Heat Capacity and Thermodynamic Properties of p'-Substituted p-n-Hexyloxybenzylideneaniline. I. p-n-Hexyloxybenzylideneamno-p'-Benzonitrile (HBAB)

Abstract

The heat capacity of the nematogenic liquid crystal, HBAB, has been measured between 15 K and 385 K by using an adiabatic calorimeter. The crystal-crystal phase transition has been discovered at 27 K below the crystal-nematic phase transition temperature. The transition temperatures, the enthalpies and the entropies of the three phase transitions have been determined: T ₁ = 306.98 K, ΔH _t = 5.11 kJ mol^?1, ΔS _t = 16.7 JK^?l; T _m = 334.05 K, ΔH _m = 23.77 kJ mol^?1, ΔS_m = 71.2 J K^?l mol^?1; and T _c = 375.10 K, ΔH _c = 1.75 kJ mol^?1, ΔS _c = 3.2 J K^?1 mol^?1, respectively. The thermodynamic functions of HBAB from 0 K to 385 K have been determined from the heat capacity data and the enthalpies of the transitions. Two crystal modifications, one yellow and granular form and the other white and needle-like form, have been obtained during the course of the preparation of the sample. It turned out that the yellow form was the stable crystal and the white the metastable modification. The crystal-crystal phase transition has been discussed as an onset of partial melting from the entropy consideration. In this connection the total entropies of the transitions, 91.1 J K^?1 mol^?1 has been proposed to be an important measure of melting.     

Etude par Calorimetrie,Diffraction des Rayons X et Diffusion Raman d'une Transition de Phase dans (C4 H4P) Mn (CO)3

Abstract

Heat capacity measurements (95-300K), X-ray diffraction (78-300K) and low frequency Raman spectroscopy (10-350K) have evidenced an order-disorder phase transition in phosphacymantrene, (C₄ H₄P) Mn (CO)₃. This transition has been characterized by a monoclinic ←→ triclinic structural change at about 110 K and by a pretransitional phenomenon. The measured transition enthalpy and entropy are 480 ± 10J.mil^?1 and 4.17 ± 0.08J.K^?1 mol^?1, at 115 K, respectively.

A complete assignment of the observed Raman bands in h₄ and d₄ derivatives is proposed. From the temperature dependence of frequencies, intensities and half-widths of some Raman bands we have discussed the order, the nature and the mechanism of the phase transition: intermolecular interactions appear to be mainly involved in the mechanism and an activation energy roughly equal to 2100 ± 840 J. mol^?1 has been determined.     

The Heat Capacity of 1,2,4,5-Tetracyanobenzene and of its 1 : 1 Charge-Transfer Complex with Pyrene from 10 K to 300 K

Abstract

The heat capacity of 1,2,4,5-tetracyanobenzene and of its 1 : 1 complex with pyrene has been measured form ～ 10 K to ～ 300 K. There is a transition in the complex which appears as an approximately symmetrical anomaly in the heat capacity-temperature curve between ～ 220 K and 250 K, but the heat capacity is not reproducible in this region even if the sample is subjected to the same preliminary thermal treatment. Moreover, the room-temperature form can be undercooled at least down to 150 K. In the two runs in which the heat capacity anomaly was most prominent. C_p reached its maximum at 232 ± 1 K. The largest measured value of the entropy of transition was 9.2 JK^?1 mol^?1. This value is compatible with but does not prove, the exisstence of static disorder above the transition, with one of the components (pyrene, in the light of the structural information) having at least two distinguishable orientations. At all temperatures in the range covered (apart from the transition region), the heat capacity of the complex is less than the sum of that of the pure components, and possible reasons for this are brifly discussed.     

Heat Capacity and Thermodynamic Properties of p'-Substituted p-n-Hexyloxybenzylideneaniline I I I. p-n-Hexyloxybenzyl ideneam i no-p'-fluorobenzene (HBAF)

Abstract

The heat capacity of HBAF has been measured between 15 K and 385 K. Four phase transitions were found at 328.07 K (crystal-smectic B); 330.33 K (smectic B-smectic A); 334.88 K (smectic A-nematic); and 336.33 K (nematic-isotropic liquid), respectively. The enthalpies and entropies of these transitions were determined to be 23.22 kJ mol^?1/70.7 JK^?1 mol^?1; 3.05/9.2; 3.41/10.2; and 1.17/3.5, respectively. The total transition entropy of HBAF agreed well with those previously reported for the present homologues. The standard thermodynamic functions were estimated up to 385 K. The heat capacity curve of HBAF in the transition region had a close resemblance to that of p-n-hexyloxybenzylideneamino-p'-chlorobenzene. The entropies of the smectic A-nematic and nematicisotropic liquid transitions were compared with those theoretically derived by McMillan. The smectic B-smectic A transition entropy was interpreted in terms of order-disorder phase transition associated with the orientation of molecule.     

Refinement of the crystal structure of the high-temperature phase G 0 in (NH4)2WO2F4 (powder, X-ray, and neutron scattering)

The (NH₄)₂WO₂F₄ compound undergoes a series of phase transitions: G ₀ → 201, K → G ₁ → 160, and K → G ₂, with a significant change in entropy (ΔS ₁ ～ Rln10 at the G ₀ → G ₁ transition), which indicates significant orientational disordering in the G ₀ phase and the order-disorder type of the phase transition. X-ray diffraction is used to identify the crystal structure of the G ₀ phase as rhombohedral (sp. gr. Cmcm, Z = 4), determine the lattice parameters and the positions of all atoms (except hydrogen), and show that [WO₂F₄]^2? ions can form a superposition of dynamic and static orientational disorders in the anionic sublattice. A determination of the orientational position of [NH₄]⁺ ions calls for the combined method of elastic and inelastic neutron scattering. Inelastic neutron scattering is used to determine the state of hindered rotation for ammonium ions in the G ₀ phase. Powder neutron diffraction shows that the orientational disorder of NH₄ ions can adequately be described within the free-rotation approximation.     

Free energy spectra for inelastic deformation of five metallic glass alloys

The activation free energy spectra for isoconfigurational flow of Al₂₀Cu₂₅Zr₅₅,Cu₄₀Zr₆₀, Cu₅₆Zr₄₄, Cu₆₀Zr₄₀, and Pd₈₀Si₂₀ have been measured in experiments of recovery creep at stepwise increasing temperatures performed on structurally stabilized specimens that have been previously mechanically polarized by creep over a long period of time at T_g ? 150 K, followed by freezing under stress to 220 K and removal of stress. The spectra are continuous functions rising sharply from very low values at about 20 K cal mol^?1 to peak cut-off values at the activation energy for steady state isostructural viscous flow at about 45–55 K cal mol^?1. The shapes of these spectra resemble mirror images of the cavity size distributions computed for hard sphere models of glasses and the known free area distributions in glassy rafts of soap bubbles, and suggest the existence of a direct mapping between them. A small low temperature peak at about 22–25 K cal mol^?1 has been observed in Cu₅₆Zr₄₄ and Cu₆₀Zr₄₀.     

Liquid-Crystalline Solvents as Mechanistic Probes. 10. Dynamics of Intramolecular Quenching of Pyrenyl Fluorescence in the Liquid-Crystalline and Isotropic Phases of a Cholesteric Solvent1

Abstract

The effect of cholesteric order in a 59.5/15.6/24.9 (w/w/w) mixture of cholesteryl oleate/cholesteryl nonanoate/cholesteryl chloride (CM) on the intramolecular fluorescence quenching of l,3-bis(l-pyrenyl) propane (P3P) has been explored. A comparison with fluorescence quenching of N,N-dimethyl-4-[3-(l-pyrenyl)propyl]aniline (P3D) in CM is made. From the Arrhenius activation parameters for quenching in the cholesteric and isotropic phases, it is concluded that the motions which take the ground state conformers of P3P to their quenching transition state are nearly impervious to macroscopic CM mesophase order: in the cholesteric phase, E'_a = 10.5±0.4 kcal mol^?1 and ΔS^? = 1 ± 1 eu; in the isotropic phase, E'_a = 10.0 ± 0.2 kcal mol^?1 and ΔS^? = 0 ± 0.5 eu. An explanation of these results is advanced.     

Transitions de Phase en Series Mesogenes:

The polymorphism of the di(4-alkylphenyl) and di(4-alkoxyphenyl) tetrathiafulvalene (TTF) is investigated by optical, crystallographic and calorimetric methods. All the studied derivatives are mesomorphic. The first mesophase is always a smectic G phase; the second one is a nematic N phase for short chains and a smectic C phase for long chains.

The entropies corresponding to the passage high-temperature crystalline phase C₁ → S_G and to the “melting” (C₁ → mesophases → isotropic phase I) increase with the length of the chain and with the presence of the oxygen atom in the radical.     

Thermodynamic characteristics of Ti-based glass-forming alloys

Based on thermodynamic characteristics of the stable metallic liquid at melting temperature and the supercooled liquid, the present work calculated the mixing enthalpy ΔH^mix, the mixing entropy ΔS^mix and the Gibbs free energy difference between the supercooled liquid and the resulting crystalline phases ΔG of typical Ti-based amorphous alloys. The results show that for the case of larger ΔS^mix, moderate ΔH^mix for the stable liquid and smaller ΔG for the supercooled liquid, Ti-based alloys tend to achieve high glass-forming ability (GFA). A new parameter, β, defined as (T_g ? T_k)/(T_l ? T_g), has been introduced to evaluate the GFA of Ti-based bulk amorphous alloys (wherein T_g, T_l, and T_k represent the glass transition temperature, the liquidus temperature, and the Kauzmann temperature, respectively). Experimental data imply that the larger the β, the better the GFA for Ti-based amorphous alloys.     

Crystal structure and phase transition in the compound [C6H5CH2NH(CH3)2]TlCl4

The N‐N dimethyl benzylammonium tetrachlorothallate (III) [C₆H₅CH₂NH(CH₃)₂]TlCl₄ crystallizes in the monoclinic system P2₁/n at room temperature with the following unit cell dimensions: a = 7.725(3) Å, b = 14.080(5) Å, c = 13.697(4) Å, β = 91.2(2)° with Z = 4. The structure shows a layer arrangement perpendicular to the b axis: planes of [TlCl₄]^‐ tetrahedra alternate with planes of [C₆H₅CH₂NH(CH₃)₂]⁺ cations. The cohesion of the atomic arrangement is ensured by hydrogen bonds N‐H…Cl. Differential scanning calorimetric and optical birefringence measurements reveals a phase transition at T = 339K. Raman spectroscopic study and dielectric measurements were performed to discuss the mechanism of the phase transition. (© 2007 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spectroscopic properties of a Tm3+:Bi2TeO5 single crystal

Single crystal of bismuth tellurite Bi₂TeO₅ (BTO) doped with trivalent thulium (Tm³⁺) was grown by the Czochralski method and investigated by spectroscopic techniques (absorption, emission). Absorption and emission of the Tm:BTO crystal collected in the VIS‐IR spectral range are presented. Spectroscopic features were investigated as a function of the excitation light polarisation (E//X, Y, and Z axis of optical indicatrix) and sample temperature. The oscillator strength of the ³H₆ → ³F₄ transition at 1.7 μm was determined by numerical integration of the X, Y and Z polarised absorption spectra. The obtained values are: P_X = 4.7 × 10⁻⁶, P_Y = 6.8 × 10⁻⁶ and P_Z = 5.9 × 10⁻⁶ that gives a mean value P_mean = 5.8 × 10⁻⁶. Emission was observed from the ¹G₄ and ³H₄ levels. The ³H₄ and ¹G₄ excited state dynamics was studied. Decay curves and time constants of luminescence were collected at 5 and 300 K and analysed. The ³F₄ → ³H₆ luminescence at around 1.8 μm was too weak to be acquired from the low concentrated sample. However, based on optical data it was possible to estimate the radiative probability A_rad of this transition and the ³F₄ radiative lifetime. The resultant values are: A_rad = 668 ± 0.4 s⁻¹ and τ_rad = 1.5 ms. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phase Transition and Phase Diagram of Anion Radical Salts of [(C6H5)3PCH3]+ [(C6H5)3AsCH3]+ ×(TCNO)− 2 (0 ≤×≤ 1)

Abstract

Much attention has been paid to the solid anion radical salts of 7,7,8,8-tetracyanoquinodimethane (TCNQ), because of their prominent electronic properties.^1–4 In particular, the salts containing mixed cations represented by [(C₆H₅)₃PCH₃]⁺ _1–x [(C₆H₅)₃AsCH₃]⁺ _× (TCNQ)^? ₂, (0 ≤×≤ 1), are known to undergo phase transitions at 1 atm pressure in the solid state.^1–4 The phase transition of pure methyltriphenylphosphonium salt, (x = 0.00), takes place at 315.7 K. Heat-capacity measurements of this phase transition have been made by Kosaki et al. ³ The transition has thus been found to be of the first order. The enthalpy and the total entropy change associated with the phase transition were experimentally determined to be 485.18 cal/mol and 1.7206 cal/deg.mol, respectively. For the solid solutions, it was found that the transition temperature (T_c ) is increased, while the magnitude of the heat of transition (δH) is decreased, progressively with an increase in the composition parameter (x) and that pure methyltriphenylarsonium salt, (x = 1.00), has no such phase transition up to the decomposition temperature of about 480 K at 1 atm pressure.^1–3 Figure 1 shows the experimental relation between T _c and x, together with the relation between δH and x.⁴ In the present paper, we attempted to explain thermodynamically the phase diagram of Figure 1 for the solid solutions of those TCNQ anion radical salts.     

Square-Planar trans-Bis-(1-p-n-octylphenylbutane-1,3-dionato) copper (II), a New Compound Exhibiting Three Kinds of ‘Double Melting’ Behaviour

The new compound, bis-(1-p-n-octylphenylbutane-1,3-dionato) copper(II) has four polymorphs, C¹ (m.p. 96°C), all having the same squareplanar trans structure. C¹, C^a, and C^m exhibit ‘double melting’ behaviour, i.e., they melt at their was observed only on very rapid heating, while that of C^a and C^m only on slow heating. Slow solid-solid phase transition from C¹ to C^h was observed at ca 50°C. Each polymorph could be obtained as a stable form at room temperature and gave a quite different X-ray diffraction powder pattern. The interrelationships of the four forms have been clarified by differential scanning calorimetric and micriscopic measurements. When the melt of the complex is rapidly cooled, it converts into a glassy state, which is stable at room temperature. The glass transition temperature T₈ and the crystallizing temperature T_e are very close to each other at 52.5°C and 58.0°C, respectively.     

Phase Characterization,Enthalpies and Entropies of Transition,of Five Substituted N-(1-Biphenylethylidene) Benzylamines

Five N-(1-biphenylethylidene) benzylamines expressed by the general formula C₆H₅C₆H₄C(CH₃) = N-CH₂-C₆4HX (X = H, m-F, m-Cl, M-Br and p-OCH₃) were synthesized and their thermal behavior studied within the temperature range of -75 to 250°C.

The solid-liquid, liquid-solid transition temperatures were recorded with a DSC analyzer and the thermodynamic parameters ΔH_m and ΔS_m were estimated. A relationship between these parameters and the molecular weigth was found. The compound m-fluoro N- (1-biphenylethylidene) benzylamine showed an l_i → l_n transition at 341.5°K, which was better observed by cooling the sample at 10°C/min. The liquid crystal behavior was confirmed by cross polarized microscopy.     

Melting enthalpy ΔHm for describing glass forming ability of bulk metallic glasses

A new melting enthalpy ΔH_m criterion for the prediction of glass forming ability (GFA) of alloys is proposed and five Zr–Al–Ni–Cu bulk metallic glasses (BMG) with critical dimension Z_max up to ? 7.5 mm are also developed by us in the light of the optimum ΔH_m of Zr–Al–Ni–Cu alloy system. And then, we researched the relationships between ΔH_m and two GFA parameters (critical cooling rate R_c and Z_max) of five bulk metallic glass (BMG) systems, such as Mg–Ni–Nd, Pd–Cu–Si, La–Al–Ni–Cu, Zr–Al–Ni–Cu and Zr–Ti–Ni–Cu–Be, respectively. The results show that the relationships between ΔH_m and R_c are all concave upward parabolas, and the optimum ΔH_ms for Mg–Ni–Nd, Pd–Cu–Si, Zr–Al–Ni–Cu, Zr–Ti–Ni–Cu–Be and La–Al–Ni–Cu are 10.3960 kJ mol^?1, 21.2202 kJ mol^?1, 19.7146 kJ mol^?1, 18.1455 kJ mol^?1 and 13.1558 kJ mol^?1, respectively. On the contrary, the relationships between ΔH_m and Z_max are all concave downward parabolas, and the optimum ΔH_ms for Mg–Ni–Nd, Pd–Cu–Si, Zr–Al–Ni–Cu, Zr–Ti–Ni–Cu–Be and La–Al–Ni–Cu are 10.5530 kJ mol^?1, 21.0830 kJ mol^?1, 19.6603 kJ mol^?1, 19.7231 kJ mol^?1 and 13.1173 kJ mol^?1, respectively. Furthermore, other BMGs’ R_cs or Z_maxs predicted by above-mentioned relationships satisfactorily agree with the tested results, which indicates that these relationships are reliable. However, the predicted results are reliable only if the main components are similar with the fitted BMGs or the additive is sparkle enough that the alloy’s character does not change. On the whole, the ΔH_m can act as a criterion for quickly predicting the alloy’s GFA and be helpful for the development of new BMGs.     

Crystal structures of four inclusion compounds of 2,2′-dithiosalicylic acid and tetraalkylammonium

Herein four inclusion compounds of 2,2′-dithiosalicylic acid and tetraalkylammonium, 2(CH₃)₄N⁺·C₁₄H₈O₄S₂^2?·H₂O (1), (C₂H₅)₄N⁺·C₁₄H₉O₄S₂^?·0.25H₂O(2), (n-C₃H₇)₄N⁺·C₁₄H₉O₄S₂^? (3) and (n-C₄H₉)₄N⁺·C₁₄H₉O₄S₂^?(4) are prepared and characterized by X-ray single crystal diffraction. As shown in the results, compounds 1 and 3 belong to orthorhombic crystal system with different space groups of P2₁2₁2₁ and Pca2₁, and 2 and 4 are monoclinic system with similar groups of P2₁/n and P2₁/c. The crystallography data are displayed below: 1: a = 10.5903(7) Å, b = 10.6651(7) Å, c = 21.9476(13) Å, V = 2478.9(3) ų, Z = 4, R₁ = 0.0359; 2: a = 8.13340(1) Å, b = 22.0741(3)Å, c = 13.2143(2)Å, β = 101.6360(1) °, V = 2323.70(6) ų, Z = 1, R₁ = 0.0385; 3: a = 15.7857(2) Å, b = 8.24830(1) Å, c = 20.2599(2) Å, V = 2637.94(5) ų, Z = 4, R₁ = 0.0308_degree4: a = 11.7476(2) Å, b = 17.1346(1) Å, c = 16.3583(3)Å, β = 109.4560(1) °, V = 3104.74(9)ų, Z = 4, R₁ = 0.0562. Interestingly, although the carbon chains of the guest templates vary from methyl group to butyl group, the host molecules of 2,2′-dithiosalicylic acid all construct the similar 2D hydrogen-bonded host layers with or without the existence of water molecules to contain the guest templates to yield analogous sandwich-like inclusion compounds. Obviously, although the guest templates will have certain effects on the ultimate formation of these crystal structures, the host molecule of 2,2′-dithiosalicylic acid is a controlling factor to form these four inclusion compounds.     

Preparation of lithium ion conducting glasses and glass–ceramics for all-solid-state batteries

Highly lithium ion conducting glasses and glass–ceramics were prepared by a mechanical milling technique in the Li₂S-based sulfide and oxysulfide systems. The Li₂S–P₂S₅ glass–ceramics showed ionic conductivity as high as 3.2 × 10^?3 S cm^?1 at room temperature. All-solid-state batteries using these sulfide-based materials as a solid electrolyte showed excellent charge–discharge performance with high capacity and high cycleability. The cells with the combination of the SnS–P₂S₅ glassy electrode and the Li₂S–P₂S₅ glass–ceramic electrolyte worked as a secondary battery, which was a first step of glassy monolithic cells with a common glass network.     

Optical absorption and photoluminescence studies of Nd doped alkali boro germanate glasses

Optical absorption and photoluminescence studies have been carried out at room temperature in 25 R₂O-25 GeO₂-49.5 B₂O₃-0.5 Nd₂O₃ glass systems, (Composition in mol%, R = Li, Na, K and Rb). Judd Ofelt Intensity parameters and other parameters like Racah (E¹, E² and E³), Slater-Condon-Shortley (F₂, F₄ and F₆) Spin-Orbit Coupling (ξ_4f) and Configuration Interaction (α,β and γ) for Nd³⁺ ion in the glass system are calculated. The variation of the Ω₂ parameters are interpreted in terms of the covalency of the RE ion in the glass matrix. Further the hypersensitive transition ⁴I_9/2 → ⁴ G_5/2, ² G_7/2 is analyzed with respect to the intensity ratio I_L/I_S and is found to be dependent on the type of alkali in the glass matrix. The Photoluminescence studies do not show any appreciable shift in the peak emission wavelength of the ⁴ F_3/2 to ⁴I_11/2 transition with the change in alkali type.     

Structural behavior of amorphous and liquid metallic alloys at elevated temperatures

The thermal behavior of the short-range order of Pd₄₀Cu₃₀Ni₁₀P₂₀ bulk metallic glasses has been investigated in situ by means of high-temperature X-ray synchrotron diffraction. The dependence of the X-ray structure factor S(q) of the glassy state on temperature follows the Debye theory up to the glass transition. Above the glass transition temperature T_g, the temperature dependence of S(q) is altered toward a continuous development of structural changes in the liquid state with temperature. The behavior of the structure factor during heating and cooling through the glass transition gives experimental evidence for melting the glass, and for freezing the liquid, respectively at the caloric glass temperature.     

Stark splitting of the ground state of Er in fluorozirconate glass at low temperature

Optical properties of Er³⁺-doped ZBLAN glass matrix have been studied by luminescence spectroscopy under 488 nm excitation. The spectrum of the ⁴S_3/2⁴I_15/2 transition, carried out at temperature T = 2 K, shows a new line in the lowest energy region. This new line, centered at 17 996 cm⁻¹, was attributed to the lower transition between the Stark components of the ⁴S_3/2⁴I_15/2 transition. Measurements from T = 2 K to room temperature show the disappearance of this new line. From the results we estimate the splitting of 415 cm⁻¹ for the ground state and 100 cm⁻¹ for the ⁴S_3/2 excited multiplet. The experimental result allows us to assign the positions of the eight Stark components of the ground state multiplet of the Er³⁺ in the ZBLAN glass matrix.