TWIST GRAIN-BOUNDARY STATES IN NONCHIRAL SMECTOGEN-CHIRAL DOPANT

The liquid crystalline systems studied consisted of non-chiral mesomor phic esters [the eutectic mixture of 4-n-hexyloxyphenyl 4-n-octyloxybe nzoate and 4-n-octyloxyphenyl 4-n-hexyloxybenzoate] and structurally s imilar chiral dopants (N-arylidene derivatives of S-1-phenyl- and S-1- benzyl-ethylamine). Twist grain boundary phases occur between the chol esteric and smectic C or smectic A phases in all the investigated sys tems. The different structures of these TGB phases (TGB(A) and TGB(C)) are proved by small angle X-ray scattering and textural studies. The concentration and temperature ranges of the TGB phases are defined by the twisting power of the chiral dopants and their own mesomorphic pec uliarities. The experimental dependences of TGB phase temperature rang e on cholesteric helical twist are influenced by a ratio change of the optically active and racemic forms of the dopant at a constant total concentration. The results obtained are discussed within Renn's theory .