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

• Published in: Molecular crystals and liquid crystals (Philadelphia, Pa. : 2003) Pa. : 2003), 2002-01, Vol.382 (1), p.97-111
• Main Authors: Mansaré, T., Decressain, R., Gors, C., Dolganov, V. K.
• Format: Article
• Language: English
• ISSN: 1542-1406; 1563-5287
• DOI: 10.1080/713738756

The polymorphism of 4-cyano-4′-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 =208 K, is formed. Upon heating up both the solid state C1 and the GLC phase, a second crystalline phase C2 (ΔH=49 J/g.K) which is more stable than C1 (ΔH=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.