A modified emulsion polymerisation synthesis route for preparing highly dispersed cationic polystyrene (PS) nanoparticles is reported. The combined use of 2,2′-azobis[2-(2-imidazolin- 2-yl)propane] di-hydrochloride (VA-044) as the initiator and acetone/water as the solvent medium afforded successful synthesis of cationic PS particles as small as 31 nm in diameter. A formation mechanism for the preparation of PS nanoparticles was proposed, whereby the occurrence of rapid acetone diffusion caused spontaneous rupture of emulsion droplets into smaller droplets. Additionally, acetone helped to reduce the surface tension and increase the solubility of styrene, thus inhibiting aggregation and coagulation among the particles. In contrast, VA-044 initiator could effectively regulate the stability of the PS nanoparticles including both the surface charge and size. Other reaction parameters i.e. VA-044 concentration and reaction time were examined to establish the optimum polymerisation conditions.
The motion of submicron particles involves the deterministic terms resulting from the aerodynamic convection and/or electrostatic attraction, and the stochastic term from the thermal displacement of particles. The Langevin equation describes such behavior. The Brownian dynamics algorithm was used for integration of the Langevin equation for the calculation of the single fiber deposition efficiency. Additionally the deterministic and stochastic of the particle motion were derived, using the Lagrangian and Eulerian approaches of particle movement and balance, for the calculation of the single fiber deposition efficiency due to both mechanisms separately. Combination of the obtained results allows us for calculation of the coupling effect of inertia and interception with the Brownian diffusion in a form of correlation. The results of calculation show that the omitting of the coupling effect of particular mechanism and using the simple additive rule for determination of the single fiber deposition efficiency introduces significant error, especially for particles with diameter below 300 nm.
Cu-Ni composite nanoparticles were successfully synthesized by electrical explosion of wire (EEW) method. Cu-Ni alloy and twisted wires with various Ni contents were used as the feeding material for a 3 kV charging voltage EEW machine in an ethanol ambient chamber. The phase structure and magnetic properties of the as-fabricated samples were studied. It was established that the prepared powders after drying have a spherical form with the particle size is under 100 nm. XRD analysis indicated that the nanopowders consisted of binary Cu-Ni phases. Only pure phases of the intermetallic compound Cu-Ni (Cu0.81Ni0.19 and Cu3.8Ni) were observed in the XRD patterns of the samples. The synthesized intermetallic Cu-Ni alloy nanopowders reveal magnetic behaviors, however, the lower Ni content samples exhibited paramagnetic behaviors, meanwhile, the higher Ni content samples exposed ferromagnetic properties.
This article presents test results of cement paste and binders with admixture of hydrophilic or hydrophobic nanosilica. The aim of the study was to determine the influence of nanosilica type and mixing method on compressive strength, porosity, and bulk density of cement paste, also on hydration heat of cement binders. The binder compounds were mixed in high speed mixer in order to provide the highest possible dispersion of nanoparticles in the binder before adding it to mixing water. Two mixing methods were studied. The admixtures increased the reactivity of cement binders. Both nanosilica types increased early compressive strength by 25% in comparison with control series. The increase in 28-day compressive strength was observed with the admixture of hydrophilic nanosilica. The differences in dynamics of binders rate of hydration and development of cement pastes compressive strength denote different reaction mechanisms of both types of nanosilica. Application of higher rotation speeds does not guarantee satisfactory mixing of the binder components. For compressive strength enhancement of cement paste prolonged mixing time occurred to be more important.
The pool boiling characteristics of dilute dispersions of alumina, zirconia and silica nanoparticles in water were studied. These dispersions are known as nanofluids. Consistently with other nanofluid studies, it was found that a significant enhancement in Critical Heat Flux (CHF) can be achieved at modest nanoparticle concentrations (<0.1% by volume). Buildup of a porous layer of nanoparticles on the heater surface occurred during nucleate boiling. This layer significantly improves the surface wettability, as shown by a reduction of the static contact angle on the nanofluid-boiled surfaces compared with the pure-water-boiled surfaces. CHF theories support the nexus between CHF enhancement and surface wettability changes. This represents a first important step towards identification of a plausible mechanism for boiling CHF enhancement in nanofluids.
The paper deals with spectral and lasing characteristics of
thulium-doped optical fibers fabricated by means of two doping
techniques,
i.e. via a conventional solution-doping method and via
a nanoparticle-doping method. The difference in fabrication was the
application of a suspension of aluminum oxide nanoparticles of defined
size instead of a conventional chloride-containing solution. Samples of
thulium-doped silica fibers having nearly identical chemical composition
and waveguiding properties were fabricated. The sample fabricated by
means of the nanoparticle-doping method exhibited longer lifetime,
reflecting other observations and the trend already observed with the
fibers doped with erbium and aluminum nanoparticles. The fiber
fabricated by means of the nanoparticle-doping method exhibited a lower
lasing threshold (by ~20%) and higher slope efficiency (by ~5% rel.).
All these observed differences are not extensive and deserve more
in-depth research; they may imply a positive influence of the
nanoparticle approach on properties of rare-earth-doped fibers for fiber
lasers.
Silver coatings have a very high reflection ability. To avoid their darkening from the hydrogen sulphide in the air, a thin layer of heat-resistant colorless lacquer is applied to the coatings. Silver plating is mainly used in jewelery, optics, electronics and electrical engineering. Depending on their application the thickness of the layer may vary from 2 to 24 μm. It can be done in several ways: chemical, electrochemical, contact, etc. The most common way of silver plating is the electrochemical deposition using cyanide and non-cyanide electrolytes. The cyanide electrolytes produce light, fine crystalline, dense and plastic coatings upon silver-plating. Usually silver coatings are applied with copper or nickel intermediate layer. In order to improve the de-oxidation of the aluminum surface new chemical treatment in acid – alkaline solution was applied. Our previous research shows that the presence of diamond nanoparticles in the electrolyte increase the metal deposition. Samples were prepared from electrolyte containing 10 g/l diamond nanoparticles. Their properties were compared to the properties of reference samples. The diamonds were obtained by detonation synthesis. The aim of this study is to obtain electrochemically deposited silver layer with high density, adhesion and electric conductivity on aluminum alloys substrate. The coatingwas directly plated without intermediate layer. Non-cyanide electrolyte composition and electrochemical parameters were determined in order to produce Ag coatings on Al alloy substrate without intermediate layer. The coating is with good adhesion, density and thickness of 14-23 μm.
The present study was conducted to evaluate the insecticidal efficiency and safety of zinc oxide nanoparticles (ZnO NPs) and hydrophilic silica nanoparticles (SiO2 NPs) against: adults of rice weevil (Sitophilus oryzae L.); red flour beetle (Tribolium castaneum Herbst.) and cowpea beetle (Callosobruchus maculatus F.) results showed that, both ZnO NPs and hydrophilic SiO2 NPs exhibited a significant toxic effect (df, F and p < 0.5) against S. oryzae and C. maculatus at the highest concentration while T. castaneum showed high resistance against the two tested materials. At the end of the experiment, recorded mortality was: 81.6, 98.3 and 58.3% at the highest concentration used for each insect (0.3, 2 and 8 gm ⋅ kg–1 of SNPs with C. maculatus, S. oryzae and T. castaneum, respectively), while mortality was 88.3, 100 and 38.3% at the highest concentration used for each insect (0.6, 2.5 and 8 gm ⋅ kg–1 of ZnO NPs with C. maculatus, S. oryzae and T. castaneum, respectively). Both tested materials caused high reductions in F1-progeny (%) with C. maculatus and S. oryzae. Histopathological examination of male mice livers showed hepatic architecture with congested blood sinusoids, binucleated hepatocytes nuclei, dilated central vein and margainated chromatin in some nuclei. Histopathological assessment of the lungs showed normal histoarchitecture. There were no differences in alveolar septa, bronchiolar and epithelium of the treated and untreated animals. Silica and zinc oxide nanoparticles have a good potential to be used as stored seed protectant alternatives if applied with proper safety precautions.
Black mold and green mold caused by Alternaria alternata and Penicillium digitatum, respectively, are the most important decay pathogens of tomato fruits during storage. Our research was aimed to control tomato phytopathogenic fungi A. alternata and P. digitatum in vitro and in vivo by using natural nanomaterials rosmarinic acid (RA-NPs) at concentrations of 0.3 and 0.6 mM, glycyrrhizic acid (GA-NPs) and glycyrrhizic acid ammounium salt (GAS-NPs) (0.1–0.2 mM). Characterizations of the tested nanoparticles were carried out by using dynamic light scattering which revealed that synthesized nanoparticles had particle sizes of less than 100 nm. In vitro studies revealed that the three tested nanoparticles reduced the growth of A. alternata and P. digitatum. Glycyrrhizic acid nanoparticles were the most effective in reducing the growth of the two tested pathogens followed by RA-NPs at 0.6 mM. Observations of A. alternata and P. digitatum by scanning electron microscopy (SEM) showed severe damage in the hyphae and deformities in the conidia due to the effect of the tested nanoparticles. In vivo results showed that, dipping tomato fruits as a post-harvest treatment in all of the tested nanoparticles at different concentrations, then stored at 10 ± 1°C and 90–95% relative humidity (RH) for 20 days greatly reduced the disease severity of infected fruits with the two tested pathogens. GA-NPs at 0.2 mM significantly reduced the development of black mold rot on tomato fruits. RA-NPs at 0.6 mM had the best effect in controlling P. digitatum of all naturally and artificially inoculated tomato fruits. Also, individual treatments of tomato fruits with RA-NPs, GA-NPs and GAS-NPs significantly reduced postharvest losses of fruit since they delayed decay and maintained fruit quality characteristics such as fruit firmness, titratable acidity and total soluble solids during cold storage.
This work presents a theoretical study for the distribution of nanocomposite structure of plasmonic thin-film solar cells through the absorber layers. It can be reduced the material consumption and the cost of solar cell. Adding nanometallic fillers in the absorber layer has been improved optical, electrical characteristics and efficiency of traditional thin film solar cells (ITO /CdS/PbS/Al and SnO2/CdS/CdTe/Cu) models that using sub micro absorber layer. Also, this paper explains analysis of J-V, P-V and external quantum efficiency characteristics for nanocomposites thin film solar cell performance. Also, this paper presents the effect of increasing the concentration of nanofillers on the absorption, energy band gap and electron-hole generation rate of absorber layers and the effect of volume fraction on the energy conversion efficiency, fill factor, space charge region of the nanocomposites solar cells.