Photoconductivity studies on nanoporous TiO2/dopamine films prepared by sol–gel method

Dopamine was encapsulated into nanoporous amorphous TiO₂ matrix by sol–gel method under atmospheric conditions. A second sample was obtained by the addition of the crown-ether 15C5 in this previous sample. Thin films were spin-coated on glass wafers. No heat treatment was employed in both films. All films were characterized using infrared spectroscopy, high resolution transmission electronic microscopy, X-ray diffraction, optical absorption and scanning electronic microscopy. Despite the films prepared with 15C5 were no calcined, a partial crystallization was identified. Anatase and rutile nanoparticles with sizes of 4–5 nm were obtained. Photoconductivity technique was used to determine the charge transport mechanism on these films. Experimental data were fitted with straight lines at darkness and under illumination wavelengths at 320, 400, and 515 nm. It indicates an ohmic behavior. Photovoltaic and photoconductivity parameters were determined from the current density vs. the applied-electrical-field results. Amorphous film has bigger photovoltaic and photoconductive parameters than the partially crystalline film. Results observed in the present investigation prove that the nanoporous TiO₂ matrix can protect the dopamine inhibiting its chemical instability. This fact modifies the optical, physical and electrical properties of the film, and is intensified when 15C5 is added.     

High‐Performance UV Protective Waterborne Polymer Coatings Based on Hybrid Graphene/Carbon Nanotube Radicals Scavenging Filler

Ultraviolet (UV) degradation is one of the most important challenges of waterborne coatings in exterior applications. One of the ways to address this issue is addition of radical scavenging species within the polymer matrix. Herein, hybrids of graphene (G) and multiwall carbon nanotubes (CNTs) in different ratios are used as radical scavenging species. Evaluated by electron paramagnetic resonance spectroscopy, it is found that the hybrid made of G/CNTs in ratio of 10:1 efficiently captures and quenches the free radicals. The waterborne polymer composites containing 1 wt% of hybrid G/CNT are synthesized by in situ miniemulsion free radical polymerization using a water soluble initiator. However, due to excellent efficiency to capture free radicals, the polymerization performed using water soluble initiators in the presence of 10:1 G/CNT filler is hindered. This is resolved by physical separation of the free radicals and the scavenging materials within different phases by use of oil soluble initiator. The resulting polymer composites, beside having excellent mechanical resistance, present exceptional stability under accelerated aging conditions during 400 h, suppressing almost completely the UV photodegradation. This is attributed to the efficient radical scavenging of the G/CNTs hybrid filler distributed within polymer matrix, resulting in high‐performance UV protective waterborne composite coatings.     

A higher order numerical scheme for generalized fractional diffusion equations

In this article, we develop a higher order approximation for the generalized fractional derivative that includes a scale function z(t) and a weight function w(t). This is then used to solve a generalized fractional diffusion problem numerically. The stability and convergence analysis of the numerical scheme are conducted by the energy method. It is proven that the temporal convergence order is 3 and this is the best result to date. Finally, we present four examples to confirm the theoretical results.     

Synthesis of highly enantioenriched hydroxy- and dihydroxy-fatty esters: substrate precursors for cytochrome P450BioI

A series of highly enantioenriched hydroxy- and dihydroxy-fatty esters were required as part of our ongoing investigation into cytochrome P450_BioI. This mediates the biosynthesis of pimelic acid via C–C bond cleavage of long chain fatty acids within Bacillus subtilis. Herein we report the synthesis of various stereoisomers of methyl 7-hydroxytetradecanoate, methyl 8-hydroxytetradecanoate, and methyl 7,8-dihydroxytetradecanoate in highly enantioenriched form, using a combination of asymmetric synthesis and a preparative enantioselective HPLC is reported.     

Experimental assessment of effectively probed volume in confocal XRF spectrometry using microparticles

Current approaches for assessing a confocal micro-X-rayfluorescence–probing volume involve the use of sharp knife edges, thin films, or wires, which are moved through this volume. The fluorescence radiation excited in the material of the object is measured, and profiles are built to enable the determination of the full width at half maximum in any of the three axes of the excited volume. Such approaches do not provide information on the shape of the volume, and the consequent alignment of both used lenses is made based on the position of the maxima of the registered intensity measurements. The use of particles that are smaller than the interaction volume (isolated enough to prevent the influence of nearby particles) and translated through the interaction volume (3D scan) is presented as an alternative methodology to determine the confocal probing volume. Spherical shaped uranium particles with diameter of 1–3 μm originally produced for scanning electron microscopy analysis calibration purposes were used in this study. The results obtained showed that the effectively probed confocal volume has a distinct prolate spheroidal shape that is longer in the axis of the confocal detector than it is wide on the axes of the plane perpendicular to it. The diameter in the longest axis (tilted accordingly to the angle between the two silicon drift detectors) was found to be approximately 25 μm, whereas the shorter was found about 15 μm each, with a volume of about 3,000 μm³.     

New copolymers of a tautomerizable β‐ketonitrile monomer: Synthesis,characterization and solution tautomerism

The monomer 2‐methyl‐3‐oxo‐5‐phenyl‐4‐pentenonitrile (MOP) was prepared by reaction of ethyl cinnamate and propionitrile in alkaline mixture. This monomer exhibits three possible tautomeric forms. The tautomeric equilibria of MOP and its copolymers with styrene in different solvents were analyzed by ¹H NMR spectroscopy. The bulk and solution radical copolymerization initiated with azobisisobutyronitrile was carried out at 60 °C. The products were characterized by ¹H NMR, ¹³C NMR, HSQC NMR, HMBC NMR, and FTIR spectroscopies. The weight‐average molecular weight and polydispersity index were analyzed with size exclusion chromatography. The monomer reactivity ratios were obtained with the Fineman‐Ross method, obtaining a value of r₁r₂ = 0.286. MOP copolymer composition as well as the nature of the solvent significantly affected the tautomeric equilibrium. Regression analysis of the copolymer composition with solvatochromic parameters showed a good linear correlation, as quantitatively expressed by means of the linear solvation energy relationship using the empirical set of Kamlet‐Taft solvent parameters. This behavior could be attributed to polymer–polymer or polymer‐solvent interactions prevalent in solvents of different polarity, which are responsible for changes in macromolecular chain conformations, as confirmed by FTIR and viscometric studies. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012