Inelastic light scattering from isotropic MBBA

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Abstract
The spectrum of light scattered from the isotropic phase of p‐methoxybenzylidene p‐ (n‐butylaniline) (MBBA) has been studied over a 50 °C temperature range above the nematic–isotropic transition temperature (46.2 °C). Light scattered through a wave vector K?2.7×105 cm−1 with frequency shifts f in the range 1 GHz<ff∼6 GHz and a depolarized 1/(f)2 tail of an unshifted line. The adiabatic sound speed and the sound attenuation coefficient in the vicinity of 6 GHz have been determined from the Brillouin splitting and width, respectively, and compared to values measured at 23, 150, and 400 MHz. It is found that at 6 GHz substantial parts of the bulk and shear viscosities have relaxed out. Dispersion in the sound speed is also observed and used along with the linewidth measurements to estimate the relaxation frequency fr, which is found to be ∼2.5 GHz. The total dispersion and relaxation frequency are similar to those found in benzene. The ratio of peak Brillouin intensity to 1/f2 intensity is analyzed and shows the local dielectric anisotropy to be weakly temperature independent for 46<T<97 °C.