Phase Transformations And Dynamics Of 4-Cyano-4′-Pentylbiphenyl (5cb) By Nuclear Magnetic Resonance, Analysis Differential Scanning Calorimetry, And Wideangle X-Ray Diffraction Analysis

Abstract

The polymorphism of 4-cyano-4 0 -pentylbiphenyl (5CB) was investigated by means of differential scanning calorimetry (DSC), X-ray diffraction, and proton nuclear magnetic resonance (NMR) experiments. Three new phases has been identified and characterized structurally and dynamically. By a slow cooling at a rate 0.2 K/min, the nematic phase crystallizes into a phase noted C1. Upon a fastest cooling ( ! 5 K/min) a glassy liquid crystal (GLC) phase with a glass transition temperature T g ¼ 208 K, is formed. Upon heating up both the solid state C1 and the GLC phase, a second crystalline phase C2 (DH ¼ 49 J/g.K) which is more stable than C1 (DH ¼ 36 J/g.K) can be obtained. The proposed phase diagram has been investigated by proton NMR lineshape analysis. The motional correlation time of end-chain methyl group motion was determined by means of spin-lattice relaxation time (T 1 ) analysis.

Low-temperature photoluminescence of 5CB liquid crystal

“…The temperatures of crystal -LC and LC -isotropic liquid phase transitions in 5CB were 22.5 and 35 1C, respectively [21,22].…”

“…Obviously, the simultaneous co-existence of the different conformers of the 5CB molecules in the low-temperature states explains the formation of different types of monomer and dimer structures, revealed by us during the analysis of the 5CB photoluminescence spectral properties. It is interesting to notice that the DSC and X-ray diffraction experiments allowed us to detect and describe several crystal modifications of 5CB, which were realized at different temperature histories [37]. So the suggestion about the formation of additional structure re-alignments in the crystal modification of 5CB is quite reasonable.…”

Rheological study of structural transitions in triblock copolymers in a liquid crystal solvent

“…12 The LC gels are formed by dissolving an ABA triblock copolymer having polystyrene (PS) endblocks (''A'') and a very long side-group liquid crystalline polymer (SGLCP) midblock (''B'') in 4-pentyl-49-cyanobiphenyl (5CB), a wellcharacterized nematic LC. 13,14 The SGLCP midblock is designed to be soluble in both the isotropic and nematic phases of the solvent. Unfavorable interactions between the PS endblocks and nematic solvent cause segregation into PS-rich domains that function as the physical crosslinks of a spacefilling polymer network.…”

Liquid Crystals into Planar Photonic Crystals

“…T c1 = T NI (LC-K15) = 35 °C (clearing point) (see also Fig. 7a) and T c2 = T KN (LC-K15) = 23 °C (melting point), respectively (Mansare et al, 2002). This makes LC-K15 more suitable than LC-E7 for infiltration and temperature tuning experiments (see Sect.…”

“…While a change in the blend composition was detected in the LC-E7 blend, for the LC-K15 molecules the location of the peaks in the heat capacity signals (see Fig. 7a), which correspond to the nematic-to-isotropic phase transition (Mansare et al, 2002), does not change after the treatment, thus showing that the physical-chemical properties of LC-K15, as well as its optical properties (i.e. the refractive index), remain stable after the infiltration.…”