scholarly journals Molecular length distribution and the formation of smectic phases

2009 ◽  
Vol 5 ◽  
Author(s):  
Nadia Kapernaum ◽  
C Scott Hartley ◽  
Jeffrey C Roberts ◽  
Robert P Lemieux ◽  
Frank Giesselmann
Keyword(s):  
Nematic Phase ◽  
Length Distribution ◽  
Stable Phase ◽  
General Interest ◽  
Structure And Dynamics ◽  
Smectic A ◽  
Smectic C ◽  
Smectic Phases ◽  
Molecular Length ◽  
Smectic A Phase

The phase diagrams of two mixtures of chemically similar smectogenic mesogens strongly differing in molecular length were investigated. In these mixtures the nematic phase present in the pure short mesogen disappeared rapidly on the addition of the longer mesogen, while the smectic state was preserved. In the smectic state the smectic A phase was the much more stable phase as the smectic C phase disappeared quite rapidly as well. In these compounds the loss of the smectic C phase is accompanied by a decrease in smectic translational order and very small tilt angles. This leads to a concentration induced smectic C to smectic A transition. Thus smectic A seems to be the most stable phase to accommodate mesogenic molecules of substantially different length. These surprising results are of general interest for the understanding of the structure and dynamics of smectic phases, as the structure of these bidisperse smectics is signified by extensive out-of-layer fluctuations.

scholarly journals Formation of smectic phases in binary liquid crystal mixtures with a huge length ratio

2012 ◽  
Vol 8 ◽  
pp. 1118-1125 ◽  
Author(s):  
Nadia Kapernaum ◽  
Friederike Knecht ◽  
C Scott Hartley ◽  
Jeffrey C Roberts ◽  
Robert P Lemieux ◽  
...  
Keyword(s):  
Phase Diagram ◽  
Liquid Crystalline ◽  
Smectic Phase ◽  
Length Ratio ◽  
Stable Phase ◽  
X Ray Diffraction ◽  
Smectic A ◽  
Smectic C ◽  
Smectic Phases ◽  
Molecular Length

A system of two liquid-crystalline phenylpyrimidines differing strongly in molecular length was studied. The phase diagram of these two chemically similar mesogens, with a length ratio of 2, was investigated, and detailed X-ray diffraction and electrooptical measurements were performed. The phase diagram revealed a destabilization of the nematic phase, which is present in the pure short compound, while the smectic state was stabilized. The short compound forms smectic A and smectic C phases, whereas the longer compound forms a broad smectic C phase and a narrow higher-ordered smectic phase. Nevertheless, in the mixtures, the smectic C phase is destabilized and disappears rapidly, whereas smectic A is the only stable phase observed over a broad concentration range. In addition, the smectic translational order parameters as well as the tilt angles of the mixtures are reduced. The higher-ordered smectic phase of the longer mesogen was identified as a smectic F phase.

Structure and Thermal Behaviour of a Thermotropic Liquid Crystalline Polyimide (PI-LC)

1998 ◽  
Vol 10 (1) ◽  
pp. 147-153 ◽  
Author(s):  
M Tanaka ◽  
M Konda ◽  
M Miyamoto ◽  
Y Kimura ◽  
A Yamaguchi
Keyword(s):  
Phase Transition ◽  
Thermal Analysis ◽  
Nematic Phase ◽  
Liquid Crystalline ◽  
Polarized Light ◽  
Isotropic Phase ◽  
X Ray ◽  
Smectic A ◽  
Smectic C ◽  
Smectic A Phase

Anomalous solid structures formed by a thermotropic liquid crystalline polyimide (PI-LC) were investigated by thermal analysis, polarized light microscopy and x-ray analysis. It was revealed that PI-LC should undergo a phase transition from the crystalline to the isotropic phase through the smectic or nematic phase in the temperature range 277–300 °C. The PI-LC filament extruded at 280 °C, at which temperature the polymer was in liquid crystalline phase, was formed to have a structure similar to the smectic C phase, while that extruded and melt-drawn at 310 °C, at which temperature the polymer was in the isotropic phase, had a structure similar to the smectic A phase.

Electric-Field-Dependent Tilt (Cone) Angle in a Chiral Smectic C Liquid Crystal Showing Electroclinic Effect in the Smectic A Phase

1991 ◽  
Vol 30 (Part 2, No. 4A) ◽  
pp. L612-L615 ◽  
Author(s):  
Ying-Bao Yang ◽  
Akihiro Mochizuki ◽  
Naoto Nakamura ◽  
Shunsuke Kobayashi
Keyword(s):  
Liquid Crystal ◽  
Electric Field ◽  
Cone Angle ◽  
Smectic A ◽  
Smectic C ◽  
Field Dependent ◽  
Smectic A Phase

Structural studies of nematic and smectic phases

1983 ◽  
Vol 309 (1507) ◽  
pp. 145-153 ◽  
Keyword(s):  
Liquid Crystal ◽  
Mean Field ◽  
Structural Studies ◽  
X Ray ◽  
Smectic A ◽  
Smectic C ◽  
X Ray Scattering ◽  
Smectic Phases ◽  
Crystal Phases ◽  
Field Behaviour

The information about liquid crystal phases that can be obtained by light scattering and by high-resolution X-ray scattering is reviewed. Results for the nematic-smectic A transition suggest the de Gennes-McMillan model is correct, but adequate theoretical solutions to the model remain elusive. Recent results on the smectic A to smectic C transition are presented that show unambiguously that it exhibits classic mean-field behaviour and this is explained by a Ginzburg criterion argument. Some preliminary results of a study of a nematic-smectic A transition in a lyotropic material are given and indicate similarity to thermotropic materials.

Sign in / Sign up

Export Citation Format

Share Document