ABSTRACT
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.
ABSTRACT
Single crystals of the mixed valence compound Pb3Ni1.5Mn5.5O15 were successfully grown. Polarized Raman spectroscopy revealed that they belong to the point group D(3d), in accordance with single-crystal x-ray diffraction data which were refined within the trigonal space group P3c1 (No. 165), with lattice parameters a = 9.941(3) Å and c = 13.543(3) Å. Strongly anisotropic long range magnetic order is established below 65 K.
