Dielectric and dynamic mechanical study of the mobility of poly(t-butylacrylate) chains in diblock copolymers: polystyrene-b-poly(t-butylacrylate)

A calorimetric, dielectric and dynamic-mechanical study of the dynamics of the poly(t-butyl acrylate) (PtBa) chains has been carried out in a PtBa homopolymer and two polystyrene (PS)-b-PtBa block copolymers with different PtBa chain lengths. The DSC results show that the size of the cooperative rearranging regions is similar in the homopolymers and the copolymers, both for the PtBa rich- and the PS-rich regions. Therefore, no significant contributions are found arising from composition fluctuations in the copolymers. The relaxation map obtained from dielectric relaxation indicates that there are no differences in the temperature dependence of the α-relaxation of the PtBa block in the three samples studied. However, there are larger differences for the values obtained from DMTA experiments. Contrary to the α-relaxation, the relaxation map for the β-transition shows that the characteristic times for the PtBa blocks are smaller in the homopolymer than in the copolymers. In principle, these are unexpected results because the β-relaxations have a more local character than the α-ones. The width of the α-relaxation increases with T for all the samples, and it is slightly larger for the copolymers. The intensity of the α-relaxation is larger (between 3 and 4 times) for the homopolymer. Considering the molecular weights of the PtBa blocks, this effect has to be ascribed to the existence of frozen amorphous PtBa due to the existence of the glassy PS domains in the microphase separated copolymers. Molecular Dynamic Simulations (MDSs) for different sequences of the polymers under study were carried out. The conformational analysis was carried out between 1000 and 1700 K. The analysis of the variation of angles 1 and 2 of the ester group of PtBa points out the existence of a correlation between the conformational changes of the side group of the polymer chains and their relaxational behaviour

X-Ray Diffraction, Calorimetric and Dielectric Relaxation Study of the Amorphous and Smectic States of a Main Chain Liquid Crystalline Polymer

Los polímeros cristales líquidos (LCP) son sistemas complejos que forman mesofases que presentan orden orientacional y polímeros amorfos. Con frecuencia, el estado amorfo isotrópico no puede ser estudiado debido a la rápida formación de mesofases. En este trabajo se ha sintetizado y estudiado un nuevo LCP: poli(trietilenglicol metil p, p '-bibenzoato), PTEMeB. Este polímero presenta una formación de mesofase bastante lenta haciendo posible estudiar de forma independiente tanto los estados amorfo y de cristal líquidos. La estructura y las transiciones de fase del PTEMeB han sido investigados por calorimetría (DSC), con MAXS / WAXS con temperatura variable que emplean radiación de sincrotrón y con difracción de rayos X. Estos estudios han mostrado la existencia de dos transiciones vítreas, relacionadas con las fases amorfa y cristal líquido. Se ha realizado un estudio de relajación dieléctrica en amplios intervalos de temperatura y presión. Se ha encontrado que la transición vítrea dinámica de la fase amorfa es más lenta que la del cristal líquido. El estudio de la relajación ? nos ha permitido seguir la formación isoterma de la mesofase a presión atmosférica. Además, con el estudio el comportamiento dinámico a alta presión se ha encontrado que se produce la formación rápida de la mesofase inducida por cambios bruscos de presión. Liquid crystalline polymers (LCPs) are complex systems that include features of both orientationally ordered mesophases and amorphous polymers. Frequently, the isotropic amorphous state cannot be studied due to the rapid mesophase formation. Here, a new main chain LCP, poly(triethyleneglycol methyl p,p'-bibenzoate), PTEMeB, has been synthesized. It shows a rather slow mesophase formation making possible to study independently both the amorphous and the liquid crystalline states. The structure and phase transitions of PTEMeB have been investigated by calorimetry, variable-temperature MAXS/WAXS employing synchrotron radiation, and X-ray diffraction in oriented fibers. These experiments have pointed out the presence of two glass transitions, related to the amorphous or to the liquid crystal phases. Additionally, the mesophase seems to be a coexistence of orthogonal and tilted smectic phases. A dielectric relaxation study of PTEMeB over broad ranges of temperature and pressure has been performed. The dynamic glass transition turns out to be slower for the amorphous state than for the liquid crystal. Monitoring of the α relaxation has allowed us to follow the isothermal mesophase formation at atmospheric pressure. Additionally, the dynamical behavior at high pressures has pointed out the fast formation of the mesophase induced by sudden pressure changes

Spatially Multiplexed Micro-Spectrophotometry in Bright Field Mode for Thin Film Characterization

Thickness characterization of thin films is of primary importance in a variety of nanotechnology applications, either in the semiconductor industry, quality control in nanofabrication processes or engineering of nanoelectromechanical systems (NEMS) because small thickness variability can strongly compromise the device performance. Here, we present an alternative optical method in bright field mode called Spatially Multiplexed Micro-Spectrophotometry that allows rapid and non-destructive characterization of thin films over areas of mm2 and with 1 μm of lateral resolution. We demonstrate an accuracy of 0.1% in the thickness characterization through measurements performed on four microcantilevers that expand an area of 1.8 mm2 in one minute of analysis time. The measured thickness variation in the range of few tens of nm translates into a mechanical variability that produces an error of up to 2% in the response of the studied devices when they are used to measure surface stress variations.The authors acknowledge the financial support by European Research Council through Starting Grant NANOFORCELLS (ERC-StG-2011-278860). P. M. Kosaka acknowledges funding from the Fundación General CSIC ComFuturo program. We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI

Nanomechanical properties of composite protein networks of erythroid membranes at lipid surfaces

Erythrocyte membranes have been particularly useful as a model for studies of membrane structure and mechanics. Native erythroid membranes can be electroformed as giant unilamellar vesicles (eGUVs). In the presence of ATP, the erythroid membrane proteins of eGUVs rearrange into protein networks at the microscale. Here, we present a detailed nanomechanical study of individual protein microfilaments forming the protein networks of eGUVs when spread on supporting surfaces. Using Peak Force tapping Atomic Force Microscopy (PF-AFM) in liquid environment we have obtained the mechanical maps of the composite lipid-protein networks supported on solid surface. In the absence of ATP, the protein pool was characterized by a Young’s Modulus Epool ≈ 5–15 MPa whereas the complex filaments were found softer after protein supramolecular rearrangement; Efil ≈ 0.4 MPa. The observed protein softening and reassembling could be relevant for understanding the mechanisms of cytoskeleton reorganization found in pathological erythrocytes or erythrocytes that are affected by biological agents

Voltammetric determination of size and particle concentration of Cd-based quantum dots

In this article, we present two novel methodologies, using a simple electrochemical approach, for the determination of the size and particle concentration of Cd-based Quantum Dots (QDs), nanoparticles widely used as photoluminescent labels in many bioanalytical applications. Such QDs were analyzed directly in organic medium and in water after derivatization with an amphiphilic polymer. Screenprinted carbon electrodes modified with a bismuth film were employed as the electrochemical platform. The herein proposed methodologies allow the reliable determination of very low nanoparticle concentrations. Detection limits achieved with the selected experimental conditions were of 3.0 1012 nanoparticles mL1 for CdSe QDs dispersed in organic medium and of 6.0 1012 nanoparticles mL1 for water-solubilized CdSe/ZnS QDs (both with a core size of 3.26 nm). However, detection limits could be improved increasing the QDs sample volume or the voltammetric deposition time. Furthermore, the proposed methodologies allowed the determination of the CdSe QDs diameters. Results obtained were validated after comparison with standard spectroscopic approaches. The electrochemical characterization of QDs, disclosed in this work, allows to perform a synthesis control with a simple, inexpensive and fast approach

Development of nanomechanical biosensors for the determination of cell mechanical properties

Póster presentado en el GEM4 Summer school, celebrado en Londres del 10 al 14 de septiembre de 2012.Peer Reviewe

Healthcare workers hospitalized due to COVID-19 have no higher risk of death than general population. Data from the Spanish SEMI-COVID-19 Registry

Aim To determine whether healthcare workers (HCW) hospitalized in Spain due to COVID-19 have a worse prognosis than non-healthcare workers (NHCW). Methods Observational cohort study based on the SEMI-COVID-19 Registry, a nationwide registry that collects sociodemographic, clinical, laboratory, and treatment data on patients hospitalised with COVID-19 in Spain. Patients aged 20-65 years were selected. A multivariate logistic regression model was performed to identify factors associated with mortality. Results As of 22 May 2020, 4393 patients were included, of whom 419 (9.5%) were HCW. Median (interquartile range) age of HCW was 52 (15) years and 62.4% were women. Prevalence of comorbidities and severe radiological findings upon admission were less frequent in HCW. There were no difference in need of respiratory support and admission to intensive care unit, but occurrence of sepsis and in-hospital mortality was lower in HCW (1.7% vs. 3.9%; p = 0.024 and 0.7% vs. 4.8%; p<0.001 respectively). Age, male sex and comorbidity, were independently associated with higher in-hospital mortality and healthcare working with lower mortality (OR 0.211, 95%CI 0.067-0.667, p = 0.008). 30-days survival was higher in HCW (0.968 vs. 0.851 p<0.001). Conclusions Hospitalized COVID-19 HCW had fewer comorbidities and a better prognosis than NHCW. Our results suggest that professional exposure to COVID-19 in HCW does not carry more clinical severity nor mortality