Block Copolymer Composite Synthesis in a Mechanistic Approach

Carbon nanotubes-block copolymer composites were synthesized via reversible addition–fragmentation chain transfer living emulsion mechanism, based on zero–one and pseudo-bulk kinetics. In conjunction with multiwalled carbon nanotubes, ab initio reversible addition–fragmentation chain transfer homopolymerization of styrene and butyl acrylate, respectively, was carried out using xanthate-based reversible addition–fragmentation chain transfer agent through ultrasonified macroemulsion and miniemulsion. Then, the second and third monomer were applied at stage II and III, respectively, to produce multiwalled carbon nanotube diblock and triblock copolymer composites such as multiwalled carbon nanotube-b-poly(styrene)-co-polybutyl acrylate-co-polymethyl acrylate and multiwalled carbon nanotube-b-polybutyl acrylate-co-polymethyl acrylate-co-poly(styrene). As multiwalled carbon nanotube-homopolymer proceeds to diblock and triblock, thermal resistance of multiwalled carbon nanotube block composite products is enhanced. A mechanistic approach of reversible addition–fragmentation chain transfer living macroemulsion and miniemulsion polymerizations, with the purified multiwalled carbon nanotubes enables us to control the composite properties such as thermal degradation, mechanical strength, and glass transition temperature of multiwalled carbon nanotube-block copolymer composites, in conjunction with reaction conditions, monomer type, blocking sequence, particle size, and molecular weight.     

Recent Advances in Lipase-Mediated Preparation of Pharmaceuticals and Their Intermediates

Biocatalysis offers an alternative approach to conventional chemical processes for the production of single-isomer chiral drugs. Lipases are one of the most used enzymes in the synthesis of enantiomerically pure intermediates. The use of this type of enzyme is mainly due to the characteristics of their regio-, chemo- and enantioselectivity in the resolution process of racemates, without the use of cofactors. Moreover, this class of enzymes has generally excellent stability in the presence of organic solvents, facilitating the solubility of the organic substrate to be modified. Further improvements and new applications have been achieved in the syntheses of biologically active compounds catalyzed by lipases. This review critically reports and discusses examples from recent literature (2007 to mid-2015), concerning the synthesis of enantiomerically pure active pharmaceutical ingredients (APIs) and their intermediates in which the key step involves the action of a lipase.     

Composition-dependent xBa(Zr0.2Ti0.8)O3-(1-x)(Ba0.7Ca0.3)TiO3 bulk ceramics for high energy storage applications

This work reports the composition dependent microstructure, dielectric, ferroelectric and energy storage properties, and the phase transitions sequence of lead free xBa(Zr_0.2Ti_0.8)O₃-(1-x)(Ba_0.7Ca_0.3)TiO₃ [xBZT-(1-x)BCT] ceramics, with x?=?0.4, 0.5 and 0.6, prepared by solid state reaction method. The XRD and Raman scattering results confirm the coexistence of rhombohedral and tetragonal phases at room temperature (RT). The temperature dependence of Raman scattering spectra, dielectric permittivity and polarization points a first phase transition from ferroelectric rhombohedral phase to ferroelectric tetragonal phase at a temperature (T_R-T) of 40?°C and a second phase transition from ferroelectric tetragonal phase - paraelectric pseudocubic phase at a temperature (T_T-C) of 110?°C. The dielectric analysis suggests that the phase transition at T_T-C is of diffusive type and the BZT-BCT ceramics are a relaxor type ferroelectric materials. The composition induced variation in the temperature dependence of dielectric losses was correlated with full width half maxima (FWHM) of A₁, E(LO) Raman mode. The saturation polarization (P_s) ≈8.3?μC/cm² and coercive fields ≈2.9?kV/cm were found to be optimum at composition x?=?0.6 and is attributed to grain size effect. It is also shown that BZT-BCT ceramics exhibit a fatigue free response up to 10⁵ cycles. The effect of a.c. electric field amplitude and temperature on energy storage density and storage efficiency is also discussed. The presence of high T_T-C (110?°C), a high dielectric constant (ε_r ≈?12,285) with low dielectric loss (0.03), good polarization (P_s ≈?8.3?μC/cm²) and large recoverable energy density (W?=?121?mJ/cm³) with an energy storage efficiency (η) of 70% at an electric field of 25?kV/cm in 0.6BZT-0.4BCT ceramics make them suitable candidates for energy storage capacitor applications.     

High surface area LaNiO<Subscript>3</Subscript> electrodes for oxygen electrocatalysis in alkaline media

LaNiO₃ coatings on nickel-foam supports were prepared by brush painting. The electrochemical properties were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Comparative studies were performed with LaNiO₃-pelleted electrodes. The roughness factors were determined by CV and found to be 5,208 ± 350 and 4,037 ± 250 for the pelleted and coated electrodes, respectively. EIS measurements confirm the results obtained by CV. Values lower than 0.3 were calculated for the morphology factors for both electrodes, indicating low electrochemical porosity. The experimental method used in this work to synthesise the oxide coupled with the use of Ni foam as support has proved to be very effective in producing oxide electrodes with surface areas higher than those referred to in relevant literature.     

New insights into the functionalization of multi-walled carbon nanotubes with aniline derivatives

Multi-walled carbon nanotubes (MWCNT) were functionalized with a variety of chemical groups by reaction of p-substituted anilines (R–Ph–NH₂) in the presence and absence of isopentyl nitrite used for the in situ generation of diazonium species. All materials were characterized by X-ray photoelectron spectroscopy, thermogravimetry and infrared spectroscopy.In the presence of isopentyl nitrite, the extent of functionalization was high and nearly independent on the amount of isopentyl nitrite and on the aniline substituents (R = F, Cl, I, NH₂, NO₂, OH, COOH, COOEt and Et). Unexpectedly, the functionalization of MWCNT with anilines bearing electron withdrawing groups was also observed in the absence of isopentyl nitrite. In the case of OH–Ph–NH₂, the reaction leads to MWCNT with the highest degree of functionalization and this can be considered as a new and efficient methodology for CNT functionalization with phenol groups. The overall reaction mechanism is discussed for both reaction conditions: confirmation of a radical chain mechanism was obtained for the reaction performed in the presence of isopentyl nitrite, while the formation of stabilized dipolar intermediate species seems to be involved in the absence of isopentyl nitrite. The materials with the highest degree of functionalization showed very good dispersions in acetonitrile even after 1 month.     

Microencapsulation of cashew apple (Anacardium occidentale,L.) juice using a new chitosan–commercial bovine whey protein isolate system in spray drying

The aim of this work was to obtain a new stable food product from cashew apple juice encapsulated by spray-drying technique using chitosan–whey protein isolate systems. The materials were evaluated according to their physicochemical stability during storage at different conditions and characterized with respect to their particle size distribution and structure. Encapsulated commercial and natural juices showed homogenous and unimodal particle size distribution with diameters ranging from 0.2 to 5.0 μm and from 0.2 to 40.0 μm, respectively. Both juices demonstrated higher physicochemical stability for vitamin C and color measurements than their respective non-encapsulated juices. X-ray diffractograms evidenced that the powder juices after the 140th day of storage were still in amorphous state. These results indicate that the new product was effective in protecting sensitive compounds present in the food matrix and it was also able to remain stable throughout the study period.     

Development of a new ion-imprinted polymer (IIP) with Cd2+ ions based on divinylbenzene copolymers containing amidoxime groups

Polymer Bulletin - In this study, we synthesized a new ion-imprinted polymer (IIP) based on introduction of amidoxime groups in acrylonitrile, complexation with Cd2+ ions and polymerization with...     

Resistance variation of conductive ink applied by the screen printing technique on different substrates

This research study focuses on the application of conductive ink by the screen printing technique to evaluate the potential of creating printed electrodes and to investigate the effect of washing upon electrical resistance and flexibility. Two conductive inks were applied by a conventional screen printing method on four different textile substrates, 100% cotton, 50%/50% cotton/polyester, 100% polyester and 100% polyamide. The inks were also applied on a multifibre fabric. Atmospheric plasma treatment was applied to improve the adhesion to the samples, and the resistance values were compared with those of non‐treated samples. The values were measured before and after cleaning and washing tests, which were performed to simulate domestic treatment for garments to predict the behaviour of the inks after normal usage of the fabrics. Comfort properties like stiffness of the fabrics were also evaluated after five and 10 washing cycles. It was observed that PE 825 ink forms a thicker film on the fabric surface, contributing to the loss of flexibility of the textile. However, PE 825 ink also produced the best results in terms of durability and lower values of resistance. Polyamide fabrics lost their conductive property after five washing cycles due to weak bonding between the ink and the fibres, whereas cotton fibres provided the best results.