Shear induced crystallization of poly(m-xylylene adipamide) with and without nucleating additives

The shear induced crystallization of the poly(m-xylylene adipamide) (MXD6) which is a semi-aromatic polyamide, was studied for a virgin (PA1) and a nucleated (PA2) grades using a shearing hot stage coupled with a microscope. Half crystallization times were measured according to the crystallization conditions (crystallization temperature, shear rate and shearing time). The effect of shear on the crystallization kinetics was shown by a strong decrease of the crystallization times for both materials. PA2 sensitivity to shear was much lower than that of PA1. This was attributed to the presence of nucleating agents which increased the primary nucleation density in the unsheared quiescent melt, leading to a higher necessary shear rate to overcome the quiescent nucleation. Kinetic models were proposed to predict the crystallization process as a function of the crystallization conditions. They were based on both Avrami and Hoffman-Lauritzen theories and modified to take into account the effect of shear. In the model the nucleation rate of the crystalline entities was related to the shear rate by a power function. Besides, crystalline morphology and orientation were studied by wide and small angle X-ray scattering to confirm the orientation effect of the shear in the crystalline part of the material.     

Spin-torque oscillator using a perpendicular polarizer and a planar free layer

Spintronics materials have recently been considered for radio-frequency devices such as oscillators by exploiting the transfer of spin angular momentum between a spin-polarized electrical current and the magnetic nanostructure it passes through. While previous spin-transfer oscillators (STOs) were based on in-plane magnetized structures, here we present the realization of an STO that contains a perpendicular spin current polarizer combined with an in-plane magnetized free layer. This device is characterized by high-frequency oscillations of the free-layer magnetization, consistent with out-of-plane steady-state precessions induced at the threshold current by a spin-transfer torque from perpendicularly polarized electrons. The results are summarized in static and dynamic current-field state diagrams and will be of importance for the design of STOs with enhanced output signals.     

Diphosphines of dppf‐Type Incorporating Electron‐Withdrawing Furyl Moieties Substantially Improve the Palladium‐Catalysed Amination of Allyl Acetates

Highly active Pd/diphosphine catalytic systems incorporating new, air‐stable ferrocenyl‐furylphosphines allow nucleophilic allylic amination at room temperature with unprecedented turnover frequencies. For instance, in the presence of 0.01 mol % catalyst the coupling of aniline to allyl acetate occurs at a TOF of more than 10,000 h⁻¹; even the addition of the less nucleophile morpholine to allyl acetate is observed with a TOF of 4250 h⁻¹. The amination of the sterically demanding geranyl acetate, a monoterpene derivative of interest in the flavour industry, at low catalyst loadings demonstrates the scope of this methodology, which provides in addition noticeable advantages in terms of economical (resource‐ and energy‐saving) and sustainable chemistry (high selectivity, no additive, low metal content, and thus easier purification).     

Low temperature solid oxide fuel cells with pulsed laser deposited bi-layer electrolyte

Solid oxide fuel cells (SOFC) using a pulsed laser deposited bi-layer electrolyte have been successfully fabricated and have shown very good performance at low operating temperatures. The cell reaches power densities of 0.5 W cm⁻² at 550 °C and 0.9 W cm⁻² at 600 °C, with open circuit voltage (OCV) values larger than 1.04 V. The bi-layer electrolyte contains a 6–7 μm thick samarium-doped ceria (SDC) layer deposited over a ∼1 μm thick scandium-stabilized zirconia (ScSZ) layer. The electrical leaking between the anode and cathode through the SDC electrolyte, which due to the reduction of Ce⁴⁺ to Ce³⁺ in reducing environment when using a single layer SDC electrolyte, has been eliminated by adopting the bi-layer electrolyte concept. Both ScSZ and SDC layers in the bi-layer electrolyte prepared by the pulsed laser deposition (PLD) technique are the highly conductive cubic phases. Poor conductive (Zr, Ce)O₂-based solid solutions or β-phase ScSZ were not found in the bi-layer electrolyte prepared by the PLD due to low processing temperatures of the technique. Excellent reliability and flexibility of the PLD technique makes it a very promising technique for the fabrication of thin electrolyte layer for SOFCs operating at reduced temperatures.     

Synthesis and characterization of new proton exchange membrane deriving from sulfonated polyether sulfone using ionic crosslinking for electrodialysis applications

In this research work, the synthesis and characterization of new ion exchange membranes made from sulfonated polyether sulfone (S PES) crosslinked by aminated PES (NH2 PES) crosslinking reagent have been investigated for electrodialysis (ED) applications. Sulfonated and aminated PES have similar chemical structures that allow a good compatibility, the only difference between them is their functional groups. This membrane (called HNH2) has been obtained by reaction between S PES with 1.3 SO₃H groups per monomer unit and the calculated equivalent amount of NH2 PES. Three HNH2 membranes have been fabricated with different degrees of sulfonation. The HNH2 membranes properties have been evaluated using different characterization analysis. The results have shown that HNH2 membranes appear to be very promising candidates for electrochemical applications.     

Crystallization behavior of poly(lactide)/poly(β‐hydroxybutyrate)/talc composites

The morphology and miscibility of commercial poly(lactide) (PLA)/poly(β‐hydroxybutyrate) (PHB, from 5 to 20 wt %) blends prepared by melt extrusion method, were investigated using differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) observations. The results show that for all the studied blend contents, PLA/PHB blends are immiscible. The effects of PHB and talc on the nonisothermal cold crystallization kinetics of PLA were examined using a differential scanning calorimetry (DSC) at different heating rates. PHB acted as a nucleating agent on PLA and the addition of talc to the blend yielded further improvement, since significant increase in the enthalpy peak was observed for samples containing 10 wt % PHB and talc (from 0.5 to 5 phr). The crystallization kinetics were then examined using the Avrami–Jeziorny and Liu–Mo approach. The simultaneous presence of PHB and talc induced a decrease of the crystallization half time. The evolution of activation energies determined with Kissinger's equation suggests that blending with PHB and incorporating talc promote nonisothermal cold crystallization of PLA. The synergistic nucleating effect of PHB and talc was also observed on isothermal crystallization of PLA from the melt. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Public hearings in environmental and social impact assessment for energy sector projects in Cameroon

In Cameroon, like in other countries, public hearings are the most common method of citizen involvement mentioned in Environmental and Social Impact Assessment (ESIA). To elicit various attributes of current practice and characteristics of these public hearings in Cameroon, with focus on access, process and outcomes, we used an interpretive approach. This research unveiled an array of problems, including shortcomings in public hearing practice, law and regulatory framework, limited access to information, and inconvenient location of reading rooms (depositories). Public hearings do take place in depositories but they do not provide participants with the opportunity for direct debate and consensus-building. This research demonstrated that, local economic stakes tend to take precedence over critical questioning during public hearing events. However, public hearings in Cameroon attest to the growing willingness to challenge ESIA reports that may be fully backed by the government. In order for public hearings to be worthwhile events in Cameroon, there is need to build credibility and mutual trust among stakeholders.