FERROELECTRIC AND ANTIFERROELECTRIC LOW MOLAR-MASS ORGANOSILOXANE LIQUID-CRYSTALS

The present paper is a study of the ferroelectric and antiferroelectri c behaviour in low molar mass organosiloxane liquid crystal materials classed as mono-mesogens (AB type) and bi-mesogens (ABA type). A syste matic study of series of materials all based on the same chiral mesoge nic moiety is presented. The mesogen is a biphenylyl benzoate with a h alogen X attached laterally to the benzoate ring which is closest to t he chiral centre. Three homologous series, where the halogen is either fluorine, chlorine or bromine, are investigated. The number of silico n atoms in the linkage or end group is varied between two and nine. It is found that the materials have a broad (similar to 40 degrees C) fe rroelectric or antiferroelectric phase with a high P-s (similar to 90 nC cm(-2)). The siloxane moiety forces the tilt angle to a temperature independent value close to 45 degrees. The antiferroelectric order is observed only in bi-mesogens with an odd number of silicon atoms in t he siloxane link. The antiferroelectric order is attributed to the con formation of the molecule rather than to antiferroelectric interaction s between layers.