Fluorescence and absorption studies of the cation-binding behavior of "crowned" liquid crystals in solution and in the nematic phase

1990 ◽  
Vol 55 (2) ◽  
pp. 548-554 ◽  
Author(s):  
Gong Xin He ◽  
Fumio Wada ◽  
Kiyoshi Kikukawa ◽  
Seiji Shinkai ◽  
Tsutomu Matsuda
Keyword(s):  
Liquid Crystals ◽  
Nematic Phase ◽  
Cation Binding ◽  
Binding Behavior ◽  
Absorption Studies

Syntheses and thermal properties of new liquid crystals bearing a crown ether ring: cation binding in the nematic phase

1990 ◽  
Vol 55 (2) ◽  
pp. 541-548 ◽  
Author(s):  
Gong Xin He ◽  
Fumio Wada ◽  
Kiyoshi Kikukawa ◽  
Seiji Shinkai ◽  
Tsutomu Matsuda
Keyword(s):  
Thermal Properties ◽  
Liquid Crystals ◽  
Crown Ether ◽  
Nematic Phase ◽  
Cation Binding

scholarly journals Synthesis of 4-Chloro-1,3-Diazobenzene Bent-Cores Liquid Crystals and Characterizations of Their Mesogenic Behaviors and Photoisomerization Phenomena

2020 ◽  
Author(s):  
Jinying Lu ◽  
Zelong Zhang ◽  
Daoren Yan ◽  
Zhiyong Zhang ◽  
Jintao Guan ◽  
...  
Keyword(s):  
Phase Transition ◽  
Liquid Crystals ◽  
Nematic Phase ◽  
Dipole Moments ◽  
Intermolecular Forces ◽  
Acetate Solution ◽  
Molecular Dipole ◽  
Practical Applications ◽  
Nematic Phases ◽  
Terminal Chain

<p></p><p>Azobenzene-based bent-core liquid crystals demonstrate a variety of mesomorphic behaviors and photochromic properties which are desirable for optical switching. Nowadays azobenzene-based bent-core liquid crystal (ABLC) compounds usually exhibit at least one of the following traits which are unfavorable for practical applications: (1) narrow temperature windows of nematic phases, (2) high phase transition temperature, and (3) long period of light stimulation to reach photostationary states. In this study, a series of ABLC compounds <b>4a–4g</b> were synthesized by adding azo functional groups and chlorine substituent to the central bent-cores to form 4-chloro-1,3-dizaophenylene bent-cores. These ABLC compounds were characterized by i. fourier-transform infrared spectroscopy (FTIR), <sup>1</sup>H and <sup>13</sup>C nuclear magnetic resonance (NMR), and mass spectrometry (MS) for their structures, ii. differential scanning calorimetry (DSC) and polarized optical microscopy (POM) for their mesogenic properties, and iii. ultraviolet–visible spectroscopy (UV-Vis) and POM for their photosensitivity. The experimental results show that all compounds exhibited broad temperature windows of mesogenic phases. In particular, compound <b>4c</b> showed a broad temperature window of 63.8 °C for nematic phase. Molecular simulations indicate that the molecular dipole moments of compounds <b>4a–4g</b> are closely associated with the temperatures of Sm – N phase transition and temperature ranges of nematic phases. In addition, simulation results reveal that the terminal alkyl chains exhibit a diphasic effect on the molecular polarity: extending the terminal chain can initially reduce and then increase the molecular dipole moments due to the severe structural disorder of overly extended terminal chain. These findings indicate that the intermolecular forces play a vital role in shaping the mesogenic behavior of ABLCs. Comprehensive characterizations of photochromatic properties show that <b>4c</b> was highly photosensitive and displayed rapid photoisomerization processes. At room temperature, compound <b>4c </b>dissolved in ethyl acetate solution can reach photostationary state in 10 seconds. At 95 °C, compound <b>4c</b> in nematic phase became isotropic liquid under UV-irradiation in 3 seconds due to the forward <i>trans – cis</i> photoisomerization and can be restored to be nematic under natural visible light in 5 seconds because of the backward <i>cis – trans</i> photoisomerization. This study linking the mechanistic details with mesogenic properties provides valuable insights to improve future design of azobenzene bent-core liquid crystals for practical applications especially in photonic applications.</p><p><br></p><p>Pertinent molecular structure files (mol2) can be downloaded from</p><p><a href="https://github.com/er1czz/ABLC">https://github.com/er1czz/ABLC</a><br></p><p></p>

scholarly journals Order Parameters, Orientational Distribution Functions and Heliconical Tilt Angles of Oligomeric Liquid Crystals

2019 ◽  
Author(s):  
Richard Mandle ◽  
John W. Goodby
Keyword(s):  
Phase Transition ◽  
Liquid Crystals ◽  
Tilt Angle ◽  
Order Parameter ◽  
Nematic Phase ◽  
Liquid Crystalline ◽  
Thermal Evolution ◽  
Order Parameters ◽  
Distribution Functions ◽  
Orientational Distribution

We compare the order parameters, orientational distribution functions (ODF) and heliconical tilt angles of the TB phase exhibited by a liquid-crystalline dimer (CB7CB) to a tetramer (O47) and hexamer (O67) by SAXS/WAXS. Following the N-TB phase transition we find that all order parameters decrease, and while 〈P2 〉 remains positive 〈P4 〉 becomes negative. For all three materials the order parameter 〈P6 〉 is near zero in both phases. The ODF is sugarloaf-like in the nematic phase and volcano-like in the TB phase, allowing us to estimate the heliconical tilt angle of each material and its thermal evolution. The heliconical tilt angle appears to be largely independent of the material studied despite the differing number of mesogenic units.

Isotropic-Nematic Phase Transition in Liquid Crystals

1970 ◽  
Vol 25 (8) ◽  
pp. 500-503 ◽  
Author(s):  
Chung-peng Fan ◽  
Michael J. Stephen
Keyword(s):  
Phase Transition ◽  
Liquid Crystals ◽  
Nematic Phase

Calix[4]pyrrole-Based Heteroditopic Ion-Pair Receptor That Displays Anion-Modulated, Cation-Binding Behavior

2012 ◽  
Vol 18 (47) ◽  
pp. 15073-15078 ◽  
Author(s):  
In-Won Park ◽  
Jaeduk Yoo ◽  
Suman Adhikari ◽  
Jung Su Park ◽  
Jonathan L. Sessler ◽  
...  
Keyword(s):  
Ion Pair ◽  
Cation Binding ◽  
Binding Behavior

scholarly journals Extremely small twist elastic constants in lyotropic nematic liquid crystals

2020 ◽  
Vol 117 (44) ◽  
pp. 27238-27244 ◽  
Author(s):  
Clarissa F. Dietrich ◽  
Peter J. Collings ◽  
Thomas Sottmann ◽  
Per Rudquist ◽  
Frank Giesselmann
Keyword(s):  
Liquid Crystals ◽  
Elastic Constant ◽  
Elastic Constants ◽  
Nematic Phase ◽  
Elastic Moduli ◽  
Building Blocks ◽  
Lyotropic Liquid Crystals ◽  
Order Of Magnitude ◽  
Typical Range ◽  
Special Case

Recent measurements of the elastic constants in lyotropic chromonic liquid crystals (LCLCs) have revealed an anomalously small twist elastic constant compared to the splay and bend constants. Interestingly, measurements of the elastic constants in the micellar lyotropic liquid crystals (LLCs) that are formed by surfactants, by far the most ubiquitous and studied class of LLCs, are extremely rare and report only the ratios of elastic constants and do not include the twist elastic constant. By means of light scattering, this study presents absolute values of the elastic constants and their corresponding viscosities for the nematic phase of a standard LLC composed of disk-shaped micelles. Very different elastic moduli are found. While the splay elastic constant is in the typical range of 1.5 pN as is true in general for thermotropic nematics, the twist elastic constant is found to be one order of magnitude smaller (0.30 pN) and almost two orders of magnitude smaller than the bend elastic constant (21 pN). These results demonstrate that a small twist elastic constant is not restricted to the special case of LCLCs, but is true for LLCs in general. The reason for this extremely small twist elastic constant very likely originates with the flexibility of the assemblies that are the building blocks of both micellar and chromonic lyotropic liquid crystals.

Molecular Ordering in Nematic MBCA and EPAPU

1990 ◽  
Vol 45 (1) ◽  
pp. 29-32
Author(s):  
S. Sreehari Sastry ◽  
V. Venkata Rao ◽  
P. Narayana Murty ◽  
G. Satyanandam ◽  
T. F. Sundar Raj
Keyword(s):  
Phase Transition ◽  
Liquid Crystals ◽  
Order Parameter ◽  
Nematic Phase ◽  
Spin Probe ◽  
Nematic Liquid Crystals ◽  
Experimental Techniques ◽  
First Order ◽  
Molecular Ordering

AbstractBy EPR, two nematic liquid crystals (MBCA and EPAPU) were investigated using a steroidal nitroxide spin probe. In both liquid crystals the isotropic-nematic phase transition is of first order. The observed variation of the order parameter with temperature is compared with predictions from the Maier-Saupe and Humphries-James-Luckhurst models and with results obtained by several other experimental techniques.

Sign in / Sign up

Export Citation Format

Share Document