Dynamics of phase transitions in a liquid crystal probed by Raman spectroscopy

Raman spectra of the Schiff's base liquid crystalline compound 505, N-(4-n- pentyloxybenzylidene)-4'-n-pentyl aniline, have been recorded as a function of temperature from 22 to 80 degreesC in the 1140-1220 cm(-1) and 1550-164 0 cm(-1) spectral regions. From careful deconvolution of the spectral featu res using Lorentzian profiles, precise values of peak positions, integrated intensities and linewidths of some selected Raman bands were obtained. The variations of the Raman spectral parameters with temperature are discussed in terms of changes in the molecular alignment and its effect on intra-/in ter-molecular interactions at the Cr-G, G-SmF, SmF-SmC and SmA-N phase tran sitions. From a detailed study, it is inferred that the increased orientati onal/vibrational freedom of the alkyl chains, as well as the delocalization of the electron clouds, is responsible for the spectral anomalies at the C r-G transition. Loss of positional ordering and twist around the -C6H4-N= b ond takes place at the SmF-SmC transition. In the SmA-N transition, some ev idence for the formation of cybotactic clusters was obtained.