Rayleigh scattering of a new lyotropic nematic liquid crystal system: crossover of propagative and diffusive behaviour

In this paper we present to our knowledge the first light-scattering measurements on a rather new lyotropic system potassium laurate, decylammonium chloride, H₂O. Relative concentrations were chosen in order to obtain the discotic N_D phase over a large temperature range. Measurements involve digital recording of the autocorrelation function resulting from selfbeating of the depolarized scattered light. They were carried out at a fixed temperature in the N_D phase range, by varying the scattering angle. A strong tendency to oscillations, superimposed on the usual relaxation signal, was found. This behaviour is quite surprising, as special precautions had been taken to minimize any eventual propagative signal. Such precautions have been tested previously, while investigating the older system potassium laurate, decanol, D₂O. Nevertheless, we have found that in the new lyotropic system, a propagative component may occur in a significant way, or even become dominant for some particular situations. Actually, the characterization of such situations is the main purpose of the present paper. Based upon a detailed analysis of photocorrelation data, it will be shown that the observed behaviour is consistent with the expected wave vector dependences of propagative and diffusive modes. Finally, a discussion is given on possible causes for the tendency to instability of lyotropic nematic liquid crystals.     

Synthetic,Fungicidal Unsaturated-γ-lactones Attached to Furanosidic Systems. Configurational Determination by Nuclear Overhauser Effect1

Abstract

Stereoselective synthesis of a butenolide sugar derivative was possible by reaction of the appropriate sugar epoxide with the dilithium salt of phenylselenoacetic acid, followed by oxidation of the α-phenylselenobutanolide obtained with hydrogen peroxide in the presence of catalytic amounts of acetic acid. On the other hand, synthesis of an exocyclic α,β-unsaturated lactone was accomplished by Reformatsky reaction on the appropriate sugar carbonyl groups with ethyl bromomethylacrylate and activated zinc, leading to the introduction of this ring at position 2 or 4 of a furanose ring. Nuclear Overhauser effect studies led to the unambiguous determination of the configuration of the new chiral centre formed by the Reformatsky reaction. The fungicidal efficacy of some unsaturated lactone sugar derivatives is given.     

Prilocaine-cyclodextrin-liposome: effect of pH variations on the encapsulation and topology of a ternary complex using 1H NMR

A better comprehension of the prilocaine (PLC)-β-cyclodextrin (β-CD) complex liberation to membranes was provided by studying the architectural supramolecular arrangements of PLC, β-CD and egg phosphatidylcholine (EPC) liposomes, a membrane model. The topologies and possible interactions of mixtures of PLC, β-CD and EPC liposomes were investigated by nuclear magnetic resonances combining experimental (1)H-NMR (1D ROESY, STD and DOSY) at different pHs. The results indicate that in the mixture PLC/β-CD/EPC at pH 10 the PLC molecules are almost totally embedded into the liposomes and little interaction was observed between PLC and β-CD. However, at pH 5.5 not only was PLC imbedded in the EPC bilayer, but PLC was also interacting with β-CD. These results were rationalized as a spontaneous PLC release from β-CD to liposomes vesicles, whereas the PLC/EPC complex formation was higher at pH 10 than pH 5.5.     

Adsorption of dyes on carbon xerogels and templated carbons: influence of surface chemistry

The removal of textile dyes by adsorption onto carbon materials with extended mesoporosity is addressed in the present work. Two types of high surface area carbon adsorbents were prepared, namely a carbon xerogel and a templated carbon. Both materials were subsequently subjected to appropriate treatments in order to modify their surface chemistries, while keeping their textural properties relatively unchanged. The carbon adsorbents were extensively characterized by different techniques in order to correlate their adsorption performances with the corresponding surface properties. The behavior of the different materials was evaluated by determining equilibrium adsorption isotherms of two anionic dyes (Reactive Red 241 and Acid Blue 113) at different pH values. The results are compared with data previously obtained with commercial activated carbons subjected to the same treatments, and discussed in terms of the carbon surface chemistry and the interaction between the dye molecules and the adsorbent surface (dispersive and electrostatic interactions).     

Reaction mechanism of aerobic oxidation of alcohols conducted on activated-carbon-supported cobalt oxide catalysts

Catalytic performances and the reaction mechanism of Co(3)O(4)/AC (AC=activated carbon) for aerobic oxidation of alcohols carried out in the liquid phase were investigated. Co(3)O(4)/AC shows a high activity for aerobic oxidation of benzyl alcohol, comparable to noble metal catalysts (e.g., Au/AC) even in the absence of additives or promoters (e.g., NaOH). Changing preparation conditions, such as treatment temperature and/or time, can affect the catalytic performances of Co(3)O(4)/AC, due to decomposition of surface groups of the carbon support. Careful studies show that low alcohol conversions are obtained with either Co(3)O(4) or AC alone, which indicates that the high conversion observed over the Co(3)O(4)/AC is due to a synergistic effect between Co(3)O(4) and AC. Parallel experiments using a high-surface-area covalent triazine framework or oxygen-inert carbon nitride as support for the Co(3)O(4) catalyst also show lower conversions, which suggest that the ability of AC (in Co(3)O(4)/AC) to activate molecular oxygen is essential for the reaction. FTIR and XPS spectra taken from catalysts before and after the reaction confirm that oxygen activation proceeds mainly on the carbon support. As a result, it can be assumed that the alcohol dehydrogenation step proceeds on the metal oxide, whereas the oxygen activation step occurs mainly on the carbon support.     

Heterogeneous ceramics formed by grain boundary engineering

Two examples were selected to emphasize the potential of grain boundary engineering in the performance design of heterogeneous ceramics. Gadolinium-doped ceria-based powders were co-fired with additions of silica, and silica and lanthanum oxide, to test the silica scavenging role of lanthanum. The formation of one ionic conducting secondary phase, instead of an insulating phase, was attempted. The structural, microstructural, and electrical characterization of these samples confirmed the formation of one apatite-type lanthanum silicate-based phase and a significant enhancement of the grain boundary conductivity of these materials. One second approach addressed the formation of one mixed conductor, with electronically conductive grain boundaries, surrounding the grains of one lanthanum gallate-based electrolyte (core-shell type microstructure). Fe-doped grain boundaries were formed by selective Fe-diffusion (thermally assisted) from lanthanum ferrite screen printed layers. Combined microstructural and electrical characterization showed that the adopted solution was also effective.     

Pt nanoparticles supported over Ce–Ti–O: the solvothermal and photochemical approaches for the preparation of catalytic materials

Ce–Ti–O supports with different Ce/Ti molar ratios were synthesized by the solvothermal method using hexadecyltrimethylammonium bromide. Pt nanoparticles were then supported by photochemical deposition. The shape, size, and structure of these materials were analyzed by high-resolution transmission electron microscopy. The single CeO₂ support was also prepared, consisting of agglomerated cubic particles ranging from ~3 to 8 nm. When titania was combined with ceria, a nanostructured architecture was produced, evidencing the strong influence of Ti in the support structure. Photodeposition of Pt nanoparticles is more efficient on Ce–Ti–O supports than in pristine CeO₂. Crystalline Pt nanoparticles (mainly of ~2 to 4 nm) were detected. The catalytic properties of the materials were tested in the selective hydrogenation of cinnamaldehyde to cinnamyl alcohol. It was observed that Pt supported on Ce–Ti–O is more active and selective than Pt on CeO₂ or TiO₂ separately. The catalyst with 40 mol% Ce leads to total conversion of cinnamaldehyde in a few minutes; however, higher selectivity toward the desired product (cinnamyl alcohol) was obtained with higher amounts of Ce (50 mol%).     

Multiple solutions for a Schrödinger–Bopp–Podolsky system with positive potentials

In this paper, we prove existence of solutions for a Schrödinger–Bopp–Podolsky system under positive potentials. We use the Ljusternick–Schnirelmann and Morse Theories to get multiple solutions with a priori given “interaction energy.”     

A singular Liouville equation on planar domains

We show the existence of a solution for an equation where the nonlinearity is logarithmically singular at the origin, namely, $-\mathrm{\Delta }u=(\log u+f(u)){\chi }_{\{u>0\}}$ in $\mathrm{\Omega }\subset {\mathbb{R}}^2$ with Dirichlet boundary condition. The function f has exponential growth, which can be subcritical or critical with respect to the Trudinger–Moser inequality. We study the energy functional $I_{\epsilon }$ corresponding to the perturbed equation $-\mathrm{\Delta }u+g_{\epsilon }(u)=f(u)$, where $g_{\epsilon }$ is well defined at 0 and approximates $-\log u$. We show that $I_{\epsilon }$ has a critical point $u_{\epsilon }$ in $H_0^1(\mathrm{\Omega })$, which converges to a legitimate nontrivial nonnegative solution of the original problem as $\epsilon \to 0$. We also investigate the problem with $f(u)$ replaced by $\lambda f(u)$, when the parameter $\lambda >0$ is sufficiently large.