Dissolved In N,N-dimethylformamide Research Articles

Effect of mixed iodine and bromine on optical properties in methylammonium lead chlorine (MAPbCl3) spin-coated on the zinc oxide film

The optical influence of mixing methylammonium lead chlorine (MAPbCl3) with iodine and bromine was studied in this work. The spin coating method deposited three layers of perovskites (MAPbCl3, MAPbCl2I, and MAPbCl2Br) on a layer of zinc oxide (ZnO). The zinc oxide solution was prepared by dissolving dehydrated zinc acetate [Zn(CH3COO)2, 2H2O]> 99.5% purity in ethanol to give a 0.5 M solution. The perovskite solutions were prepared using lead chloride (PbCl2), methylammonium chloride (MACl), methylammonium iodide (MAI), and methylammonium bromide (MABr). The precursor containing iodine was dissolved in N, N-dimethylformamide (DMF) and the others in dimethyl sulphoxide (DMSO 99.9%). The films produced were characterized by UV-Visible. The analysis showed that the sample mixed with iodine has good properties. This sample absorbs the most and has a small band gap of 2 eV. The degradation study reveals that the unmixed sample (MAPbCl3) is the most stable.

Bioinspired perovskite quantum dots microfibers from microfluidics

As perovskite quantum dots (PeQDs) are performing their outstanding characteristics, incremental efforts have been devoted to such materials. Here, inspired by the spider spinning process, we present novel PeQDs microfibers with tailorable morphologies and functions from a multi-injection microfluidic approach. The microfibers were generated by introducing PeQDs precursors into each barrel of the inner capillary array and mixing them in the spindle middle channel, where the poly(vinylidene fluoride) (PVDF) dissolved in N,N-dimethyl formamide (DMF) was also injected as their sheath fluid. During this process, the PeQDs were in situ synthesized with the connection of precursor cations and anions in the core fluid; while the PVDF formed solidified microfibers to encapsulate PeQDs with the fast dispersion of DMF into the outer aqueous solution. Thus, the good encapsulation of PeQDs was achieved in PVDF microfibers, which effectively protected them from different hostile environments. Because of the highly tunable spinning processes, the microfibers exhibited controllable diameters and helical geometric structures, and the encapsulated PeQDs could yield adjustable emission peaks. Based on the PeQDs microfibers, we have explored their potential as luminescent materials in barcodes and as flexible photodetectors, which make such microfibers highly versatile for different areas.

Fluorescent Cationic Conjugated Polymer-Based Adaptive Developing Strategy for Both Sebaceous and Blood Fingerprints.

Both latent sebaceous and blood fingerprints may provide valuable information for forensic investigation. To detect both types of fingerprints with no need to predistinguish them, a new adaptive developing strategy was proposed. A cationic conjugated polymer with poly[p-(phenylene ethylene)-alt-(thienylene ethynylene)] backbone (PPETE-NMe3+) was synthesized, which was dissolved in N,N-dimethylformamide (DMF) to form the developing solution. Fingerprints were developed by a simple dropping and incubating process without any pre-/post-treatments. Fluorescent photographs of the developed fingerprints on various substrates demonstrated that this developing strategy was effective for both types of fingerprints on nonporous substrates. Gray value analysis further confirmed the enhancement of the legibility of the fingerprint images. The preliminary mechanism exploration suggested that certain weak interactions, such as hydrophobic interaction and electrostatic interaction, may synergistically contribute to the interaction between the polymer and fingerprint components. The molecular design of the polymer combined with an appropriate solvent endowed the developing system the adaptiveness toward different types of fingerprints. This adaptive developing strategy made the fingerprint-developing process more efficient and may be further extended to more practical application scenes.

Self-Organized Implanting of Micro/Nanofiltration Membranes in Advanced Flow μ-Reactors.

A low-cost, simple, and one-step synthesis of cellulose acetate nanoparticles (CANPs) has been invented using a continuous-flow advanced microfluidic reactor. For this purpose, the CANPs are self-organized inside a cross-junction microchannel by flowing cellulose acetate (CA) dissolved in N,N-dimethylformamide (DMF) through the axial inlet and the antisolvent water through the pair of side inlets. The preferential solubility (insolubility) of DMF (CA) to antisolvent water stimulates the in situ synthesis of CANPs at the DMF/water miscible interface following a phase-inversion process. Subsequently, nanofiltration, ultrafiltration, and microfiltration membranes of different porosities and permeabilities have been prepared from freshly synthesized CANPs. The porosity, thickness, transparency, and wettability of the membranes are tuned by varying the thickness of the membranes, size of the nanoparticles, and the porosity of the membranes. The as-synthesized CANPs show enhanced bactericidal properties with and without loading an external drug, curcumin, which has been validated against the Gram-negative Pseudomonas aeruginosa species. Importantly, enabling a pulsatile flow during the synthesis, the CANPs are embedded as nanofiltration membranes inside the microfluidic channel. Such microfluidic devices have been used to separate a corrosive dye from water. Concisely, the proposed in situ synthesis of CANPs in the continuous-flow microfluidic reactors, their usage for fabricating membranes with tunable wettability and transparency, and their subsequent integration into the microfluidic channel show the potential of the invention for a host of applications related to health care and environmental remediation.

Electrospun Polyacrylonitrile-Keratin Derived Carbon Nanofiber as Electrode for Asymmetric Supercapacitor

Electrospinning is one method to produce nanosized materials in a form of fibers with a large variety of polymeric solutions. In this research, Polyacrylonitrile (PAN) dissolved in N,N-Dimethylformamide (DMF) as the primary solvent, loaded with keratin protein solution, was blended using the said fabrication method to change its properties. The loading of the keratin solution concentrates varied from 5%, 7%, and 10% relative to the volume of the solution. The PAN-keratinnano substances were characterized using Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Cyclic Voltammetry (CV), and Galvanostatic Cycling with Potential Limitation (GCPL) to illustrate the properties of the fiber. The SEM micrographs showed that upon adding keratin into the PAN the diameter lengths of the imaged fibers were still nanofiber. As the viscosity of the solution is increased, the beads become bigger, the average distance between beads and the fiber diameter increases, and the shape of the beadings changes from spherical to spindle-like. In addition, CV and GCPL revealed that as the potential scan rate is being increased, the surrounded area of the CV also increases. The presence of redox peaks implies that a faradaic process occurs. The migration and diffusion of ions can be supported by the carbonized fibers. GCPL shows the triangular shape with symmetric charging and discharging slopes at a current density of 0.5mah, 1mah, 1.5mah and 2.5mah, confirming that the electrodes behave as a pure electric double layer capacitor (EDLC).

Infrared spectroscopic and computational studies of Co(ClO4)2 dissolved in N,N-dimethylformamide (DMF). Vibrations of DMF influenced by Co2+ or ClO4− or both

Infrared (IR) spectroscopy for N,N-dimethylformamide (DMF) shows that the OCN bend (δOCN) and the CO stretch (νCO) vibrations undergo an upshift and a downshift, respectively, on the dissolution of Co(ClO4)2. Quantum chemical calculations are performed for optimizing the structures and predicting the IR spectra of model complexes for solute species. The calculations reveal that Co2+ exerts a much larger influence than ClO4− on the vibrations of DMF. For Co2+(DMF)6, in which each DMF molecule is coordinated to Co2+ via the O atom, the Co2+⋯DMF interaction upshifts the δOCN frequencies (+24 cm−1 on average) while the dipole coupling gives rise to splitting (12 cm−1) of the modes. On the other hand, the Co2+⋯DMF interaction downshifts the νCO frequencies (−15 cm−1 on average) while the splitting of the modes amounts to 37 cm−1. As a result, one of the νCO modes is located at an upshifted position (+13 cm−1) despite the O-atom coordination. For six-coordinated isomers of Co2+(DMF)7, the δOCN and νCO frequencies of the second-sphere DMF are close to those of bulk DMF in neat liquid. The calculations indicate that it is difficult to prove or exclude the formation of contact ion pairs [Co(DMF)5ClO4]+ and solvent-shared ion pairs [Co(DMF)6ClO4]+ by IR spectroscopy in the δOCN and νCO regions. However, asymmetric ClO stretches of the ClO4− moiety suggest that conceivable is the coexistence of solvent-shared ion pairs only.

Discovering Biomass Structural Determinants Defining the Properties of Plant-Derived Renewable Carbon Fiber

SummaryTraditional lignocellulosic feedstock research has focused on biomass characteristics essential for improving saccharification efficiency, yet the key biomass features underlying high-quality renewable lignin materials remain unknown. Nevertheless, modern biorefinery cannot achieve sustainability and cost-effectiveness unless the lignin stream can be valorized. We hereby addressed these scientific gaps by investigating biomass characteristics defining lignin-based carbon materials properties. Lignin from eight sorghum samples with diverse characteristics was fabricated into carbon fibers (CFs). Remarkably, only lignin uniformity was found to define CF mechanical performance, highlighting the new structure-property relationship. Contrarily, lignin content and composition did not impact on carbon material properties. Mechanistic study by XRD and Raman spectroscopy revealed that higher lignin uniformity enhanced CF microstructures, in particular, turbostratic carbon content. The study for the first time highlighted lignin uniformity as an important biomass structure determinant for renewable products, which opened up new avenues for feedstock design toward diverse products enabling sustainable and cost-effective bioeconomy.

Development of multifunctional polyacrylonitrile/silver nanocomposite films: Antimicrobial activity, catalytic activity, electrical conductivity, UV protection and SERS-active sensor

The formulation of polymer with embedded nanoparticles results in promising nanocomposites and substrates for smart, medical and analytical applications. Nanocomposite polyacrylonitrile (PAN) films containing silver nanoparticles (Ag NPs) were developed to introduce multifunctional film matrix with antimicrobial activity, electrical conductivity, ultraviolet blocking and catalytic activity. In addition, the prepared PAN/Ag NPs nanocomposite films can be applied in the identification of biological molecules using surface enhanced Raman scattering (SERS). PAN/Ag NPs nanocomposites were prepared by reducing Ag+ to Ag0 under microwave irradiation. The reduction process of Ag+ to Ag NPs was performed in-situ within the matrix of polyacrylonitrile fibers dissolved in N, N-dimethylformamide (DMF). Thus, DMF was functioned as a reducing agent for the generation of Ag NPs from silver nitrate (AgNO3) and as a solvent for polyacrylonitrile. The Ag NPs were evaluated Via UV–vis spectrum TEM. The PAN and PAN/Ag NPs nanocomposite were analyzed, by using SEM, EDX, FTIR, XRD, XPS, TGA and DSC. The reaction mechanism for in-situ deposition of Ag NPs onto PAN polymer matrix was also explored. The influence of Ag NPs on multifunctional properties of PAN nanocomposite films such as coloration properties, antimicrobial activity, electrical conductivity property, UV protection activity, SERS and catalytic activity were evaluated. The results displayed that, the PAN/Ag NPs nanocomposites films were exhibited excellent antimicrobial activities against different micro-organisms as well as very good electrical conductivity and UV protection properties. Moreover, the PAN/Ag NPs nanocomposites films were shown highly SERS sensitivity at low concentration as well as high catalytic activity. In straightforward, this simple, fast and inexpensive novel approach will pave the way for a variety of smart medical applications, such as scar-less burn wound healing and biological protective substrates as well as analytical application.

The Influence of Graphene Addition on the Properties of Composite rGO/PAN Membranes and Their Potential Application for Water Disinfection.

The paper presents a method of obtaining composite polyacrylonitrile-based (PAN) membranes with the addition of reduced graphene oxide (rGO). The membranes were obtained using phase inversion method from a homogeneous rGO dispersion in a solution of PAN dissolved in N, N-dimethylformamide (DMF). The impact of the amount of rGO addition to the PAN matrix on the physicochemical, structural, transport, and separation properties and on fouling resistance was studied. Composite membranes, due to the method of preparation used and the addition of rGO, are characterized by very good transport properties (~390 L/m2 h) and by a high degree of protein retention (85%). Reduced graphene oxide has biocidal properties, which, as we have shown, depend on the size of nanoparticles and the type of microorganism. rGO/PAN membranes, on the other hand, show biostatic properties against Gram-negative bacteria (Escherichia coli), Gram-positive bacteria (Staphylococcuc aureus) and fungi (Candida albicans). Thus, the obtained composite membranes can be potentially used in water disinfection.

Synthesis and Application of Magnesium Diethylphosphate for Rechargeable Magnesium Battery

AbstractAn attempt has been made to synthesize chloride free Magnesium salt. Magnesium Diethylphosphate (Mg(DEP)) by adopting a novel and economically viable chemical route. The salt is dissolved in N,N‐Dimethylformamide (DMF) and used as electrolyte for rechargeable magnesium battery (RMB). Reversible magnesium dissolution and deposition was examined in Mg‐half cell and full cell at varying potential windows. The reversible Mg intercalation and de‐intercalation at graphite cathode was analyzed by cyclic voltammetry, galvanostatic charge‐discharge and impedance analysis. Mg‐Graphite full cell has shown a discharge capacity of 70 mAh/g for 180 cycles. The cycled electrode's SEM, XRD, XPS analysis conclude the plausible Mg‐ions intercalation into the graphite. The studies could help in the development of chloride free Mg salts with potential application to serve as electrolyte for RMBs.

SOLUTION PARAMETER EFFECT ON POLYSULFONE FIBERS VIA ELECTROSPINNING: FABRICATION, CHARACTERIZATION AND WATER FLUX PROPERTY

This research investigates the solution parameters, i.e., polymer concentration and addition of manganese (IV) oxide (MnO2) nanoparticles, for the fabrication of polysulfone (PSF) fibers via electrospinning. Initially, PSF was dissolved in N,N-dimethylformamide (DMF) solvent and electrospun fibers with different morphologies were obtained using the range of PSF concentration of 10% (w/v) to 25% (w/v). Subsequently, PSF with the concentration of 20% (w/v) (denoted as PSF(20%)) was chosen to blend with 0.2% (w/v) of MnO2 as it gave the most stable electrospinnability and uniform fiber diameter. The fabricated electrospun PSF(20%) and PSF(20%)-MnO2 fibrous membranes were characterized to determine the morphology, wettability property, zeta potential, and tensile strength. The presence of MnO2 improved tensile strength as it reduced the fiber diameter that eventually made a more compact fiber mat membrane. The results of contact angle confirmed that the fabricated fiber exhibited more hydrophobic property in the presence of MnO2 nanoparticles. Thus, it reduced the pure water flux of PSF fiber membrane. The more hydrophobic nature of the proposed nanofiber might be useful in enhancing the application of PSF fiber in oil-water separation process.

Understanding the supercapacitor properties of electrospun carbon nanofibers from Powder River Basin coal

We present a zero-waste approach where raw coal from Powder River Basin was depolymerized using environmentally friendly solvents. Sequentially, the depolymerized coal, referred to as coal chars, was dissolved in N,N-dimethylformamide (DMF). Then, the coal chars/DMF mixture was combined with polymeric precursors (PAN/PVP) to form a homogeneous solution for carbon nanofiber fabrication via electrospinning. By incorporating 20 wt% coal chars to PAN/PVP mixture, X-ray photoelectron spectroscopy results revealed 1.36% quinone oxygen and 21.2% overall oxygen on the surface of coal-derived carbon nanofibers (CCNF), referred to 20CCNF. Compared to the CNF derived only from PAN/PVP, 20CCNF revealed wider pore size range of 2–7 nm and higher surface area (1678.8 m2/g) in the microporous region (<2 nm). Furthermore, 20CCNF showed significantly enhanced conductivity (7.6 S/cm), which may be attributed to the high graphitization degree of coal chars. The combined effects of O2-enriched surface and microstructures resulted in much higher specific capacitance of 20CCNF (299.4 F/g) than the PAN/PVP CNF (157.8 F/g) at a current density of 1 A/g. Additionally, CCNF showed greatly reduced internal and ion diffusion resistances. Finally, 93.0% specific capacitance of 20CCNF remained after 10,000 cycles of galvanostatic charge-discharge, demonstrating that CCNF possessed desirable durability.

Doxycycline release and antibacterial activity from PMMA/PEO electrospun fiber mats.

Objective:To investigate the use of polymethyl methacrylate (PMMA) electrospun fiber mats containing different amounts of polyethylene oxide (PEO) as a doxycycline delivery system and to test antibacterial activity against an oral pathogen.Methodology:PMMA powders or PEO (mol wt 200 Kd) (10,20,30% w/w/) were dissolved in N, N-dimethylformamide (DMF) to obtain a final polymer concentration of 15% in DMF (w/v). 2% Doxycycline monohydrate was added to the solutions and submitted to vortex mixing. The solution was transferred to a plastic syringe and fit into a nanofiber electrospinning unit. The parameters applied were: voltage at 17.2 kV; distance of 20 cm between the needle tip and the collector plate; target speed at 2 m/min; and transverse speed at 1cm/min. Syringe pump speed was 0.15 mm/min. The drug release analysis was performed by removing aliquots of the drug-containing solution (in PBS) at specific periods. Doxycycline release was quantified using RP-HPLC. Fiber mats from all groups had their antibacterial action tested against S. mutans based on inhibition halos formed around the specimens. The experiments were performed in triplicate. Gravimetric analysis at specific periods was performed to determine any polymer loss. Morphological characterization of the electrospun fibers was completed under an optical microscope followed by SEM analysis.Results:The addition of PEO to the PMMA fibers did not affect the appearance and diameter of fibers. However, increasing the %PEO caused higher doxycycline release in the first 24 h. Fibers containing 30% PEO showed statistically significant higher release when compared with the other groups. Doxycycline released from the fibers containing 20% or 30% of PEO showed effective against S. mutans.Conclusion:The incorporation of PEO at 20% and 30% into PMMA fiber mat resulted in effective drug release systems, with detected antibacterial activity against S. mutans.

联苯衍生物的光折变效应

The photorefractive phenomenon was observed in biphenyl derivatives materials under continuous wave laser(532nm) irradiation. Two types of sample were prepared:biphenyl derivatives(2-(4-hydroxypheny)-5-pyrimidinol, 4'-hydroxy-4-biphenyl carbonitrile, 3-amino-4-phenylphenol and 4, 4'-Biphenol) were respectively dissolved in N, N-dimethylformamide(DMF) detaining 4-solution samples, and the concentration was 2wt%; biphenyl derivatives were dissolved into a saturated solution of anhydrous ethanol as a solute, and the single crystals of biphenyl derivatives were obtained by slow evaporation of the ethanol solution at an ambient temperature. The experimental results show that cyclic symmetric bright-dark spatial stripes were formed after the laser beam transmitted through the 2-(4-hydroxypheny)-5-pyrimidinol, 4'-hydroxy-4-biphenyl carbonitrile and 3-amino-4-phenylphenol solutions with an asymmetric chromophore. On the other hand, the transmitted laser spot has no change in 4, 4'-Biphenol solution, no matter how the laser power density was increased. A distorted beam was observed when the 2-(4-hydroxypheny)-5-pyrimidinol, 4'-hydroxy-4-biphenyl carbonitrile, and 3-amino-4-phenylphenol single crystals were irradiated by high optical power density, while the laser beam spot experienced no change in the 4, 4'-Biphenol single crystal. The different values of the Open/Dark current were about 10 nA in biphenyl derivatives with an asymmetric chromophore. The distorted optical spot stretched along the laser polarization. The threshold value of laser power density for distorted spot was about 100 W/cm2 and 10 W/cm2 in the solutions and single crystals of biphenyl derivatives with an asymmetric chromophore. An explanation was proposed for the symmetric cyclic bright-dark spatial stripes, being that they were induced by the photorefractive effect. The photorefractive effect relies on the formation of a space-charge field through the illumination of inhomogeneous light intensity patterns. The biphenyl derivatives were found to be photorefractive materials.

Electrospinning of PAN and composite PAN-GO nanofibres

Purpose: The aim of this study was to present the influence of used reinforcement phase – graphene oxide (GO) and the electrospinning process parameters (the distance between the nozzle and collector) on the morphology and the structure of the obtained composite PAN-GO nanofibres. Design/methodology/approach: To produce pure polymer nanofibers, a 10% (wt.) electrospinning solution the polyacrylonitrile (PAN) was dissolved in N, N-dimethylformamide (DMF). The spinning solution used for electrospinning PAN-GO composite fibres was made by dissolving the PAN in a mixture of GO and DMF. By changing the configuration of the distance between the nozzle and collector (10 and 20 cm) and maintaining the remaining parameters (solution flow rate and potential difference between the electrodes), four samples in the form of nanofibrous mats were made. In order to identify the structure and morphology of the reinforcing phase, X-ray microanalysis (EDX) and scanning electron microscopy (SEM) were performed. In addition, the structure of graphene oxide microparticles was investigated by a Raman spectrometer. In order to determine the influence of the distance between the nozzle and the collector used in the electrospinning process and the addition of the reinforcing phase to the morphology and structure of the obtained PAN polymer nanofibres and PAN-GO composite nanofibres, they were examined using SEM. The analysis of the chemical composition of PAN and PAN-GO fibres was carried out using X-ray microanalysis. Findings: The morphology and structure analysis indicated that polymer nanofibres PAN for both the distances between the nozzle and the collector show no structural defects and presented same diameter over the entire length of the fibre. Nanofibres with the addition of GO obtained at both distances between the electrodes, showed defects in the form of beads. In addition, it was observed that with increasing distance between the nozzle and collector the diameter of obtained nanofibres is smaller for both pure PAN and composite PAN-GO samples. Research limitations/implications: The paper is the basis for further research in the field of the use of PAN-GO composite nanofibres as water purification materials. Originality/value: The electrospinning method can be an alternative to conventional methods for the production of filtering membranes due to the ease of carrying out the process and the fact that a material with a high specific surface area is obtained.

Force induced piezoelectric effect of polyvinylidene fluoride and polyvinylidene fluoride-co-trifluoroethylene nanofibrous scaffolds.

Polyvinylidene fluoride and its co-polymer with trifluoroethylene are promising biomaterials for supporting nerve regeneration processes because of their proven biocompatibility and piezoelectric properties that could stimulate cell ingrowth due to electrical activity upon mechanical deformation. This study reports the piezoelectric effect of electrospun polyvinylidene fluoride scaffolds in response to mechanical loading. An impact test machine was used to evaluate the generation of electrical voltage upon application of an impact load. Scaffolds were produced via electrospinning from polyvinylidene fluoride and polyvinylidene fluoride-co-trifluoroethylene with concentrations of 10-20 wt% dissolved in N,N-dimethylformamide (DMF) and acetone (6:4). The structural and thermal properties of scaffolds were analyzed using Fourier Transform Infrared Spectroscopy and Differential Scanning Calorimetry, respectively. The piezoelectric response of the scaffolds was induced using a custom-made manual impact press machine. Impact forces between 0.4 and 14 N were applied. Fourier Transform Infrared Spectroscopy and Differential Scanning Calorimetry results demonstrated the piezoelectric effect of the electrospun polyvinylidene fluoride and polyvinylidene fluoride-co-trifluoroethylene scaffolds. All the scaffolds exhibited a piezoelectric polar beta-phase formation. Their thermal enthalpies were higher than the value of the initial materials and exhibited a better tendency of crystallization. The electrospun scaffolds exhibited piezoelectric responses in form of voltage by applying impact load. Polyvinylidene fluoride-co-trifluoroethylene scaffolds showed higher values in the range of 6-30 V as compared to pure polyvinylidene fluoride. Here, the mechanically induced electrical impulses measured were between 2.5 and 8 V. Increasing the impact forces did not increase the piezoelectric effect. The results demonstrate the possibility of producing electrospun polyvinylidene fluoride and polyvinylidene fluoride-co-trifluoroethylene scaffolds as nerve guidance with piezoelectric response. Further experiments must be carried out to analyze the piezoelectricity at dynamic conditions.

Gold Catalyst-Assisted Metal Organic Chemical Vapor Deposition of Bi-Te-Ni-Cu-Au Complex Thermoelectric Materials on Anodic Aluminum Oxide Nanoporous Template

Complex materials have unique thermal and electron transport properties. In this work, a novel catalyst-assisted metal organic chemical vapor deposition approach was employed to make Bi-Te-Ni-Cu-Au complex materials on an anodic aluminum oxide nanoporous substrate. Nickel acetate, copper nitrate, bismuth acetate, and tellurium (IV) chloride dissolved in N,N-dimethylformamide (DMF) were used as the metal sources for Ni, Bi, Cu, and Te, respectively. Hydrogen was used as the carrier gas. The anodic aluminum oxide substrate sputter-coated on a thin gold coating and was kept at 500 °C in a quartz tube in the reaction chamber. The chemical vapor deposition time was two hours. Scanning electron microscopy was used to reveal the morphology of the deposited materials. Due to metal catalyst assisted growth, the Bi-Te-Ni-Cu-Au materials were self-assembled into islands distributed fairly uniformly on the substrate. The mechanism for the morphological development of the materials was investigated. It was found that the Au nanoparticles facilitated the formation of the complex Bi-Te-Al-Ni-Cu materials. The prepared nanostructure has the highest absolute Seekbeck coefficient value of 260 µV/K, which is more than twice the value obtained from the bulk material.

Effect of Processing Parameters on the Morphology of PVDF Electrospun Nanofiber

Electrospinning is a process that produces continuous polymer fibers with diameters in the submicron range through the action of an external electric field imposed on a polymer solution or melt. Because of the tiny diameter in several hundreds of nanometers and the high porosity, electrospun membranes show potential applications in extensive areas such as filtration systems, biomedical tissue templates, drug delivery membranes, and so on. In the electrospinning process, some parameters such as polymer concentration, feeding rate of the polymer solution, additives, humidity, viscosity, surface tension, applied voltage, and nozzle-to ground collector distance will affect the fiber diameter and morphology. In this work, we have evaluated the effects of two processing parameters including the flow rate of the polymer solution and nozzle-to ground collector distance, on the morphology of the fibers formed. The solutions used in the electrospinning experiments were prepared using Poly(vinylidene fluoride) (PVDF). This material was dissolved in N,N-dimethylformamide (DMF) to make solutions with concentrations of 20 wt%. These solutions was electrospun using a 5 mL plastic syringe with an 8 gauge stainless needle at an applied voltage of 20.0 kV, a flow rate of 0.02-0.04 mL/min and nozzle-to ground collector distance of 12 and 15 cm. Electrospinning of PVDF polymer solution was performed in horizontal alignment having a grounded aluminum foil which serves as a collector. The nanofibers obtained were characterized by polarizing optical microscope. We find that the low flow rate of the polymer solution and nozzle-to ground collector distance are strongly correlated with the formation of bead defects in the fibers.

Direct Visualization of Ligands Exchange on the Surfaces of Quantum Dots by a Two‐Phase Approach

AbstractSemiconductor quantum dots (QDs) have a wide range of applications owing to their uniquely photoelectric performance. It is helpful to modify QDs with desired polymer chains for improving their steric stabilization and compatibilization. Although various strategies have been successfully developed to graft polymer chains onto the surfaces of QDs, few methods can directly monitor the process of grafting. In this study, we took advantages of the color labels of QDs and developed a simple and convenient “grafting‐to” method by ligand exchange, which occurred in a two‐phase system with direct visualization. Briefly, cadmium selenide@cadmium sulphide core‐shell QDs capped by n‐trioctylphosphine oxide (TOPO‐CdSe@CdS QDs), dispersed in n‐hexane, and amino/thiol terminated polystyrene (PS‐NH2/PS‐SH), dissolved in N,N‐dimethylformamide (DMF), were mixed to form a novel two‐phase system. A direct visualization of the QDs from n‐hexane to DMF confirmed the ligand exchange on the surfaces of QDs. Further evidences for the ligand exchange were provided by both Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (1H NMR) studies, as well as by the grafting density of the PS on the surface of QDs. The PS‐grafted QDs can improve the compatibility with the polymers chemically or structurally similar to PS, which makes them useful as functional additives in the polymer matrix to construct nanocomposites with desired optical and mechanical properties.

Chemical Vapor Deposition of Bi-Te-Ni-Fe on Magnesium Oxide Substrate and Its Seebeck Effect

In this work, a Bi-Te-Ni-Fe complex coating material was obtained on magnesium oxide substrate by a single step ambient pressure chemical vapor deposition (CVD). Nickel acetate, bismuth acetate, iron (III) nitrate, and tellurium (IV) chloride dissolved in N,N-dimethylformamide (DMF) served as the metal sources for Ni, Bi, Fe, and Te, respectively. Hydrogen was used as the carrier gas. The substrate was kept at 500 °C in a quartz tube reaction chamber. The chemical vapor deposition time was two hours. Scanning electron microscopic observation revealed porous morphology of the deposited material with a needle-like submicron fine structure. These needle-like entities form networks with fairly uniform distribution on the substrate. Thermoelectric property test showed that the coating is p-type with a Seebeck coefficient of 179 µV/K. Time-dependent potential data were obtained to show the sensitivity of the Seebeck effect to temperature changes.