X-RAY PHOTOGRAPHIC STUDIES OF LIQUID-CRYSTALS .4. ISOTROPIC, NEMATIC, AND SMECTIC A PHASES OF SOME 4-ALKOXYBENZAL-4'-ETHYLANILINES

From X-ray photographs of some 4-alkoxybenzal-4 prime -ethylanilines (C//nH//2//n// plus //1O - C//6H//4 - C//6H//4 - C//2H//5; n equals 5,6,7) the average intermolecular distance (D) betweeen neighboring parallel molecules in the isotropic, nematic and smectic A phases, the apparent length (l) of the molecules in the isotropic phase, and the thickness (d) of the smectic layers are calculated. In the isotropic phase, the slopes of the D versus t plots for C//5 the slope is (0. 0038); for the nematic phase are of the order of 0. 01 A/ degree C, and for the smectic phase of C//7 the slope is about half of this; for the nematic phases the slope appears to incrase with decreasing length of the stability range. All l versus t plots were definitely concave. Extrapolation of the curves to the N-I point yielded l values very close (within 0. 4 A) to lengths calculated from molecular models. For C//7, d is apparently constant, and about 1. 5 A less than the molecular length.