Conformational studies of bipyrimidine-based mesogens by combination of DFT calculations and temperature-dependent infrared studies

International audienceCombination of DFT calculations and solid-state temperature-dependent infrared spectroscopy has confirmed that the central core of recently developed bipyrimidine-based mesogens is not flat, i.e. do not adopt a disc shape, inside the columnar liquid-crystalline phase. For this purpose, the intensities and the frequency shifts of the most sensitive C–N and C–C bands of the central bipyrimidine core have been studied as a function of the temperature and of the dihedral angle. The results support the reported packing model in which the molecules are interdigitated alternatively along their long axis and their short axis to form columns inside the mesophase

Structural studies of thermally stable, combustion-resistant polymer composites

Composites of the industrially important polymer, poly(methyl methacrylate) (PMMA), were prepared by free-radical polymerization of MMA with varying amounts (1–30 wt. %) of sodium dioctylsulfosuccinate (Aerosol OT or AOT) surfactant added to the reaction mixture. The composites with AOT incorporated show enhanced resistance to thermal degradation compared to pure PMMA homopolymer, and micro-cone combustion calorimetry measurements also show that the composites are combustion-resistant. The physical properties of the polymers, particularly at low concentrations of surfactant, are not significantly modified by the incorporation of AOT, whereas the degradation is modified considerably for even the smallest concentration of AOT (1 wt. %). Structural analyses over very different lengthscales were performed. X-ray scattering was used to determine nm-scale structure, and scanning electron microscopy was used to determine μm-scale structure. Two self-assembled species were observed: large phase-separated regions of AOT using electron microscopy and regions of hexagonally packed rods of AOT using X-ray scattering. Therefore, the combustion resistance is observed whenever AOT self-assembles. These results demonstrate a promising method of physically incorporating a small organic molecule to obtain a highly thermally stable and combustion-resistant material without significantly changing the properties of the polymer

Liquid-crystalline functional carbazole and naphthalene platforms

International audienc

Simulation of SAXS patterns of hexa-n-alkoxy-2,3,6,7,10,11-triphenylene mesophase

International audienceSmall-angle X-ray scattering (SAXS) experiments and molecular dynamic modelling of the mesomorphic organisation of hexa-n-pentoxy-2,3,6,7,10,11-triphenylene are reported. Simulated SAXS patterns extracted from molecular dynamic simulations account for the fact that despite a perfect organisation of the columns in a 2D hexagonal array, in most case, SAXS patterns show only the fundamental diffraction peak with a limited number of higher order reflections. [GRAPHICS]

Instabilités et singularités (des films minces aux plaques élastiques)

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Magnetically induced large mesoporous single-domain monoliths using a mineral liquid crystal as a template

International audienceIn this paper, we report on how the properties of the suspensions of a lyotropic nematic mineral liquid crystal (MLC) based on V$_2$O$_5$ ribbons are exploited to synthesize single‐domain mesostructured inorganic–inorganic composites, aligned at the centimeter length scale by application of a relatively small magnetic field (0.85 T). In addition, the removal of the mineral template from the inorganic matrix leaves aligned empty channels, fingerprints of the V$_2$O$_5$ ribbons. Large colorless and birefringent mesoporous material is obtained where the orientational order of the channel director has retain the magnetic‐field alignment of its mineral template up to the centimeter length scale within the porous macroscopic silica matrix. A representative material exhibits slit‐like pores with cross‐sectional dimensions of 2 × 20 nm over 600 nm, and has a specific surface area of 207 m$^2$ g$^{–1}$