Extrusion of Nanocellulose‐Reinforced Nanocomposites Using the Dispersed Nano‐Objects Protective Encapsulation (DOPE) Process

Cross‐linked alginate capsules a few millimeters in diameter have been formed by immersion in a CaCl₂ solution. When adding cellulose whiskers or microfibrillated cellulose to the aqueous alginate solution, nanocomposite capsules containing 40 wt.% cellulosic nanoparticles were obtained. The morphology and compression strength of these capsules were investigated by microscopic observations and crushing tests, respectively. The capsules were extruded with a thermoplastic polymer. Visual inspection of the ensuing films shows a nonhomogeneous dispersion of the capsules that kept their integrity after extrusion. It results in preliminary disappointing mechanical properties of the composite films. However, further investigation is in progress to optimize this simple and ecofriendly process.

     

In Vitro Antiprotozoal Activity of Abietane Diterpenoids Isolated from Plectranthus barbatus Andr.

Chromatographic separation of the n-hexane extract of the aerial part of Plectranthus barbatus led to the isolation of five abietane-type diterpenes: dehydroabietane (1); 5,6-didehydro-7-hydroxy-taxodone (2); taxodione (3); 20-deoxocarnosol (4) and 6α,11,12,-trihydroxy-7β,20-epoxy-8,11,13-abietatriene (5). The structures were determined using spectroscopic methods including one- and two-dimensional NMR methods. Compounds (1)–(3) and (5) are isolated here for the first time from the genus Plectranthus. The isolated abietane-type diterpenes tested in vitro for their antiprotozoal activity against erythrocytic schizonts of Plasmodium falciparum, intracellular amastigotes of Leishmania infantum and Trypanosoma cruzi and free trypomastigotes of T. brucei. Cytotoxicity was determined against fibroblast cell line MRC-5. Compound (2) 5,6-didehydro-7-hydroxy-taxodone showed remarkable activity with acceptable selectivity against P. falciparum (IC₅₀ 9.2 μM, SI 10.4) and T. brucei (IC₅₀ 1.9 μM, SI 50.5). Compounds (3)–(5) exhibited non-specific antiprotozoal activity due to high cytotoxicity. Compound (1) dehydroabietane showed no antiprotozoal potential.     

Constant hue bands in boundary colors discovered using a new appearance model

Boundary colors are observed when light from a scene is dispersed by a prism or diffraction grating. We discovered that patterns with repeating black and white stripes can produce repeating bands of boundary colors with two hues. These hues are virtually constant as measured by chromaticity or CIELAB. We found seven cases of this kind using a new appearance model for boundary colors. The model correctly predicts that green and magenta bands recur as stripe widths and dispersion strength vary. The first green/magenta case in the sequence traces out an accurate ellipse in XYZ color space. Green and magenta bands are prominent in supernumerary rainbows and interference rings, and we explain why that might be the case. The explanation is based on an interesting property of the visible spectrum. In addition to the green/magenta cases, the other cases are orange/cyan, yellowish‐green/purple, and yellow/violet. The success of the boundary color appearance model implies that bands are perceived as if the wavelength responses of the cones were essentially independent, which contradicts the actual behavior of cones. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 135–146, 2015     

Effect of Silica‐Coated Poly(butyl methacrylate)‐block‐poly(methyl methacrylate) Double‐Shell Particles on the Mechanical Properties of PMMA Composites

Silica nanoparticles with an average diameter of 12 nm are grafted with PBMA‐b‐PMMA double shells through typical sequential ATRP from bromoisobutyrate initiators anchored at the silica surface using an epoxysilane. A commercially available PMMA homopolymer is used for the preparation of composites with unmodified, silane‐modified and double‐shell‐modified silica particles. Good mechanical properties are obtained for silica double shell containing systems. The silica content in double shell particle systems is varied from 0 to 2.5 wt%. A significant improvement in impact properties is observed. The surface‐modified silica particles are characterized by ATR‐FTIR, NMR, GPC, and thermal analyses. TEM analysis is used to analyze the nature of dispersion of particles in the composites.

     

Effect of temperature on friction and wear behaviour of CuO–zirconia composites

Results of wear tests using an alumina ball sliding against 5 wt% copper oxide doped tetragonal zirconia polycrystalline (CuO-TZP) ceramics are reported as a function of temperature up to 700 °C. The specific wear rate and friction coefficient are strongly dependent on temperature. Below a critical temperature (T < 600 °C), CuO-TZP showed a high coefficient of friction as well as a high wear rate. This was ascribed to the formation of a rough surface, caused by brittle fracture and abrasive wear, based on observations by scanning electron microscopy (SEM), laser scanning microscopy (LSM) and X-ray photoelectron spectroscopy (XPS). However, above 600 °C a self-healing layer is formed at the interface and results in low friction and wear. The mechanism of layer formation and restoration is discussed and rationalized by onset of plastic deformation caused by a reduction reaction of CuO to Cu₂O at high temperatures.     

Characterization of biodegradable core–clad borosilicate glass fibers with round and rectangular cross-section

Here, we report on core–clad bioactive borosilicate fibers, that we have prepared both with round and rectangular cross-section profile. The exposed approach, which relies on the stacking and drawing of glass slabs, demonstrates our ability to develop bioactive-based glass fibers with tailored cross-section profiles. Tens-of-meters-long fibers were successfully drawn, although suffering from elevated losses in the case of the rectangular ones. The response of the fibers in simulated body fluid was studied for both geometries. We found that a round cladding can act as protective layer, tempering effects of the corrosion. We also noticed that rectangular fibers are more prone to degradation, the enhanced corrosion beginning from their sharp corners as they accumulated residual tensile stress during drawing. To the best of our knowledge, this is the first report on the effect of residual tensile stresses from surface tension deformations applied to the corrosion of rectangular fibers. As geometry plays a critical role on the biodegradation behavior of the fiberglass, we believe the enclosed results could lead to the design of fiber devices with tailored cross-section profile in order to tune their rate of degradation on solely based geometrical effects.     

D-Peptide and D-Protein Technology: Recent Advances,Challenges, and Opportunities**

Total chemical protein synthesis provides access to entire D-protein enantiomers enabling unique applications in molecular biology, structural biology, and bioactive compound discovery. Key enzymes involved in the central dogma of molecular biology have been prepared in their D-enantiomeric forms facilitating the development of mirror-image life. Crystallization of a racemic mixture of L- and D-protein enantiomers provides access to high-resolution X-ray structures of polypeptides. Additionally, D-enantiomers of protein drug targets can be used in mirror-image phage display allowing discovery of non-proteolytic D-peptide ligands as lead candidates. This review discusses the unique applications of D-proteins including the synthetic challenges and opportunities.     

Diffusion in porous silicon: effects on the reactivity of alkenes and electrochemistry of alkylated porous silicon

Alkenes are known to react with hydrogen-terminated silicon surfaces to produce robust organic monolayers that are attached to the surface via covalent SiC bonds. In this report we investigate the dependence of the rate of alkylation of porous silicon samples on the reaction time using photochemical initiation. The kinetics of the photochemical alkylation of hydrogen-terminated porous silicon by undec-1-ene in toluene were observed to be pseudo first order, however the apparent rate constant decreased as the concentration of undec-1-ene increased. This behaviour is opposite to what would be expected if the rate-limiting process was an elementary chemical reaction step involving the alkene. Instead, it suggests that transport of the alkene to reactive sites and in the correct orientation is the rate-limiting step. Comparison of the rates of alkylation of porous silicon by undec-1-ene and dimethoxytrityl (DMT)-undecenol is consistent with such an interpretation as the bulky DMT headgroup gives a lower rate of alkylation. The diffusion of some simple redox-active probe molecules in porous silicon was investigated using a scanning electrochemical microscope (SECM). The probe molecules are converted at diffusion-controlled rate at an inlaid disk ultramicroelectrode (UME) consisting of the cross-section of a microwire sealed in glass. If the microelectrode is placed a short distance above the porous silicon, the microelectrode current depends on kinetics of the electrochemical reactions at the porous silicon and the mass transport properties within the open thin layer cell formed by the microelectrode and the alkylated porous silicon. In order to differentiate the effects of finite heterogeneous kinetics at silicon from diffusion limitations, current-distance curves were fitted over a wide range of applied potentials (on the Si) and it was observed that the diffusion coefficient in the porous layer was strongly anisotropic. The measured diffusion rates are comparable to those in bulk water along the pores, but with negligible diffusion between pores. This indicates that few pore-pore interconnections exist in the porous silicon.     

Short poly(phenylene vinylene) chains grafted poly(organophosphazene)

Brominated poly(bis(4-methylphenoxyphosphazene) was allowed to react with 1,4-bischloromethylbenzene or 1,4-bischloromethyl-2,5-dimethoxybenzene in solution using phase transfer catalyst or potassium t-butoxide. Poly(p-phenylene vinylene) or poly(2,5-methoxy-1,4-phenylene vinylene) grafted organophosphazene copolymers were obtained. The UV-Vis absorption, photoluminescent, and thermal properties of the copolymers were measured. The copolymers are complete soluble in common organic solvents and fluoresce in the blue color range. The copolymers were used to build a series of organic light emitting diode (OLED). Only weak to nominated intensities with emission color from blue to red were obtained. The photoluminescent and electroluminescent (EL) spectra indicated there is a distribution in the PPV conjugated length. The compositions of the copolymers before and after the graft reaction were analyzed using NMR.