MOLECULAR ORDER AND DYNAMICS OF LIQUID-CRYSTALS FORMED FROM HYDROGEN-BONDED NETWORKS OF 5-OCTADECYLOXYISOPHTHALIC ACID

The supramolecular organization of 5-octadecyloxyisophthalic acid (C(1 8)ISA) and its complexes with different bases has been studied by pola rization microscopy, differential scanning calorimetry (DSC), IR spect roscopy and X-ray diffraction (XRD). The molecular dynamics have been elucidated using solid-state H-1 NMR and H-2 NMR spectroscopy of C(18) ISA selectively deuteriated in the 2-, 4- and 6-positions of the aroma tic ring. These systems form novel mesogenic structures. The stability of the liquid-crystalline phase depends on intermolecular interaction s such as hydrogen and ionic bonding, as well as hydrophobic interacti ons due to the side-chain packing between the complementary components of the system. On cooling from the melt, C(18)ISA shows a monotropic liquid-crystalline phase with a non-interdigitated lamellar structure, Optical textures on hydrophobic substrates exhibit a highly fluid sme ctic phase. On heating, a new type of crystalline mesophase in the tem perature range 385-433 K is observed that rests on the hydrophobic int eractions of the alkyl chains, while the hydrogen-bonded layer breaks down at the phase transition at 386 K. Similar behaviour is observed f or most of the C(18)ISA-4,4'-bipyridyl complexes. The C(18)ISA-piperaz ine complex forms a different enantiotropic liquid-crystalline phase w ith a broad mesophase range of 150 K. Solid-state H-2 NMR spectroscopy proves the high molecular order of the complex, which can be macrosco pically oriented in the magnetic field, IR spectral data of the comple x indicate both ionic and hydrogen-bonding character, The conformation al order of the alkyl chains is reduced at the phase transition into t he liquid-crystalline phase so that for this complex the mesophase is stabilized by hydrogen and ionic bonds.