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

Abstract

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% ${\mathrm{DB}}_{8}{\mathrm{ONO}}_{2}$+52.6% ${\mathrm{DB}}_{10}{\mathrm{ONO}}_{2})$. This mixture exhibits at temperatures below 127 \ifmmode^\circ\else\textdegree\fi{}C the liquid-crystal phase sequence: smectic-${A}_{d},$ reentrant nematic phases ${N}_{d}$ and ${N}_{1}$, smectic-${A}_{1}$, tilted antiphase $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{C},$ smectic-${A}_{2},$ and smectic-${C}_{2}$ phases. Detailed investigations of several order-disorder transitions and the evolution of fluctuation effects in this system are reported.