Short−range order fluctuations in the isotropic phase of a liquid crystal MBBA

Abstract

We have measured the polarized (I_∥) and the depolarized (I_⊥) scattered light intensities by fluctuations of the orientational order parameter as a function of two scattering angles over a range of temperatures close to and above the isotropic−nematic phase transition of para−methoxybenzylidine para−n−butylaniline (MBBA). The coherence length χ was found to diverge as ε^{−0.50±0.01}, in essential agreement with the last results of Stinson and Litster and the theoretical predictions of de Gennes, where ε = (T − T_c*)/T_c* and T_c* is a pseudocritical temperature slightly below T_p. We have also measured the temperature dependence of the extinction coefficient of MBBA using the 632.8 nm wavelength of He−Ne laser light and observed that (limKμ0) 1/I_∥ or _⊥ after attenuation correction diverges as ε^γ with γ = 0.85±0.05 which differs from γ = 1 as reported by previous studies. K represents the magnitude of the momentum transfer vector.