³ T ₁(F),¹ E(D),¹ T ₂(D and³ T ₁(P). The crystal field parameters evaluated areD _q=630 cm^–1,B=850 cm^–1, andC=3600 cm^–1. In assigning the location of Ni²⁺ ions within the lattice, evaluations are made of the (limited) extant comparable data. It is then concluded that Ni²⁺ enters an octahedral interstitial, rather than a substitutional, site. It is surrounded by four bromide ions, in a plane, with two polarized water molecules at the opposing fifth and sixth positions.     

Structural characterization of 2,6-bis(N-methylenepiperidino)-4-nitrophenol (MPN) and 2,6-bis-(N-methylenemorpholino)-4-nitrophenol (MMN)3

MPN: C₁₈H₂₇N₃O₃,M _r=333.43, monoclinic,P2₁/n. a=6.207(2),b=21.893(6),c=13.693(3) Å; =96.12(2)^o,V=1850.1(8) ų.,Z=4,D _cal=1.20 mg/m³,F(000)=720, (CuK)=1.5418 Å, andT=298K.R=0.042 andwR=0.049 for 1675 observed reflections. MMN: C₁₆H₂₃N₃O₅,M _r=337.38, triclinic,P,a=9.642(1) Å,b=10.123(5) Å,c=9.341(2) Å, =93.00(3)^o, =90.96(1)^o, =110.46(1)^o, V=852.5(5) ų,D _cal=1.31 mg m^–3.F(000)=360,Z=2, (CuK)=1.5418 Å,R=0.054 andwR=0.074 for 2804 observed reflections. The piperidine and morpholino rings assumechair conformation and orient each other at an angle of 44.8(1)^o (MPN) and 47.1(1)^o (MMN), respectively.Contribution No. 827 from DCB.     

Microhardness of tetrahedrally bonded elemental and binary semiconductors

An analysis of experimental microhardness data shows that the microhardness at room temperature of the diamond, zincblende and wurtzite structure compounds follows the simple relation H = h_oa^−xT_m(1 –g_of_i) where a is the lattice parameter T_m the melting temperature, f_i the spectroscopically defined bond ionicity and h_o, x, and g_o are constants having the same values for all compounds. The close relation between microhardness and bulk modulus is discussed.     

The iso-structural viscosity,configurational entropy and fragility of oxide liquids

This paper describes how the fragility of a liquid is linked to the ratio between the energy barrier (E_eq) for the equilibrium viscous behavior and that (E_iso) for the non-equilibrium iso-structural viscous behavior. Using the concept of iso-structural viscosity, two functions describing the variation of the configurational entropy (S_c) with temperature (T) are obtained from the Avramov-Milchev (AM) and the Vogel-Fulcher-Tammann (VFT) viscosity equations, respectively. The two S_c(T) functions exhibit different relations to the liquid fragility. The AM S_c(T) function is a power function with the exponent of F ? 1, where F is the AM fragility index. In this case, S_c vanishes at T = 0 K. For the VFT function, S_c vanishes as T is lowered to a finite temperature T₀, whereas it reaches the maximum value S_c,max at infinitively high T. S_c,max is proportional to the VFT fragility index. Thus, the VFT equation is not only a dynamical, but also a thermodynamic model. It is proved that for oxide liquids, the VFT equation describes viscosity data better than the AM equation, provided the pre-exponential factor η₀ is fixed to a generally accepted value, e.g., 10^?3.5 Pa s.     

Crystal structure of 2,2′-diformyl 4,4′-dimethyl 6,6′-[piperazine-1,4-diyl bis-(methylene)]bis phenol

The title compund C₂₂H₂₆N₂O₄,Mr=382.46 crystallizes in the orthorhombic space group P2₁2₁2₁ with =8.867(1)Å,b=13.228(2)Å,c=17.029(3)Å,V=1956.7(2)ų,Z=4, D_cal=1.30 Mgm^–3,F(000)=816, =6.89 cm^–1, (CuK)=1.5418 Å andT=298 K. The structure was solved by direct methods and refined by full-matrix least-squares. The finalR=0.046 for 1995 unique reflections. The phenyl rings are coplanar (oriented at an angle of 6.4(1)^o) and orients at an angle of 112.2(1)^o and 115.7(1)^o, respectively with the piperazine ring. The piperazine ring adopts achair conformation and the substituents at the N-atoms are in an equatiorial position.DCB Contribution No. 823.     

Imidazolium chloride organophosphate antidotes

The structures of four imidazolium oxime derivatives were solved by direct methods. These compounds have been shown to be effective in the treatmen of organophosphate poisoning. Despite substantial differences in the nature of the substituent on N1, all four compounds have similar shapes when viewed down the plane of the imidazole ring. The potency of these compounds in the treatment of organophosphate poisoning correlates well with the distance between the imidazole ring and the oxygen moiety on the side chain. 2-(hydroxyimino)methyl-3-methyl-1-[1-(3-methyl-sulfonylpropyloxy) methyl]imidazolium chooride (1) crystallizes in the triclinic space groupPī (Z=2). The unit cell parametersa, b, c (?) and α, β, and γ (^o) were: 8.506(2), 8.787(4), 10.070(4), 73.68(3), 81.37(3), 85.39(3). 2-(hydroxyimino)-methyl-3-methyl-1-(2′-N-phenylsulfonylamino-1′-ethyl) imidazolium chloride (2) crystallizes in the monoclinic space groupP2 ₁ la(Z=4). The unit cell parametersa, b, c (?) and β (^o) were: 12.690(2), 6.317(4), 20.193(4), 91.47(2). 1-(2′-ethyl-2′-trifluoromethanesulfonyl-aminoethyl)-2-(hydroxyimino) methyl-3-methylimidazolium chloride (3) crystallizes in the triclinic space groupPī (Z=2). The unit cell parametersa, b, c (?) and α, β, and γ (^o) were: 6.635(1), 11.333(2), 12.274(3), 115.05(3), 98.46(3), 90.11(3). 2-(hydroxyimino)-methyl-3-methyl-1-[2-(2-methyl-3-nitrobutyloxy) methyl]-imidazolium chloride (4) crystallizes in the orthorhombic space groupP2₁2₁2₁ (Z=4). The unit cell parametersa, b, andc (?) were: 10.034(1), 11.401(2), 13.352(2).     

X-ray diffraction studies oncis-[Ru(bpy)2(PMe3)Cl+][ClO4?] andcis-[Ru(bpy)2{PMe2(o-tol)}Cl+][ClO4?]; two ordered structures in thecis-bis(bipyridyl)chloro(phosphine)-ruthenium(II) series

The complexcis-[Ru(bpy)₂(PMe₃)Cl⁺][ClO₄ ⁻] crystallizes in space group P2₁/c andcis-[Ru(bpy)₂{PMe₂(o-tol)]Cl⁺][ClO₄ ⁻] crystallizes in space group ; each is present as a racemate and neither structure suffers from disorder. The Ru−PMe₂(o-tol) bond length of 2.324(2)? is slightly longer than the simple Ru−PMe₃ bond length of 2.310(2) ?.     

Dielectric characteristics of neodymium heptamolybdate crystals grown by gel encapsulation technique

Results obtained from the dielectric studies of neodymium heptamolybdate crystals grown in the system Nd(NO₃)₃ –MoO₃ –NH₄OH– HNO₃ —Na₂SiO₃ by gel encapsulation technique are presented. The variation of dielectric constant (ε′), dielectric loss (tanδ) and conductivity (σ) with frequency at different temperatures is studied. The dielectric constant of the material increases sharply, attains a peak value and then decreases rapidly, as material's temperature rises from room temperature to higher degrees. The temperature at which the peak value is attained is the transition temperature of the material. Dielectric loss (tan δ) follows almost a similar behaviour. The conductivity (σ) is also found to be temperature-and frequency-dependent. This sharp rise in ε′ is attributed to the contribution from space charge polarization. Theoretically obtained data using the expression ε′ = a₀ + a₁ T² and —In σ = a + b(T — T₀)² for T < T₀) fits very well with the experimentally obtained data indicating that space charge polarization increases as some power of temperature larger than one.     

Synthesis and Liquid Crystal Behaviour of Further 4,4″-Disubstituted 2'-Fluoro-1,1':4',1”-Terphenyls

Further to earlier work on the liquid crystal properties of fluoro-1,1':4',1”-terphenyls¹ we have now extended this series to include terminally fluoro-and cyano-substituted 2'-fluoro-1,1':4',1″-terphenyls, chiral 2'-fluoro-1,1':4',1″-terphenyls, and esters derived from 2'-fluoro-1,1':4',1”-terphenyls and incorporating the alkylcyclobutyl group. The preparations and transition temperatures for these series of compounds are presented and their transition temperatures and mesophase types are discussed. An interesting result from this work was the appearance of an S^* _C phase for one chiral homologue and of S _c phases for the esters incorporating the alkylcyclobutyl group. The S _c formation is attributed to the presence of the fluoro-substituent.

Keywords: terphenyls, fluoroterphenyls, smectic C phases, cyclobutyl esters     

Nematic-Isotropic Transition in MBBA and its Mixtures with 4-Methoxybenzaldehyde: Applications to the Purity Control of Liquid Crystals

The nematic-isotropic transition temperatures of MBBA(1) + 4-methoxybenzaldehyde(2) mixtures (where MBBA=N(4-methoxybenylidene)-4-n-butylaniline) for 0  x₂  0.06 and additionally the transition enthalpy of pure MBBA were measured by a calorimetric method. Straight lines were found for the T¹(x₂) and Tⁿ(x₂) curves respectively where T¹ and Tⁿ are the upper and the lower limiting temperatures of the transition range for a given x₂. The results are compared with literature data on similar systems and confirm the wellknown rule that the decrease of the nematic-isotropic transition temperature with increasing x₂ depends more strongly on the size and the shape than on the polarity of component 2. From a plot of δT [tbnd] T¹ - Tⁿ against x₂ the mole fraction of impurity in the original sample can be extrapolated.