Phase Identification in a Series of Liquid Crystalline TPP Polyethers and Copolyethers Having Highly Ordered Mesophase Structures. 1. Phase Diagrams of Odd-Numbered TPP Polyethers

Abstract

A series of liquid crystalline polyethers has been synthesized from 1-(4-hydroxy-4‘-biphenylyl)-2-(4-hydroxyphenyl)propane and α,ω-dibromoalkanes [TPP(n)]. From the differential scanning calorimetry experiments, the TPP(n=odd)s show multiple phase transitions during cooling and heating. For each TPP(n=odd) the supercooling dependence of these transitions is found to be small. A phase diagram of the transition temperatures and the enthalpy and entropy changes of the transitions with respect to the number of methylene units (n) for TPP(n=odd)s have been obtained. Analyses have been conducted regarding the contributions of both the mesogenic groups and the methylene units to the differently ordered structures. Identification of the ordered structures in each phase has been carried out by combining wide angle X-ray powder and fiber diffraction experiments at different temperatures with polarized light and transmission electron microscopy experiments on the liquid crystal morphology and defects. It is found that for TPP(n≤13)s the highest temperature transition is from the isotropic melt to a nematic phase. However, for TPP(n≥15)s, the isotropic melt directly converts to a smectic F phase having a monoclinic unit cell (a pseudohexagonal packing tilted toward a side). The WAXD fiber patterns for this phase show that the chain orientation is parallel to the fiber direction. For TPP(n≤13)s formation of a smectic F phase with a monoclinic unit cell from the nematic phase can also be determined and the WAXD fiber pattern shows that the chain orientation is at an angle ranging between 0 and 20° with respect to the fiber direction. With an increase in the number of methylene units, this angle gradually decreases until n = 15, where this angle becomes zero. Further cooling leads to a smectic crystal G phase for all TPP(n=odd)s, and the different chain orientations with respect to the fiber direction in the WAXD fiber patterns still exist. TPP(n≤9)s remain in the smectic crystal G phase down to their glass transition temperatures, while TPP(n≥11)s form a smectic crystal H phase (a tilted herringbone, orthorhombic packing tilted toward the b-axis side, and a > b) in a low temperature range.

Surface‐Induced Polymer Crystallization in High Volume Fraction Aligned Carbon Nanotube–Polymer Composites

“…This phenomenon represents the characteristic transition of the nematic liquid crystalline phase to the isotropic liquid melt state. [56][57][58] Our experimental results are consistent with recent molecular dynamic simulations of temperature-dependent conformations of PE molecules adsorbed on CNT surfaces. [59,60] These studies predicted an isotropic-to-nematic liquid crystalline phase transition at the CNT interface at high temperatures.…”

Ionic liquid crystalline phases in 3-hexadecylimidazolium bromide and binary mixtures with 1-decanol

“…Interestingly, it is accompanied by the appearance of one or two diffraction peaks situated at 23.49°and 25.36°at the high 2h angles. The similar observations are reported by Yoon et al [15] and Zheng et al [16]. In most of the cases, the low-angle diffraction peak represents the layer spacing in the mesophase structure, and the diffraction peaks appearing in the high-angle diffraction should be ascribed to the structure order within, and even among, the layer structures [16].…”

“…3a), indicating the presence of a well-structured 3D crystalline compound [15]. These more regular solid phase can also be seen from the POM picture of 3-hexadecylimidazolium bromide at 42°C that shows parallel solidlines in fan-shaped conic picture, indicating that the structure order within or among the lamellar is better-ordered compared to 1-hexadecyl-3-methylimidazolium bromide and 1-hexadecyl-2,3-dimethy-limidazolium bromide [5,7].…”

Phase behaviors and supra-molecular structures of a series of symmetrically tapered bisamides

“…Therefore, these two-phase transitions must correspond to transitions from the isotropic (I) state to a LC phase at the high-temperature transition and a LC to another LC phase transition at the lowtemperature transition. [34][35][36][37] Compared with thermal transitions of C14PhBA and C16PhBA, both C10PhBA and C12PhBA exhibited three transition processes during cooling as shown in Fig. 1a.…”