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.

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.

scholarly journals Nanostructure of Unconventional Liquid Crystals Investigated by Synchrotron Radiation

Nanomaterials ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1679
Author(s):  
Francesco Vita ◽  
Fabrizio Corrado Adamo ◽  
Michela Pisani ◽  
Oriano Francescangeli
Keyword(s):  
Liquid Crystals ◽  
Electric Fields ◽  
Nematic Phase ◽  
X Ray Diffraction ◽  
Space Resolution ◽  
Polymer Dispersed Liquid Crystals ◽  
Macroscopic Properties ◽  
Polymer Dispersed ◽  
Synchrotron Xrd ◽  
Selection Of

The macroscopic properties of novel liquid crystal (LC) systems—LCs with unconventional molecular structure as well as conventional LCs in unconventional geometries—directly descend from their mesoscopic structural organization. While X-ray diffraction (XRD) is an obvious choice to investigate their nanoscale structure, conventional diffractometry is often hampered by experimental difficulties: the low scattering power and short-range positional order of the materials, resulting in weak and diffuse diffraction features; the need to perform measurements in challenging conditions, e.g., under magnetic and/or electric fields, on thin films, or at high temperatures; and the necessity to probe micron-sized volumes to tell the local structural properties from their macroscopic average. Synchrotron XRD allows these problems to be circumvented thanks to the superior diffraction capabilities (brilliance, q-range, energy and space resolution) and advanced sample environment available at synchrotron beamlines. Here, we highlight the potentiality of synchrotron XRD in the field of LCs by reviewing a selection of experiments on three unconventional LC systems: the potentially biaxial and polar nematic phase of bent-core mesogens; the very high-temperature nematic phase of all-aromatic LCs; and polymer-dispersed liquid crystals. In all these cases, synchrotron XRD unveils subtle nanostructural features that are reflected into macroscopic properties of great interest from both fundamental and technological points of view.

Thermal Behaviour of Candesartan Active substance and in pharmaceutical compounds

2017 ◽  
Vol 68 (8) ◽  
pp. 1895-1902
Author(s):  
Ioana Cristina Tita ◽  
Eleonora Marian ◽  
Bogdan Tita ◽  
Claudia Crina Toma ◽  
Laura Vicas
Keyword(s):  
Thermal Behaviour ◽  
Active Substance ◽  
Pharmaceutical Research ◽  
Pharmaceutical Product ◽  
Nitrogen Atmosphere ◽  
Pure Substance ◽  
Scanning Calorimetry ◽  
X Ray ◽  
Ft Ir

Thermal analysis is one of the most frequently used instrumental techniques in the pharmaceutical research, for the thermal characterization of different materials from solids to semi-solids, which are of pharmaceutical relevance. In this paper, simultaneous thermogravimetry/derivative thermogravimetry (TG/DTG) and differential scanning calorimetry (DSC) were used for characterization of the thermal behaviour of candesartan cilexetil � active substance (C-AS) under dynamic nitrogen atmosphere and nonisothermal conditions, in comparison with pharmaceutical product containing the corresponding active substance. It was observed that the commercial samples showed a different thermal profile than the standard sample, caused by the presence of excipients in the pharmaceutical product and to possible interaction of these with the active substance. The Fourier transformed infrared spectroscopy (FT-IR) and X-ray powder diffraction (XRPD) were used as complementary techniques adequately implement and assist in interpretation of the thermal results. The main conclusion of this comparative study was that the TG/DTG and DSC curves, together with the FT-IR spectra, respectively X-ray difractograms constitute believe data for the discrimination between the pure substance and pharmaceutical forms.

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