Calorimetric study of the cubic mesogen,ACBC(16)

The heat capacity of the cubic mesogen ACBC(16) was measured between 16 and 500?K by adiabatic calorimetry. As well as the known condensed phases, a new crystalline phase was found to undergo a glass transition at around 165?K. Phase transitions between crystal, SmC, cubic, and isotropic liquid phases took place at 399.16, 431.15, and 474.30?K, respectively. As in the case of ANBC, a broad hump was observed in the heat capacity of the isotropic liquid phase. The first order nature of the SmC–cubic phase transition was confirmed for the first time by the observation of supercooling of the cubic phase. The broad hump in the isotropic liquid phase was shown to extend to a low temperature side if the isotropic liquid was supercooled, suggesting that the event occurring at the hump is not directly related to the cubic–isotropic liquid phase transition.     

Calorimetric study on the thermotropic cubic mesogen, 4'-n-hexadecyloxy-3'-nitrobiphenyl-4-carboxylic acid, ANBC(16)

The heat capacity of ANBC(16) has been measured between 15 and 500 K by adiabatic calorimetry. Three (one known and two newly found) crystal-crystal phase transitions and all the known liquid crystalline phases (SmC, cubic D and SmA) were detected. The temperatures, enthalpies and entropies of transition were determined for all the phase transitions observed. The entropy of transition is very small for the transition from/to the cubic D mesophase. The results are compared with the thermal properties of another cubic mesogen, BABH(8). The logical possibility is pointed out that the cubic mesophases of ANBC(16) and BABH(8) are of identical higher order structure, while discussing the fact that they are immiscible.     

Thermodynamic investigation of the thermotropic cubic mesogen, 1,2-bis(4- n -octyloxybenzoyl)hydrazine

Themolar heat capacity of the thermotropic cubic mesogen 1,2-bis(4- n -alkoxybenzoyl)hydrazine, BABH(8) for short, with a purity of 99.43 mol% has been precisely measured with an adiabatic calorimeter at temperatures between 14 and 480 K. The enthalpy and entropy gained at each phase transition across the phase sequence of \[crystal(2) crystal(1) cubic mesophase SmC isotropic liquid] have been determined. The existence of a solid-to-solid phase transition with a fairly large entropy change seems to be necessary for the alkyl moieties attached to both sides of the molecule to play the role of 'solvent' in the cubic mesophase. On the basis of curvature elasticity considerations, the small energy difference between the cubic and SmC phases is favourably accounted for in terms of the jointed-rod micelles model. The reason for the immiscibility of BABH(8) with the cubic D mesogen, 4- n -hexadecyloxy-3- nitrobiphenyl-4-carboxylic acid is discussed in terms of the large difference in their molecular size and of 'structure breaking' arising from the admixture of heterogeneously hydrogen-bonded materials.     

Phase behaviour of the thermotropic cubic mesogen 1,2-bis(4-n-decyloxybenzoyl)hydrazine under pressure

The phase transition behaviour of an optically isotropic, thermotropic cubic mesogen 1,2-bis(4-n-decyloxybenzoyl)hydrazine, BABH(10), was investigated under pressures up to 300 MPa using a high pressure differential thermal analyser, a wide angle X-ray diffractometer and a polarizing optical microscope (POM) equipped with a high pressure optical cell. The reversible change in structure and optical texture between the cubic (Cub) and smectic C (SmC) phases was associated with a change from a spot-like X-ray pattern and dark field for the Cub phase to the Debye-Sherrer ring pattern and sand-like texture for the SmC phase under both isobaric and isothermal conditions. The Cub phase was found to disappear at pressures above about 11 MPa. The phase transition sequence, low temperature crystal (Cr₃)-intermediate temperature crystal (Cr₂)-high temperature crystal (Cr₁)-Cub-SmC-isotropic liquid (I) observed at atmospheric pressure, is maintained in the low pressure region below 10 MPa. The transition sequence changes to Cr₃-Cr₂-(Cr₁)-SmC-I in the high pressure region. Since the Cub-SmC transition line determined by POM has a negative slope (dT/dP) in the T-P phase diagram, a triple point is estimated approximately at 10-11 MPa, and 143-145°C for the SmC, Cub and Cr₁ phases, giving the upper limit of pressure for the observation of the cubic phase.     

Phase behaviour of the thermotropic cubic mesogen 1,2-bis-(4- n -octyloxybenzoyl)hydrazine under pressure

The phase transition behaviour of an optically isotropic, thermotropic cubic mesogen 1,2-bis-(4- n -octyloxybenzoyl)hydrazine, BABH(8), was investigated under pressures up to 200 MPa using a high pressure differential thermal analyser, wide-angle X-ray diffraction and a polarizing optical microscope equipped with a high pressure optical cell. The phase transition sequence, low temperature crystal (Cr 2 )-high temperature crystal (Cr 1 ) - cubic (Cub)-smectic C (SmC)-isotropic liquid (I) observed at atmospheric pressure, is seen in the low pressure region below about 30 MPa. The cubic phase disappears at high pressures above 30-40 MPa, in conjunction with the disappearance of the Cr 1 phase. The transition sequence changes to Cr 2 -SmC-I in the high pressure region. Since only the Cub-SmC transition line among all the phase boundaries has a negative slope (d T /d P ) in the temperature-pressure phase diagram, the temperature range for the cubic phase decreases rapidly with increasing pressure. As a result, a triple point was estimated approximately as 31.6 ±2.0 MPa, 147.0 ±1.0°C for the SmC, Cub and Cr 1 phases, indicating the upper limit of pressure for the observation of the cubic phase. Reversible changes in structure and optical texture between the Cub and SmC phases were observed from a spot-like X-ray pattern and dark field for the cubic phase to the Debye-Sherrer pattern and sand-like texture for the SmC phase both in isobaric and isothermal experiments.     

Phase behaviour of the thermotropic cubic mesogen 1,2-bis-(4- n -octyloxybenzoyl)hydrazine under pressure

The phase transition behaviour of an optically isotropic, thermotropic cubic mesogen 1,2-bis-(4-n-octyloxybenzoyl)hydrazine, BABH(8), was investigated under pressures up to 200 MPa using a high pressure differential thermal analyser, wide-angle X-ray diffraction and a polarizing optical microscope equipped with a high pressure optical cell. The phase transition sequence, low temperature crystal (Cr₂)-high temperature crystal (Cr ₁)- cubic (Cub)-smectic C (SmC)-isotropic liquid (I) observed at atmospheric pressure, is seen in the low pressure region below about 30 MPa. The cubic phase disappears at high pressures above 30–40 MPa, in conjunction with the disappearance of the Cr₁ phase. The transition sequence changes to Cr₂-SmC-I in the high pressure region. Since only the Cub-SmC transition line among all the phase boundaries has a negative slope (dT/dP) in the temperature-pressure phase diagram, the temperature range for the cubic phase decreases rapidly with increasing pressure. As a result, a triple point was estimated approximately as 31.6 ±2.0 MPa, 147.0±1.0°C for the SmC, Cub and Cr₁ phases, indicating the upper limit of pressure for the observation of the cubic phase. Reversible changes in structure and optical texture between the Cub and SmC phases were observed from a spot-like X-ray pattern and dark field for the cubic phase to the Debye-Sherrer pattern and sand-like texture for the SmC phase both in isobaric and isothermal experiments.     

Thermal behaviour of the thermotropic cubic mesogen 4'-n-hexadecyloxy-3'-nitrobiphenyl-4-carboxylic acid (ANBC-16) under hydrostatic pressure

The phase behaviour of 4'-n-hexadecyloxy-3'-nitrobiphenyl-4-carboxylic acid (ANBC-16) was investigated under hydrostatic pressures up to 200 MPa using high pressure differential thermal analysis. The phase transition sequence crystal 4 (Cr4)-crystal 3 (Cr3)-crystal 2 (Cr₂)-crystal 1 (Cr₁)-smectic C (SmC)-Cubic (Cub)-smectic A (SmA)-'structured liquid' (I₁)-isotropic liquid (I₂) was observed for a virgin sample on heating at atmospheric pressure. The stable temperature region of the optically isotropic cubic phase becomes narrower on increasing pressure and disappears at pressures above 65 MPa. The T vs. P phase diagram exhibits the existence of a triple point (65 MPa, 207.6°C) for the cubic phase, a new mesophase (X), and the SmA phase, indicating the upper limit for the cubic phase. The new mesophase, denoted here as X, appears in place of the cubic phase at pressures above 65 MPa. The phase diagram also indicates that the Cr₄-Cr₃, Cr₃-Cr₂, and Cr₂-Cr₁ transition lines merge at about 40-50 MPa and then only the Cr₄-Cr₁ transition is observed in the solid state at higher pressures. Thus the phase transition process on heating changes from the sequence Cr₄-Cr₃-Cr₂-Cr₁-SmC-Cub-SmA-I₁-I₂ at atmospheric pressure to Cr₄-Cr₁-SmC-X-SmA-I₁-I₂ in the high pressure region above 65 MPa, via Cr₄-Cr₃-Cr₂-Cr₁-SmC-(X)-Cub-SmA-I₁-I₂ in the low pressure region.     

Thermal behaviour of the thermotropic cubic mesogen 4'-n-hexadecyloxy-3'-nitrobiphenyl-4-carboxylic acid (ANBC-16) under hydrostatic pressure

The phase behaviour of 4'-n-hexadecyloxy-3'-nitrobiphenyl-4-carboxylic acid (ANBC-16) was investigated under hydrostatic pressures up to 200 MPa using high pressure differential thermal analysis. The phase transition sequence crystal 4 (Cr4)-crystal 3 (Cr3)-crystal 2 (Cr₂)-crystal 1 (Cr₁)-smectic C (SmC)-Cubic (Cub)-smectic A (SmA)-'structured liquid' (I₁)-isotropic liquid (I₂) was observed for a virgin sample on heating at atmospheric pressure. The stable temperature region of the optically isotropic cubic phase becomes narrower on increasing pressure and disappears at pressures above 65 MPa. The T vs. P phase diagram exhibits the existence of a triple point (65 MPa, 207.6°C) for the cubic phase, a new mesophase (X), and the SmA phase, indicating the upper limit for the cubic phase. The new mesophase, denoted here as X, appears in place of the cubic phase at pressures above 65 MPa. The phase diagram also indicates that the Cr₄-Cr₃, Cr₃-Cr₂, and Cr₂-Cr₁ transition lines merge at about 40-50 MPa and then only the Cr₄-Cr₁ transition is observed in the solid state at higher pressures. Thus the phase transition process on heating changes from the sequence Cr₄-Cr₃-Cr₂-Cr₁-SmC-Cub-SmA-I₁-I₂ at atmospheric pressure to Cr₄-Cr₁-SmC-X-SmA-I₁-I₂ in the high pressure region above 65 MPa, via Cr₄-Cr₃-Cr₂-Cr₁-SmC-(X)-Cub-SmA-I₁-I₂ in the low pressure region.     

Calorimetric study of Diepoxide Chain-Extended Poly(Ethylene Terephthalate)

A series of chain-extended PET samples were obtained by the use of different amounts of a diepoxide as chain extender, which was prepared for this purpose. These samples exhibited different intrinsic viscosities and degrees of branching or cross-linking. The effects of this differentiation on the thermal properties were studied by differential scanning calorimetry. The thermal parameters studied were the glass transition temperature (T_g), the cold-crystallization temperature (T_cc), the melting temperature (T_m), the enthalpy (ΔH_m) and the degree of crystallinity. The data revealed that, the higher the quantity of chain extender or the chain extension time, the higher T_gand T_cc, but the lower T_mand ΔH_m, i.e. the more amorphous the chain-extended samples, as also shown by density measurements. This revised version was published online in July 2006 with corrections to the Cover Date.     

Coexistence of two aggregation modes in exotic liquid-crystalline superstructure: systematic maximum entropy analysis for cubic mesogen, 1,2-bis(4'-n-alkoxybenzoyl)hydrazine [BABH(n)

Structure of a complex superstructure self-organized by thermotropic mesogen, 1,2-bis(4'- n-alkoxybenzoyl)hydrazine [BABH(n), where n is the number of carbon atoms in an alkoxy chain] was studied while paying special attention to the structure at the molecular level. Maximum entropy (MEM) analysis revealed that the molecular cores form two kinds of aggregates: Jungle gym with 3-fold junctions roughly on P minimal surface and spherical shells.     

Dilatometry of the discotic mesogen 2,3,6,7,10,11-hexa-n-octanoyloxytriphenylene (HAT-C8)

The title compound HAT-C8 exhibits a columnar to isotropic phase transition at 402·16 K. Dilatometric studies of pure HAT-C8 as a function of temperature show the higher temperature isotropic phase to be denser than the lower temperature columnar mesophase. The fractional volume change is similar to that observed for benzene hexa-n-alkanoates, but of opposite sign. Such anomalous density changes are rare. Since the columnar-isotropic transition entropy has been measured, dp/dT has been estimated from the Clapeyron equation.     

Calorimetric measurements and first principles to study the (Ag-Li) liquid system

Integral molar enthalpies of mixing were determined by drop calorimetry for (Ag-Li) liquid alloys at two temperatures (1253 and 873) K. The integral molar enthalpies of mixing are negative in the entire range of concentrations. For the mole fraction of lithium X_Li = 0.5664, minimum value of the integral enthalpy of mixing of at ΔH_m = −11.679 kJ/mol was observed. For (Ag-Li) liquid alloys, between T = (873 and 1253) K no temperature dependence was observed. Ab initio molecular dynamics was used to simulate liquid phase structures at T = 873 K (Li-rich side) and at T = 1250 K (Ag-rich phase) for subsequent calculation of the vibrational energy, respectively. Our measured and calculated data were compared with literature data.     

Calorimetric study and thermal analysis of [ErY(Ala)4(H2O)8](ClO4)6 (Ala=ALANINE)

A solid complex of rare-earth compounds with alanine, [ErY(Ala)₄(H₂O)₈](ClO₄)₆ (Ala=alanine), was synthesized, and a calorimetric study and thermal analysis for it was performed through adiabatic calorimetry and thermogravimetry. The low-temperature heat capacity of [ErY(Ala)₄(H₂O)₈](ClO₄)₆ was measured with an automated adiabatic precision calorimeter over the temperature range from 78 to 377 K. A solid-solid phase transition was found between 99 and 121 K with a peak temperature at 115.78 k. The enthalpy and entropy of the phase transition was determined to be 1.957 Kj mol^-1, 16.90 j mol^-1 k^-1, respectively. Thermal decomposition of the complex was investigated in the temperature range of 40~550°C by use of the thermogravimetric and differential thermogravimetric (TG/DTG) analysis techniques. The TG/DTG curves showed that the decomposition started from 120 and ended at 430°C, completed in three steps. A possible mechanism of the thermal decomposition was elucidated. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mesomorphic imines and their complexes with rhenium(I): a cubic mesophase in a rod-like mesogen with perfluorinated terminal chains

A cubic mesophase is found in an extended rod-like mesogen in which the terminal chains are perfluorinated.     

Calorimetric study of free-radical polymerized poly(p-biphenyl acrylate) and poly(p-cyclohexylphenyl acrylate)

DSC traces and specific heat data for poly(p-diphenyl acrylate) (PPBA) and poly(p-cyclohexylphenyl acrylate) (PPCPA) obtained by radical polymerization are reported. The results indicate the existence of a definite ordered phase and of a reversible firstorder solid–liquid transition in both polymers although x-ray diffraction studies showed that they are not crystalline in the conventional sense. The extent of the ordered phase present in each polymer is calculated, and the problems involved in such determination by thermal measurements are discussed. On the basis of the experimental results reported here in conjunction with the x-ray data, models are proposed for the morphology of these polymers.     

Mesomorphic imines and their complexes with rhenium(I): a cubic mesophase in a rod-like mesogen with perfluorinated terminal chains

A cubic mesophase is found in an extended rod-like mesogen in which the terminal chains are perfluorinated.     

First-principles study of the (001) surface of cubic SrHfO(3) and SrTiO(3)

We have performed first-principles calculations on the (001) surface of cubic SrHfO(3) and SrTiO(3) with SrO and BO(2) (B = Ti or Hf) terminations. Surface structure, partial density of states, band structure, and surface energy have been obtained. For the BO(2)-terminated surface, the largest relaxation appears on the second-layer atoms but not on the first-layer ones. The analysis of the structure relaxation parameters reveals that the rumpling of the (001) surface for SrHfO(3) with SrO termination is stronger than that for SrTiO(3). For the HfO(2)-terminated surface of SrHfO(3), the surface state appears near the M point of its band structure.     

Calorimetric study of polymerizing complexes of acrylamide with cobalt(ii) nitrate

Thermal polymerization of complexes of acrylamide with Co^II nitrate has been investigated by differential scanning calorimetry. The conditions of the synthesis of the samples and their treatment have been found to affect the thermal and polymerization properties of the complexes. The existence of several structural modifications of the complex differing noticeably in their polymerization ability has been revealed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1414–1417, August, 1993.