Dynamic Dielectric Anisotropy of Nematics with Respect to Molecular Structure

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Abstract
The dielectric spectra of several nematics, such as derivatives of cyclohexane and biphenyl, azoxybenzenes, benzoate esters and tolanes are reported. In each case, the complex permittivity measurements are performed for the two main directions of the nematic sample (parallel and perpendicular to the optical axis), up to the microwave region. A comparison of the spectra has led to a partial assignment of the absorptions observed. In fact, the spectra differ significantly with molecular structure. The dielectric dispersion is analyzed and interpreted as a function of the specificity of the different molecular groups, i.e., the bridging groups, the rings, or the terminal substituent groups. The interpretations proposed (reorientation motions, molecular interaction) are discussed.