High resolution x-ray diffraction study of smectic polymorphism and fluctuations in a mixture of octyl- and decyl-oxyphenyl nitrobenzoyloxy benzoate

Reentrant nematic phases and smectic antiphases occur as intermediate states between two one-dimensionally ordered frustrated smectic phases, characterized by two competing and, in general, incommensurate smectic density waves. Using high-resolution x-ray diffraction, we have examined the evolution of the two density waves as a function of temperature in all phases of a mixture of polar liquid crystals octyl- and decyl-oxyphenyl nitrobenzoyloxy benzoate (47.4 mol% DB₈ONO₂+52.6% DB₁₀ONO₂). This mixture exhibits at temperatures below 127 ^∘{}C the liquid-crystal phase sequence: smectic-Ad, reentrant nematic phases Nd and N₁, smectic-A₁, tilted antiphase ̃ \~C, smectic-A₂, and smectic-C₂ phases. Detailed investigations of several order-disorder transitions and the evolution of fluctuation effects in this system are reported.