Characterization of Nano-Structured Poly(D,L-lactic acid) Nonwoven Mats Obtained from Different Solutions by Electrospinning

Two different solvent mixtures, chloroform/dimethylformamide (DMF) and chloroform/ acetone, in 60/40 v/v concentrations, were used to electrospin poly(D,L-lactic acid) (PDLLA). The influence of solvent type, solution concentration, and processing conditions on the morphology and properties of the electrospun mats was studied. The nanofibers characterization was done by scanning electron microscopy (SEM), wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC). The smallest nanofibers’ diameters from both mixtures were obtained from solutions with 5 wt%/v PDLLA concentration using a 1.0 kV/cm electrical field. In general the nanofibers from the chloroform/DMF mixture had smaller diameters than the nanofibers from the chloroform/acetone mixture. However, the latter ones were porous, while the nanofibers from the chloroform/DMF mixtures were not. All the PDLLA nanofibers, independent of solvent mixture, had a very low amount of crystallinity and were composed of very small and imperfect α and β crystals.     

Preparation and Characterization of Poly(Vinyl Alcohol) (PVA)/SiO2, PVA/Sulfosuccinic Acid (SSA) and PVA/SiO2/SSA Membranes: A Comparative Study

Abstract

New organic–inorganic nanocomposites based on PVA, SiO₂ and SSA were prepared in a single step using a solution casting method, with the aim to improve the thermomechanical properties and ionic conductivity of PVA membranes. The structure, morphology, and properties of these membranes were characterized by Raman spectroscopy, small- and wide-angle X-ray scattering (SAXS/WAXS), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), water uptake (Wu) measurements and ionic conductivity measurements. The SAXS/WAXS analysis showed that the silica deposited in the form of small nanoparticles (～ 10?nm) in the PVA composites and it also revealed an appreciable crystallinity of pristine PVA membrane and PVA/SiO₂ membranes (decreasing with increasing silica loading), and an amorphous structure of PVA/SSA and PVA/SSA/SiO₂ membranes with high SSA loadings. The thermal and mechanical stability of the nanocomposite membranes increased with the increasing silica loading, and silica also decreased the water uptake of membranes. As expected, the ionic conductivity increased with increasing content of the SSA crosslinker, which is a donor of the hydrophilic sulfonic groups. Some of the PVA/SSA/SiO₂ membranes had a good balance between stability in aqueous environment (water uptake), thermomechanical stability and ionic conductivity and could be potential candidates for proton exchange membranes (PEM) in fuel cells.     

Preparation of Chitosan/Polyvinyl Alcohol Electrospinning Nano-Membranes Using the Green Solvent,Plasma Acid

Abstract

In this paper, a green solvent for chitosan, plasma acid, was made and chitosan/plasma-acid solutions were prepared. An environmentally friendly chitosan/polyvinyl alcohol (PVA) nano-membrane was prepared via electrospinning due to the difficulty of electrospinning of pure chitosan/plasma-acid solutions. Two blending methods of chitosan with PVA were investigated. One way was to mix a chitosan/plasma-acid solution (1%) and a PVA/water solution (10%) with the volume ratios of 2:8, 3:7, 4:6, 5:5, 6:4, 7:3 and 8:2, respectively. The results showed that fibrous nano-membranes could start to be formed at a chitosan/PVA mixing ratio of 7:3 up to the ratio of 2:8 with increasing PVA. The average fiber diameters increased with increased adding of PVA, ranging from 74.7?nm for the 7:3 ratio to 280.7?nm for the 2:8 ratio. The other way to prepare the chitosan/PVA solutions was to put PVA and chitosan powders into the plasma acid together. Fibrous nano-membranes could also be formed at 6% PVA and 10% PVA solution, both with 1% chitosan compositions. The average diameters of the resulting nano-fibers were 144.67?nm and 300.7?nm, respectively. The Fourier transform infrared (FTIR) spectroscopy results showed that the chitosan was bonded to the PVA by hydrogen bonds in the nano-membranes (6% PVA, 1% chitosan). It is noted that both of the two blending methods permitted obtaining chitosan/PVA nano-membranes. As indicated, the PVA in the solution had a large effect on the diameters of the nano-fibers. The first method permitted obtaining nano-fibers with smaller diameter. The maximum concentration of chitosan in the solution was 0.7% (7:3 ratio). The second method was simpler and permitted increasing the chitosan concentration in the solution to 1% for both the 6% and 10% concentrations of PVA.     

Fabrication and Optimization of Poly(vinyl alcohol)/Zirconium Acetate Electrospun Nanofibers Using Taguchi Experimental Design

This paper presents an investigation regarding poly(vinyl alcohol)/zirconium acetate (organic–inorganic) (PVA/Zrace) nanofibers prepared by electrospinning which could be used as a precursor for fabricating ceramic metal oxide nanofibers. The effect of some processing variables, including polymer solution concentration, tip to collector distance and applied voltage of electrospinning, and the amount of Zrace and their interactions, on the diameter of the nanofibers were studied. Taguchi experimental design and a statistical analysis (ANOVA) were employed and the relationship between experimental conditions and yield levels determined. It was concluded that to obtain a narrow diameter distribution as well as maximum fiber fineness, a polymer concentration of 10 wt%, tip to collector distance of 18 cm and applied voltage of 20 kV variables were the optimum. Furthermore, it was also concluded that the ratio of Zrace (6 g) to PVA solution (10% wt) played an important role for achieving the minimum fiber diameter. Under these optimum conditions, the diameters of the electrospun composite fibers ranged from 86 nm to 381 nm with a diameter average of 193 nm. The experiments were done with Qualitek-4 software with “smaller is better” as the quality characteristics. The optimized conditions showed an improvement in the fibers diameter distribution and the average fibers diameter showed good resemblance with the result predicted using the Taguchi method and the Qualitek-4 software. The ANOVA results showed that all factors had significant effects on the fibers diameter and distribution, but the effect of PVA concentration and zirconium acetate were more significant than the other factors.     

Effect on Structure,Processability, and Conductivity of Poly(m-aminophenol) of the Initial Acidity/Basicity of the Polymerization Medium

Poly(m-aminophenol) was synthesized chemically from aqueous solutions of the monomer meta-aminophenol (mAP) in the initially acidic or basic medium by using ammonium persulfate as an oxidant. The polymer (PmAPA) synthesized in initially aqueous HCl medium was insoluble in organic solvents even after dedoping, while the polymer (PmAPB) synthesized in initially aqueous NaOH solution was found to be soluble in high pH water, dimethyl sulfoxide (DMSO), and dimethylformamide. It was possible to obtain a stable, free-standing film from the DMSO solution of PmAPB but, due to insolubility and infusibility, film casting was not possible for PmAPA. The synthesized polymers were characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analyses, X-ray diffraction spectroscopy, and four-probe DC electrical conductivity. A ladder-type structure was formed during the chemical polymerization of mAP in aqueous HCl, while a hydroxyl derivative of polyaniline was obtained in aqueous NaOH. The conductivity of sulfuric acid-doped PmAPB was 10⁴ times higher than that of in situ HCl-doped PmAPA. An explanation of the difference in properties of both polymers is given based on molecular modeling.     

A simple and effective route for the preparation of poly(vinylalcohol) (PVA) nanofibers containing gold nanoparticles by electrospinning method

Poly(vinylalcohol) (PVA) nanofibers containing gold nanoparticles have been simply obtained by electrospinning a solution containing gold nanoparticles without the additional step of introducing other stabilizing agents. The optical property of gold nanoparticles in PVA aqueous solution was observed by UV-visible absorption spectra. Morphology of the Au/PVA nanofibers and distribution of the gold nanoparticles were characterized by transmission electron microscopy (TEM). The structure transformation was characterized from PVA to PVA/Au composite by Fourier transform infrared spectroscopy (FTIR).     

Bionanocomposites including bacteriorhodopsin and carbon nanofibers. Atomic-force microscopy

The interaction of bacteriorhodopsin with carbon nanofibers (40–100 nm in diameter) was studied for the first time by atomic-force microscopy. The formation of planar nanostructures 200–250 nm wide in films grown by evaporation of an aqueous solution was demonstrated. Langmuir films containing nanofibers and lipid were obtained. The interaction between nanofibers and Triton X-100 was studied.     

Nanofibers and nanoplatelets of MoO3 via an electrospinning technique

Polyvinyl alcohol (PVA)/ammonium molybdate composite fibers were prepared by using sol-gel processing and electrospinning technique. After calcinations of the above precursor fibers at 500 °C, MoO₃ nanofibers with a diameter of 100-150 nm were successfully obtained. MoO₃ nanoplatelets and submicron platelets were prepared by further calcinations of the MoO₃ nanofibers at 600 and 700 °C. The products were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). A possible growth mechanism for the MoO₃ nanofibers and nanoplatelets was suggested.     

双核磺化酞菁钴在混合溶液中聚集现象的光谱和电化学研究

用光谱法研究了双核磺化酞菁钴(bi-CoPc)在水溶液中的聚集现象,讨论了各种有机溶剂与水按不同体积比形成的混合溶液对其解聚的作用,以及pH值对bi-CoPc聚集的影响。用透射电子显微镜观察了bi-CoPc在水溶液及30％丙醇-水混合溶液中的形貌。研究了bi-CoPc在混合溶液中的电化学行为。     

电纺ZnO纳米纤维电子传输层提高倒置PTB7∶PC70BM电池效率

研究利用静电纺丝制备的不同直径ZnO纳米纤维作为倒置结构有机太阳能电池的电子传输层对器件转化效率的影响。首先通过静电纺丝技术成功制备了半径在43～110 nm之间的ZnO纳米纤维,然后将ZnO纳米纤维作为电子传输层加入到倒置结构有机太阳能电池（ITO/ZnO∶ZnO nanofiber/PTB7∶PC₇₀BM/MoO₃/Al）。与平面结构的ZnO电子传输层相比,ZnO纳米纤维具有比表面积大等优点,增加了电子传输和抽取能力,提高了器件的光电转化效率。实验发现ZnO纳米纤维的直径越小,电池效率越大。当ZnO纳米纤维直径为(46±5)nm,接收时间为30 s时,作为电子传输层的电池效率提高了8%。     

PSSS50-b-PNIPAM300嵌段共聚物在二元溶剂中自组装的NMR研究

本文结合核磁共振（NMR）、动态光散射（DLS）和透射电子显微镜（TEM）等表征方法,对自主合成的聚阴离子型温敏嵌段共聚物—聚（苯乙烯磺酸钠）-b-聚（N-异丙基丙烯酰胺）（PSSS₅₀-b-PNIPAM₃₀₀）在纯水、水/甲醇以及水/丙酮三种溶剂中的温度响应性和自组装行为进行了系统研究.结果发现PNIPAM链段在水/丙酮以及水/甲醇二元溶剂中的临界溶解温度（LCST）比在纯水溶液中略低,而在水/丙酮体系中的塌缩程度却明显低于纯水和水/甲醇体系.同时,PSSS₅₀-b-PNIPAM₃₀₀在不同溶剂体系中的聚集形貌也存在显著差异,表明加入有机溶剂小分子可以有效地调控温敏嵌段共聚物在水溶液中的自组装过程和聚集形貌.     

Synthesis of SnO2/ZnO composite nanofibers by electrospinning method and study of its ethanol sensing properties

In this paper, we report the synthesis of SnO₂/ZnO composite nanofibers via electrospinning method. Polyvinyl alcohol (PVA)/zinc acetate/stannous chloride nanofibers were electrospun using a solution containing PVA, zinc acetate and stannous chloride in distilled-water followed by calcination at 650 °C for 2 h, obtaining the related composite nanofibers. The nanofibers were characterized by simultaneous thermal analysis (STA), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and Fourier Transform Infrared spectroscopy (FTIR). Ethanol sensing of the nanofibers showed a good and desirable sensing behavior such as high sensitivity, quick response and recovery times.     

Preparation and photoluminescence properties of electrospun nanofibers of C60/PVK

Ultrafine fullerene (C60)/poly(N-vinylcarbazole) (PVK) composite fibers with 1 μm diameter were prepared by electrospinning C60/PVK blend solutions in solvent mixtures of N,N-dimethylformamide (DMF)/toluene. The UV absorption spectra of nanofibers have a similar behavior as observed in the thin films for the same doping condition. It is interesting to observe that the PVK nanofibers have a very strong blue-violet luminescence, while ‘bright spots’ due to C60 can be observed on the C60/PVK fibers under UV irradiation in a fluorescence optical microscope. Compared to the emission spectra of PVK thin films, the photoluminescence of the PVK nanofibers shows a new emission peak at 437 nm. Efficient energy transfer was observed in C60/PVK thin films, as well as in blend nanofibers.     

Effect of ammonium acetate addition on crystal growth,spectral, thermal and optical properties of glycine single crystals

Gamma glycine single crystal is a potential organic nonlinear optical (NLO) material. It has been grown from a mixture of aqueous solutions of glycine and ammonium acetate by slow evaporation solution growth technique at room temperature for the first time. Powder X-ray diffraction studies are carried out and the results are compared. CHN analysis confirms the non-inclusion of ammonium acetate species in to the solution. FTIR studies are performed to identify the presence of various functional groups in the grown crystal. Differential scanning calorimetry analysis (DSC) was carried out to study the thermal stability and phase transition of the grown crystal. The optical analysis shows that UV cut-off of γ-glycine is at 190 nm and it has a wide transparency window. The second harmonic generation relative efficiency of the grown crystals was observed to be 1.72 times that of potassium dihydrogen orthophosphate (KDP).     

Characterization of nanoparticles of lidocaine in w/o micro emulsions using small-angle neutron scattering and dynamic light scattering

Microemulsions (MEs) are of special interest because a variety of reactants can be introduced into the nanometer-sized aqueous domains, leading to materials with controlled size and shape [1,2]. In the past few years, significant research has been conducted in the reverse ME-mediated synthesis of organic nanoparticles [3,4]. In this study, a w/o ME medium was employed for the synthesis of lidocaine by direct precipitation in w/o microemulsion systems: water/isopropylpalmitat/Tween80/Span80. The particle size as well as the location of nanoparticles in the ME droplet were characterized by means of dynamic light scattering (DLS) and small angle neutron scattering (SANS). It is observed that lidocaine precipitated in the aqueous cores because of its insolubility in water. Hydrodynamic radius and gyration radius of microemulsion droplets were estimated as ∼15 nm and ∼4.50 nm from DLS and SANS respectively. Furthermore, different size parameters obtained by DLS and SANS experiments were compared     

A Novel Approach to Prepare CaCO3/Polyvinylpyrrolidone (PVP) Composite Nanofibers

A new route to prepare CaCO₃ nanoparticles/polyvinylpyrrolidone (PVP) nanofibers is reported. An aqueous solution of K₂CO₃ was added to a solution of CaCl₂/PVP, resulting in in-situ preparation of CaCO₃ nanoparticles. Then composite nanofibers containing CaCO₃ nanoparticles were successfully prepared by electrospinning. The morphology of the resulting composite nanofibers was characterized by field-emission scanning electron microscopy. In addition, the products were characterized by thermogravimetry analysis and Fourier transform infrared spectra.     

Formation of uniform PVDF fibers under ultrasound exposure in presence of anionic surfactant

Polyvinylidene fluoride (PVDF) was electrospun into fibrous membranes from its solutions in mixture of dimethylformamide (DMF) and acetone with and without an anionic fluorosurfactant. The results indicate that PVDF fibers contain a number of beads at any solvents compositions and solution concentrations. Addition of the surfactant does not affect considerably the morphology of fibers, however it helps to decrease the surface tension of the solution and reduce the beading of fibers. The most important factor affecting the fiber morphology is sonication. Sonication of the spinning solution promotes the formation of perfect, uniform, thin and cylindrical PVDF nanofibers without any beading.     

Formation of high aspect ratio polyamide-6 nanofibers via electrically induced double layer during electrospinning

In the present study, the formation of high aspect ratio nanofibers in polyamide-6 was investigated as a function of applied voltage ranging from 15 to 25 kV using electrospinning technique. All other experimental parameters were kept constant. The electrospun polyamide-6 nanofibers were characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF). FE-SEM images of polyamide-6 nanofibers showed that the diameter of the electrospun fiber was decreased with increasing applied voltage. At the critical applied voltage, the polymer solution was completely ionized to form the dense high aspect ratio nanofibers in between the main nanofibers. The diameter of the polyamide-6 nanofibers was observed to be in the range of 75-110 nm, whereas the high aspect ratio structures consisted of regularly distributed very fine nanofibers with diameters of about 9-28 nm. Trends in fiber diameter and diameter distribution were discussed for the high aspect ratio nanofibers. TEM results revealed that the formation of double layers in polyamide-6 nanofibers and then split-up into ultrafine fibers. The electrically induced double layer in combination with the polyelectrolytic nature of solution is proposed as the suitable mechanisms for the formation of high aspect ratio nanofibers in polyamide-6.     

Ultrasonic cavitation in CO2-expanded N,N-dimethylformamide (DMF)

Due to the tunability in mass transfer, solvation and solubility, gas-expanded liquids show advantages over traditional organic solvents in many characteristics. Ultrasonication is a commonly used method to promote heat and mass transfer. The introduction of ultrasonic technology into the gas-expanded liquid system can promote the polymerization of polymer monomers, enhance extraction efficiency, and control the growth size of nanocrystals, etc. Although acoustic cavitation has been extensively explored in aqueous solutions, there are still few studies on cavitation in organic liquids, especially in gas-expanded liquid systems. In this article, the development of cavitation bubble cloud structure in CO₂-expanded N, N-dimethylformamide (DMF) was observed by a high-speed camera, and the cavitation intensity was recorded using a spherical hydrophone. It was found that the magnitude of the transient cavitation energy was not only related to input power, but also closely related to CO₂ content. The combination of ultrasound (causing a rapid alternation of gas solubility) and gas-expanded liquid system (causing a decrease in viscosity and surface tension of liquids) is expected to provide a perfect platform for high-speed mass transfer.     

Preparation of alkaline solid polymer electrolyte based on PVA-TiO2-KOH-H2O and its performance in Zn-Ni battery

A novel composite alkaline polymer electrolyte based on poly(vinyl alcohol) (PVA) polymer matrix, titanium dioxide (TiO₂) ceramic fillers, KOH, and H₂O was prepared by a solution casting method. The properties of PVA-TiO₂-KOH alkaline polymer electrolyte films were studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and AC impedance techniques. DSC and XRD results showed that the domain of amorphous region in the PVA polymer matrix augmented when TiO₂ filler was added. The SEM result showed that TiO₂ particles dispersed into the PVA matrix although some TiO₂ aggregates of several micrometers were formed. The alkaline polymer electrolyte showed excellent electrochemical properties. The room temperature (20 °C) ionic conductivity values of typical samples were between 0.102 and 0.171 S cm⁻¹. The Zn-Ni secondary battery with the alkaline polymer electrolyte PVA-TiO₂-KOH had excellent electrochemical property at the low charge-discharge rate.