Rational design and direct fabrication of multi-walled hollow electrospun fibers with controllable structure and surface properties

Multi-walled hollow fibers with a novel architecture are fabricated through utilizing a direct,one-step tri-axial electrospinning process with a manufacturing methodology which does not require any post-treatments for the removal of core material for creating hollowness in the fiber structure. The hydrophilicity of both inner and outer layers’ solution needs to be dissimilar and carefully controlled for creating a two-walled/layered hollow fiber tructure with a sharp interface. To this end, Hansen solubility parameters are used as n index of layer solution affinity hence allowing for control of diffusion across the layers and the surface porosity whereby an ideal multi-walled hollow electrospun fiber is shown to be producible by tri-axial electrospinning process. Multi-walled hollow electrospun fibers with different inner and outer diameters and different surface morphology are successfully produced by using dissimilar material combinations for inner and outer layers (i.e., hydrophobic polymers as outer layer and hydrophilic polymer as inner layer). Upon using different material combinations for inner and outer layers, it is shown that one may control both the outer and inner diameters of the fiber. The inner layer not only acts as a barrier and thus provides an ease in the encapsulation of functional core materials of interest with different viscosities but also adds stiffness to the fiber. The structure and the surface morphology of fibers are controlled by changing applied voltage, polymer types, polymer concentration, and the evaporation rate of solvents. It is demonstrated that if the vapor pressure of the solvent for a given outer layer polymer is low, the fiber diameter decreases down to 100 nm whereas solvents with higher vapor pressure result in fibers with the outer diameter of up to 1 μm. The influence of electric field strength on the shape of Taylor cone is also monitored during the production process and the manufactured fibers are structurally investigated by relevant surface characterization techniques

Performance comparison of CVD grown carbon nanofiber based on single- and multi-layer graphene oxides in melt-compounded PA6.6 nanocomposites

In the present study, newly design hybrid nanostructures were produced by growing long carbon nanofibers (CNF) on single- and multi-layer graphene oxide (GO) sheets in the presence of catalyst by chemical vapor deposition (CVD). Chemical composition analysis indicated the formation of Fe-C bonds by the deposition of carbon atoms on catalyst surface of Fe2O3 and increasing in C/O atomic ratio confirming CNF growing. These hybrid additives were distributed homogeneously through polyamide 6.6 (PA6.6) chains by high shear thermokinetic mixer in melt phase. Spectroscopic studies showed that the differences in the number of graphene layer in hybrid structures directly affected the crystalline behavior and dispersion state in polymer matrix. Flexural strength and flexural modulus of PA6.6 nanocomposites were improved up to 14.7% and 14% by the integration of 0.5 wt% CNF grown on multi-layer GO, respectively, whereas there was a significant loss in flexural properties of single-layer GO based nanocomposites. Also, the integration of 0.5 wt% multi-layer GO hybrid reinforcement in PA6.6 provided a significant increase in tensile modulus about 24%. Therefore, multi-layer GO with CNF increased the degree of crystallinity in nanocomposites by forming intercalated structure and acted as a nucleating agent causing the improvement in mechanical properties

Multiscale Analysis of the Gold Dust Defect in AISI 430 Industrial Stainless Steels: Influence of the Aluminum Content

The "Gold Dust Defect" affects the surface quality of AISI 430 ferritic stainless steels. However, there is a very limited number of studies focusing on it. To better understand its nature, we have combined several techniques, such as x-ray photoelectron spectroscopy, atomic force microscopy, and transmission electron microscopy, in order to extract a maximum of structural and compositional information. Our results show that the surface quality, microstructure, and chemistry of the samples are strongly affected by the aluminum content, the severity of the defect being the highest at the lowest Al concentration. Not only is the concentration of the defects at the surface strongly reduced when increasing the Al. at.% but the depth of the cavities is also reduced by a factor of 3 when the Al content is increased from 0.09 at.% to 0.59 at.%. Our results provide new information on the nature of this defect, and show that an increase of the aluminum content allows the Cr concentration to be maintained in the range of values required to maintain the passivity of the steel, thus improving the surface quality

Rapid, low temperature synthesis of germanium nanowires from oligosilylgermane precursors

New oligosilylgermane compounds with weak Ge–H bonds have been used as precursors for the rapid synthesis of germanium (Ge) nanowires in high yields (>80%), via a solution–liquid–solid (SLS) mechanism, using indium (In) nanoparticles as a seeding agent over a temperature range between 180 and 380 °C. Even at low growth temperatures, milligram quantities of Ge nanowires could be synthesized over a reaction period of between 5 and 10 min. The speed of release of Ge(0) into the reaction environment can be tuned by altering the precursor type, synthesis temperature, and the presence or lack of an oxidizing agent, such as tri-n-octylphosphine oxide (TOPO). Energy-dispersive X-ray analysis showed that silicon atoms from the precursors were not incorporated into the structure of the Ge nanowires. As both In and Ge facilitate reversible alloying with Li, Li-ion battery anodes fabricated with these nanowires cycled efficiently with specific capacities, i.e., >1000 mAh g–

Coating-Dependent Effects of Silver Nanoparticles on Tobacco Seed Germination and Early Growth

Silver nanoparticles, AgNPs, are used in a wide range of consumer products because of their excellent antimicrobial properties. AgNPs released into the environment are prone to transformations such as aggregation, oxidation, or dissolution so they are often stabilised by coatings that a ect their physico-chemical properties and change their e ect on living organisms. In this study we investigated the stability of polyvinylpyrrolidone PVP and cetyltrimethylammonium bromide CTAB coated AgNPs in an exposure medium, as well as their e ect on tobacco germination and early growth. AgNP-CTAB was found to be more stable in the solid Murashige and Skoog MS medium compared to AgNP-PVP. The uptake and accumulation of silver in seedlings was equally effcient after exposure to both types of AgNPs. However, AgNP-PVP induced only mild toxicity on seedlings growth, while AgNP-CTAB caused severe negative e ects on all parameters, even compared to AgNO3. Moreover, CTAB coating itself exerted negative e ects on growth. Cysteine addition generally alleviated AgNP-PVP-induced negative e ects, while it failed to improve germination and growth parameters after exposure to AgNP-CTAB. These results suggest that the toxic e ects of AgNP-PVP are mainly a consequence of release of Ag+ ions, while phytotoxicity of AgNP-CTAB can rather be ascribed to surface coating itself

Structure of the Malpighian tubule cells and annual changes in the structure and chemical composition of their spherites in the cave cricket Troglophilus neglectus Krauss, 1878 (Rhaphidophoridae, Saltatoria)

Periodical changes in the structure of spherites in the Malpighian tubule cells of the cave cricket Troglophilus neglectus were studied to elucidate their role during the cricket\u27s life cycle in natural circumstances. Special interest was given to the dormant overwintering period when we hypothesized that the primary role of spherites is to supply minerals for basic vital processes. The investigation was carried out by light and transmission electron microscopy, energy dispersive X-ray spectroscopy, electron energy-loss spectroscopy and energy-filtering TEM. Spherites are present only in the middle Malpighian tubule segment, consisting of Type 1 cells, characterized, among other features, by a round, apically placed nucleus and numerous spherites, and a few Type 2 cells with an elongated nucleus in the centre and sparse spherites. At the beginning of dormancy in November juveniles, minerals are accumulated in spherites and then decline until March.In one-year-old May larvae, spherites are commonly rich in minerals, and from July onwards they are progressively exploited in the adults. Spherite destruction starts with apoptosis in senile October individuals. The findings suggest that the mineral supply of spherites in Malpighian tubules is crucial to supporting vital processes throughout the life cycle of T. neglectus

Analysis of Trisiloxane Phosphocholine Bilayers

We have synthesized unique siloxane phosphocholines and characterized their aggregates in aqueous solution. The siloxane phosphocholines form nearly monodisperse vesicles in aqueous solution without the need for secondary extrusion processes. The area/lipid, lipid volume, and bilayer thickness were determined from small-angle X-ray scattering experiments. The impetus for the spontaneous formation of unilamellar vesicles by these compounds is discussed

Dispersoids in Al-Mg-Si Alloy AA 6086 Modified by Sc and Y

The aluminium alloy AA 6086 attains the highest room temperature strength among Al-Mg-Si alloys. This work studies the effect of Sc and Y on the formation of dispersoids in this alloy, especially L12-type ones, which can increase its high-temperature strength. A comprehensive investigation was carried out using light microscopy (LM), scanning (SEM), and transmission (TEM) electron microscopy, energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and dilatometry to obtain the information regarding the mechanisms and kinetics of dispersoid formation, particularly during isothermal treatments. Sc and Y caused the formation of L12 dispersoids during heating to homogenization temperature and homogenization of the alloys, and during isothermal heat treatments of the as-cast alloys (T5 temper). The highest hardness of Sc and (Sc + Y) modified alloys was attained by heat-treating alloys in the as-cast state in the temperature range between 350 °C and 450 °C (via T5 temper)