CRITICAL REGION AT THE NEMATIC-ISOTROPIC PHASE TRANSITION

1996 ◽  
Vol 10 (16) ◽  
pp. 771-775 ◽  
Author(s):  
PRABIR K. MUKHERJEE
Keyword(s):  
Phase Transition ◽  
Liquid Crystal ◽  
Critical Point ◽  
Nematic Liquid Crystal ◽  
Critical Region ◽  
Isotropic Phase ◽  
Transition Line ◽  
Isotropic Liquid ◽  
Phase Transition Line ◽  
First Order

The phase transition from isotropic liquid to nematic liquid crystal is a weak first order one. The present paper investigate the possibility of the critical region near the isolated critical point at the first order nematic-isotropic phase transition line.

scholarly journals Dissipative structures induced by photoisomerization in a dye-doped nematic liquid crystal layer

2018 ◽  
Vol 376 (2135) ◽  
pp. 20170382 ◽  
Author(s):  
I. Andrade-Silva ◽  
U. Bortolozzo ◽  
C. Castillo-Pinto ◽  
M. G. Clerc ◽  
G. González-Cortés ◽  
...  
Keyword(s):  
Phase Transition ◽  
Liquid Crystal ◽  
Nematic Liquid Crystal ◽  
Dissipative Structures ◽  
Input Power ◽  
Isotropic Phase ◽  
Crystal Layer ◽  
Liquid Crystal Layer ◽  
Nematic Liquid Crystal Layer ◽  
Interface Propagation

Order–disorder phase transitions driven by temperature or light in soft matter materials exhibit complex dissipative structures. Here, we investigate the spatio-temporal phenomena induced by light in a dye-doped nematic liquid crystal layer. Experimentally, for planar anchoring of the nematic layer and high enough input power, photoisomerization processes induce a nematic–isotropic phase transition mediated by interface propagation between the two phases. In the case of a twisted nematic layer and for intermediate input power, the light induces a spatially modulated phase, which exhibits stripe patterns. The pattern originates as an instability mediated by interface propagation between the modulated and the homogeneous nematic states. Theoretically, the phase transition, emergence of stripe patterns and front dynamics are described on the basis of a proposed model for the dopant concentration coupled with the nematic order parameter. Numerical simulations show quite a fair agreement with the experimental observations. This article is part of the theme issue ‘Dissipative structures in matter out of equilibrium: from chemistry, photonics and biology (part 2)’.

scholarly journals Probing a Local Viscosity Change at the Nematic-Isotropic Liquid Crystal Phase Transition by a Ratiometric Flapping Fluorophore

2021 ◽  
Author(s):  
Ryo Kimura ◽  
Hidetsugu Kitakado ◽  
Takuya Yamakado ◽  
Hiroyuki Yoshida ◽  
Shohei Saito
Keyword(s):  
Phase Transition ◽  
Liquid Crystal ◽  
Isotropic Phase ◽  
Molecular Rotor ◽  
Isotropic Liquid ◽  
Viscosity Change ◽  
Thermal Phase Transition ◽  
Crystal Phase Transition ◽  
Liquid Crystal Phase Transition ◽  
Liquid Crystal 5Cb

Local viscosity change in the thermal phase transition of a nematic liquid crystal, 5CB, has been analyzed by doping fluorescent viscosity probes, flapping fluorophores (FLAP) as well as a molecular rotor BODIPY-C12. As a result, only flapping anthraceneimide has successfully monitored a small viscosity change (corresponding to a few cP (centipoise) change in shear viscosity around 25 cP) in the nematic-to-isotropic phase transition by ratiometric spectroscopy. In addition, analysis of fluorescence anisotropy indicates that the emissive species (planarized flapping anthraceneimides) are aligned parallel to the director of 5CB in the nematic phase.

Some Advances in Liquid Crystal Elastomers: From Crosslinks Affected Ordering to Carbon Nanoparticles Enabled Actuation

2007 ◽  
Vol 1005 ◽  
Author(s):  
Slobodan Zumer ◽  
Martin Chambers ◽  
George Cordoyiannis ◽  
Heino Finkelmann ◽  
Zdravko Kutnjak ◽  
...  
Keyword(s):  
Phase Transition ◽  
Liquid Crystal ◽  
Length Change ◽  
Crosslinking Density ◽  
Isotropic Phase ◽  
Geometrical Shape ◽  
High Concentration ◽  
First Order ◽  
Open Questions ◽  
Liquid Crystal Elastomers

AbstractLiquid crystal elastomers (LCE) exhibit a combination of elasticity and mesogenic ordering, yielding large thermally stimulated changes in shape. These LCE systems although well characterised, still yield open questions in the nature of how the crosslinking affects the LCE phase transition. Therefore calorimetry and deuteron-nuclear magnetic resonance were used to study the isotropic-nematic phase transition of uniformly ordered LCE. We observed that the density of crosslinkers strongly affects the nematic-isotropic phase transition. The observed spread critical transitions are explained with a dispersion of local mechanical fields that yields a weakly disordered orientational state composed of regions that exhibit temperature profiles of the nematic order parameter ranging from first order to supercritical. On increasing crosslinking density, the predominantly first order thermodynamic response transforms into a predominantly supercritical one.Additionally, to illustrate the response of these actuating systems, it was demonstrated that a LCE can be electrically heated. The insulating LCE network was reprocessed using conducting nanoparticles dispersed in a solvent with high LCE swelling capability. This results in a low electrical resistivity surface layer of LCE network with a high concentration of conducting nanoparticles. The reprocessing allows the effective resistivity of a LCE film to be reduced from highly insulating values to values useable for electrical actuation. This layer in addition withstands large changes in geometrical shape both in contraction and expansion. Utilizing a resistive “Joule” heating effect, the reprocessed system exhibits an indirect electromechanical effect characterised by a 150% length change that can be cycled for more than 10, 000 times.

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