Crystallization of 2D Hybrid Organic–Inorganic Perovskites Templated by Conductive Substrates

2D hybrid organic–inorganic perovskites are valued in optoelectronic applications for their tunable bandgap and excellent moisture and irradiation stability. These properties stem from both the chemical composition and crystallinity of the layer formed. Defects in the lattice, impurities, and crystal grain boundaries generally introduce trap states and surface energy pinning, limiting the ultimate performance of the perovskite; hence, an in-depth understanding of the crystallization process is indispensable. Here, a kinetic and thermodynamic study of 2D perovskite layer crystallization on transparent conductive substrates are provided—fluorine-doped tin oxide and graphene. Due to markedly different surface structure and chemistry, the two substrates interact differently with the perovskite layer. A time-resolved grazing-incidence wide-angle X-ray scattering (GIWAXS) is used to monitor the crystallization on the two substrates. Molecular dynamics simulations are employed to explain the experimental data and to rationalize the perovskite layer formation. The findings assist substrate selection based on the required film morphology, revealing the structural dynamics during the crystallization process, thus helping to tackle the technological challenges of structure formation of 2D perovskites for optoelectronic devices.     

4D Printing at the Microscale

3D printing of adaptive and dynamic structures, also known as 4D printing, is one of the key challenges in contemporary materials science. The additional dimension refers to the ability of 3D printed structures to change their properties—for example, shape—over time in a controlled fashion as the result of external stimulation. Within the last years, significant efforts have been undertaken in the development of new responsive materials for printing at the macroscale. However, 4D printing at the microscale is still in its early stages. Thus, this progress report will focus on emerging materials for 4D printing at the microscale as well as their challenges and potential applications. Hydrogels and liquid crystalline and composite materials have been identified as the main classes of materials representing the state of the art of the growing field. For each type of material, the challenges and critical barriers in the material design and their performance in 4D microprinting are discussed. Importantly, further necessary strategies are proposed to overcome the limitations of the current approaches and move toward their application in fields such as biomedicine, microrobotics, or optics.     

Star-shaped hexaaryltriindoles small molecules: Tuning molecular properties towards solution processed organic light emitting devices

We present a series of differently substituted star-shaped hexaaryltriindoles with tunable light-emitting properties. The deep blue emission is unchanged by donor peripheral substituents while an increasing acceptor character produces a reduction of the optical gap, an increased Stokes shift and eventually leads to the appearance of a new electronic level and to the simultaneous deep blue (413 nm) and green (552 nm) emission in solution. Quenching by concentration increases with the acceptor character but is lower as the tendency of these compounds to aggregate is stronger. Solution processed thin films present optical and morphological qualities adequate for device fabrication and similar electronic structure compared to solutions with an emission range from 423 nm up to 657 nm (red), demonstrating the possibility of tuning the energy levels by chemical functionalization. We have fabricated and characterized single-layer solution processed organic light emitting diodes (OLED) to investigate the influence on transport and emission properties of the substituting species. We analyzed the I–V response using a single-carrier numerical model that includes injection barriers and non-uniform electric-field across the layer. As a result, we obtained the electric field dependence of the mobility for each device. Best results are obtained on the most electron rich derivative functionalized with six donor methoxy groups. This material shows the highest emission efficiency in solid state, due to aggregation-induced enhancement, and better transport properties with the highest mobility and a very low turn-on voltage of 2.8 V. The solution processed OLED devices produce stable deep blue (CIE coordinates (0.16, 0.16)) to white (CIE coordinates (0.33, 0.3)) emission with similar luminous efficiencies.     

3D Scaffolds to Study Basic Cell Biology

Mimicking the properties of the extracellular matrix is crucial for developing in vitro models of the physiological microenvironment of living cells. Among other techniques, 3D direct laser writing (DLW) has emerged as a promising technology for realizing tailored 3D scaffolds for cell biology studies. Here, results based on DLW addressing basic biological issues, e.g., cell‐force measurements and selective 3D cell spreading on functionalized structures are reviewed. Continuous future progress in DLW materials engineering and innovative approaches for scaffold fabrication will enable further applications of DLW in applied biomedical research and tissue engineering.     

The discipline dependence of citation statistics

This study compares the citations characteristics of researchers in engineering disciplines with other major scientific disciplines, and investigates variations in citing patterns within subdisciplines in the field of engineering. Utilizing citations statistics including Hirsch’s (Proc Natl Acad Sci USA 102(46):16569–16572, 2005) h-index value, we find that significant differences in citing characteristics exist between engineering disciplines and other scientific fields. Our findings also reveal statistical differences in citing characteristics between subdisciplines found within the same engineering discipline.     

Free amino acid content of goat's milk cheese made with animal rennet and plant coagulant

BACKGROUND: Enzymes present in the flowers of Cynara cardunculus (cyprosins) are used in the production of some traditional Spanish and Portuguese cheeses, replacing animal rennet. The aim of this work was to study the changes that take place in free amino acids during the ripening of a goat's milk cheese (Murcia al Vino) manufactured with plant coagulant (PC) or animal rennet (AR). RESULTS: The total free amino acid (TFAA) concentration increased during ripening, with Ile, Val, Ala, Phe, Gaba, Arg and Lys representing more than 50% of the TFAA content at 60 days in both types of cheese. The TFAA concentration was significantly higher in cheeses made with PC (854 mg 100 g^?1 total solids (TS)) than those made with AR (735 mg 100 g^?1 TS). The concentration of most free amino acids, especially His, Ser, Gln, Thr, Ala, Met and Ile, was higher in the PC cheese. CONCLUSION: Cheese made using PC as coagulant presented higher contents of free amino acid throughout the ripening period than cheese made using AR. Therefore we can conclude that the use of PC to produce Murcia al Vino goat's cheese would accelerate the ripening process as a result of increased cyprosin proteolytic activity. Copyright © 2011 Society of Chemical Industry     

The Influence of Different Processing Stages on Particle Size,Microstructure, and Appearance of Dark Chocolate

The effect of different process stages on microstructural and visual properties of dark chocolate was studied. Samples were obtained at each phase of the manufacture process: mixing, prerefining, refining, conching, and tempering. A laser light diffraction technique and environmental scanning electron microscopy (ESEM) were used to study the particle size distribution (PSD) and to analyze modifications in the network structure. Moreover, colorimetric analyses (L*, h°, and C*) were performed on all samples. Each stage influenced in stronger way the microstructural characteristic of products and above all the PSD. Sauter diameter (D [3.2]) decreased from 5.44 μm of mixed chocolate sample to 3.83 μm, of the refined one. ESEM analysis also revealed wide variations in the network structure of samples during the process, with an increase of the aggregation and contact point between particles from mixing to refining stage. Samples obtained from the conching and tempering were characterized by small PS, and a less dense aggregate structure. From color results, samples with the finest particles, having larger specific surface area and the smallest diameter, appeared lighter and more saturated than those with coarse particles.     

The effects of cereal additives in low-fat sausages and meatballs. Part 1: Untreated and enzyme-treated rye bran

Rye bran was added to frankfurter-type sausages and meatballs with the aim of producing low-fat products with increased dietary fibre content. The addition of untreated rye bran to sausages was detrimental, causing a substantial increase in frying loss (20% compared to 13.2%). The addition of rye bran treated with hydrolytic enzymes reduced the frying loss to 15.2–16.4%. The firmness was also improved by the treatments (12.8–14.2 N compared to 8.8 N). Enzymatic treatment of rye bran did not however improve the water-holding capacity or the texture of sausages compared to the rye bran that had only been soaked in water. The reason could be that enzymes degraded the solubilized fraction of the dietary fibre, leaving small fragments that cannot contribute to the water-holding capacity and the texture of the sausages. The benefits of treating rye bran in water were not seen in meatballs, probably due to the more particulate structure of meatballs, which is not as sensitive to additives.     

Enhanced bactericidal effect of enterocin AS-48 in combination with high-intensity pulsed-electric field treatment against Salmonella enterica in apple juice

The effect of the broad spectrum cyclic antimicrobial peptide enterocin AS-48 combination with high-intensity pulsed-electric field (HIPEF) treatment (35 kV/cm, 150 Hz, 4 micros and bipolar mode) was tested on Salmonella enterica CECT 915 in apple juice. A response surface methodology was applied to study the bactericidal effects of the combined treatment. The process variables were AS-48 concentration, temperature, and HIPEF treatment time. While treatment with enterocin AS-48 alone up to 60 microg/ml had no effect on the viability of S. enterica in apple juice, an increased bactericidal activity was observed in combination with HIPEF treatments. Survival fraction was affected by treatment time, enterocin AS48 concentration and treatment temperature. The combination of 100 micros of HIPEF treatment, 30 microg/ml of AS-48, and temperature of 20 degrees C resulted in the lowest inactivation, with only a 1.2-log reduction. The maximum inactivation of 4.5-log cycles was achieved with HIPEF treatment for 1000 micros in combination with 60 microg/ml of AS-48 and a treatment temperature of 40 degrees C. Synergism between enterocin AS-48 and HIPEF treatment depended on the sequence order application, since it was observed only when HIPEF was applied in the presence of previously-added bacteriocin. The combined treatment could improve the safety of freshly-made apple juice against S. enterica transmission.