Study of Orientational Order of in Nematic and Smectic Phases by means of Optical Spectroscopy Methods

Abstract

The long-range orientational order of 4-n-pentylphenylthio-4 0 -n-decyloxybenzoate (10S5Þ doped with a dichroic dye was studied as a function of temperature in the nematic, smectic A, smectic C and smectic J phases by means of two optical spectroscopy methods: dichroism of absorption in the visible spectral region and fluorescence depolarization. On the basis of absorption and fluorescence spectra the order parameters <P 2 > and <P 4 > as well as the orientational distribution function were determined. The discontinuous change of both <P 2 > and <P 4 > parameters at the smectic A -nematic phase transition for dye= 10S5 mixtures was observed, in an agreement with the microscopic theory proposed by McMillan. An influence of the dye molecular structure on the orientational order of the dye= 10S5 mixture was observed. The correlation between the order parameter values and the shift of the phase transitions temperatures due to the dye addition was confirmed.

Oriental behaviour of some homologues of 4-n-pentyl-phenylthio-4′-n-alkoxybenzoate doped with dichroic dye

“…This can be a confirmation of the fact that there exists a strong correlation between the order parameter and the shift of the phase transition temperatures of the dye/liquid crystal mixture with respect to that of pure liquid crystal. Such correlation had been found previously for dyes 1-3 dissolved in 8S5 [18] and 10S5 [19], as well as for many other dye/liquid crystal systems [9,[20][21][22]. Figure 3(a) shows the order parameters <P 2 > A (crosses), <P 2 > F (squares) and <P 4 > F (circles) as a function of the reduced temperature for dye 1 in 7S5 in the nematic phase, whereas in Figs.…”

“…Figure 3(a) shows the order parameters <P 2 > A (crosses), <P 2 > F (squares) and <P 4 > F (circles) as a function of the reduced temperature for dye 1 in 7S5 in the nematic phase, whereas in Figs. 3(b) and 3(c), for comparison, the temperature dependence of <P 2 > F and <P 4 > F values for mixtures of dye 1/8S5 [18] and dye 1/10S5 [19], respectively, in the SmC, SmA and N phases are presented.…”

Characterization of Some Fluorinated Mesogens for Application in Liquid Crystal Displays

“…However, with the rise of temperature, S varies somewhat differently for various liquid crystals. The liquid crystal 5DBF3 has additional smectic A phase, in which the temperature dependence of S is significantly weaker than that in the nematic phase, as it was observed also for other liquid crystals [15][16][17].…”