Dielectric studies of barium bismuth titanate as a material for application in temperature sensors

Ceramic nanocrystalline samples with composition Ba_1?3aBi_2aTiO₃ were synthesized by sol–gel method, for different values of parameter a (for a = 0.0165, 0.033, 0.050). In order to determine whether barium bismuth titanate is suitable for application in temperature sensors, dielectric properties measurements were conducted on the prepared samples, as a function of both temperature (from room temperature up to 190 °C) and frequency (from 50 kHz to 1 MHz). Real and imaginary parts of dielectric constant were determined using an Impedance Analyzer HP-4194A. Depending on parameter a two different behavior were determined: (1) classical ferroelectric behavior, for the sample with low a value and (2) relaxor behavior for the samples with higher a values. Thus, a typical characteristic of relaxor ferroelectrics with a broad and dispersive dielectric maximum was observed for the samples Ba_0.85Bi_0.1TiO₃ and Ba_0.90Bi_0.066TiO₃. Temperature dependence (for real part of dielectric constant ε_r′) is almost linear, for lower temperatures than peak value (slope +1.3 1/ °C), and higher than this value (slope ?1 1/ °C). The feature of linearity is very important from practical aspects of application of this material in wireless temperature sensors. The temperature coefficient of dielectric constant for the sample with the best linearity (Ba_0.95Bi_0.033TiO₃ at 1 MHz) was found to vary from positive one +3.72 × 10^?3 1/ °C to negative value ?2.85 × 10^?3 1/ °C, in the temperature range 25–190 °C.     

Fire Performance of External Thermal Insulation Composite System (ETICS) Facades with Expanded Polystyrene (EPS) Insulation and Thin Rendering

External Thermal Insulation Composite System (ETICS) facades with expanded polystyrene (EPS) insulation and thin rendering are applied frequently in buildings. Considering high combustibility of EPS, with these facades concerns also arise regarding spread of a possible fire between neighbouring compartments of high-rise buildings. Fire tests of two large-scale facades were performed to study two parameters presumably influencing significantly the fires of such facades in real-life settings, i.e. incident heat flux upon the facade’s surface (IHFFS) and damage of the facade’s render (the latter being a consequence of poor or unfinished construction work, ageing or fire-induced thermal strain). The first facade was rendered fully and was exposed to moderately-fast increasing IHFFS. In the second (partially unrendered) facade case the IHFFS progressed faster. The facade flame body (temperatures and shape) was monitored by thermocouples, photo and video cameras. For detection of melting of EPS and internal burning, thermocameras were used within the facades areas outside the visible plume. In the plume zone, however, a group of thermocouples was embedded inside EPS and the shapes (plateaus and slopes) of the collected time-temperature graphs were observed for these purposes. The IHFFS imposed on the facades during fire testing were estimated by numerical calculations. In both cases the first pronounced render crack was evolved at the estimated average between-windows IHFFS of around 30 kW/m\(^2\) and was followed by internal burning of EPS. While the latter did not seem to spread across the facade for the fully-rendered facade, a fast fire spread was detected for the second specimen.     

Manganese Functionalized Silicate Nanoparticles as a Fenton‐Type Catalyst for Water Purification by Advanced Oxidation Processes (AOP)

Wet hydrogen peroxide catalytic oxidation (WHPCO) is one of the most important industrially applicable advanced oxidation processes (AOPs) for the decomposition of organic pollutants in water. It is demonstrated that manganese functionalized silicate nanoparticles with interparticle porosity act as a superior Fenton‐type nanocatalyst in WHPCO as they can decompose 80% of a test organic compound in 30 minutes at neutral pH and room temperature. By using X‐ray absorption spectroscopic techniques it is also shown that the superior activity of the nanocatalyst can be attributed uniquely to framework manganese, which decomposes H₂O₂ to reactive hydroxyls and, unlike manganese in Mn₃O₄ or Mn₂O₃ nanoparticles, does not promote the simultaneous decomposition of hydrogen peroxide. The presented material thus introduces a new family of Fenton nanocatalysts, which are environmentally friendly, cost‐effective, and possess superior efficiency for the decomposition of H₂O₂ to reactive hydroxyls (AOP), which in turn readily decompose organic pollutants dissolved in water.     

The Rule of Thirds: Controlling Junction Chirality and Polarity in 3D DNA Tiles

The successful self-assembly of tensegrity triangle DNA crystals heralded the ability to programmably construct macroscopic crystalline nanomaterials from rationally-designed, nanoscale components. This 3D DNA tile owes its “tensegrity” nature to its three rotationally stacked double helices locked together by the tensile winding of a center strand segmented into 7 base pair (bp) inter-junction regions, corresponding to two-thirds of a helical turn of DNA. All reported tensegrity triangles to date have employed $\left(Z+2/3\right)$ turn inter-junction segments, yielding right-handed, antiparallel, “J1” junctions. Here a minimal DNA triangle motif consisting of 3-bp inter-junction segments, or one-third of a helical turn is reported. It is found that the minimal motif exhibits a reversed morphology with a left-handed tertiary structure mediated by a locally-parallel Holliday junction—the “L1” junction. This parallel junction yields a predicted helical groove matching pattern that breaks the pseudosymmetry between tile faces, and the junction morphology further suggests a folding mechanism. A Rule of Thirds by which supramolecular chirality can be programmed through inter-junction DNA segment length is identified. These results underscore the role that global topological forces play in determining local DNA architecture and ultimately point to an under-explored class of self-assembling, chiral nanomaterials for topological processes in biological systems.     

Polymer-Lipid Matrices based on Carboxymethyl Cellulose/Solagum and Liposomes for Controlled Release of Folic Acid

Liposome-encapsulated folic acid is incorporated into the films made from sodium carboxymethyl cellulose (CMC) (2 mas%) and a mixture of CMC and solagum (9:1 w/w) using the film-forming cast solution method. Histidine is used to increase solubility for folic acid in liposomes (1–5 mg mL⁻¹), and propylene glycol is used as a film plasticizer (2.6 mas%). The obtained films (50–60 µm tick) containing 3.12–20.19 mg of folic acid per gram of film are envisaged to be used as patches for transdermal delivery of folic acid. Therefore, some physical, mechanical, release and structural attributes of the films are scrutinized. Folic acid gives yellow color to the films and contributes to stronger chemical bonds which result in improved strength of the film. Liposomes prolong the release of folic acid from films to 24 h without adverse effects on mechanical properties of the films, but degrade homogeneity of the films, which can be ascribed to its agglomeration within the film matrix as revealed by atomic force microscopy. According to the release at pH 5.5, the film formulation based on a blend of CMC and solagum containing 3 mg mL⁻¹ liposome-encapsulated folic acid is recommended. Practical Application: Folic acid is effective in reducing oxidative stress levels in the skin and neutralizing the harmful free radicals and is also essential for various metabolic reactions in the body. However, the limited solubility of folic acid linked with its poor absorption in an organism, low storage stability, short half-life upon oral consumption, specific food preferences of some people, extensive liver metabolism, and pregnancy-induced vomiting point to a large potential in transdermal usage of folic acid. This has motivated us to design new multicomponent polymer-lipid systems as an alternative solution to overcome some of these drawbacks. The results obtained for these multicomponent films pointed to their potential for prolonged release of folic acid to 24 h, which can also be useful for scientists interested in encapsulating similar poorly soluble compounds in CMC patches. The finding can be also valuable information for pharmaceutical manufacturers and scientists worldwide.