Structural reorganization of cylindrical nanoparticles triggered by polylactide stereocomplexation

YesCo-crystallization of polymers with different configurations/tacticities provides access to materials with enhanced performance. The stereocomplexation of isotactic poly(L-lactide) and poly(D-lactide) has led to improved properties compared with each homochiral material. Herein, we report the preparation of stereocomplex micelles from a mixture of poly(L-lactide)-b-poly(acrylic acid) and poly(D-lactide)-b-poly(acrylic acid) diblock copolymers in water via crystallization-driven self-assembly. During the formation of these stereocomplex micelles, an unexpected morphological transition results in the formation of dense crystalline spherical micelles rather than cylinders. Furthermore, mixture of cylinders with opposite homochirality in either THF/H2O mixtures or in pure water at 65 °C leads to disassembly into stereocomplexed spherical micelles. Similarly, a transition is also observed in a related PEO-b-PLLA/PEO-b-PDLA system, demonstrating wider applicability. This new mechanism for morphological reorganization, through competitive crystallization and stereocomplexation and without the requirement for an external stimulus, allows for new opportunities in controlled release and delivery applications.University of Warwick, Swiss National Science Foundation and the EPSRC. The Royal Society - an Industry Fellowship to A.P.D. The Engineering and Physical Sciences Research Council (EP/G004897/1) - funding to support postdoctoral fellowships for A.P.B. as well as funding for J.S. and M.A.D. through the Warwick Centre for Analytical Science (EP/F034210/1). The Science City Research Alliance and the HEFCE Strategic Development Fund - funding support. Some items of equipment that were used in this research were funded by Birmingham Science City, with support from Advantage West Midlands and part-funded by the European Regional Development Fund

Crosslinking of poly(vinylene fluoride) separators by gamma-irradiation for electrochemical high power charge applications

Macroporous poly(vinylene fluoride) (PVdF) separators were prepared by phase inversion method and introduced to a gamma (γ) radiation with and without cross-linking agents. Triallyl isocyanurate (TAIC) and a macromonomer of ethylene oxide- propylene oxide (MEP) were used as a cross-linking agent. The resulting membranes were characterized in terms of thermal and mechanical properties. Ionic conductivities were determined in a molar solution of tetraethylammonium tetrafluoroborate (TEABF4) in acetonitrile (AN) and propylene carbonate (PC). Excellent mechanical properties (250 MPa at 25 °C) and conductivities (14 mS cm−1) were obtained for the cross-linked separator prepared with TAIC

Characterization of thermal barrier coatings with a gradient in porosity

A major problem in thermal barrier coatings (TBC) applied to gas turbine components is the spallation of ceramic coating under thermal cycling processes. In order to prevent spallation and improve the thermomechanical behaviour of the TBC, graded ceramic coatings can be produced. For this purpose we are developing a new concept of Thermal Barrier Coating (TBC) that consist of a conventional NiCoCrAlY bond coat and an atmospheric plasma sprayed ZrO2-8 Wt.%Y2O3 top coat graded in porosity on an Inconel 738 LC substrates. The aim of this work is to produce coatings with low thermal conductivity and better thermomechanical behaviour due to the gradient in porosity which reflects a gradient in the elastic properties. Absolute porosity was measured with a mercury porosimetry and by image analysis. The second technique was also used to estimate the porosity variation along the cross-section. Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) were used to observe the morphology and coating microstructure. The microhardness was measured with a Vickers indenter and 0.981 N load. The microhardness has been evaluated for coatings in as-sprayed condition and after annealing at 1100 degrees C during 100 h. The results show a fast increase of the hardness after annealing. After thermal shock heating at 1000 degrees C, 1 h and quickly cooling in water no spallation was observed for 100 cycles. (c) 2004 Published by Elsevier B.V

Residual stresses and elastic modulus of thermal barrier coatings graded in porosity

Zirconia (ZrO2) stabilized with 8 wt.% Y2O3 is the most common material to be applied in thermal barrier coatings (TBC) owing to its excellent properties: low thermal conductivity; high toughness and thermal expansion coefficient similar to iron. Nevertheless, in order to increase the coatings lifetime, improvements in their thermomechanical behavior are still needed. With that purpose, we propose in this paper a graded ceramic coating. These TBC have been produced by depositing a conventional NiCoCrAlY bond coat on a Inconel 738 LC substrate followed by an atmospheric plasma sprayed top coat of ZrO2–8wt.%Y2O3 with a porosity gradient along the cross section. The aim of the present contribution is to study residual stresses and elastic properties of the coating as a function of the porosity gradient. For the characterization of the TBCs residual stresses, we have used Raman and X-ray diffraction (XRD) in different thermal conditions: as sprayed, after thermal shock at 1000 8C, and annealing at 1100 8C in air during 100 h. The top coatings show compressive stresses near the interface with the bond coat. A decrease of the stress level is observed along the cross section towards the surface. The residual stresses increase after annealing, however, have smaller variations after thermal shock. The elastic properties were evaluated by Brillouin scattering: the scattering of laser light by acoustic waves in the GHz frequency range. The spectra at different depths indicate that in the annealed condition the acoustic velocity increases when approaching the external surface