Sepiolite-based epoxy nanocomposites: relation between processing, rheology, and morphology

Rheology of sepiolite-based epoxy suspensions as well as morphology and dynamic mechanical properties of the corresponding nanocomposites are discussed in this paper. The influence of the type of sepiolite used, i.e. non-modified, aminosilane and glycidylsilane surface modified, and of the process developed to prepare the epoxy suspensions were investigated. Except for low amount of filler, a shear thinning behavior was observed in the others sepiolite-based epoxy suspensions. The interactions developed between the sepiolite and the epoxy matrix are responsible for the magnitude of the shear thinning effect and are related to the morphology of the nanocomposites. The best dispersion of sepiolite was achieved using either an emulsion process or a glycidyl functionalized sepiolite.     

Solvent-free synthesis of reactive inorganic precursors for preparation of organic/inorganic hybrid materials

Prehydrolyzed-condensed precursors containing amino or glycido groups were prepared via sol gel process using various alkoxysilanes in the bulk, without addition of solvent in any step of their preparation. The influence of the experimental set-up, the functionality and ratio of alkoxysilanes, and type of catalyst, on the structure buildup was studied. In the case of amino precursors, the sol–gel process was carried out at weak basic conditions while in the case of glycido precursors the sol–gel process was catalyzed by acid or neutral pH. The sol–gel process was monitored by ²⁹Si NMR in solution and the structure of the prehydrolysed-condensed precursors was characterized by small-angle X-Ray scattering. The systems with high content of tetraethoxysilane led to the fast gel formation. In weak acid medium tetraethoxysilane formed larger, more condensed species as well as small structures (based on Q ₁, Q ₂ and Q ₃ species) with silanol groups. Strong acidic conditions led to the fast formation of insoluble silica particles in liquid (sol) phase containing monomeric alkoxysilanes. The most suitable precursor formulations based on the alkoxysilanes with amino groups, as well as the most efficient set-up, were selected and used to prepare hybrid organic/inorganic networks based on an epoxy matrix. These networks were characterized using dynamic mechanical analysis.     

High Accuracy Solution of Three-Dimensional Biharmonic Equations

In this paper, we consider several finite-difference approximations for the three-dimensional biharmonic equation. A symbolic algebra package is utilized to derive a family of finite-difference approximations for the biharmonic equation on a 27 point compact stencil. The unknown solution and its first derivatives are carried as unknowns at selected grid points. This formulation allows us to incorporate the Dirichlet boundary conditions automatically and there is no need to define special formulas near the boundaries, as is the case with the standard discretizations of biharmonic equations. We exhibit the standard second-order, finite-difference approximation that requires 25 grid points. We also exhibit two compact formulations of the 3D biharmonic equations; these compact formulas are defined on a 27 point cubic grid. The fourth-order approximations are used to solve a set of test problems and produce high accuracy numerical solutions. The system of linear equations is solved using a variety of iterative methods. We employ multigrid and preconditioned Krylov iterative methods to solve the system of equations. Test results from two test problems are reported. In these experiments, the multigrid method gives excellent results. The multigrid preconditioning also gives good results using Krylov methods.     

Head-to-head and head-to-tail multilayer n-alkylsilsesquioxane films

Two lamellar organosilica films made up of stacks of head-to-head and head-to-tail alkyl bilayers were synthesized by a UV-driven polymerization of n-C₁₈H₃₇SiCl₃ and n-C₁₈H₃₇Si(OCH₃)₃, respectively. In addition to thermogravimetry and small-angle X-ray scattering, the characterization of these multilayer systems was focused on a variety of multinuclear solid-state NMR methods (¹H, ²⁹Si, ¹³C, 2D WISE). The chemical structure of the siloxane interlayer, the alkyl chain conformation and thermal stability were systematically investigated and compared. Through its marked sensitivity to molecular motion, solid-state NMR was used to investigate the effect of interdigitation on alkyl chain dynamics.     

Investigation of tetracaine complexation with beta-cyclodextrins and p-sulphonic acid calix[6]arenes by nOe and PGSE NMR

Cyclodextrins (CD) and calixarenes are complexing agents that have been successfully used as pharmaceutical drug carriers, to improve the bioavailability of medicines. The aim of this work was to investigate the complexation of the local anesthetic tetracaine 1 with β-cyclodextrin 2, as well as with p-sulphonic acid calix[6]arene 3. ¹H NMR experiments were carried out in D₂O, i.e., with the charged tetracaine species 1. HR-DOSY ¹H NMR allowed determination of the fraction of complexed population (%p _bound = 55% and 70%) and the apparent association constants (K _a = 1358 and 3889 M⁻¹), respectively, for 1/2 and 1/3. These results confirm that a strong association takes place between 1 and 2, while the 1/3 complex is even more stable, due to the negatively charged sulphonic groups of 3. Studies conducted at pH 10 revealed that the association of the uncharged form of 1 with 3 is considerably weaker, while that with 2 increased significantly (K _a = 6597 M⁻¹), protecting the anesthetic against alkaline hydrolysis. ¹H-ROESY 1D NMR experiments allowed determination of the host-guest relative positions, revealing that the proposed topologies for the 1/2 and 1/3 complexes were quite different. The complexation of 1 with either 2 or 3 is being investigated in view of its potential use in new therapeutic formulations, designed to increase the bioavailability and/or to decrease the systemic toxicity of tetracaine, in anesthesia procedures.     

Effect of coal on the rheological and mechanical properties of epoxy matrix

An experimental study was conducted to investigate the effect of coal used as a new type of filler in epoxy networks. For this purpose two series of epoxy composites with different coal weight fraction were studied and their thermo-mechanical properties were characterized. The work demonstrated that coal-filled epoxy networks show a typical behavior of a particulate filled material and follows the theoretical models already used.     

Terpenoids from the dorid nudibranch cadlina luteomarginata

Methanol extracts of intact specimens of Cadlina luteomarginata, collected in Howe Sound and Barkley Sound, British Columbia, have been shown to contain sesquitepenoids and a degraded terpenoid. Albicanol (2) and its acetate 1 possess the drimane skeleton. Furodysin (4) and microcionin-2 (5) and microcionin-2 (6) are furanosesquiterpenoids of sponge origin. Luteone (8), the degraded terpenoid, represents a new carbon skeleton.     

A FLOW LINEAR DICHROISM STUDY OF THE ORIENTATION OF 4'',5''-PSORALEN-DNA PHOTOADDUCTS

Abstract— The flow linear dichroism properties of covalent adducts derived from the photochemical binding of various psoralen derivatives to salmon sperm DNA were investigated. The psoralens studied include bifunctional derivatives (8-methoxypsoralen,5-methoxypsoralen, tetrahydropyrido [3,4: 4',5'] psoralen) and monofunctional derivatives (pyrido [3,4-c] psoralen, 7-methylpyrido [3,4-c] psoralen, 3-carbethoxypsoralen). The orientation of the psoralen moieties (furan-side monoadducts) relative to the orientation of the DNA bases was determined. All of the furan-side monoadducts are characterized by a similar orientation, with mean angles between the psoralen moiety and the normals of the planes of the DNA bases ranging between 70° and values close—but not equal—to 90°. The results are consistent with a pseudo-intercalative adduct geometry, most probably involving stacking interactions with the DNA bases.     

Oxidative stress and immunologic responses following a dietary exposure to PAHs in <Emphasis Type="Italic">Mya arenaria</Emphasis>

Background  

The aim of this research was to investigate oxidative stress and immune responses following a dietary polycyclic aromatic hydrocarbon (PAH) exposure in a marine bioindicator organism, the soft shell clam, Mya arenaria. Immune parameters in hemolymph (haemocyte number, efficiency of phagocytosis and haemocyte activity) and assessment of oxidative stress using catalase (CAT) activity and levels of malondialdehyde (MDA) performed on the digestive gland were estimated as biomarkers in clams fed in mesocosm with PAH contaminated phytoplankton. MDA levels and CAT activities were also measured in situ in organisms sampled in a control site (Metis Beach, Québec, Canada) as well as organisms sampled in a site receiving domestic effluents (Pointe-au-Père, Québec, Canada), to assess effects of abiotic variables related to seasonal variations and mixed contamination on the selected parameters.