scholarly journals Thermal and Optical Characterization of Polymer-Dispersed Liquid Crystals

2012 ◽  
Vol 2012 ◽  
pp. 1-13 ◽  
Author(s):  
Robert A. Shanks ◽  
Daniel Staszczyk
Keyword(s):  
Liquid Crystals ◽  
Liquid Crystalline ◽  
Scanning Calorimetry ◽  
Uv Curable ◽  
Polymer Dispersed Liquid Crystals ◽  
The Matrix ◽  
Polymer Dispersed ◽  
Acrylate Resin ◽  
Display Order

Liquid crystals are compounds that display order in the liquid state above the melting temperature and below the mesogenic isotropic temperature. Polymer-dispersed liquid crystals (PDLCs) are composite materials in which liquid crystalline material is dispersed within a polymer matrix to form micron-sized droplets. The aim was to prepare several cholesteryl esters or alkoxybenzoic acid PDLCs and characterise thermal and optical properties. Differential scanning calorimetry and polarized optical microscopy were employed. The matrix polymer was a one-component UV-curable epoxy-acrylate resin. PDLCs were formed through entropy controlled phase separation resulting from UV-initiated crosslinking. The liquid crystals, both as mesogenic moieties and as dispersed droplets, exhibited various textures according to their molecular order and orientation. These textures formed in constrained regions separated by phase boundaries that occurred at temperatures characteristic of each liquid crystal used. The PDLC phase transitions occurred at temperatures lower than those exhibited by the mesogenic components in the neat state.

Electro-Optical Characterization of E48:PVP Polymer Dispersed Liquid Crystals

2001 ◽  
Vol 365 (1) ◽  
pp. 305-311
Author(s):  
Cheryll Lei E. Mahinay ◽  
Claire M. Macale ◽  
Fairland F. Amos ◽  
Zenaida B. Domingo ◽  
Leonorina G. Cada
Keyword(s):  
Liquid Crystals ◽  
Optical Characterization ◽  
Polymer Dispersed Liquid Crystals ◽  
Polymer Dispersed

scholarly journals Oxadiazolyl-Pyridinium as Cationic Scaffold for Fluorinated Ionic Liquid Crystals

2021 ◽  
Vol 11 (21) ◽  
pp. 10347
Author(s):  
Melina S. Weber ◽  
Margit Schulze ◽  
Giuseppe Lazzara ◽  
Antonio Palumbo Piccionello ◽  
Andrea Pace ◽  
...  
Keyword(s):  
Ionic Liquid ◽  
Liquid Crystals ◽  
Liquid Crystalline ◽  
Alkyl Chain ◽  
Scanning Calorimetry ◽  
New Class ◽  
Structural Variables ◽  
Ionic Liquid Crystals ◽  
Thermotropic Properties

The synthesis and characterization of a new class of 1,2,4-oxadiazolylpyridinium as a cationic scaffold for fluorinated ionic liquid crystals is herein described. A series of 12 fluorinated heterocyclic salts based on a 1,2,4-oxadiazole moiety, connected through its C(5) or C(3) to an N-alkylpyridinium unit and a perfluoroheptyl chain, differing in the length of the alkyl chain and counterions, has been synthesized. As counterions iodide, bromide and bis(trifluoromethane)sulfonimide have been considered. The synthesis, structure, and liquid crystalline properties of these compounds are discussed on the basis of the tuned structural variables. The thermotropic properties of this series of salts have been investigated by differential scanning calorimetry and polarized optical microscopy. The results showed the existence of an enantiotropic mesomorphic smectic liquid crystalline phase for six bis(trifluoromethane)sulfonimide salts.

Orientation in stretched polymer-dispersed liquid crystals

1998 ◽  
Vol 76 (11) ◽  
pp. 1642-1647 ◽  
Author(s):  
Julien Brazeau ◽  
Yanick Chénard ◽  
Yue Zhao
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Molecular Orientation ◽  
Liquid Crystalline ◽  
Polymer Dispersed Liquid Crystals ◽  
Polymer Dispersed ◽  
Infrared Dichroism ◽  
Semicrystalline Matrix ◽  
Macroscopic Orientation ◽  
Strain Direction

The orientation behavior of liquid crystal molecules in stretched films of polymer-dispersed liquid crystals (PDLC) was investigated by means of infrared dichroism. The liquid crystal used is 4prime-octyl-4-biphenyl-carbonitrile (8CN); the polymer matrices are semicrystalline poly(epsilon-caprolactone) (PCL) and an amorphous miscible blend of PCL with poly(vinyl chloride) (PVC). 8CN was found to have a limit of solubility below 5 wt.% in PCL. We show that an uniaxial stretching can effectively induce a macroscopic orientation of 8CN, and that this orientation can be preserved in the films after removal of the extensional force at room temperature, where 8CN is in its liquid crystalline phase. The molecular orientation is obtained even by stretching PDLC films with 8CN in the liquid state. These results suggest that an elongated polymer cavity in stretched PDLC imposes LC director fields with respect to the long axes of the droplets, which are aligned parallel to the strain direction. The experiments also reveal that the orientation of 8CN is higher in stretched PDLC with a semicrystalline matrix (PCL) than with an amorphous matrix (the PCL-PVC blend), and that the sizes of the LC droplets also have a slight effect on the induced orientation. This work represents a first step in the exploration of new electrooptical effects of PDLC through the presence of a uniform orientation of the liquid crystal molecules and modifications of the polymer cavity at the electrical field-off state.Key words: polymer-dispersed liquid crystals, molecular orientation, infrared dichroism, electrooptical materials.

Characterization and Thermal Behaviour of Polymer-Dispersed Liquid Crystals

2010 ◽  
Vol 152-153 ◽  
pp. 284-287 ◽  
Author(s):  
Xian Gen Han ◽  
Xian Yong Wei ◽  
Xing Yong Wang ◽  
Robert A. Shanks
Keyword(s):  
Liquid Crystals ◽  
Thermal Behaviour ◽  
Nematic Phase ◽  
Polarized Light ◽  
Nitrogen Atmosphere ◽  
Scanning Calorimetry ◽  
Polymer Dispersed Liquid Crystals ◽  
Polymer Dispersed ◽  
Clearing Temperature ◽  
Poly Ethylene

The thermal behaviour of polymer dispersed liquid crystals (PDLC), blends of poly(ethylene-co-methylacrylic acid) (PEMA) with 4-(n-hydroxypropoylxy)-4'-cyanobiphenyl (H3CB) prepared by solvent-induced phase separation (SIPS) method, has been characterized using differential scanning calorimetry (DSC) and polarized light microscopy (POM). Study shows that the concentration of the mixture of PEMA/ H3CB must be least 30%, which will exhibit nematic to isotropic transition phase during heating or cooling. Above 30 wt % 3CB the mixtures exhibited nematic phase, and this was detected as a splitting of the nematic-isotropic peak in the DSC thermograms. The clearing temperature of the PEMA/H3CB mixtures was higher than that of pure H3CB’s, the average increasing being 14°C, which is the evident that the polymer matrix could stable the nematic phase. This behaviour is in contrast with other reports about polymer-dispersed liquid crystals. In addition, thermal decomposition was also studied by thermogravimetry in nitrogen environments. A double-stage decomposition process was found in nitrogen atmosphere, and this was mainly due to H3CB for the first step and the PEMA decomposition for the second step.

Synthesis and Characterization of Bowl-Shaped Liquid Crystals with a Core of Calix[6]arene

2011 ◽  
Vol 396-398 ◽  
pp. 2202-2205
Author(s):  
Dan Shu Yao ◽  
Feng Li ◽  
Hao Jie Wang ◽  
Xiao Yun Li ◽  
Mei Tian ◽  
...  
Keyword(s):  
Liquid Crystals ◽  
Liquid Crystalline ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Cholesteric Phase ◽  
Chemical Structures ◽  
Liquid Crystalline Phases ◽  
Clearing Temperature ◽  
Mesomorphic Properties

A new kind of bowl-shaped liquid crystals were designed and synthesized by esterification. They used a calix[6]arene as central unit and ω- cholesteric alkyl diacid monoester as mesogenic arms. Their chemical structures were confirmed by FTIR and 1HNMR spectra, their mesomorphic properties and phase behavior were investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X-Ray Diffraction (XRD) measurements. The results showed that the kind of calix[6]arene bowl-shaped liquid crystals N1-N3 exhibited broad range liquid crystalline phases at moderate temperature, and they displayed cholesteric phase focal-conic texture in liquid crystal states. With increasing the flexibility of monomers M1-M3, the melting point and the clearing temperature decreased in the macromolecules.

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