Modeling the heat transfer by conduction of nanocellular polymers with bimodal cellular structures

Nanocellular polymers are a new generation of materials with the potential of being used as very efficient thermal insulators. It has been proved experimentally that these materials present the Knudsen effect, which strongly reduces the conductivity of the gas phase. There are theoretical equations to predict the thermal conductivity due to this Knudsen effect, but all the models consider an average cell size. In this work, we propose a model to predict the thermal conductivity due to the conduction mechanisms of nanocellular materials with bimodal cellular structures, that is, with two populations of cells, micro and nanocellular. The novelty of our work is to consider not only the average cell size, but the cell size distribution. The predictions of the model are compared with the experimental conductivity of two real bimodal systems based on poly(methyl methacrylate) (PMMA), and it is proved that this new model provides more accurate estimations of the conductivity than the models that do not consider the bimodality. Furthermore, this model could be applied to monomodal nanocellular polymers. In particular, for monomodal materials presenting a wide cell size distribution and at low densities, the model predicts important variations in comparison with the current models in the literature. This result indicates that the cell size distribution must be included in the estimations of the thermal conductivity of nanocellular polymer

Low-density PMMA/MAM nanocellular polymers using low MAM contents: Production and characterization

Low-density nanocellular polymers are required to take advantage of the full potential of these materials as high efficient thermal insulators. However, their production is still a challenging task. One promising approach is the use of nanostructured polymer blends of poly(methyl methacrylate) (PMMA) and a block copolymer poly(methyl methacrylate)-poly(butyl acrylate)-poly(methyl methacrylate) (MAM), which are useful for promoting nucleation but seem to present a severe drawback, as apparently avoid low relative densities. In this work, new strategies to overcome this limitation and produce low-density nanocellular materials based on these blends are investigated. First, the effect of very low amounts of the MAM copolymer is analysed. It is detected that nanostructuration can be prevented using low copolymer contents, but nucleation is still enhanced as a result of the copolymer molecules with high CO2 affinity dispersed in the matrix, so nanocellular polymers are obtained using very low percentages of the copolymer. Second, the influence of the foaming temperature is studied. Results show that for systems in which there is not a clear nanostructuration, cells can grow more freely and smaller relative densities can be achieved. For these studies, blends of PMMA with MAM with copolymer contents from 10 wt% and as low as 0.1 wt% are used. For the first time, the production strategies proposed in this work have allowed obtaining low density (relative density 0.23) nanocellular polymers based on PMMA/MAM blends. Graphical abstrac

Understanding the role of MAM molecular weight in the production of PMMA/MAM nanocellular polymers

Nanostructured polymer blends with CO2-philic domains can be used to produce nanocellular materials with controlled nucleation. It is well known that this nanostructuration can be induced by the addition of a block copolymer poly(methyl methacrylate)-poly(butyl acrylate)-poly(methyl methacrylate) (MAM) to a poly(methyl methacrylate) (PMMA) matrix. However, the effect of the block copolymer molecular weight on the production of nanocellular materials is still unknown. In this work, this effect is analysed by using three types of MAM triblock copolymers with different molecular weights, and a fixed blend ratio of 90 wt% PMMA and 10 wt% of MAM. Blends were produced by extrusion. As a result of the extrusion process, a non-equilibrium nanostructuration takes place in the blends, and the micelle density increases as MAM molecular weight increases. Micelle formation is proposed to occur as result of two mechanisms: dispersion, controlled by the extrusion parameters and the relative viscosities of the polymers, and self-assembly of MAM molecules in the dispersed domains. On the other hand, in the nanocellular materials produced with these blends, cell size decreases from 200 to 120 nm as MAM molecular weight increases. Cell growth is suggested to be controlled by the intermicelle distance and limited by the cell wall thickness. Furthermore, a theoretical explanation of the mechanisms underlying the limited expansion of PMMA/MAM systems is proposed and discussed

Unveiling the shape of N-Acetylgalactosamine: A cancer-associated sugar derivative

Producción CientíficaIn the present work, we report the first rotational study of N-acetylgalactosamine, a cancer-associated sugar derivative, by means of high-resolution rotational spectroscopy. Two different conformers have been conclusively characterized using broadband Fourier transform microwave spectroscopy coupled with a laser ablation vaporization system. Additionally, we performed a comprehensive analysis of the intramolecular interactions that govern these structures, which allowed us to both characterize the existence of intramolecular hydrogen bond networks that drive the intrinsic conformation panorama of N-acetylgalactosamine and further rationalize the biological role of this aminosugar derivative as part of the Tn antigen.Ministerio de Ciencia, Innovación y Universidades (project PID2019-111396GB-I00)Junta de Castilla y León (project VA244P20)European Union’s Seventh Framework Programme (FP/2007-2013)/ERC-2013-SyG (grant 610256 NANOCOSMOS

Shape‐shifting molecules: unveiling the valence tautomerism phenomena in bare barbaralones

Producción CientíficaWe report a state-of-the-art spectroscopic study of an archetypical barbaralone, conclusively revealing the valence tautomerism phenomena for this bistable molecular system. The two distinct 1- and 5-substituted valence tautomers have been isolated in a supersonic expansion for the first time and successfully characterized by high-resolution rotational spectroscopy. This work provides irrefutable experimental evidence of the [3,3]-rearrangement in barbaralones and highlights the use of rotational spectroscopy to analyze shape-shifting mixtures. Moreover, this observation opens the window toward the characterization of new fluxional systems in the isolation conditions of the gas phase and should serve as a reference point in the general understanding of valence tautomerism.Ministerio de Ciencia e Innovación y Agencia Estatal de Investigación (grants MCIN/A EI/10.13039/ 501100011 033, PID2019-111396GB-I00, PID2019-104815GB-I00, CEX2019-000925-S)Junta de Castilla y Leon (projects VA077U16 and VA244P20)Agencia de Gestión de Ayudas Universitarias y de Investigación y el Programa CERCA/Generalitat de Catalunya de apoyo financiero (2017 SGR 1257)Ministerio de Ciencia, Innovación y Universidades (grant FPU17/02987

Formation of interstellar cyanoacetamide: a rotational and computational study

Producción CientíficaContext. Cyanoacetamide is a –CN bearing molecule that is also an amide derivative target molecule in the interstellar medium. Aims. The aim of our investigation is to analyze the feasibility of a plausible formation process of protonated cyanoacetamide under interstellar conditions and to provide direct experimental frequencies of the ground vibrational state of the neutral form in the microwave region in order to enable its eventual identification in the interstellar medium. Methods. We used high-level theoretical computations to study the formation process of protonated cyanoacetamide. Furthermore, we employed a high-resolution laser-ablation molecular beam Fourier transform spectroscopic technique to measure the frequencies of the neutral form. Results. We report the first rotational characterization of cyanoacetamide, and a precise set of the relevant rotational spectroscopic constants have been determined as a first step to identifying the molecule in the interstellar medium. We fully explored the potential energy surface to study a gas-phase reaction on the formation process of protonated cyanoacetamide. We found that an exothermic process with no net activation barrier is initiated by the high-energy isomer of protonated hydroxylamine, which leads to protonated cyanoacetamide.Ministerio de Ciencia, Innovación y Universidades (Project CTQ2016-76393-P)Ministerio de Economía, Industria y Competitividad (Grant AYA2017-87515-P)Junta de Castilla y León (Grants VA077U16 and Grant VA010G18)European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013)/ERC-2013- SyG, Grant Agreement no. 610 256 NANOCOSMO

Outer-shell photodetachment of the metastable Mg− [core]3s3p2 and Ca− [core]4s4p2 4Pe states

ABSTRACT: We report on calculated outer-shell photodetachment cross sections from the metastable (core)nsnp2 4Pe states in Mg− (n=3) and Ca− (n=4) negative ions in the photon energy range w=0–10 eV. Double-ionization thresholds for Mg II and Ca II as well as doubly excited thresholds of the residual atoms Mg I and Ca I are located within the photon energy range considered and thus doubly and triply excited states of both Mg− and Ca− are reached. We use a complex scaled configuration interaction (CSCI) method for the three active electrons supplemented with a sophisticated model potential as developed by Laughlin (Phys. Scr. 45, 238 (1992)) to account for core-valence interactions. The CI calculations are based on Mg+ and Ca+ one-electron orbitals expanded in terms of B-spline basis set. We compare our cross sections with the only calculation available up to a photon energy 0.25 Ry (w~3.4 eV) (Zeng et al., Phys. Rev. A 62, 022713(2000)) performed by using the R-matrix method, in which only one 4Po resonance for Mg− and two (4Po and 4Do) for Ca− were predicted. In this work, by analyzing both the cross sections and the locations of the S-matrix poles in the complex plane, we are able to predict six 4Po, four 4Do, and four 4So resonant states for Mg−, and three 4Po and two 4Do resonant states in Ca−

A journey across dopamine Metabolism: A rotational study of DOPAC

Producción CientíficaDOPAC, a relevant scaffold in dopamine metabolism, was probed in the gas phase and interrogated by high-resolution rotational spectroscopy. Herein, three distinct conformers were isolated in a supersonic jet and identified for the first time through an examination of the trend of the rotational constants and the dipole moment selection rules. Additionally, we examined the plausible relaxation pathways of the low-energy conformers of DOPAC, which helped us to claim the indirect detection of two additional conformers, providing conclusive experimental evidence of the flexible nature of this biomolecule. The current investigation sheds some light on the differences between jet-cooled rotational experiments and matrix-isolation infrared spectroscopy.Ministerio de Ciencia e Innovación (CTQ2016-76393-P and PID2019- 111396 GB-I00)Junta de Castilla y León (VA077U16 and VA244P20)European Research Council under the European Union’s Seventh Framework Programme (FP/2007- 2013)/ERC-2013-SyG, Grant Agreement n. 610256 NANOCOSMO

The nicotinic agonist cytisine: The role of the NH···N interaction

Producción CientíficaWe report a detailed structural study of cytisine, an alkaloid used to help with smoking cessation, looking forward to unveiling its role as a nicotinic agonist. High-resolution rotational spectroscopy has allowed us to characterize two different conformers exhibiting axial and equatorial arrangements of the piperidinic NH group. Unexpectedly, the axial form has been found as the predominant configuration, in contrast to that observed for related molecules, such as piperidine. This anomalous behavior has been justified in terms of an intramolecular NH···N hydrogen bond. Moreover, this interaction justifies the overstabilization of the axial conformer over the equatorial one and is crucial for the mechanism of action of cytisine over the nicotinic receptor, further rationalizing its behavior as a nicotinic agonist.Ministerio de Ciencia, Innovación y Universidades (project PID2019-111396GB-I00)Junta de Castilla y León (project VA244P20)European Research Council under the European Union’s Seventh Framework Programme (FP/2007- 2013)/ERC-2013-SyG (grant 610256 NANOCOSMOS

AIGORA: Repositorios abiertos y colaborativos para aprender a programar

Este artículo presenta la iniciativa desarrollada bajo el proyecto de innovación educativa AIGORA (Aprendizaje de Informática con GitHub Organizado en Repositorios Abiertos) para aprender a programar. El artículo explica cómo el uso de repositorios de software colaborativos y abiertos a través de la plataforma GitHub permite fomentar el aprendizaje entre estudiantes y el autoaprendizaje, facilitando además el desarrollo del trabajo por equipos y la evaluación de grupos numerosos. Además, se exponen los resultados alcanzados durante el primer año de su implantación en el curso 2018/2019 con estudiantes de los Grados de diferentes especialidades del área industrial en la Escuela Técnica Industrial de Ingeniería y Diseño Industrial