HIGH-PRESSURE STUDIES ON NEW CHIRAL COMPOUNDS EXHIBITING TGB(A) PHASE

Effects of high pressures on phase sequences of the two homologous n = 16 and n = 18 of the (3-fluoro-4 ((R) or (S)-methylheptyloxy) 4,(4 '' -fluoro benzoyloxy) tolans) series have been studied. Both compounds e xhibit the new twisted Smectic A phase called Twist Grain Boundary TGB (A) phase. The high pressure experiments were performed by thermobarom etric analysis. The order of the transitions (first or second) have be en determined in respect to pressure and temperature. The pressure-tem perature phase diagrams show that the TGB(A) phase is stabilized by in creasing pressure; an induced N phase appears under high pressure for n = 18 leading to the observation of TGB(A)-N-I triple point.