High-temperature Mesophase Research Articles

X-Ray Study of the Mesophase-Mesophase Transition of Octaalkyloxyorthocyclophanes

Previous studies of the mesomorphic octaether derivatives of cyclotetraveratrylene, CTTV-I- n (n is the number of carbon atoms per ether chain), have shown two columnar mesophases for 9<n<16. In the higher temperature mesophase the columns are packed in a two-dimensional hexagonal unit cell, while in the lower phase the packing is two-dimensional centered rectangular. DSC showed no heat of transition between the two mesophases. For n=13, the transition occurred over a wide temperature range. We find this wide transition region is a third mesophase, with an oblique net intermediate between the other two. The upper boundary of this phase marks breaking of hexagonal symmetry by the appearance of a unit cell having γ=120°, but with a≠b. With decreasing temperature, b is essentially constant while a and γ increase until -2b cosγ=a, marking the transition to the primitive cell for the two dimensional centered rectangular net. Similar behavior is observed for n=14.

Thermotropic liquid crystals of main-chain polyesters having a mesogenic 4,4′-biphenyldicarboxylate unit. 8. X-ray analyses of structural change on S A to S C transition

We have prepared main-chain liquid crystalline copolyesters made from biphenyldicarboxylic acid as a mesogenic component and a certain mixture of 2-methylbutanediol and hexanediol as spacer components. These copolymers exhibit the novel polymorphism with the smectic A as a higher temperature mesophase and the smectic C phase as a lower temperature one. The transition behavior of smectic A to smectic C has been examined by X-ray diffraction method and the layered structure of smectic C phase has been described by a comparison with the preceding smectic A structure.

A new high temperature mesophase of a double-swallow-tailed compound with weak optical anisotropy

Abstract A new six-ring double-swallow-tailed compound is presented which shows four liquid crystalline phases. In addition to a smectic C phase and two columnar phases (oblique and hexagonal), a high temperature mesophase was observed which exhibits a very weak birefringence and which shows unusual optical textures.

Novel Amphiphilic Phthalocyanine Mesogens

Abstract A number of novel amphiphilic phthalocyanines (Pcs) have been prepared containing long alkyl (-C16H33) and oligo(ethyleneoxy) chains (-O(C2H4O)3CH3) in the peripheral positions. All the Pcs prepared showed liquid crystalline behaviour, with most compounds giving two mesophases. Optical microscopy suggests that the lower temperature mesophase (M1) is a discotic rectangular mesophase, and that the higher temperature mesophase (M2) is a discotic hexagonal phase.

Liquid-crystalline polyethers based on conformational isomerism. Part 22—Hexagonal columnar mesophase in polyethers and copolyethers based on 1,4-bis[2-(4-hydroxyphenyl)ethyl]benzene, 1,2-bis(4-hydroxyphenyl)ethane and 1,9-dibromononane

The syntheses of the following compounds are presented: 1,4-bis[2-(4-hydroxyphenyl)ethyl]benzene (PEB); polyethers based on PEB and α,ω-dibromoalkanes (PEB-X, where X represents the number of methylene units in the flexible spacer, i.e. X= 5, 7, 8, 9, 10 and 12); polyethers based on 1,2-bis(4-hydroxyphenyl)ethane (BPE) and 1,9-dibromononane (BPE-9); copolyethers based on 1,9-dibromononane with various ratios of BPE to PEB [BPE/PEB(A/B)-9, where A/B is the molar ratio of BPE to PEB]. The phase behaviour of these polymers was characterized by a combination of techniques consisting of differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD) and thermal optical polarized microscopy. The high-temperature mesophase of all homopolymers and copolymers is hexagonal columnar (Φh). The temperature and the corresponding thermo-dynamic parameters of the i–Φh phase transition of BPE/PEB(A/B)-9 copolymers display continuous linear dependences of composition. The d100hex of the hexagonal columnar phase of the copolymers BPE/PEB(A/B)-9 determined at 150 °C is independent of copolymer composition.

Inosose-Flüssigkristalle / Inosose Liquid Crystals

Six S,S-dialkyl acetals 2a-f of inosose (1), tripodal in structure, have been synthesized, characterized and investigated by optical microscopy and differential scanning calorimetry (d.s.c.). The four S,S-acetals 2c-f with sufficiently long alkyl chains are thermotropic liquid crystalline; 2 e and 2 f are even dithermomesomorphic. Each of these four inosose derivatives 2c-f exhibits monotropically a most likely cubic mesophase (MI); in addition 2e and 2f show enantiotropically a hexagonal mesophase (Hx) with a non-covalent, supramolecular H-bridge architecture. Whereas the nature of the optically isotropic mesophase MI needs further clarification the stable high temperature mesophase Hx of 2 e and 2 f has been established by a miscibility test using a sugar S,S-dialkyl acetal also tripodal in structure and with a Hx phase proved by X-ray diffraction, but in contrast to 2 with an acyclic hydrophilic part. Similarities of structural features between the Hx-phases of 2e and 2f as well as of other thermotropic and lyotropic liquid crystal systems are discussed briefly.

Thermotropic Polymorphism in Liquid-Crystalline Lead(II) Alkanoates

Abstract Lead(II) carboxylates with even chain lengths from octanoate to octadecanoate have been investigated by differential scanning calorimetry, polarizing optical microscopy, X-ray diffraction, and dilatometry, together with Raman, infrared, and 207Pb N.M.R. spectroscopy. The reassignment of the high temperature mesophase as smectic A (Lx) for the octanoate to dodecanoate is confirmed. This phase is most stable for the decanoate. The intermediate temperature mesophase is a highly ordered three dimensional lamellar structure based on ionic layers. The alkyl chains in this phase are partially disordered (melted) through the introduction of gauche conformations and show decreased lateral interactions; however, they remain largely in an extended conformation due to the constraints imposed by the ionic network. Melting of the alkyl chains occurs therefore in more than one step. Re-cooling to the crystalline phase appears to result in a different polymorphic crystalline form (albeit still lamellar) from the...

Thermodynamic properties in the liquid state of high melting polymers containing phenylene and naphthylene groups

AbstractHigh melting polymers of three different types of crystallization behavior were analyzed as to their thermal properties. The heat capacity at constant pressure of liquid poly(butylene terephthalate) (PBT) from 490 to 540 K was measured by scanning calorimetry. Combining with prior measured liquid heat capacity data of poly(oxy‐1,4‐phenylene) (PO) (358 – 620 K), poly‐(thio‐1,4‐phenylene) (PPS) (540 – 600 K), poly(ethylene 2,6‐naphthalenedicarboxylate) (PEN) (400 – 450 K, 530 – 600 K), an addition scheme for liquid heat capacities was constructed. In addition, the thermodynamic functions H and S have been calculated for those five polymers. The absolute, molar, residual entropy for the glassy state at zero kelvin is estimated to be 6,6,15,2, 7,48, 5,70, and 19,9 J/(K · mol) for PPS, PEN, PPO, PO, and PBT, respectively. Another two polymers with similar structure, poly(1,4‐oxybenzoic acid) (POB) and poly(2,6‐oxynaphthoic acid) (PON), were also studied in their high temperature mesophase states. A test of the addition scheme has been made to predict their heat capacities.

Phase Diagrams of Eutectic Mixed Systems with Monotropic Liquid-Crystalline Phases

Abstract The phase diagrams of three different eutectic liquid-crystalline systems with monotropic transitions have been investigated by differential scanning calorimetry (DSC) as well as by polarization microscopy. In all systems the monotropic transition becomes enatiotropic as a function of composition, because of the intersection of a phase equilibrium line with one liquidus line. Consequently, a horizontal phase equilibrium line occurs which separates two two-phase regions. The special features of these complicated phase diagrams are discussed and experimentally verified. In the case of systems with more than one mesomorphic phase, the high temperature mesophase again appears in the low temperature two-phase region. This effect may simulate a reentrant behaviour of liquid crystall line systems.