Raman investigation of the low-temperature phase transition in a liquid crystalline system: terephthalidine-bis-heptylaniline (TB7A)

✍ Scribed by Ranjan K. Singh; S. Schluecker; B. P. Asthana; W. Kiefer

• Publisher: John Wiley and Sons
• Year: 2002
• Tongue: English
• Weight: 124 KB
• Volume: 33
• Category: Article
• ISSN: 0377-0486
• DOI: 10.1002/jrs.906

✦ Synopsis

Abstract

Raman spectra of terephthalidine‐bis‐heptylaniline (TB7A) were recorded in the region 1125–1225 cm^−1^ from room temperature to 10 K at 18 different temperatures. The splitting of the ∼1165 cm^−1^ band, and the variation of the ratio of integrated intensities of the original band at ∼1165 cm^−1^ to the new component at 1170/1171 cm^−1^ reveals a solid modification. The analysis of the temperature dependence of the linewidth was made using Rakov's relation. A logarithmic plot as a function of 1/T gives two straight lines with an abrupt discontinuity, which clearly exhibits a phase transition at about 210 K. The temperature dependence of the linewidth of the ∼1165 cm^−1^ band was used to characterize this transition. A relatively large variation (∼3 cm^−1^) of the linewidth on going from 250 to 10 K in TB7A having an odd (n = 7) number of carbon atoms in the alkyl tail compared with those observed (∼1 cm^−1^) in other homologues having an even (n = 2 or 10) number of carbon atoms in the alkyl tail is a clear demonstration of the even–odd effect. Copyright © 2002 John Wiley & Sons, Ltd.