Orientational order and dynamics of nematic multipodes based on carbosilazane cores using optical and dielectric spectroscopy

The birefringence, refractive indices, and dielectric measurements have been carried out for the double- and triple-branched multipodes based on the carbosilazane cores. The orientational order parameters have been obtained using both the optical and the dielectric measurements. The dielectric response is identified to arise from the dipoles of the carboxyl and the alkoxy groups in the ortho position of the benzene ring. Results are analyzed in the framework of the mean-field theory. At least three molecular modes are resolved in the dielectric relaxation spectra in the nematic phase. The lower frequency process is retarded, and the other two processes are accelerated significantly with respect to the relaxation rate in the isotropic phase. The acceleration effect is even much stronger than the retardation effect. The acceleration factors are also found to be much higher than those for the low molar mass nematic liquid crystals. These results show that the anisotropy of the macromolecule plays a significant role in determining the nematic potential which governs the relaxation dynamics. The results on the relaxation dynamics show that the mesogens are decoupled from the core of the macromolecules.