THE EFFECT OF THE LENGTH OF FLEXIBLE CHAI N FRAGMENTS ON ELECTROOPTICAL PROPERTIES OF MESOPHASE FORMED BY CHAIN MOLECULES

The optical and dielectric properties of planar nematic films of liqui d crystals representing a series of 4,4'-bis-cyanobiphenyloxyalkanes c ontaining from 2 to 12 CH2 groups in the alkyl chain were studied by p olarization microscopy and threshold elastic deformations in the elect ric field. The optical anisotropy Delta n, threshold potentials V-0 of elastic deformation, and the temperature variation of Delta n and V-0 values were measured for the entire homologous series. The Delta n va lues were used to determine the nematic order parameters S. The depend ence of the Delta n, S, and V-0 values on the number Delta n of CH2 gr oups in the oxyalkyl chain exhibits a strong odd-even effect. This is explained by structural features of the molecules in which a flexible core links two rigid mesogenic terminal fragments. Several conclusions are made concerning the role of intramolecular orientational polar an d intermolecular (nematic) orders in the formation of dielectric prope rties of nematic liquid crystals.