Silicone-modified cellulose. Crosslinking of the cellulose acetate with 1,1,3,3-tetramethyldisiloxane by Pt-catalyzed dehydrogenative coupling

Cellulose acetate was reacted with different amounts of 1,1,3,3-tetramethyldisiloxane in presence of Karstedt’s catalyst, in solution, by using dry acetone as a solvent. A dehydrocoupling reaction between Si-H and C-OH groups with H₂ evolving and the formation of Si-O-C bond occured, as proved by FTIR and NMR spectra, having as a result the crosslinking of cellulose derivative. A model reaction was followed online by ¹H NMR spectroscopy. Morphological changes as a result of the siloxane coupling to the cellulose derivative were emphasized by Environmental Scanning Electron Microscopy (ESEM). The surface (water contact angle and water vapor sorption capacities) and mechanical properties (breaking strength, breaking strain and Young modulus) of the networks processed as films were investigated and the results were correlated with the reactants ratios.     

Graphene Liquid Cells Assembled through Loop‐Assisted Transfer Method and Located with Correlated Light‐Electron Microscopy

Graphene liquid cells (GLCs) for transmission electron microscopy (TEM) enable high‐resolution, real‐time imaging of dynamic processes in water. Large‐scale implementation, however, is prevented by major difficulties in reproducing GLC fabrication. Here, a high‐yield method is presented to fabricate GLCs under millimeter areas of continuous graphene, facilitating efficient GLC formation on a TEM grid. Additionally, GLCs are located on the grid using correlated light‐electron microscopy (CLEM), which reduces beam damage by limiting electron exposure time. CLEM allows the acquisition of reliable statistics and the investigation of the most common shapes of GLCs. In particular, a novel type of liquid cell is found, formed from only a single graphene sheet, greatly simplifying the fabrication process. The methods presented in this work—particularly the reproducibility and simplicity of fabrication—will enable future application of GLCs for high‐resolution dynamic imaging of biomolecular systems.     

Thermal and mechanical characterization of maleimide‐functionalized copoly(urethane‐urea)s

Maleimide functionalized copoly(urethane‐urea)s were prepared by the reaction of a binary mixture of dibenzyldiisocyanate and 5‐maleimidoisophthalic diisocyanate with a macrodiol (PEGA‐2000), using diethylene glycol and trimethylol‐propane as chain extender and crosslinkers in toluene‐dichloromethane solutions at the ratio NCO/OH = 1.2. Structures of polymers were confirmed by IR spectroscopy and properties were studied by thermal and mechanical analysis (dynamic mechanical analysis (DMA), differential scanning calorimetry, thermogravimetric analysis, stress‐strain) and other physical methods. Maleimide modification increased the storage modulus and Young's modulus of copoly(urethane‐urea)s, slightly increased their glass transition temperature from ?10.6°C to ?6.3°C. Copoly(urethane‐urea) networks obtained by thermal polymerization of maleimide functions showed significantly increased of the mechanical properties. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Influence of archaeological environment factors in alteration processes of copper alloy artifacts

The article presents the experimental results obtained by combining noninvasive techniques (OM, SEM/EDX, XRF) to analyze three artifacts made of copper alloys discovered in a inhumation tomb (2) and in the soil profile (1) in archaeological sites from Neamt County Romania. To uncover the mechanism of alteration thereof during their longtime underground stay in specific chemical conditions and under the influence of other pedological factors, the corrosion products must be identified. The excess of the chloride ion, from burial site, disturbs the Liesegang effect, transforming the bulk in a stratified sponge structure with chlorapatite and hydroxyapatite. Some of the compounds from primary and secondary patina can be found on the surface of the bulk, as color stains. The presence of alloy components (Cu, Sn, Pb, Zn, Fe, etc.) and of the underground contamination components, allowed us to establish the origin of the ore, the manufacture technology and we identified other materials which affected the artifacts after abandonment. Microsc. Res. Tech., 2012. © 2012 Wiley Periodicals, Inc.     

Crosslinked polysulfone obtained by Wittig‐Horner reaction in biphase system

Phase transfer catalyzed reactions are often more easily and cheaply performed than conventional method and they are therefore of particular interest. A polysulfone functionalized with phosphonate (2‐PSF) was prepared under phase transfer catalysis (PTC) conditions, and it was evaluated by spectrometric method (Fourier transform infrared spectroscopy, using potassium bromide (KBr) pellet). The phosphorus content of the modified polysulfone was determined, and it was used for the determination the fraction of repeating units functionalized with phosphonate groups. The modified polysulfone contains 1.40 mmol phosphonate/g polysulfone. Polysulfone functionalized with phosphonate groups and polysulfone functionalized with aldehyde groups (3‐PSF) were used in Wittig‐Horner reaction, to introduce double bonds on polymer and to obtain crosslinked polysulfone (4‐PSF). The reactions were performed using PTC method, solid‐liquid (potassium carbonate (K₂CO₃), tetrahydrofuran (THF), tetraethylammonium iodide (TEAI)) system. The structure of polysulfone functionalized with phosphonate groups and polysulfone functionalized with aldehyde group were confirmed by ¹H‐, ¹³C‐, and ³¹P‐nuclear magnetic resonance (NMR). The peak for phosphorus in PSF‐phosphonate appears in ³¹P NMR spectrum as a singlet at 25.712 ppm. The thermal properties of aldehyde, phosphonate, and crosslinked polysulfone were studied by thermogravimetric analysis (TG) and differential thermogravimetric analysis (DTG). Scanning electron microscopy images for polysulfone functionalized with phosphonate and crosslinked polysulfone are in concordance with nitrogen (N₂) adsorption‐desorption isotherms.POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Adsorption of anionic textile dye Acid Green 9 from aqueous solution onto weak or strong base anion exchangers

The aim of this work is to study the thermodynamic and kinetic studies with regard to the adsorption of Acid Green 9 (AG9) on the most efficient resin, namely, acrylic weak base anion exchange resin with ethylenediamine‐functional groups (A1) selected from several anion exchange resins. The influence of the various experimental parameters such as, pH, initial dye concentration, contact time, temperature, and adsorbent dose was investigated by batch experiments. The extent of the dye adsorption increased with the decrease of the initial dye concentration and the increase of the contact time, temperature, and amount of the adsorbent. Adsorption process was quantitative and very fast at low concentrations of the dye. To investigate the mechanism of the adsorption and potential rate‐controlling steps, pseudo first‐ and second‐order, as well as intraparticle diffusion kinetic equations have been used. The adsorption kinetic of AG9 dye from aqueous solution onto A1 could be described by the pseudo second‐order reaction model. The obtained results are in agreement with the Langmuir and Freundlich models. In the optimum conditions established, an adsorption capacity of 500 mg textile dye (72% purity) g^?1 adsorbent (at 293 K) was reached. Desorption experiments by batch and dynamic methods were performed using a solution of 0.05 mol L^?1 NaOH. A series of 13 adsorption–desorption cycles were carried out by the dynamic method with a quantitative adsorption and the desorption efficiency higher than 95%. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Fracture in epoxy matrix resins

The occurrence of fracture-energy-enhancing steps and welts on fracture surfaces of crosslinked matrix resins has been studied in an epoxy obtained from a trifunctional epoxy resin cured with an anhydride. It is suggested that the steps and welts arise from an underlying basic longitudinal texture, which was revealed by strongly tilting fracture specimens toward the collector in a scanning electron microscope. A model for the development of the basic longitudinal texture is proposed involving a meniscus instability of the propagating crack front, which gives rise to a series of fingers protruding into the bulk resin ahead of the nominal crack front. The periodicity of the basic longitudinal texture seen in the epoxy specimens studied was roughly 350 nm, which was independent of the epoxy resin: hardener ratio within at least 10% of stoichiometry. Because the periodicity of the basic longitudinal texture is roughly equal to the separation of the fracture surfaces immediately behind the crack, a considerable blunting of the crack by plastic deformation or yielding is suggested, a property that should depend on the matrix resin.