Advanced optical microscopies for materials: new trends

Podeu consultar el llibre complet a: http://hdl.handle.net/2445/32166This article summarizes the new trends of Optical Microscopy applied to Materials, with examples of applications that illustrate the capabilities of the technique

Nanomechanics of Langmuir-Blodgett films

La caracterització topogràfica i nanomecànica de pel·lícules moleculars és important degut al creixent interès que aquestes desperten, tant des del punt de vista científic com tecnològic. Com a cas particular tenim les pel·lícules Langmuir i Langmuir- Blodgett (LB), les quals permeten el control de l'àrea per molècula i per tant de la nanoestructura de la mostra. Les pel·lícules Langmuir poden caracteritzar-se en la interfase aire-aigua mitjançant les isotermes de pressió superficial-àrea i amb el Microscopi d'Angle de Brewster (BAM). Les mesures de pressió superficial proporcionen informació global de la pel·lícula mentre que el BAM proporciona imatges òptiques d'àrees de dimensions mil·limètriques amb resolució lateral a escala micromètrica. Les pel·lícules Langmuir poden ser transferides a un substrat pla (pel·lícules LB) i poden estudiar-se a escala nanomètrica mitjançant les Microscopies de Sonda Local (SPMs). Entre elles, la Microscòpia de Forces Atòmiques proporciona imatges topogràfiques, mentre que la Microscòpia de Forces Laterals i l'Espectroscòpia de Forces proporcionen informació sobre les propietats nanotribològiques i nanomecàniques de les pel·lícules. En aplicar aquestes tècniques a l'estudi de pel· lícules mixtes, proporcionen informació sobre miscibilitat, separació de fases, estructura de dominis i propietats mecàniques. Degut a la possibilitat de controlar la pressió superficial de la pel·lícula, es pot correlacionar aquest valor amb l'estructura i el comportament nanomecànic de les capes.The topographical and nanomechanical characterization of molecular films is an important issue due to the increasing interest in this kind of 2-dimensional structure, both from a scientific and technological point of view. In particular, Langmuir and Langmuir-Blodgett (LB) films have been widely studied as it is possible to control the area per molecule in the layer, with the consequent control over the sample nanostructure. Langmuir films can be characterized at the air-water interphase by using surface pressure-area isotherms and Brewster Angle Microscopy (BAM). Surface pressure measurements provide information on the films as a whole and BAM provides optical images of areas in the millimetric range with lateral resolution on the micrometric scale. Langmuir films can be transferred onto an atomically flat substrate and the transferred films (LB films) can be studied in the nanometric range using Scanning Probe Microscopies (SPMs). Of these, Atomic Force Microscopy provides topographical information, while Lateral Force Microscopy and Force Spectroscopy provide information about the nanotribological and nanomechanical properties of the films. These techniques, when applied to the study of mixed films, provide information about miscibility, phase separation, domain structure and mechanical properties. In this respect, SPMs can provide information at a nanometric level that it is not available using BAM. Thanks to the possibility of controlling the film surface pressure, correlation between sample nanostructure and nanomechanics can be established

Competency-based learning and relaxation techniques: an interdisciplinary approach

This project focuses on the possibility of integrating yoga and relaxation techniques in the new competency-based paradigms that will unfold in Catalonia during the years to come. To do so, this project engages theory and practice so as to assess the feasibility and application of the proposed techniques in a real high school environment. It must be clearly stated that the proposed practices are completely disconnected from religion, dogma or cultural Asian background; the present proposal, then, points out to detect and apply breathing and relaxation techniques that have been widely used both in western and Asian cultures in the form of mind-centering practices. To tackle with this goal, the present project deals with three different approaches with the main objective of providing the reader with an objective perspective regarding the possibility of applying relaxation techniques to the daily routine of Catalan high schools: -Yoga and relaxation to improve the classroom management. -Teachers and students in danger: the snowball effect unleashed by stress. Competency-based learning and relaxation/yoga techniques: a promising future together

Primordial black holes capture by stars and induced collapse to low-mass stellar black holes

Primordial black holes in the asteroid-mass window, which might constitute all the dark matter, can be captured by stars when they traverse them at low enough velocity. After being placed on a bound orbit during star formation, they can repeatedly cross the star if the orbit happens to be highly eccentric, slow down by dynamical friction and end up in the stellar core. The rate of these captures is highest in halos of high dark matter density and low velocity dispersion, when the first stars form at redshift ∼ 20. We compute this capture rate for low-metallicity stars of 0.3 to 1 M, and find that a high fraction of these stars formed in the first dwarf galaxies would capture a primordial black hole, which would then grow by accretion up to a mass that may be close to the total star mass. We show the capture rate of primordial black holes does not depend on their mass over this asteroid-mass window, and should not be much affected by external tidal perturbations. These low-mass stellar black holes could be discovered today in low-metallicity, old binary systems in the Milky Way containing a surviving low-mass mainsequence star or a white dwarf, or via gravitational waves emitted in a merger with another compact object. No mechanisms in standard stellar evolution theory are known to form black holes below the Chandrasekhar mass, so detecting a low-mass black hole would fundamentally impact our understanding of stellar evolution, dark matter and the early Universe.We would like to acknowledge helpful discussions and advice fromN. Bellomo, J. L. Bernal, A. Escrivà, C. Germani, and J. Sal-vadó. This work was supported in part by Spanish grants CEX-2019-000918-M funded by MCIN/AEI/10.13039/501100011033,AYA2015-71091-P, and PID2019-108122GB-C32.Peer ReviewedPostprint (author's final draft

Physico-chemical and mechanical properties of microencapsulated phase change material

Microencapsulated phase change materials (MPCM) are well known in advanced technologies for the utilization in active and passive systems, which have the capacity to absorb and slowly release the latent heat involved in a phase change process. Microcapsules consist of little containers, which are made of polymer on the outside, and paraffin wax as PCM in the inside. The use of microencapsulated PCM has many advantages as microcapsules can handle phase change materials as core allowing the preparation of slurries. However there are some concerns about cycling of MPCM slurries because of the breakage of microcapsules during charging/discharging and the subsequent loss of effectiveness. This phenomenon motivates the study of the mechanical response when a force is applied to the microcapsule. The maximum force that Micronal® DS 5001 can afford before breaking was determined by Atomic Force Microscopy (AFM). To simulate real conditions in service, assays were done at different temperatures: with the PCM in solid state at 25 °C, and with the PCM melted at 45 °C and 80 °C. To better understand the behavior of these materials, Micronal® DS 5001 microcapsules were characterized using different physic-chemical techniques. Microcapsules Fourier Transform Infrared Spectroscopy (FT-IR) results showed the main vibrations corresponding to acrylic groups of the outside polymer. Thermal stability was studied by Thermogravimetrical Analysis (TGA), and X-ray Fluorescence (XRF) was used to characterize the resulting inorganic residue. The thermal properties were determined using Differential Scanning Calorimetry (DSC) curves. Particles morphology was studied with Scanning Electron Microscopy (SEM) and Mie method was used to evaluate the particle size distribution. Samples had a bimodal distribution of size and were formed by two different particles sizes: agglomerates of 150 μm diameter formed by small particles of 6 μm. Atomic Force Microscopy in nanoindentation mode was used to evaluate the elastic response of the particles at different temperatures. Different values of effective modulus Eeff were calculated for agglomerates and small particles. It was observed that stiffness depended on the temperature assay and particle size, as agglomerates showed higher stiffness than small particles, which showed an important decrease in elastic properties at 80 °C

Structure vs. properties chirality, optics and shapes in amphiphilic porphyrin J-aggregates

The structure of the meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS4) J-aggregates could be determined by X-ray and electron diffraction methods. A sheet-like architecture reveals the relationship between structure and chirality, optics and shapes of the J-aggregate of the meso 4-sulfonatophenyl- and phenyl- substituted porphyrins. The structure of the J-aggregates of H4TPPS4 belongs to the chiral space group P21 and includes four porphyrin molecules in its unit cell. The intermolecular stabilization of the zwitterionic units by hydrogen bonding and electrostatic interactions between the positively charged central NH groups and the periphery anionic sulfonato groups results in a structure of porphyrins sheets along the [ ] plane direction. The structure of the sheet on the [ ] plane is already chiral and its molecular architecture explains the simultaneous presence of H- and J-aggregate bands in their absorption spectra. This structure also accounts for the high similarity observed between the absorption spectra of different mesophorms of the same substance and even between different members of the series of meso-4-sulfonatophenyl-and-aryl substituted diprotonated porphyrins. The possibility, or not, of the sheet-like structure on [ ] to interact with other layers, either through ionic or hydrophobic interactions, depends on the substitution pattern at the meso-positions of the porphyrin ring. Thus, the different morphologies of the particles [mono- bi- and multilayered] of this series of J-aggregates are explained taking into account the role that the fourth meso-subtituent plays in the interlayer stabilization. The results suggest that supramolecular helicity, previously detected in several J-aggregates, is not the explanation of their chirality but would be the expression of the intrinsic chirality of the packing between building blocks

Nanomechanics of Organic Layers and Biomenbranes

[eng] The main objective of this work was to quantitatively measure the nanotribological properties or organic layers and rationalize them from a physicochemical point of view. To accomplish that, a wide array of samples was selected, ranging from technological coatings as alkanethiols to biological coatings as phospholipid bilayers, which can be used to functionalize miniaturized electromechanical systems. Although the studied molecules are different in nature and functionality, the intermolecular forces that determine the layers structure are the same: van der Waals, electrostatic and water-related interactions. We are interested in quantifying these interactions as a function of the intermolecular distances, the nature of the medium the molecules are immersed in (liquid or air) and also assess external factors that have specific effects on the samples. These external factors were overall tested in biological membranes (phospholipid bilayers), where temperature and the presence of ions play a decisive role in their structure. In order to achieve our objectives, two experimental techniques were mainly used. The first one is the Lateral Force Microscopy, which was implemented in our lab during the execution of this project. As the nature of the measurements we wanted to perform was quantitative, it was also necessary to implement the methods to calibrate Atomic Force Microscopy probes both vertically and laterally. Besides, as we wanted to test the biological samples in liquid environment, a new methodology to perform Lateral Force Microscopy measurements in liquid had to be implemented. The second main technique is Force Spectroscopy, which was used to complement the nanomechanical information obtained from the friction measurements and that gave us a more detailed picture of the mechanical response of layers. Our technical goal was to obtain fast, reproducible and consistent Force Spectroscopy results, fact that implied the development of a dedicated software routine and the systematic control of the probes shape.[spa] En esta tesis se han usado varias técnicas nanométricas con el objetivo de estudiar diversas monocapas orgánicas. El tipo de superficies estudiadas se puede clasificar en dos tipos; Primeramente, monocapas aplicadas a reducir la fricción en dispositivos de tipo MEMS y NEMS (Micro y NanoElectroMechanical Systems). Las moléculas estudiadas han sido ácido araquídico, ácido alcanofosfónico completamente hidrogenado y parcialmente fluorado y capas de tipo DLC (Diamon-Like Carbon films). El segundo tipo de muestras comprende recubrimientos adecuados para el desarrollo de MEMS y NEMS para aplicaciones biológicas, esto es, dispositivos que necesitan recubrimientos biocompatibles. Como primera aproximación se han estudiado bicapas fosfolipídicas en media acuoso desde el punto de vista nanomecánico. Las técnicas empleadas han sido la microscopia de fuerzas atómicas(AFM) en el modo topográfico, la espectroscopia de fuerzas para comprimir las capas y estudiar su respuesta nanomecánica en condiciones de comprensión vertical y la microscopia de fuerzas laterales o de fricción (LFM), con la cual se pueden obtener las propiedades nanotribológicas de las muestras de estudio afectando áreas tan pequeñas como 25 X 25 nanómetros cuadrados. Mediante el uso de la microscopia de fuerzas a temperatura variable ha sido posible estudiar in-situ las transiciones de fase de bicapas fosfolipídicas soportadas sobre mica en medio acuoso y su combinación con la espectroscopia de fuerzas ha permitido la obtención de la fuerza de rotura de dichas capas a temperatura variable

Competency-based learning and relaxation techniques: an interdisciplinary approach

This project focuses on the possibility of integrating yoga and relaxation techniques in the new competency-based paradigms that will unfold in Catalonia during the years to come. To do so, this project engages theory and practice so as to assess the feasibility and application of the proposed techniques in a real high school environment. It must be clearly stated that the proposed practices are completely disconnected from religion, dogma or cultural Asian background; the present proposal, then, points out to detect and apply breathing and relaxation techniques that have been widely used both in western and Asian cultures in the form of mind-centering practices. To tackle with this goal, the present project deals with three different approaches with the main objective of providing the reader with an objective perspective regarding the possibility of applying relaxation techniques to the daily routine of Catalan high schools: -Yoga and relaxation to improve the classroom management. -Teachers and students in danger: the snowball effect unleashed by stress. Competency-based learning and relaxation/yoga techniques: a promising future together

Competency-based learning and relaxation techniques: an interdisciplinary approach

This project focuses on the possibility of integrating yoga and relaxation techniques in the new competency-based paradigms that will unfold in Catalonia during the years to come. To do so, this project engages theory and practice so as to assess the feasibility and application of the proposed techniques in a real high school environment. It must be clearly stated that the proposed practices are completely disconnected from religion, dogma or cultural Asian background; the present proposal, then, points out to detect and apply breathing and relaxation techniques that have been widely used both in western and Asian cultures in the form of mind-centering practices. To tackle with this goal, the present project deals with three different approaches with the main objective of providing the reader with an objective perspective regarding the possibility of applying relaxation techniques to the daily routine of Catalan high schools: -Yoga and relaxation to improve the classroom management. -Teachers and students in danger: the snowball effect unleashed by stress. Competency-based learning and relaxation/yoga techniques: a promising future together