THE EFFECT OF MOLECULAR-STRUCTURE ON MOLECULAR-DYNAMICS AND ORDERING IN A CHIRAL SMECTIC LIQUID-CRYSTAL

The effect of a branched alkyl chain on molecular dynamics and ordering in a chiral smectic liquid crystal has been investigated by means of DSC, optical microscopy, powder X-ray diffraction, and solid state C-13 NMR. The introduction of a second branched alkyl chain into a S(C)* molecule increases the molecular tilt angle, the value of the spontaneous polarization in the S(C)* phase, and the S(A)-S(C)* transition enthalpy. The long-range order observed by X-ray measurements and the molecular motion detected by C-13 spin relaxation are not influenced by the branched group. On the other hand, marked NMR line broadenings for the core carbons occur in the oriented S(C)* phase. The results obtained suggest that the branched group affects the dynamics and ordering of the molecular core in the S(C)* phase through the interlayer interaction.