Diverse configurations of columnar liquid crystals in cylindrical nano- and micropores.

Using 2D X-ray diffraction and AFM we studied the configuration, in cylindrical confinement, of hexagonal columnar phases that anchor homeotropically, i.e. with the columns normal to the pore wall. A wide range of pore diameters, from 20 nm to 100 μm, were explored by employing anodic alumina membranes and glass capillaries. The compounds used were a small discotic, hexakis(hexyloxy)triphenylene (HAT6), a large discotic hexa-peri-hexabenzocoronene (HBC), and a T-shaped bolaamphiphile, forming a honeycomb-type columnar phase. It was found that in pores up to tens of μm in diameter the columns adopt the "logpile" configuration with parallel columns crossing the pore perpendicular to its axis. Starting with 20 nm pores, with increasing pore diameter up to 5 different configurations are observed, the sequence being the same for all three compounds in spite of their structural diversity. One of the {100} planes of the hexagonal logpile starts from being parallel to the pore axis, then rotates by 90° as the pore size increases, and eventually becomes tilted to the pore axis by (8.5 ± 1)° as the pore widens further. Finally, in glass capillaries of tens of μm and beyond, the columns become axially oriented, parallel to the capillary axis. This latter finding was particularly unexpected as common sense would suggest axial columns to be favoured by planar anchoring, where in fact, it was shown to be hard to achieve. The present findings should help in the design of low-dimensional semiconductor or ionic conductor devices based on oriented columnar phases

Biomimetic adsorption of zwitterionic–xyloglucan block copolymers to CNF: towards tailored super-absorbing cellulose materials

A biomimetic, facile approach to cellulose modification is the utilisation of self-adsorbing, naturally occurring biopolymers, such as the hemicellulose xyloglucan (XG). Herein, XG-block-poly(sulfobetaine methacrylate) (XG-b-PSBMA) zwitterionic block copolymers have been prepared and assessed for their ability to adsorb to cellulose, specifically cellulose nanofibrils (CNF). The polymers were synthesised using reversible addition–fragmentation chain-transfer (RAFT) polymerisation, employing an XG macromolecular RAFT agent (XG-RAFT), polymerising a sulfobetaine methacrylate (SBMA) under aqueous conditions. The incorporation of the XG block shifted the upper critical solution temperature (UCST) values to higher temperatures (20 and 30 °C) compared with the PSBMA homopolymers (17 and 22 °C) and the transition was also broadened. The adsorption of the polymers to a CNF surface was monitored using quartz crystal microbalance with dissipation monitoring (QCM-D), showing that the XG block enhanced the adsorption of the zwitterionic polymer. The formation of CNF-composite films was achieved utilising a facile vacuum filtration methodology, and the targeted compositions were confirmed by FT-IR and TGA analyses. The films exhibited high degrees of swelling in water, which were investigated at two different temperatures, 5 and 60 °C (below and above the polymer USCT values). These results highlight the advantage of using an XG block for the biomimetic modification of cellulose to form new cellulose-composite materials such as super-absorbing films

Columnar Liquid Crystals in Cylindrical Nanoconfinement

Axial orientation of discotic columnar liquid crystals in nanopores of inorganic templates, with the columns parallel to the axis of the nanochannels, is considered desirable for applications such as production of molecular wires. Here, we evaluate experimentally the role of the rigidity of the LC columns in achieving such orientation in nanopores where the planar anchoring (i.e., columns parallel to wall surface) is enforced. We studied the columnar phase of several discotic compounds with increasing column rigidity in the following order: dendronized carbazole, hexakis(hexyloxy)triphenylene (HAT6), a 1:1 HAT6-trinitrofluorenone (TNF) complex, and a helicene derivative. Using 2-D X-ray diffraction, AFM, grazing incidence diffraction, and polarized microscopy, we observed that the orientation of the columns changes from circular concentric to axial with increasing column rigidity. Additionally, when the rigidity is borderline, increasing pore diameter can change the configuration from axial back to circular. We derive expressions for distortion free energy that suggest that the orientation is determined by the competition between, on the one hand, the distortion energy of the 2-d lattice and the mismatch of its crystallographic facets with the curved pore wall in the axial orientation and, on the other hand, the bend energy of the columns in the circular configuration. Furthermore, the highly detailed AFM images of the core of the disclinations of strength +1 and +1/2 in the center of the pore reveal that the columns spiral down to the very center of the disclination and that there is no amorphous or misaligned region at the core, as suggested previously

La sensitive : polka-mazurka : [piano] / Melle A. Cerclier

Titre uniforme : Cerclier, Adrienne. Compositeur. [La sensitive. Piano

Marie : redowa : [pour piano] / par Madame Adrienne Cerclier

Titre uniforme : Cerclier, Adrienne. Compositeur. [Marie

Films multicouches à base de polymères végétauxb (élaboration et application à la détection d'activités enzymatiques)

Cellulose and xyloglucan represent a major network from plant cell wall. Theses molecules are linked by Van der Waals interactions and hydrogen bonds and we have used these interactions in order to elaborate nanometric multilayered films. According to their thickness and refractive index, nanometric films can present bright colours due to interference phenomena. Such films composed of cellulose nanocrystals and xyloglucan can be used as cellulases enzymatic activities detector. Hydrolytic enzyme action can actually be detected by film thickness decrease and results in a colour change. Growth mode has been studied for two kinds of film and the better conditions were chosen to obtain coloured films. Films internal structure has been investigated by neutron reflectometry on dry films and films in solution in order to evaluate the structures differences. Films hydrolysis kinetics has also been compared by QCM-D. Cellulases activities detection using nanometric films is faster and more sensitive than a colorimetric method usually used. We have also proved that this technique can be used for other enzyme/substrate systems.La cellulose et le xyloglucane constituent un réseau majeur de la paroi des cellules végétales. Ces molécules sont liées par des interactions de Van der Waals et des liaisons hydrogène que nous avons mis à profit pour l élaboration de films multicouches nanométriques. En fonction de leur épaisseur et de leur indice de réfraction, les films nanométriques peuvent présenter des couleurs qui sont dues à des phénomènes d interférences. De tels films composés de nanocristaux de cellulose et de xyloglucane peuvent être valoriser comme détecteurs d activité enzymatique de cellulases. En effet, l action d une enzyme hydrolytique peut être détectée par une diminution de l épaisseur du film qui résulte en un changement de couleur. Les modes de croissance de deux types de films ont été étudiés afin de déterminer les conditions opératoires les plus appropriées pour l obtention de films colorés. La structure interne de ces films a été déterminée par réflectivité de neutrons à l état sec et en solution pour évaluer les différences de structures. Les cinétiques de dégradation des films par les cellulases ont également été comparées par QCM-D. Il s avère que la détection de l activité de cellulases avec les films nanométriques est plus rapide et plus sensible qu une méthode colorimétrique utilisée usuellement. L utilisation des films nanométriques pour la détection d activité est également applicable à d autres systèmes enzyme/substrat.NANTES-BU Sciences (441092104) / SudocSudocFranceF

Performance of carbon black-slurry electrodes for 4-chlorophenol oxidation

International audienceThe degradation of 4-chlorophenol (4-CP) by electrochemical oxidation in the presence of carbon black (CB) was studied in a laboratory reactor. This reactor consisted of a stack of Ti/Pt electrodes. After the mixing of the solution to be treated with CB, the slurry electrode thus obtained flows through the electrode grids. The reaction pathways and kinetics were studied by means of high performance liquid chromatography coupled with a UV detection, ionic chromatography coupled with a conductimetric detection and gaseous chromatography coupled with mass spectrometry. The reaction pathways were thus determined: after the C–Cl bond breaking, phenol and chloride ions were detected in the solution. The formation of 2-chlorophenol was also detected. The influence of the amount of CB used on the degradation yield of 4-CP was also studied. The full mineralization of 4-CP could be reached if CB was present in a sufficient amount and, in this case, no chlorine was detected

Réflectivité de HfSe2, NiTe2, TiTe2 de 12 eV à 42 e

The reflectivity of the layer structure compounds : HfSe2, NiTe 2, TiTe2 has been measured between 12 eV and 42 eV, using synchrotron radiation at Orsay (L.U.R.E.). The Hf, Te and Ti core level excitation spectra are discussed in terms of the conduction band densities of states.La réflectivité des composés lamellaires HfSe2, NiTe2 et TiTe2 a été mesurée entre 12 eV et 42 eV en utilisant le rayonnement synchrotron d'Orsay (L.U.R.E.). Les structures observées dues à l'excitation de niveaux profonds de Hf, Te et Ti servent de base pour un modèle qualitatif de densité d'états de conduction

Voltammetric studies of the behavior of carbon black during phenol oxidation on Ti/Pt electrodes

International audienceOxidation of phenol on platinum electrodes rapidly leads to the formation of a passivating film on the surface of these electrodes. Studies of cyclic voltammetry and chronoamperometry combined with high-performance liquid chromatography (HPLC) analyses have shown that the presence of carbon black avoids these phenomena of passivation and thus allows the complete mineralization of phenol. The nature of carbon black and the pH value are two important factors which are studied here. VULCAN XC-72 R, an intrinsic p-type semiconductor, having a large specific area, showed all its efficiency when cyclic voltammetry experiments were carried out in an acid medium (pH 2.2). HPLC analyses revealed the appearance of several by-products such as hydroquinone and benzoquinone, and maleic and fumaric acids