Experimental Results in the Investigation of Mesophases

The two liquid phases—the liquid amorphous and the liquid crystalline (occasionally several liquid crystalline phases have been observed)—differ from each other in many respects. While the amorphous is optically isotropic, the crystalline liquid systems always exhibit the behavior of crystals with several optical axes and are also frequently highly pleochroitic (Mauguin, Zocher, Grandjean). 

There are numerous experiments on viscosity. Table 75 is taken from R. Schenck and the data indicate that the crystalline liquids can be considerably more viscous than the corresponding amorphous phases of the same chemical composition, but that the reverse is sometimes observed also. 

The dielectric properties have been studied, especially by W. Kast, who was able to show that the dielectric constant of these substances changes abruptly at the transition points. Fig. 68 shows this effect in the case of the diethyl ester of ethoxybenzal amino-a-methylcinnamic acid. 

Anis u/i oiropic iquid II A niso ropi c liqu d 1 amo / rphou9 iquid  

The x-ray diffraction phenomena in crystalline liquids are particularly clear and informative. The investigations of W. Kast and P. W. Gla-mann, of K. Hermann and A. H. Krummacher and of P. A. Thiessen and his co-workers should be mentioned especially here. 

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