The heptyl-, octyl- and nonyl-benzoic acids present dimerized nematic and smectic C liquid-crystal phases. Using polarized optical microscopy and X-ray scattering, we have measured the orientational and positional order close to the surface of the nematic single-crystal, oriented between SiO evaporation-coated glass plates. Decreasing the temperature, we observe a spontaneous twist and bifurcation of the surface orientation, a surface induced texture instability and the growth of a surface layer with “batonnets” of smectic A. These transitions are tentatively explained by an increase of the surface monomer concentration. The correlated decrease of surface nematic order would allow for the growth of surface smectic A rather than C. The surface twist and textural instability could be the first examples of recently predicted surface flexoelectric instabilities

An elastic model for the twisted nematic texture observed in nematic cells containing octyloxybenzoic acid is proposed. According to the model the twisted textures are due to the presence of cybotactic groups which are responsible for the chirality of the liquid crystal. We show that by assuming for the density of cybotactic groups a critical temperature behaviour close to a special temperature, the experimental data can be well interpreted by our mechanical model.

We investigated a series of nanocomposites, built of the hydrogen-bonded liquid crystal (LC) p-n-heptyloxybenzoic acid (7OBA) and single-walled carbon nanotubes (SWCNTs) by optical microtexture analysis and other complementary methods. The surface orientation strength of the LC cell and the bulk interaction of the dimeric LC molecules with the SWCNTs turn out to mainly govern the type (symmetry), thermal stability, and chirality of the LC states induced in these nanocomposites. As a result, a cascade of phase transitions and phases not typical for pristine 7OBA were observed and additionally confirmed by temperature-dependent Raman spectroscopy and differential scanning calorimetry. The most effective SWCNT concentrations in the LC matrix, ensuring both the necessary conformability between these materials and induction of liquid crystal phases with unique optical and electro-optical properties, were found to be in the range of 0.01-0.007 wt%. Reversal of smectic phases into reentrant nematic states as well as induction of chirality in all LC phases were observed in the SWCNT-7OBA nanocomposite, even though pure 7OBA is typically achiral. However, our most intriguing result is the detection below the reentrant nematic of a triclinic smectic-C(G) phase, which is chiral and biaxial, and exhibits bulk ferroelectricity.