Fluorinated networks dynamics studied by means of broadband dielectric spectroscopy

The influence of the surface chemical modification on the bulk behavior of epoxy based networks has been studied. In particular, the bulk dynamics of epoxy‐amine networks modified with fluorinated side chains has been characterized by means of broadband dielectric spectroscopy (BDS), differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy. The fluorination effect on the structure and dynamics of the materials has been related with the observed changes in both segmental and secondary relaxations. An acceleration of the segmental dynamics as the fluorination degree increases has been clearly observed. As a result, a compromise between fluorine surface enrichment and bulk modification has been proposed for these materials. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42690.     

Vulcanization of EPDM rubber compounds with and without blowing agents: Identification of reaction events and TTT‐diagram using DSC data

Vulcanization of industrial‐like ethylene propylene diene termonomer rubber compound is studied using a differential scanning calorimetry (DSC). The analysis starts with DSC information to obtain the total transformation heat, followed by an isothermal‐dynamic temperature ramp that captures diffusion‐controlled reaction kinetics. The vulcanization is modeled by an auto‐catalytic Kamal–Sourour model, complemented with a Kissinger model for the prediction of one energy of activation, DiBenedetto's equation for the glass transition temperature, and adjusted reaction constants to include diffusion mechanisms. Two rubber formulations, with and without blowing agents, containing crosslinking agents, primary and secondary accelerators, activators, promoters, and processing aids are studied. The identification and separation of multiple reaction events, occurring during crosslinking of the compound without a blowing agent, is done through a 2^k design of experiments. Time–temperature–transformation (TTT) diagrams are calculated, integrating the kinetic model, thereby delineating processability windows, providing avenues for optimization, design, and online processing control. According to the kinetics and the TTT diagrams, the blowing agent induces several differences to the vulcanization reaction: decreases reaction temperatures while increasing reaction heats. It eliminates the exothermic peak before vulcanization and decreases the fully cured resin's glass transition temperature. Therefore, the presence of the blowing agent drives a shift in the vitrification line, resulting in a reduced operational window. POLYM. ENG. SCI., 55:2073–2088, 2015. © 2014 Society of Plastics Engineers     

Carbon nanotubes/chitin nanowhiskers aerogel achieved by quaternization‐induced gelation

Organic aerogels from polysaccharides such as cellulose and chitin are of particular importance because they utilize renewable feedstocks. In this article, the aerogels were prepared through the self‐assembly of chitin nanowhiskers previously modified. The surface of chitin nanowhiskers was rendered cationic through two reactions. A first reaction between hydroxyl groups of chitin and 2‐chloroethyl isocyanate and a second reaction between the chloride groups of isocyanate anchored to the surface and 1‐methylimidazole. This modification led to stable aqueous suspensions of the chitin nanowhiskers with gelation and rheological properties. Additionally, chitin nanowhiskers aerogels containing modified carbon nanotubes were obtained. The addition of modified carbon nanotubes provoked a change in the morphology of the hydrogels and as a consequence, the rheological properties of the hydrogel are modified as well. In contrast from previous procedures, this method has not required any kind of solvent exchange or high pressure in order to obtain the final materials. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42547.     

Morphological Control for High Performance,Solution‐Processed Planar Heterojunction Perovskite Solar Cells

Organometal trihalide perovskite based solar cells have exhibited the highest efficiencies to‐date when incorporated into mesostructured composites. However, thin solid films of a perovskite absorber should be capable of operating at the highest efficiency in a simple planar heterojunction configuration. Here, it is shown that film morphology is a critical issue in planar heterojunction CH₃NH₃PbI_3‐xCl_x solar cells. The morphology is carefully controlled by varying processing conditions, and it is demonstrated that the highest photocurrents are attainable only with the highest perovskite surface coverages. With optimized solution based film formation, power conversion efficiencies of up to 11.4% are achieved, the first report of efficiencies above 10% in fully thin‐film solution processed perovskite solar cells with no mesoporous layer.     

Reversible Switching of Liquid Crystalline Order Permits Synthesis of Homogeneous Populations of Dipolar Patchy Microparticles

The spontaneous positioning of colloids on the surfaces of micrometer‐sized liquid crystal (LC) droplets and their subsequent polymerization offers the basis of a general and facile method for the synthesis of patchy microparticles. The existence of multiple local energetic minima, however, can generate kinetic traps for colloids on the surfaces of the LC droplets and result in heterogeneous populations of patchy microparticles. To address this issue, herein it is demonstrated that adsorbate‐driven switching of the internal configurations of LC droplets can be used to sweep colloids to a single location on the LC droplet surfaces, thus resulting in the synthesis of homogeneous populations of patchy microparticles. The surface‐driven switching of the LC can be triggered by addition of surfactant or salts, and permits the synthesis of dipolar microparticles as well as “Janus‐like” microparticles. By using magnetic colloids, the utility of the approach is illustrated by synthesizing magnetically responsive patchy microdroplets of LC with either dipolar or quadrupolar symmetry that exhibit distinct optical responses upon application of an external magnetic field.     

Drastic influence of minor Fe or Co additions on the glass forming ability,martensitic transformations and mechanical properties of shape memory Zr–Cu–Al bulk metallic glass composites

The microstructure and mechanical properties of Zr₄₈Cu_48 − xAl₄M_x (M ≡ Fe or Co, x = 0, 0.5, 1 at.%) metallic glass (MG) composites are highly dependent on the amount of Fe or Co added as microalloying elements in the parent Zr₄₈Cu₄₈Al₄ material. Addition of Fe and Co promotes the transformation from austenite to martensite during the course of nanoindentation or compression experiments, resulting in an enhancement of plasticity. However, the presence of Fe or Co also reduces the glass forming ability, ultimately causing a worsening of the mechanical properties. Owing to the interplay between these two effects, the compressive plasticity for alloys with x = 0.5 (5.5% in Zr₄₈Cu_47.5Al₄Co_0.5 and 6.2% in Zr₄₈Cu_47.5Al₄Fe_0.5) is considerably larger than for Zr₄₈Cu₄₈Al₄ or the alloys with x = 1. Slight variations in the Young’s modulus (around 5–10%) and significant changes in the yield stress (up to 25%) are also observed depending on the composition. The different microstructural factors that have an influence on the mechanical behavior of these composites are investigated in detail: (i) co-existence of amorphous and crystalline phases in the as-cast state, (ii) nature of the crystalline phases (austenite versus martensite content), and (iii) propensity for the austenite to undergo a mechanically-driven martensitic transformation during plastic deformation. Evidence for intragranular nanotwins likely generated in the course of the austenite–martensite transformation is provided by transmission electron microscopy. Our results reveal that fine-tuning of the composition of the Zr–Cu–Al–(Fe,Co) system is crucial in order to optimize the mechanical performance of these bulk MG composites, to make them suitable materials for structural applications.     

Automatic synthesis of embedded SW for evaluating physical implementation alternatives from UML/MARTE models supporting memory space separation

The proposed approach presents a method for automatically synthesizing the SW code of complex embedded systems from a model-driven system specification. The solution is oriented to enabling easy exploration and design of different allocations of SW components in heterogeneous platforms, minimizing designer effort. The system is initially described following the UML/MARTE standard. Applying this standard, the system is modeled, describing its components, interfaces and communication links, the system memory spaces, the resource allocations and the HW architecture. From that information, a SW infrastructure containing the communication infrastructure is generated ad-hoc for the system depending on the HW architecture and the resource allocations evaluated. The consequent communication overhead reduction can result in an important advantage for system performance optimization.     

Electronically Reconfigurable Antenna Terminals for Energy Efficient Routing and Propagation Path Optimization Applied to Mobile Ad Hoc Networks (MANET)

In this paper, the influence of the features of the propagation channel in the performance of Mobile Ad Hoc Networks (MANET) is studied. In order to overcome the possible propagation limitations, a particular reconfigurable multiantenna terminal configuration for MANETs is provided, along with an optimization procedure to select the proper radiation pattern at each node of the network. The adequate selection of the radiation pattern at each node lets maximize the transmission/reception capabilities of the wireless network, depending on the propagation channel features and their evolution in time. In addition, a modified routing strategy is proposed, based on the existence of an alternative route at each node, provided that the main one is not available because of propagation issues or incidences in the network.     

Improved phenomenological model for an isothermal winemaking fermentation

An improved phenomenological model of the varietals must fermentation in a batch bioreactor under controlled bench-scale conditions is presented. The model allows predicting satisfactorily the behavior of the main bioprocess variables to adjust potential deviations from a predefined trajectory. It avoids possible discontinuities when it is used equations like the Blackman’s type for modelling bioprocesses, allowing a more accurate and smooth approximation to the experimental data. The cellular growth term is modeled as a variant of the Verlhurst’s logistic equation. The validation with own and published experimental data and, an exhaustive sensitivity analysis about its properties are presented. The model shows an excellent performance for the main variables and great potential to be used as biomass state estimator into control strategies to avoid abnormal fermentations and, tracks predefined trajectories.