The dielectric and elastic properties of cyano-substituted nematic liquid crystals are investigated. The results are discussed in terms of molecular properties and molecular association.

We report on measurements of the ultrasonic attenuation in GaAs: Mn at frequencies between 400 and 2000 MHz and at temperatures between 1 and 35 K. The results indicate that there is a level 3 meV above the acceptor ground state.

We have measured the dielectric constants of cyanobiphenyls (CB), cyanophenylcyclohexanes (PCH), and cyanocyclohexylcyclohexanes (CCH) using a capacitance bridge with a dielectric cell having a guard ring. The ratio Δχ/Δε was also measured for these materials using a new technique which is applicable when Δχ is small or even negative. As a surprising result we have found that this ratio is almost independent of temperature. The temperature dependence of the diamagnetic anisotropies and the dielectric constants of these compounds are given and the results are discussed in terms of the molecular properties.

The thermodynamic stability, the dielectric, diamagnetic, and elastic properties of mixtures of polar as well as those of nonpolar nematic liquid crystals were investigated and compared to the properties of their components. Small deviations from the ideal behavior were observed and attributed to differences in the packing of unlike molecules which mainly depend on steric factors. Clearing points obtained by the extrapolation method are shown to appreciably deviate from the actual values.(3) 906

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