Step-type and step-density influences on CO adsorption probed by reflection absorption infrared spectroscopy using a curved Pt(1 1 1) surface

In comparison to flat single crystals, the continuous variation of structure provided by curved crystals offers many benefits for the study of physical and chemical processes at surfaces. However, the curvature of the surface also creates experimental challenges. For infrared spectroscopy, in particular, adsorbates on metal samples are typically probed by grazing-incidence reflection-absorption infrared spectroscopy (RAIRS). In this geometry, a convex crystal acts as a strongly diverging mirror. The authors describe how the experimental difficulties introduced by a cylindrical surface can be resolved for RAIRS. A complementary mirror, placed directly downfield of the curved crystal within the vacuum chamber, minimizes the divergence created by the sample. By simply translating the infrared focus across the sample, the authors probe adsorbate vibrational spectra as a function of local step-type and step-density with high sensitivity and spatial resolution. Time-consuming sample exchange, and the concomitant sample-to-sample experimental errors, are eliminated. The authors apply this new technique to carbon monoxide adsorption on a curved Pt(1 1 1) crystal and use it to resolve the influence of step-type and step-density on the CO stretch vibration as a function of coverage.</p

In Situ Compatibilization of Biopolymer Ternary Blends by Reactive Extrusion with Low-Functionality Epoxy-Based Styrene Acrylic Oligomer

[EN] The present study reports on the use of low-functionality epoxy-based styrene¿acrylic oligomer (ESAO) to compatibilize immiscible ternary blends made of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), polylactide (PLA), and poly(butylene adipate-co-terephthalate) (PBAT). The addition during melt processing of low-functionality ESAO at two parts per hundred resin (phr) of biopolymer successfully changed the soften inclusion phase in the blend system to a thinner morphology, yielding biopolymer ternary blends with higher mechanical ductility and also improved oxygen barrier performance. The compatibilization achieved was ascribed to the in situ formation of a newly block terpolymer, i.e. PHBVb- PLA-b-PBAT, which was produced at the blend interface by the reaction of the multiple epoxy groups present in ESAO with the functional terminal groups of the biopolymers. This chemical reaction was mainly linear due to the inherently low functionality of ESAO and the more favorable reactivity of the epoxy groups with the carboxyl groups of the biopolymers, which avoided the formation of highly branched and/or cross-linked structures and thus facilitated the films processability. Therefore, the reactive blending of biopolymers at different mixing ratios with low-functionality ESAO represents a straightforward methodology to prepare sustainable plastics at industrial scale with different physical properties that can be of interest in, for instance, food packaging applications.This research was funded by the EU H2020 project YPACK (Reference number 773872) and by the Spanish Ministry of Science, Innovation, and Universities (MICIU) with project numbers MAT2017-84909-C2-2-R and AGL2015-63855-C2-1-R. L. Quiles-Carrillo wants to thank the Spanish Ministry of Education, Culture, and Sports (MECD) for financial support through his FPU Grant Number FPU15/03812. Torres-Giner also acknowledges the MICIU for his Juan de la Cierva contract (IJCI-2016-29675).Quiles-Carrillo, L.; Montanes, N.; Lagaron, J.; Balart, R.; Torres-Giner, S. (2019). In Situ Compatibilization of Biopolymer Ternary Blends by Reactive Extrusion with Low-Functionality Epoxy-Based Styrene Acrylic Oligomer. 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4D Numerical Analysis of Scaffolds: A New Approach

A large range of biodegradable polymers are used to produce scaffoldsfor tissue engineering, which temporarily replace the biomechanical functions ofa biologic tissue while it progressively regenerates its capacities. However, the mechanicalbehavior of biodegradable materials during its degradation, which is an importantaspect of the scaffold design, is still an unexplored subject. For a biodegradablescaffold, performance will decrease along its degradation, ideally in accordanceto the regeneration of the biologic tissue, avoiding the stress shielding effect or thepremature rupture. In this chapter, a new numerical approach to predict the mechanicalbehavior of complex 3D scaffolds during degradation time (the 4th dimension)is presented. The degradation of mechanical properties should ideally be compatibleto the tissue regeneration. With this new approach, an iterative process of optimizationis possible to achieve an ideal solution in terms of mechanical behavior anddegradation time. The scaffold can therefore be pre-validated in terms of functionalcompatibility. An example of application of this approach is demonstrated at the endof this chapter

CO2 adsorption and dissociation on kinked Cu surfaces at (near-)ambient pressure

Resumen del trabajo presentado al Symposium on Surface Science (3S), celebrado en St. Christoph am Arlberg (Austria) del 13 al 19 de marzo de 2022.Peer reviewe

Site-specific CO2 adsorption and surface oxidation of Cu catalysts at near-ambient pressure

Resumen del trabajo presentado al 9th Annual Ambient Pressure X-ray Photoelectron Spectroscopy Workhop, celebrado en Switzerland del 6 al 9 de diciembre de 2022.Peer reviewe

Site-specific reactivity of molecules with surface defects - the case of H2 dissociation on Pt

The classic system that describes weakly activated dissociation in heterogeneous catalysis has been explained by two dynamical models that are fundamentally at odds. Whereas one model for hydrogen dissociation on platinum(111) invokes a preequilibrium and diffusion toward defects, the other is based on direct and local reaction. We resolve this dispute by quantifying site-specific reactivity using a curved platinum single-crystal surface. Reactivity is step-type dependent and varies linearly with step density. Only the model that relies on localized dissociation is consistent with our results. Our approach provides absolute, site-specific reaction cross sections