Исследование электрического взрыва Al проводников в среде He

Электрический взрыв проводника является одним из перспективных методов получения металлических нанопорошков. Дисперсностью частиц, получаемых данным методом, можно управлять либо с помощью начальных условий взрыва, либо изменяя состав и давление газа в котором осуществляется синтез порошка. В настоящее время практически все металлические порошки получают в среде аргона. Осуществление ЭВП в среде гелия, может привести к образованию частиц с меньшим средним размером, что обуславливается меньшей плотностью газа более высоким коэффициентом теплопроводности. В работе приведены исследования электрического взрыва алюминиевых проводников в среде гелия, установлены основные закономерности процесса, а так же влияния газа на средний размер получаемых частиц.One of the promising methods for obtaining metallic nanopowders is electrical explosion of wire. The dispersion of the particles received by this method can be operated or by means of entry conditions of explosion, or changing structure and pressure of gas in which powder synthesis is carried out. Now practically all metal powders receive in the environment of argon. The implementation of EEW in a helium environment can lead to the formation of particles with a smaller average size, which is caused by a lower gas density with a higher thermal conductivity. Researches of electric explosion of aluminum conductors in the environment of helium are given in work, the main consistent patterns of process and also influences of gas on the average size of the received particles are determined

Removal of polycyclic aromatic hydrocarbons (PAHs) from water through degradable polycaprolactone electrospun membrane

Polycyclic aromatic hydrocarbons (PAHs) are common and persistent environmental pollutants produced during the incomplete combustion of fuels. They are known for their carcinogenic and mutagenic properties. Thus, their removal from water bodies is highly crucial and has become a critical issue globally. As a solution, here an electrospun polycaprolactone (PCL) membrane with a mean fiber diameter of 2.74 ± 1.3 μm was produced by electrospinning. Water contact angle (WCA) analysis confirmed the hydrophobic nature of the PCL membrane with a WCA of 124°, which remained stable over time. Differential scanning calorimetry analysis (DSC) revealed the semicrystalline nature of the membrane with the respective melting temperature (Tm) of 61.5 °C and crystallization temperature (Tc) of 29.6 °C. X-ray diffraction (XRD) analysis demonstrated that the crystalline structure of the PCL membrane could be preserved after electrospinning. Scanning electron microscopy analysis revealed that the membrane could be stretched without any rupture. The PCL membrane was used to scavenge PAHs (i.e. phenanthrene and anthracene) from water; the membrane could reach equilibrium capacity in a few hours, demonstrating the rapid removal of PAHs from water. The adsorption capacities for anthracene and phenanthrene were found to be 173 ± 17 and 560 ± 51 μg/g, respectively. The adsorption data fitted well with the pseudo-first-order kinetics model for both PAH molecules. The sorption could be attributed to hydrophobic adsorption, which allowed using the PCL membrane repeatedly with ethanol exposure to get rid of the adsorbed PAHs from the membrane’s surface. The partial degradation of the fibrous membrane in water was observed due to their hydrolysis-induced bulk erosion. However, the degradation was slow for the membrane kept in the air for 3 months. Overall, the PCL membrane with inherent biocompatibility, biodegradability, and good PAH sorption performance is a promising material for water depollution from toxic PAH compounds

Functional star-type polyethylene glycol copolymers for hydrogels and biohybrid gels

Poly(ethylene oxide) (PEG), polyether molecule of repeating ethylene oxide segments, is the most used synthetic polymer with many advantages, such as hydrophilicity, inert structure, non-immunogenic nature, and biocompatibility. Those unique features made possible their wide use in industrial and biorelated fields. Although the presence of a vast number of application areas, PEGs have come up with some notable problems, i.e., LCST, crystallinity, metal ion complexation. Many attempts have already been done for the synthesis of alternative molecules with the copolymerization of ethylene oxide with different comonomers (e.g., caprolactone, propylene oxide, lactide acid, and styrene). In this study, we studied six-armed star-type poly(EO-stat-PO) with various molecular weights (e.g., 6, 12 and 1 kg/mol) and terminal functionalities. The thesis started with a comprehensive review on the chemical nature and current limitations of the PEGs and insights into alternative PEG copolymers. In that section, the limitations of the PEGs were stated, and their alternatives were described with a particular focus on their applications. In the following section, rheology and dynamics of the copolymers were studied at entangled and melt states. Those molecules exhibited relatively low viscosity with strong shear thinning behavior. The relaxation of the copolymers showed variations with the polymer content and the molecular weight of the arm. Amorphous configuration was revealed for the copolymers and their interactions with water varied than their solutions in organic solvents with a possible scenario of configurational changes of helical chains. Those molecules did not reveal thermoresponsivity, however, nanoscale aggregates of the stars have been revealed due to hydrophobic interactions and hydrogen bonds with water molecules. Thereafter, we investigated properties of the six-armed sP(EO-stat-PO) and star PEG molecules having comparable molecular weights over viscosity, dynamics in water, phase behavior, and configuration. Both molecules exhibited similar viscous properties with a strong-shear thinning behavior and low elasticity. Amorphous configuration was revealed for the copolymer while the homopolymer was shown to be consisted of the highly crystalline segments. The size range of both molecules were in the range of 7-9 nm and the clusters of ca. 100 nm. In later section, those molecules were functionalized with various reactive groups (e.g., maleimide, vinyl sulfone, allyl, alkyne, succinimide carbonate, ethyl chloride, carboxylic acid, acrylate, aldehyde and silyl). An illustrative example, sP(EO-stat-PO) macromers with terminal acrylate and succinimide carbonate groups used for the layer preparation, and the coatings were evaluated over cell adhesion experiments. Isocyanate (NCO) terminated stars were used for in situ forming macromolecular networks with tunable structural inhomogeneity and elastic stiffness. In that context, water-diglyme solvent mixture at various combinations was used to control the kinetics of the hydrolysis of NCO groups and their subsequent cross-linking reactions. Such control over the cross-linking reactions significantly influenced the mechanical properties of the hydrogels and extends gelation times. Structural inhomogeneity of the gels was decreased due to the occurrence of homogeneous gel matrix. Those molecules were later used for cross-linking of elastin polypeptides over lysine amino acids, which present free nucleophilic amine groups to couple with NCO groups. Those gels were simultaneously functionalized with bicyclononynes (BCN) motives to create functional elastin scaffolds. In the last part of the thesis, star molecules and linear polyvinyl amine molecules were successfully used for the design of ultrathin nanolayers assemblies, which exhibited good stability at humidity conditions over three months.Beyond of the scope of the thesis, three different studies were also described. In the first part, alginate gel formation with well-known non-gelling ion, magnesium (Mg) was shown. Gelation in this system occurs at ca. 5–10 times higher concentration of ions than the reported for calcium-based gels. Alginate network formation with magnesium ions is very slow and is typically accomplished within 2–3 hours. Gelation with magnesium ions is also strongly dependent on alginate chemical composition as the presence of long guluronic units privileges faster gel formation. In the second part, redox-sensitive hydrogels and nanogels were produced by enzymatic cross-linking of thiol-functionalized polymer under mild conditions. Cells can be embedded in the hydrogels and proteins can be entrapped and released from the nanogels. These gels are fully degradable under mild and cytocompatible reductive conditions. In the last part of the appendix section, thermo and pH- responsive microgels from native elastin polypeptides were described, and the cross-linking of polypeptides was carried out by using either hydrophilic or hydrophobic cross-linkers. Both cross-linking approaches yielded elastin microgels, which revealed a volume change transition at 37 and 35.5°C and pH responsivity in the range of 5-7. Preliminary experiments were conducted to evaluate the suitability of these microgels for use as a drug-release system and demonstrated cytocompatibility, enzymatic degradability by elastase, and entrapping and slow release of a water-soluble biopolymerTo conclude, this study describes dynamics and intrinsic properties of the star typed PEG copolymers consisting of randomly distributed ethylene oxide and propylene oxide having various reactivities and their use as for gels and biohybrid hydrogels. These functional star type prepolymers are ideal candidates for a diverse range of applications as described above and have some advantages compared to the PEG homopolymers, which are respected gold stealth polymers for biological applications. We thereby believe that with further control of the structure together with appropriate degradable end groups might create multifunctional platforms at various length scales

Cyclodextrin-assisted synthesis of tailored mesoporous silica nanoparticles

Mesoporous silica nanoparticles (MSNs) have sparked considerable interest in drug/gene delivery, catalysis, adsorption, separation, sensing, antireflection coatings and bioimaging because of their tunable structural properties. The shape, size and pore structure of MSNs are greatly influenced by the type of additives used, e.g., solvent and pore-templating agent. Here, we studied the influence of cyclodextrin (CD) molecules on the formation of MSNs. The nanoparticles over 100 nm in diameter were synthesized by surfactant-templated, hydrolysis–polycondensation reactions in the presence of pristine CD (β-CD) or hydroxypropyl-functionalized CDs (HP-γ-CD and HP-β-CD). Depending on the formulation conditions, differently shaped MSNs, such as bean-like, spherical, ellipsoid, aggregate and faceted were generated. The morphology and size of MSNs varied with the CD-type used. Generally, spherical particles were obtained with β-CD, while a faceted morphology was observed for the particles synthesized using HP-CDs. The particle size could be tuned by adjusting the amount of CD used; increasing the CD concentration led to larger particles. MSNs synthesized in the presence of β-CD displayed a smaller particle size than those produced with HP-functional CDs. FTIR, TGA and solid-state 13C NMR demonstrated the adsorption of CDs on the particle surfaces. The proposed concept allows for the synthesis of silica nanoparticles with control over particle shape and size by adjusting the concentration of additives in a simple, one-pot reaction system for a wide range of applications

Electrospinning of Cyclodextrin Nanofibers: The Effect of Process Parameters

Cyclodextrin (CD) nanofibers have recently emerged as high-performance materials owing to their large surface area-to-volume ratio, along with the presence of high active CD content for their applications in drug delivery and water treatment. Even though there are several studies on the polymer-free electrospinning of CD molecules of different types, the effects of electrospinning process parameters on the morphology and diameter of the resultant fibers have not addressed yet. In this study, the influence of electrospinning process variables on the morphology and diameter of the resultant CD nanofibers is systematically studied using two different solvent systems, i.e., water and N, N-dimethylformamide (DMF). On adjusting the electrospinning process parameters (i.e., electrical field, flow rate, tip-to-collector distance (TCD), and needle diameter), uniform CD nanofibers could be produced from aqueous and DMF solutions. Generally, the electrospinning of thicker fibers was observed by increasing the applied voltage and flow rate due to higher mass flow. Increasing TCD boosted the fiber diameter. Likewise, the use of needles with larger diameters resulted in the electrospinning of thicker fibers from DMF solutions, which might be attributed to higher viscosity due to reduced shear rate

Influence of Hydrogen-Bonding Additives on Electrospinning of Cyclodextrin Nanofibers

The electrospinning of highly concentrated solutions of cyclodextrin (CD) leads to bead-free nanofibers without the need of a polymeric carrier. The occurrence of numerous hydrogen bonds among CD molecules is the main driving force for their electrospinning, and hence, additives with hydrogen-bonding potential can disturb the aggregation of CD molecules and affect their electrospinning. In this study, we systematically investigated the influence of five different hydrogen-bonding additives, i.e., methylamine (MA), ethylenediamine (ED), urea, 2,2,2-trifluoroethanol (TFE), and 1,1,1,3,3,3-hexafluoroisopropanol (HFIP), on the solution behavior of hydroxypropyl-β-CD (HP-β-CD) by rheology, conductivity, and NMR analyses, and the morphology of the electrospun HP-β-CD nanofibers by scanning electron microscopy. The 1H NMR chemical shifts of the HP-β-CD protons in D2O were observed with the incorporation of hydrogen-bonding molecules due to the occurrence of intermolecular associations between HP-β-CD and additives. Dynamic light scattering measurements revealed a clear decrease in the aggregate size with the introduction of additives. Unlike other additives, which showed a general decreasing trend in viscosity with increasing additive content, the addition of MA led to a significant increase in the viscosity with increasing concentration and gave rise to HP-β-CD nanofibers at lower concentrations. The addition of low concentrations of ED, urea, TFE, and HFIP led to thinner nanofibers due to the lower viscosity of the respective solutions. Increasing additive content deteriorated the electrospinnability of HP-β-CD solutions, resulting in beaded fibers. A systematic relationship was found between the solution viscosity and morphology of the respective electrospun fibers. Overall, this study, for the first time, reports the influence of hydrogen bonding on the polymer-free electrospinning of CD molecules and shows a correlation between solution properties and morphology of their electrospun nanofibers

Electrospinning of uniform nanofibers of Polymers of Intrinsic Microporosity (PIM-1): The influence of solution conductivity and relative humidity

WOS: 000483922700023Polymers of Intrinsic Microporosity (PIMs) are ultra-permeable macromolecules, which can be cast as a dense membrane and exploited in a wide spectrum of applications, particularly for gas separation owing to their extremely large inner surface area, free volume and high gas permeability. While they are mostly intended to serve as membranes for gas separation, in recent years, they have been also employed in water treatment applications owing to their solution processability, which enables the production of fibrous membranes by electrospinning. The fibrous form provides an increase in sorption performance, water permeability and flux for their application in water treatment. However, owing to the low conductivity of PIM-1 solutions in 1,1,2,2-tetrachloroethane (TeCA) that is the ideal solvent for the electrospinning of PIM-1 solutions, a higher polymer concentration is required to produce bead-free fibers. Furthermore, the electrospinning of highly concentrated PIM-1 solutions leads to the formation of microfibers. To tackle these problems, we herein incorporated an ammonium salt (i.e., tetraethylammonium bromide, TEAB) to increase the conductivity of PIM-1 solutions and study the impact of solution conductivity on the electrospinning of PIM-1 solutions. In parallel to the conductivity study, the influence of relative humidity on the electrospinning and morphology of PIM-1 fibers was explored. The addition of TEAB significantly increased the solution conductivity and drastically enhanced the electrospinnability of PIM-1. The electrospinning of PIM-1 solutions (10% (w/v)) in the presence 7.5 wt% TEAB (with respect to PIM-1) led to bead-free fibers, while at the same concentration, electrosprayed beads and droplet splashing were observed in the absence of TEAB. On the other hand, increasing humidity did not influence the electrospinnability of PIM-1 and the fiber texture, however, less fibers were formed in a given time at very high humidity conditions (similar to 80%). Overall, the experimental findings revealed that the addition of the salt drastically enhanced the electrospinnability of PIM-1 solutions owing to the enhanced conductivity and could lead to the formation of very thin PIM-1 fibers with 160 nm in diameter while no significant effect of relative humidity on the electrospinnability of PIM-1 solutions was observed

Efficient Removal of Polycyclic Aromatic Hydrocarbons and Heavy Metals from Water by Electrospun Nanofibrous Polycyclodextrin Membranes

Here, a highly efficient membrane based on electrospun polycyclodextrin (poly-CD) nanofibers was prepared and exploited for the scavenging of various polycyclic aromatic hydrocarbons (PAHs) and heavy metals from water. The poly-CD nanofibers were produced by the electrospinning of CD molecules in the presence of a cross-linker (i.e., 1,2,3,4-butanetetracarboxylic acid), followed by heat treatment to obtain an insoluble poly-CD nanofibrous membrane. The membrane was used for the removal of several PAH compounds (i.e., acenaphthene, fluorene, fluoranthene, phenanthrene, and pyrene) and heavy metals (i.e., Pb2+, Ni2+, Mn2+, Cd2+, Zn2+, and Cu2+) from water over time. Experiments were made on the batch sorption of PAHs and heavy metals from contaminated water to explore the binding affinity of PAHs and heavy metals to the poly-CD membrane. The equilibrium sorption capacity (qe) of the poly-CD nanofibrous membrane was found to be 0.43 ± 0.045 mg/g for PAHs and 4.54 ± 0.063 mg/g for heavy metals, and the sorption kinetics fitted well with the pseudo-second-order model for both types of pollutants. The membrane could be recycled after treatment with acetonitrile or a 2% nitric acid solution and reused up to four times with similar performance. Further, dead-end filtration experiments showed that the PAH removal efficiencies were as high as 92.6 ± 1.6 and 89.9 ± 4.8% in 40 s for the solutions of 400 and 600 μg/L PAHs, respectively. On the other hand, the removal efficiencies for heavy metals during the filtration were 94.3 ± 5.3 and 72.4 ± 23.4% for 10 and 50 mg/L solutions, respectively, suggesting rapid and efficient filtration of heavy metals and PAHs by the nanofibrous poly-CD membrane