Mesogenic derivatives of 2S,3S-2-halogeno-3-methylpentanoic acid with helix twist inversion in the smectic C* phase

Two homologous series of chloro and bromo derivatives of S,S-3-methylpentan oic acid were synthesized and studied. For some of these compounds an inver sion of helix twist sense in the smectic C* phase was observed. Dielectric dispersion measurements showed a pronounced anomaly of the Goldstone mode r elaxation frequency and strength close to the helix inversion point. Moreov er, a qualitative difference in behaviour of the mode in samples with plana r and with homeotropic alignment was detected; this is due to surface inter actions.