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1.
《Liquid crystals》2001,28(12):1785-1791
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. 相似文献
2.
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. 相似文献
3.
In situ observation of the optical texture, and X-ray patterns of the pressure-induced mesophase seen for 4′-n-hexadecyloxy-3′-nitrobiphenyl-4-carboxylic acid (ANBC-16) was performed under hydrostatic pressures up to 100MPa using a polarizing optical microscope equipped with a high pressure hot stage and a wide angle X-ray diffractometer equipped with a high pressure vessel respectively. It was found that the pressure-induced mesophase (hereafter refered to as ‘X’) appeared at pressures above 60 MPa, and exhibits a birefringent broken-fan or a sand-like texture that remain unaltered in the SmC phase. The POM-transmitted light intensity curve measured on heating clearly showed the Cr4 → Cr1 → SmC → ‘X’ → SmA → I transition sequence at 80 MPa. The optical texture and the POM-transmitted light intensity measured during a pressure cycle at 185°C showed a reversible change between the cubic and ‘X’ phases. The WAXD pattern of the ‘X’ phase showed a spot-like pattern, suggesting no layered structure for this phase, and also revealed a substantial decrease in the d-spacing of the low angle reflection at 80 and 100 MPa, compared with the d-spacings of the (0 0 1) reflection of the SmC phase and also the (2 1 1) reflection of the cubic phase. It is concluded from these data that the ‘X’ phase is a birefringent hexagonal columnar phase. 相似文献
4.
Two polycatenar materials composed of a four‐aromatic‐ring core with a perfluorinated moiety attached in one terminal position through either butylene‐ or pentylene spacer groups, and three tetradecyloxy chains at the other end (abbreviated as 14PC4F and 14PC5F), were investigated to study the effect of pressure on the phase transition behaviour. A polarizing optical microscope equipped with a high pressure optical hot stage, was used for the purpose. The T vs. P phase diagrams of 14PC4F and 14PC5F were constructed in the pressure region up to 100 MPa. 14PC4F showed the stable crystal (Cr1)–columnar tetragonal (Coltet)–smectic A (SmA)–columnar hexagonal (Colh)–isoropic liquid (I) phase transition sequence under all pressures. 14PC5F exhibited the phase sequence metastable crystal (Cr2)–cubic (Cub)–Coltet–SmA–I in a melt‐cooled sample on heating under pressure. But when the melt‐cooled Cr2 sample was annealed at 52–54°C for 2–3 h, the stable crystal (Cr1) was formed slowly, giving a stable Cr1–Cub–Coltet–SmA–I phase sequence. The temperature region of the stable cubic phase broadened with increasing pressure. Furthermore a new mesophase of 14PC5F was pressure‐induced between the I and SmA phases on cooling at pressures above about 16 MPa. Since the monotropic mesophase exhibited a texture very similar to that of the high temperature Colh phase of 14PC4F with planar orientation, the new phase was assigned at a high temperature columnar hexagonal phase of 14PC5F. 相似文献
5.
In situ observation of the optical texture, and X-ray patterns of the pressure-induced mesophase seen for 4'-n-hexadecyloxy-3'-nitrobiphenyl-4-carboxylic acid (ANBC-16) was performed under hydrostatic pressures up to 100MPa using a polarizing optical microscope equipped with a high pressure hot stage and a wide angle X-ray diffractometer equipped with a high pressure vessel respectively. It was found that the pressure-induced mesophase (hereafter refered to as 'X') appeared at pressures above 60 MPa, and exhibits a birefringent broken-fan or a sand-like texture that remain unaltered in the SmC phase. The POM-transmitted light intensity curve measured on heating clearly showed the Cr4 →Cr1 →SmC →'X' →SmA →I transition sequence at 80 MPa. The optical texture and the POM-transmitted light intensity measured during a pressure cycle at 185°C showed a reversible change between the cubic and 'X' phases. The WAXD pattern of the 'X' phase showed a spot-like pattern, suggesting no layered structure for this phase, and also revealed a substantial decrease in the d-spacing of the low angle reflection at 80 and 100 MPa, compared with the d-spacings of the (0 0 1) reflection of the SmC phase and also the (2 1 1) reflection of the cubic phase. It is concluded from these data that the 'X' phase is a birefringent hexagonal columnar phase. 相似文献
6.
The phase behavior of an optically isotropic cubic mesogen 4'-n-hexadecyloxy-3'-nitrobiphenyl-4-carboxylic acid (ANBC-16) was investigated under hydrostatic pressures up to 200 MPa using
a high-pressure DTA, a polarizing optical microscope equipped with a high-pressure hot-stage and a wide-angle X-ray diffractometer
equipped with a high-pressure vessel. In the T vs. P phase diagram constructed in the heating mode, a triple point exists at 54±1 MPa and 205±1°C for the SmC, cubic, and SmA
phases. A new mesophase, denoted here as X, appears in place of the cubic phase under pressures above about 60 MPa, while
the X phase appears on cooling in the whole pressure region studied. Thus the X phase is a monotropic (metastable) phase between
the SmA and Cub phases in the low pressure region, while being an enantiotropic phase between the SmA and SmC phases in the
high pressure range. The X phase exhibits broken-fan or sand-like textures under pressure and a spot-like diffraction pattern,
indicating the birefringent feature and no layered structure. It is suggested that the X phase is tetragonal or hexagonal
columnar phase.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
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. 相似文献
8.
The thermal behaviour of members of a homologous series which exhibits the optically isotropic cubic phase, the 4'- n -alkoxy-3'-nitrobiphenyl-4-carboxylic acids having alkoxy chains containing 16, 20 and 22 carbon atoms (referred to as ANBC-16, -20 and -22, respectively) was investigated under pressures up to 200-400 MPa by high pressure differential thermal analysis. In the phase diagram of ANBC-16 obtained on heating, a triple point was estimated at 54 ±1 MPa and 205 ±1°C for the SmC, Cub and SmA phases. It was found that the X phase is formed on cooling under all pressures, while appearing on heating at high pressures above about 54 MPa. Thus the X phase appears monotropically between the SmA and Cub phases in the low pressure region and enantiotropically between the SmA and SmC phases under higher pressures. It is strongly suggested that the X phase is a columnar mesophase. For ANBC-20 and -22, the cubic phase tends to be destabilized with increasing pressure. The temperature region of the cubic phase of ANBC-20 becomes narrower with increasing pressure and a triple point for the SmC, Cub and I phases is estimated to be at about 309 MPa. On the other hand, the cubic phase of ANBC-22 is still observed at the highest pressure examined. 相似文献
9.
Two polycatenar materials composed of a four-aromatic-ring core with a perfluorinated moiety attached in one terminal position through either butylene- or pentylene spacer groups, and three tetradecyloxy chains at the other end (abbreviated as 14PC4F and 14PC5F), were investigated to study the effect of pressure on the phase transition behaviour. A polarizing optical microscope equipped with a high pressure optical hot stage, was used for the purpose. The T vs. P phase diagrams of 14PC4F and 14PC5F were constructed in the pressure region up to 100 MPa. 14PC4F showed the stable crystal (Cr1)-columnar tetragonal (Coltet)-smectic A (SmA)-columnar hexagonal (Colh)-isoropic liquid (I) phase transition sequence under all pressures. 14PC5F exhibited the phase sequence metastable crystal (Cr2)-cubic (Cub)-Coltet-SmA-I in a melt-cooled sample on heating under pressure. But when the melt-cooled Cr2 sample was annealed at 52-54°C for 2-3 h, the stable crystal (Cr1) was formed slowly, giving a stable Cr1-Cub-Coltet-SmA-I phase sequence. The temperature region of the stable cubic phase broadened with increasing pressure. Furthermore a new mesophase of 14PC5F was pressure-induced between the I and SmA phases on cooling at pressures above about 16 MPa. Since the monotropic mesophase exhibited a texture very similar to that of the high temperature Colh phase of 14PC4F with planar orientation, the new phase was assigned at a high temperature columnar hexagonal phase of 14PC5F. 相似文献
10.
S. Krishna Prasad Yoji Maeda Corresponding author D. S. Shankar Rao S. Anitha Nagamani Uma S. Hiremath C. V. Yelamaggad 《Liquid crystals》2013,40(11):1277-1283
The phase behaviour of two achiral bent core banana-shaped compounds, the hexyloxy (compound I) and decyloxy (compound II) members of the 1,3-phenylene bis[N-(2-hydroxy-4-n-alkoxybenzylidene)-4′-aminobenzoate] series was investigated under hydrostatic pressures up to 300?MPa using high pressure differential thermal analysis and light transmission methods. The reversible transition sequence crystal (Cr1)–B1 phase–isotropic liquid (I), observed at room pressure for compound I, remains in the pressure region up to c 70?MPa. At higher pressures a pressure-induced crystalline phase (Cri) appears between the Cr1 and B1 phases, its temperature region becoming wider with increasing pressure. The temperature vs. pressure phase diagram shows a triple point of 72.9?MPa and 160.3°C for the Cr1, Cri and B1 phases, indicating the lower limit of pressure for the Cri phase. In compound II the reversible transition sequence crystal (Cr1)–B2 phase–I is seen over the whole pressure region, and the temperature range of the B2 phase remains unaltered. It is concluded that both the B1 and B2 banana phases are stable over the whole pressure region studied. 相似文献
11.
The phase transition behaviour of two optically isotropic, thermotropic cubic mesogens 1,2-bis-(4-n-undecyloxy- and 4-n-dodecyloxy-benzoyl)hydrazine, BABH(11) and BABH(12), was investigated under hydrostatic pressures up to 300 MPa using a high pressure differential thermal analyser, a wide angle X-ray diffractometer and a polarizing optical microscope equipped with a high pressure optical cell. It is found that for BABH(11) and BABH(12), a smectic C (SmC) phase is induced between the isotropic liquid (I) and the cubic (Cub) phases by applying pressures above 10-12 and 16-17 MPa, respectively. A sea-island texture consisting of bright sand-like sea regions (SmC phase) and areas of dark islands (Cub phase) appears in the mesophase under pressures up to 140 MPa, while the sand-like texture of the SmC phase is formed predominantly on cooling under pressure. These observations indicate the destabilization of the cubic phase with increasing pressure. The phase transition sequence of BABH(11) and BABH(12), Cr-Cub-I at atmospheric pressure, changes to Cr-Cub-SmC-I under intermediate pressures and would change to Cr-SmC-I under elevated pressure. 相似文献
12.
The pressure-scanning differential thermal analyzer (DTA) measurements of the cubic (Cub)-smectic C (SmC) transition of thermotropic cubic mesogens of 1,2-bis-(4-n-octyloxybenzoyl)- and 1,2-bis-(4-n-dodecyloxybenzoyl)hydrazine, BABH(8) and BABH(12), were performed at isothermal condition using a high-pressure differential thermal analyzer. BABH(8) showed the same endothermic peak of the Cub-SmC transition in the pressurizing process as on heating at isobaric condition. On the other hand, BABH(12) showed only the cubic phase between the crystal and the isotropic liquid under pressures up to 16-17 MPa, but a high-pressure smectic C (SmC(hp)) phase was induced instead of the cubic phase under higher pressure. The Cub-SmC(hp) phase transition with a small exothermic peak occurred in the pressurizing process and the transition was observed reversibly. The Cub-SmC(hp) phase transition was in accordance with the morphological and structural observations mentioned before. The strange phenomenon of the inversion of sign of the Cub-SmC transition heat of BABH(n) homologues can be explained by the “Alkyl-chains as entropy reservoir” mechanism proposed by Saito et al. 相似文献
13.
The phase transition behaviour of three homologous discotic mesogens, the hexa‐n‐alkoxyanthraquinones HOAQ(n), n indicating the number of carbon atoms in the alkoxy group, was investigated under hydrostatic pressures up to 500?MPa using a high pressure differential thermal analyser. The T vs. P phase diagrams of HOAQ(6), HOAQ(8) and HOAQ(9) were constructed for solution‐ (Cr0) and melt‐crystallized (Cr1) samples of the compounds. HOAQ(6) shows the reversible Cr0–rectangular columnar phase (Colr)–hexagonal columnar phase (Colh)–isotropic liquid (I) phase sequence at atmospheric pressure. The stable Colr phase of HOAQ(6) has a decreased temperature range with increasing pressure and then the Colr phase disappears under pressures above about 350?MPa; instead the Cr0–Colh–I phase sequence is exhibited. For HOAQ(8), the solution‐grown sample exhibits the stable Cr0–Colh–I phase sequence at atmospheric pressure. Applying pressure to the solution‐grown sample induces the formation of the stable Colr phase in the pressure region between 10 and 350?MPa, leading to the Cr0–Colr–Colh–I phase sequence. The pressure‐induced Colr phase disappears under higher pressures. The melt‐cooled sample of HOAQ(8) shows the formation of the metastable crystal (Cr1), unknown mesophase (X) and Colr phases at lower temperatures under atmospheric pressure, and exhibits the reversible Cr1–X–Colr–Colh–I phase sequence on subsequent thermal cycles. The metastable phase sequence was observed under pressures up to 100?MPa, but the phase transitions were too small to be detected under higher pressures. In HOAQ(9) the stable Cr0–Colh–I phase sequence is observed at all pressures, while the melt‐cooled sample shows the metastable Cr1–Colr–Colh–I phase sequence under pressures up to 300?MPa. The metastable Colr phase disappears under higher pressures. 相似文献
14.
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. 相似文献
15.
The interactions in the GeS2-Cr2S3 and Cu2GeS3-Cr2S3 sections were studied by differential thermal analysis and X-ray powder diffraction. The GeS2-Cr2S3 section was shown to be quasi-binary, with a degenerate eutectic; no ternary compound was formed. In the Cu2GeS3-Cr2S3 section, a quaternary phase of variable composition having a homogeneity range of 69–75 mol % Cr2S3 crystallized in the cubic system. The samples of this composition are spin glasses with freezing temperatures of 20–25 K. 相似文献
16.
The synthesis of four new chiral mesogenic monomers (M1–M4) and side chain ferroelectric liquid crystalline polymers containing (2S, 3S)-2-chloro-3-methylpentanoate is described. The chemical structures and phase behaviour of the monomers and polymers obtained in this study were characterised by Fourier transform infrared, proton nuclear magnetic resonance, polarising optical microscopy, differential scanning calorimetry, thermogravimetric analysis and X-ray diffraction. The selective reflection of light was investigated with ultraviolet/visible (UV/Vis). Their structure–mesomorphism relationships were discussed. M1 and P1 all showed a chiral smectic C (SmC*) phase. M2 and M3 revealed a SmC* phase and cholesteric phase, while their corresponding polymers P2 and P3 revealed a SmC* phase and smectic A (SmA) phase. M4 only exhibited a cholesteric phase, whereas the corresponding polymers P4 showed a SmA phase. Moreover, the selective reflection of light shifted to the long-wavelength region at the SmC* phase range and to the short-wavelength region at the cholesteric range with increasing temperature, respectively. The results seemed to demonstrate that the tendency towards melting temperature (Tm), glass transition temperature (Tg), isotropic temperature (Ti) and mesophase range for the monomers and polymers increased by increasing the mesogenic core rigidity or the number of phenyl ring. The polymerisation effect could lead to higher liquid crystalline to isotropic phase transition temperature, wider mesophase range and more ordered smectic phase formed. In addition, all the obtained polymers had a very good thermal stability and the corresponding Td increased by increasing the number of phenyl ring. 相似文献
17.
A series of methyl 4-(4-alkoxystyryl)benzoates was synthesised and studied for liquid crystalline and fluorescence properties. The peculiarity of the reaction scheme involved condensation between 4-alkoxybenzaldehyde and 4-(methoxycarbonyl)benzyltriphenyl phosphonium bromide in dichloromethane without any phase separation. The compounds were found thermally stable up to 200°C. The banded or arced focal-conic fan texture of CrE phase was exhibited on cooling the compounds (with chain length > C4) below the SmA phase. It was observed that increasing chain length up to C10 enhances mesophase stability. No LC behaviour was manifested by small (up to C3) and branched small chain (up to C4) members of the series. 相似文献
18.
R. Cardoso‐Gil R. Niewa M. Schmidt M. Armbrüster M. Hanfland K. Klementiev Ulrich Schwarz 《无机化学与普通化学杂志》2003,629(3):454-458
Pressure‐induced structural changes and electronic properties of rhombohedral Eu4P3 were characterised by means of X‐ray powder diffraction and X‐ray absorption spectroscopy at the Eu LIII threshold. The measurements at low pressures indicate oxidation states of the europium atoms which are compatible with a composition Eu32+Eu3+P3. At a pressure of 8(1) GPa, Eu4P3 undergoes a structural phase transition. The cubic high pressure modification with (anti‐)Th3P4 type crystal structure is also identified as a compound with a non‐integer average oxidation state of the europium atoms. 相似文献
19.
Eniko Berei Cornelia Muntean Oana Ştefănescu Mircea Niculescu Mircea Ştefănescu 《Journal of Thermal Analysis and Calorimetry》2018,131(1):137-144
CuCr2O4 spinel powders were synthesized starting from different chromium sources, namely (i) chromium oxide (α-Cr2O3) and (ii) ammonium dichromate ((NH4)2Cr2O7). The copper source was a Cu(II) carboxylate-type complex. The Cu(II) carboxylate complex was obtained by the redox reaction between Cu(NO3)2·3H2O and 1,3-propanediol (1,3PG) at 130 °C. In the first case (i), we have started from a mixture of α-Cr2O3, Cu(NO3)2·3H2O and 1,3PG that upon heating formed the copper malonate complex, which decomposed around 220 °C forming an oxide mixture (CuO + α-Cr2O3). In the second case (ii), (NH4)2Cr2O7, Cu(NO3)2·3H2O and 1,3PG were homogenously mixed. Heating this mixture at 130 °C resulted, in situ, in the Cu(II) complex. On controlled temperature increase, the violent decomposition of (NH4)2Cr2O7 took place at 180 °C along with the decomposition of the Cu(II) complex, leading to an amorphous oxide mixture of Cr2O3+x and CuO. By annealing the samples in the temperature range 400–1000 °C, the spinel phase (CuCr2O4) was obtained in both cases: (i) at 800 °C and (ii) at 600 °C as a result of the interactions between the precursors used, when the oxide system was amorphous and highly reactive. The presence of CuCr2O4 was highlighted by XRD and FTIR analyses. 相似文献
20.
Al2O3-Cr2O3 solid solutions with 0, 4, 7, 10 and 20 mol% of corundum were synthesized using a high-pressure/high-temperature apparatus
and characterized by X-ray powder diffraction.
Calorimetric measurements were carried out using DSC-111 (Setaram). Heat capacity was measured by the enthalpy method in a
temperature range of 260–340 K, near magnetic phase transition in pure Cr2O3 (305 K). Magnetic contribution into the heat capacity was derived and found to change irregularly with the composition. 相似文献