Pilar Leret

Towards materials with enhanced electro-mechanical response: CaCu3Ti4O12-polydimethylsiloxane composites

We describe a straightforward production pathway of polymer matrix composites with increased dielectric constant for dielectric elastomer actuators (DEAs). Up to date, the approach of using composites made of high dielectric constant ceramics and insulating polymers has not evidenced any improvement in the performance of DEA devices, mainly as a consequence of the ferroelectric nature of the employed ceramics. We propose here an unexplored alternative to these traditional fillers, introducing calcium copper titanate (CCTO) CaCu3Ti4O12, which has a giant dielectric constant making it very suitable for capacitive applications. All CCTO–polydimethylsiloxane (PDMS) composites developed display an improved electro-mechanical performance. The largest actuation improvement was achieved for the composite with 5.1 vol% of CCTO, having an increment in the actuation strain of about 100% together with a reduction of 25% in the electric field compared to the raw PDMS matrix.

Nanostructured ZnO/sepiolite monolithic sorbents for H2S removal

ZnO presents favorable thermodynamics, equilibrium constant and stability for H2S chemisorption and sepiolite has excellent sorptive and rheological properties to be employed as a support. Four conformed ZnO/sepiolite composites are prepared, two by impregnation in zinc nitrate solution – one using activated carbon as a dispersing and pore generating agent – and two by dry mixing of the clay with dispersed or hierarchically assembled ZnO nanoparticles. The extrudates obtained with a mixture of sepiolite and nanodispersed ZnO particles are the most active for H2S chemisorption in temperature-programmed tests performed in an inert atmosphere, which can be correlated with the higher and homogeneous ZnO dispersion. ZnO sulfidation is reversible in the presence of O2. Thus, the activity can be regenerated, and these materials act as catalysts for H2S to SO2 oxidation in air.

Self-Forming 3D Core-Shell Ceramic Nanostructures for Halogen-Free Flame Retardant Materials.

The synthesis of aluminum phosphates-based composites has been widely studied during the past decade because of the promising industrial application of these materials. Here we show a simple one-pot heterogeneous precipitation approach to fabricate a sepiolite-phosphate (SepP) composite with adequate control of the size and dispersion of the phosphate nanoparticles. This coupling between aluminum phosphate and sepiolite nanofibers results in the development of a novel three-dimensional rigid supported phosphate structure, which is generated during the thermal treatment. According to our results, this phenomenon can be explained by a migration-coalescence mechanism of phosphate nanoparticles over the sepiolite support, assisted by a liquid phase. It is worth pointing out that this stimulant behavior observed here could have potential technological applications such as halogen-free flame retardant materials.

Influence of the pH and ageing time on the acid aluminum phosphate synthesized by precipitation

Acid aluminum phosphates have been obtained by precipitation in aqueous solution. The influence of two important synthesis parameters, pH and ageing time, has been studied and important differences in the final materials have been observed. All precipitated phosphates present acid character regardless of pH and ageing time. An increase of phosphate acidity, crystallinity and size is favored with decreasing pH. Moreover, at synthesis pH below 4.8, increase of these characteristics have been also observed with increasing ageing time. In addition, the growth mechanism of phosphate particles has been established as a mechanism based on aggregation of globular primary nanoparticles regardless of the size and morphology of the final powders.