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The three elastic constants of a number of structurally related nematic liquid crystalline Schiff's bases have b~e~ m~as~red as ~ function of temperature. The results are new in the sense that they exhibit a clear dlstmctlOn m behavIOr between compounds with a rigid molecular structure and compounds with a molecular structure consisting of a rigid core and a flexible alkyl chain. In particular, it has been found that the ratio of the bend and splay elastic constants K /K I increases for compounds with a rigid molecular structure with increasing length to width ratio. This trend is the reverse of that observed wihin homologous series, for which K 31 K I has been found to decrease with increasing length of the alkyl chain. New is the experimental finding t~at the twist e1as.tic constant K 2 of the homologs studied is in~pendent of the length of the alkyl chain.Fmally, the expenments show that the average elastic constant K = (K I + K 2 + K 3)/3 is proportional to the smectic-isotropic transition temperature. The results can only be partly understood within the framework of existing theoretical models.

The anisotropy of the diamagnetic susceptibility, the density and the entropy change at the nematic-isotropic transition of a number of structurally related Schiff's bases are reported. Order parameters have been calculated from the anisotropies of the susceptibility. The results indicate that there is a close correspondence between the order parameter and the relative volume change at the nematic-isotropic transition. The experimental data suggest that there exists considerable flexibility of the alkylene chains both in the nematic and isotropic phases. The experimentally observed trends can be understood within the framework of theoretical models, which take account of molecular flexibility

A new, low bias tilt field-effect liquid crystal display (LCD) is presented with better image quality than supertwist or superbirefringence LCD’s at the same high level of multiplexing. In its positive contrast mode, the display image is black on white with virtually no inherent coloration and with a comparably large contrast as that of twisted nematic LCD’s. The viewing range of the display is as wide as that of superbirefringence LCD’s, whereas its image quality is an order of magnitude less dependent on cell gap variations. With specifically designed liquid crystal mixtures, multiplexing ratios of 1000:1 and response times below 300 ms result.

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