Creep behavior of PLA‐based biodegradable plastic exposed to a hydrocarbon liquid

This study explores the effect of hydrocarbon liquid on creep behavior of polylactic acid (PLA)‐based plastic. Evolution of the mechanical properties of the material was investigated experimentally by measurement of creep under tensile load. Tensile creep behavior was studied with a constant load over a temperature range from 30 to 50°C using specimens containing different levels of liquid. It was shown that the hydrocarbon liquid diffusion obeys the Fickian law of diffusion. The viscoelastic properties vary with temperature and these properties dramatically decrease above the glass transition temperature (T_g). Significant decreases in modulus and in the peak of tan δ were observed with an increase in liquid concentration at low temperatures. In contrast, at high temperatures, drier material recorded lower storage modulus. However, only small changes of T_g were recorded. Dependence of compliance on temperature was observed in the creep test at all levels of liquid content. With respect to drier samples, it was noted that the high liquid content material had a lower rate of increasing creep strain with temperature. Therefore, at elevated temperatures, higher creep strain of dry specimens was observed compared to those with a higher liquid content. The improvement of creep resistance and stiffening of material at high temperatures can be attributed to the significant increase of crystallinity fraction induced by liquid absorption. Understanding the effect of liquid diffusion in conjunction with temperature provides useful information for assessment of the potential use of this biodegradable plastic in load‐bearing applications exposed to an organic liquid. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Pyridinedicarboxylic Acid Diamides as Selective Ligands for Extraction and Separation of Trivalent Lanthanides and Actinides: DFT Study

This article presents a general approach to solving the urgent practical problem of separation of 4f-(lanthanides, Ln³⁺) and 5f-elements (actinides, An³⁺) very similar in properties based on the DFT quantum-chemical supercomputer simulation of Ln³⁺ and An³⁺ complexes with polydentate nitrogen-containing heterocyclic ligands. The method allows to calculate the geometry parameters of ligands and complexes and the metal to ligand binding energies with accuracy, permitting a direct comparison of calculation results with the experimental data, and estimate selectivity factors for separation of Eu³⁺/Am³⁺ model pair cations (SF_Am/Eu) in extraction experiments on a semi-quantitative level.

The applicability of the method and the approach demonstrated by DFT-modeling (nonempirical PBE functional, extended relativistic full-electron basis set) of a large series of diamides of pyridine-2,6-dicarboxylic (dipicolinic) acid (L) with different substituents at the amide nitrogen atoms and in the pyridine cycle, as well as their complexes [LM]³⁺, (H₂O)_nM(NO₃)₃ (n = 3, 4), and LM(NO₃)₃ (M = Eu, Am).

Based on the theoretical analysis a new model is proposed that describes the mechanism of Ln³⁺ and An³⁺ extraction in two-phase system highly acidic water solution-organic solvent, according to which the formation of An³⁺ and Ln³⁺ complexes occurs at the water/organic interface as a substitution reaction of hydroxonium ion in a cavity of a protonated ligand for the metal cation.

Calculation results confirm the experimentally established higher extraction ability of dipicolinic acid diamides containing one aryl and one alkyl substituent at the amide nitrogen atoms compared to the N,N,N′,N′-tetraalkyl diamides (“effect of anomalous aryl strengthening”). Based on the simulation results the structure of the modified ligand L suggested that it should ensure maximum An³⁺/Ln³separation selectivity in the series of dipicolinic acid diamides.     

Nanoparticle Synthesis by Copper (II) Acetylacetonate Vapor Decomposition in the Presence of Oxygen

Crystalline nanometer-sized Cu 2 O and CuO particle formation was studied by vapor thermal decomposition of copper (II) acetylacetonate in a vertical laminar flow reactor at ambient pressure. Experiments were carried out at 3 furnace temperature profiles (maximum values of t furn = 432, 596, 705°C) and with 2 carrier gases (oxygen/nitrogen with mixture ratios of 0.5/99.5 and 10.0/90.0). The results of computational fluid dynamics simulations are presented. The introduction of oxygen into the system was found to increase the decomposition rate and removed impurities from particles. The size of produced primary particles varied from 10 to 200 nm. Particle crystallinity was found to depend on both the oxygen concentration and the furnace temperature. A model taking into account the detailed chemical reaction mechanisms during the particle formation is proposed. The model allows one to build a dynamic phase diagram of the condensed products formed during the decomposition and is in good agreement with the experimental results.     

Bioaerosol Contamination of Ambient Air as the Result of Opening Envelopes Containing Microbial Materials

Mailing envelopes containing pathogenic spores of bacillus anthraxes, which have recently been used by terrorists to infect humans, calls for a new investigation to identify a level of possible contamination of ambient air as a result of the opening of such envelopes. Here we show that opening an envelope and unfolding a letter aerosolize microbial particles located inside and create their cloud with the diameter equivalent to the length of the letter side along which it was folded. With no motion of an envelope recipient (first case study presented in this paper), the front of the cloud moves due to forced convection caused by the impulse at opening and reaches a human face (approximately 50 cm from the opening zone) in about 6 sec. The concentration of particles at that distance is about three times lower compared to the concentration in the source. Further spread of the cloud brings its front to the distances of 1 and 1.5 meters within 25 and 55 seconds with the corresponding concentrations of around 10% and 5% compared to the source respectively. The second case study presents the results for a more realistic scenario when an envelope recipient, after observing a dust cloud appearing as the result of the opening of the envelope, recoils in fright creating additional air flows significantly disturbing the aerosol propagation described in the former study. It was found theoretically and verified by experiments that the amount of particles captured by the letter recipient varies significantly depending on the geometrical characteristics of the human, distance to the opening zone, reaction time, and recoil velocity.     

Enhancement of the Performance of Low-Efficiency HVAC Filters Due to Continuous Unipolar Ion Emission

Our novel concept utilizing continuous emission of unipolar ions, which has been recently proven to enhance the efficiency of facepiece respirators, was applied to conventional HVAC filters. Laboratory study demonstrated that the air ion emission in the vicinity of a low-efficiency HVAC filter significantly improves its performance. For example, the collection efficiency of two commercial HVAC filters challenged with 1μm PSL particles jumped from 5–15% (measured with no ion emission) to 40–90% (when the ion output rate was ～ 10¹² e^?/sec). The enhancement effect depends on the filter type and, generally, on the distance from the ion emitter to the filter surface. The results were explained as follows. The air ions with high mobility are deposited on the fibers forming a macroscopic electric field, which shield out some incoming unipolarly charged particles due to repelling forces. The field estimate has shown that this explanation is feasible. The enhancement effect seems to have a good potential to be employed in industrial and residential ventilation systems as it enhances the aerosol collection efficiency of a low-efficiency HVAC filter while not affecting its pressure drop.     

Differential Activity of Plasma and Vacuolar Membrane Transporters Contributes to Genotypic Differences in Salinity Tolerance in a Halophyte Species,Chenopodium quinoa

Halophytes species can be used as a highly convenient model system to reveal key ionic and molecular mechanisms that confer salinity tolerance in plants. Earlier, we reported that quinoa (Chenopodium quinoa Willd.), a facultative C3 halophyte species, can efficiently control the activity of slow (SV) and fast (FV) tonoplast channels to match specific growth conditions by ensuring that most of accumulated Na⁺ is safely locked in the vacuole (Bonales-Alatorre et al. (2013) Plant Physiology). This work extends these finding by comparing the properties of tonoplast FV and SV channels in two quinoa genotypes contrasting in their salinity tolerance. The work is complemented by studies of the kinetics of net ion fluxes across the plasma membrane of quinoa leaf mesophyll tissue. Our results suggest that multiple mechanisms contribute towards genotypic differences in salinity tolerance in quinoa. These include: (i) a higher rate of Na⁺ exclusion from leaf mesophyll; (ii) maintenance of low cytosolic Na⁺ levels; (iii) better K⁺ retention in the leaf mesophyll; (iv) a high rate of H⁺ pumping, which increases the ability of mesophyll cells to restore their membrane potential; and (v) the ability to reduce the activity of SV and FV channels under saline conditions. These mechanisms appear to be highly orchestrated, thus enabling the remarkable overall salinity tolerance of quinoa species.     

The synthesis of single phase WC nanoparticles/C composite by solid state reaction involving nitrogen-rich carbonized polyaniline

Single phase tungsten carbide nanoparticles (WC-NPs), (mean particle diameter 5.4 nm), distributed over carbonized polyaniline (C-PANI) nanotubes/nanosheets were synthesized by a solid state reaction between WO₃ and nitrogen-rich carbonized polyaniline at 1000 °C in a reducing atmosphere. The resulting composite was characterized by X-ray diffractometry, electron microscopy, thermogravimetry in oxidizing and reduction atmospheres and elemental analysis. We suggested that the synthesis of WC as a single phase was facilitated by reactive C atoms with dangling bonds, formed upon nitrogen removal.     

Effect of oxide nanofillers on fabrication,structure, and properties of zirconia-based composites

We have studied the effect of NiO on the sintering of yttria-stabilized zirconia at temperatures ranging from 1300 °C to 1500 °C in air and argon environments. It was found that the addition of NiO stabilized the cubic phase of ZrO₂ independently from the sintering atmosphere. The monoclinic phase of ZrO₂ formed only during sintering within the air environment at temperatures higher than 1450 °C. The transformation of NiO to Ni by reversible decomposition depends on the sintering atmosphere, and this can lead to variations in the nature of inclusions and in changes of the structure and properties of nanocomposite materials in the system ZrO₂–NiO(Ni). NiO and Ni inclusions can increase the indentation fracture toughness of zirconia–nickel oxide composite material more than 50%, which can be compared with zirconia ceramics during sintering in a neutral atmosphere alone.     

Effect of filler size on thermophysical and electrical behavior of nanocomposites based on expanded graphite nanoparticles filled in low‐density polyethylene matrix

Various aspects of electrical and thermophysical properties of nanocomposites based on low‐density polyethylene matrix filled with nanostructuralized expanded graphite (EG) and standard, microsized graphite are presented in this article. A periodical method developed in the laboratory was used to measure simultaneously thermal conductivity, specific heat, and diffusivity of composites at room temperature. The effect of micro‐ and nanosized fillers on the final thermophysical and electrical behavior is investigated. It was found that the electrical conductivity of composites strongly depends not only on the filler content but also on the filler size. When the microsized graphite was used, the percolation concentration of the filler was found to be 15 vol%, whereas the percolation concentration of the filler in nanocomposites filled with EG of large sizes was significantly lower. Similarly, it was shown that the graphite significantly improves the thermophysical behavior of composites filled with micro‐ and nanofiller sizes. The thermal conductivity measured values were also compared with some theoretical models for the prediction of the thermal conductivity. POLYM. COMPOS., 2012. © 2013 Society of Plastics Engineers     

Nanoporous artificial proboscis for probing minute amount of liquids

We describe a method of fabrication of nanoporous flexible probes which work as artificial proboscises. The challenge of making probes with fast absorption rates and good retention capacity was addressed theoretically and experimentally. This work shows that the probe should possess two levels of pore hierarchy: nanopores are needed to enhance the capillary action and micrometer pores are required to speed up fluid transport. The model of controlled fluid absorption was verified in experiments. We also demonstrated that the artificial proboscises can be remotely controlled by electric or magnetic fields. Using an artificial proboscis, one can approach a drop of hazardous liquid, absorb it and safely deliver it to an analytical device. With these materials, the paradigm of a stationary microfluidic platform can be shifted to the flexible structures that would allow one to pack multiple microfluidic sensors into a single fiber.