Evidence for a nematic-nematic transition in thin cells of a highly polar compound

We report experimental evidence for a weak first-order nematic-nematic transition in thin ( ∼ 1–2 μm) cells of the strongly polar nematogen, p -cyanophenyl p - n heptylbenzoate. The transition temperature T NN increases as the thickness of the cell decreases indicating that, in the bulk, this transition may occur at temperatures well below the ambient one. Optical and dielectric measurements of the order parameters in thin cells show that there is considerable enhancement compared to the bulk values. T NN can be increased significantly by moderate electric and magnetic fields. The transition probably indicates a jump in the concentration of neighbours with antiparallel configurations compared to those with parallel configurations. The results imply that the order parameter coherence length in the compound is relatively large.