Non-symmetric ether-linked liquid crystalline dimers with a highly polar end group

<p>A new class of non-symmetric dimeric compounds derived from 4-cyano-4′-hydroxybiphenyl in which two rigid parts are connected via flexible spacers have been designed and synthesised. These materials possess trialkoxy chains attached at one end of the molecule, while the other end consists of a biphenyl moiety terminated with the highly polar cyano group. The molecular structures of these dimers have been confirmed by elemental analysis and spectroscopic data and their phase behaviour has been characterised by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). Almost all of the synthesised materials exhibit liquid crystalline properties depending on the number of carbon atoms in the terminal chains, where all short chains derivatives form nematic phases and depending on the length of the internal spacer long terminal chains homologues display crystalline or unidentified smectic phase.</p

Cybotactic nematic phases of photoisomerisable hockey-stick liquid crystals

<p>New five-ring hockey-stick liquid crystalline materials with 4-bromoresorcinol as the central core unit and an azobenzene-based side arm were synthesised and their mesophase behaviour was investigated by polarising optical microscopy, differential scanning calorimetry, X-ray diffraction and under a triangular wave electric field. Additional structural modification was done by introducing a lateral fluorine atom in the terminal ring of one of the side arms. It is found that regardless of the alkyl chain length or the lateral fluorine substitution, all of the prepared materials are liquid crystalline exhibiting nematic phases composed of cybotactic clusters of the SmC-type (N_CybC) in addition to a monotropic SmC phase for the longest homologue.</p

Supramolecular meso-Trick: Ambidextrous Mirror Symmetry Breaking in a Liquid Crystalline Network with Tetragonal Symmetry

Bicontinuous and multicontinuous network phases are among nature's most complex structures in soft matter systems. Here, a chiral bicontinuous tetragonal phase is reported as a new stable liquid crystalline intermediate phase at the transition between two cubic phases, the achiral double gyroid and the chiral triple network cubic phase with an I23 space group, both formed by dynamic networks of helices. The mirror symmetry of the double gyroid, representing a meso-structure of two enantiomorphic networks, is broken at the transition to this tetragonal phase by retaining uniform helicity only along one network while losing it along the other one. This leads to a conglomerate of enantiomorphic tetragonal space groups, P41212 and P43212. Phase structures and chirality were analyzed by small-angle X-ray scattering (SAXS), grazing-incidence small-angle X-ray scattering (GISAXS), resonant soft X-ray scattering (RSoXS) at the carbon K-edge, and model-dependent SAXS/RSoXS simulation. Our findings not only lead to a new bicontinuous network-type three-dimensional mesophase but also reveal a mechanism of mirror symmetry breaking in soft matter by partial meso-structure racemization at the transition from enantiophilic to enantiophobic interhelical self-assembly

Hierarchical Macroporous PolyDCPD Composites from Surface-Modified Calcite-Stabilized High Internal Phase Emulsions

High Internal Phase Emulsions (HIPEs) of dicyclopentadiene (DCPD) were prepared using mixtures of surface-modified calcite (mCalcite) and a non-ionic surfactant. Twelve different emulsion formulations were created using an experimental design methodology. Three distinctive levels of the internal phase ratio, the amount of mCalcite loading, and the surfactant were used to prepare the HIPEs. Accordingly, macroporous polyDCPD composites were synthesized by performing ring-opening metathesis polymerization (ROMP) on the HIPEs. The variations in the morphological and physical properties of the composites were investigated in terms of experimental parameters. In the end, five different model equations were derived with a confidence level of 95%. The main and binary interaction effects of the experimental parameters on the responses, such as the average cavity size, interconnecting pore size, specific surface area, foam density, and compression modulus, were demonstrated. The synergistic interaction between the amount of surfactant, the amount of mCalcite loading, and the internal phase ratio appeared to have a dominant role in the average cavity diameter. The solo effect of the internal phase ratio on the interconnecting pore size, foam density, and compression modulus was confirmed. In addition, it was demonstrated that the specific surface area of the composites was mainly changed depending on the amount of mCalcite loading

Azopyridine-based hydrogen-bonded liquid crystals with thioether tail

The first examples of azopyridine-based hydrogen-bonded liquid crystals (HBLCs) with thioether tail are reported. For this purpose, new HBLCs were designed and synthesised using 4-octylthiobenzoic acid as the proton donor and two different types of 4-alkoxyazopyridines as the proton acceptors. The first group of HBLCs has no lateral substitution, whereas the second has a lateral fluorine atom next to the alkoxy chain attached to the azopyridine derivative. Therefore, it was possible to investigate not only the effect of thioalkyl tail but also the influence of the aromatic core fluorination on the phase behaviour of the newly synthesised HBLCs. Hydrogen bond formation between the proton donor and the proton acceptors was confirmed using FTIR spectroscopy and X-ray diffraction (XRD), while the liquid crystalline behaviour of the HBLCs was investigated using differential scanning calorimetry (DSC) and polarised light microscope (PLM). It was found that all the reported HBLCs are mesomorphic exhibiting smectic A (SmA) and/or smectic C (SmC) phases depending on the length of the alkoxy chain as well as the presence or absence of the lateral fluorine atom. The possibility of photo-switching of the reported HBLCs under UV light irradiation was demonstrated for some selected examples in solution as well as in the bulk state.</p