Electrospinning and Mechanical Properties of Polystyrene and Styrene-Isoprene-Styrene Block Copolymer Blend Nanofibres

Electrospinning of polystyrene (PS) and styrene–isoprene–styrene block copolymer (SIS) blends with different composition weight ratios was carried out with a mixed solvent, tetrahydrofuran (THF) and N,N-dimethylformamide (DMF) (80/20, v/v). Electrospun PS/SIS blend fibers were characterized using scanning electron microscopy. The results indicated that the presence of DMF resulted in a beneficial effect on fiber formation and greater electrospinnability of as-spun fibers. Furthermore, the morphological structure and diameters of as-spun fibers from PS and SIS blends were affected by the composition weight ratio and the solution properties. The fibers from 10 wt% solution exhibited the best mechanical properties compared to the fibers from other concentrations for the same composition, and increasing the SIS content one observes a vanishing of PS-related properties, while SIS-related properties emerges.     

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.     

PMMA nanofibers production by electrospinning

Electrospinning is a process by which polymer nanofibers (with submicron scale diameters) can be formed when a droplet of viscoelastic polymer solution is subjected to high voltage electrostatic field. As this droplet travels in air, the solvent evaporates leaving behind a charge fiber that can be electrically deflected on a substrate. A series of nanofibers with various wt.% of PMMA (poly-methyl-methacrylate) to acetone were produced and characterized regarding their morphology and chemical composition. The nanofibers were characterized by Secondary Electron Microscopy, Atomic force microscopy and X-ray photoelectron spectroscopy.     

纳米ZnO墨水的溶剂及浓度优化及其在钙钛矿太阳能电池中的应用

纳米金属Zn O作为界面缓冲材料能够有效提高基于有机金属卤化物-甲基碘化铵的钙钛矿(PVSK)太阳能电池的水氧稳定性,是溶液制备高稳定性钙钛矿太阳能电池的一个关键技术。而在器件的制备过程中,Zn O分散溶剂的渗透可能导致下层钙钛矿薄膜的结构物性发生变化,从而对器件性能造成显著的影响。为解决该问题,本文详细分析了不同极性有机溶剂对Zn O分散性的影响,研究了不同溶剂对PVSK/PCBM薄膜的吸收光谱和晶体结构的影响,最终获得了甲醇-正丁醇混合溶剂的体积比为1∶1、Zn O质量浓度为10 mg·m L-1的优化分散体系,为进一步开展全溶液法制备钙钛矿太阳能电池提供了重要指导。     

四（3,4-亚甲二氧基苯基）卟啉的合成及光谱分析

研究了以3,4-亚甲二氧基苯甲醛和吡咯为原料合成四（3,4-亚甲二氧基苯基）卟啉的方法,探索了溶剂、催化剂等反应条件对合成的影响。新化合物结构分别被UV-Vis,IR,1H NMR及元素分析所证实。利用紫外-可见分光光度法和荧光光谱法研究了四（3,4-亚甲二氧基苯基）卟啉在四氢呋喃（THF）、丙酮、氯仿、N,N-二甲基甲酰胺（DMF）4种溶剂中的光谱性质。     

Effects of blending 2,5-dimethylfuran on the laminar burning velocity and ignition delay time of isooctane/air mixture

The prospects of 2,5-dimethylfuran (DMF) as a bio-derived fuel that can be blended with gasoline are believed to be impressive. However, the effects of blending DMF on the key combustion parameters like the laminar burning velocity and ignition delay time of gasoline/air mixture need to be studied extensively for the successful implementation of the fuel mixture in spark ignition engines. Therefore, a skeletal chemical kinetic mechanism, comprising of 999 reactions among 218 species, has been developed in the present work for this purpose. The proposed chemical kinetic model has been validated against a wide range of experimental data for the laminar burning velocity and ignition delay time of isooctane (representing gasoline), DMF and their blends. It has been found from the present study that the thermal diffusivity of the unburnt gas mixture changes by a very small amount from the corresponding value for the pure isooctane/air mixture when DMF is added. Unlike isooctane, the DMF molecule does not consume H radicals during its primary breakup. Therefore, the maximum laminar burning velocity increases marginally when 50% DMF is blended with isooctane due to the increased presence of H radicals in the flame. The negative temperature coefficient behaviour in the ignition delay time of the isooctane fuel vanishes when 30% DMF (v/v) is blended to it.     

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.     

Study on the Electrospinnability of Polyvinyl Alcohol Solutions by Using Water/N,N-dimethylacetamide or Water/N,N-dimethylformamide as Solvents

The electrospinning of poly(vinyl alcohol) (PVA) (99% hydrolysis degree) aqueous solution with added organic solvents N, N-dimethylacetamide (DMAc) or N, N-Dimethylformamide (DMF) was investigated. After the addition of the organic solvents to the PVA aqueous solutions, the surface tension and conductivity decreased and the viscosity significantly increased, which caused an improved electrospinnability of the PVA solutions. The micro-structures of the three solutions were investigated by dynamic light scattering (DLS), differential scanning calorimetry (DSC) and dynamic viscoelastic measurements. The DLS data revealed that the swelling of the PVA coils was slightly increased but the overlaps of PVA coils decreased greatly after one of the organic solvents was added to the aqueous solution. The DSC data showed both the water-rich phase and PVA-rich phase were destroyed and the solution became more homogenous after the addition due to the interaction between the organic solvent and water. Viscoelastic data showed there was an obvious difference in the storage modulus behavior between the aqueous solutions and the water/solvents solutions. These changes in the micro-structure and properties were the reason for the improved electrospinnability of the PVA solution. According to scanning electron microscopy (SEM), the average diameter of the electrospun PVA nanofibers was about 308 nm for the DMF/water system, and 255 nm for the DMAC/water system, as compared with uneven diameter nanofibers for the water system.     

Electrospun cross linked rosin fibers

In this study, we describe the first reported preparation of rosin in fiber form through use of an electrospinning technique utilizing various solvent systems. The polymer concentration of the formed fiber was studied by using various solvents such as chloroform, ethanol, N-N dimethylformamide (DMF), tetrahydrofuran (THF), acetone, and methylene chloride (MC). An electrospray of the solution resulted in the beaded form of the rosin. By varying the polymer concentration with MC, we were then able to obtain uniform fibers. However, the fibers exhibited large diameter. We believe that it is possible to reduce the diameter of the rosin fibers through appropriate selection of electrospinning parameters. In addition, the morphological transitions from beads, to beaded fiber, to fiber were studied at different polymer concentrations. We propose a possible physical cross linking mechanism for the formation of rosin fibers during the electrospinning process. Our results demonstrate the feasibility of producing fiber nanostructures of rosin by using an electrospinning technique.     

Choice of dispersants for the nano-apatite filler of polylactide-matrix composite biomaterial

The aim of this study is to compare de-aggregative ability of common organic dispersants for the acicular nano-apatite crystallite with main composition of calcium hydroxyapatite (HA) as a filler of composite containing polylactide (PLA) matrix. Firstly, the acicular nano-apatite powders with an average length of 70–120 nm were synthesized based on traditional chemical co-precipitation and freeze-drying techniques. Common organic dispersants including tetrahydrofuran, acetone, chloroform, N,N-dimethyl formamide (DMF) and ethanol were then employed to disperse synthetic freeze-dried ultra-fine nano-powders. The observations and weight of sediments showed that nano-apatite suspension dispersed by DMF and ethanol presented homogeneous and stable colloid after vigorly stirred for 24 h and then kept still for same time, respectively. Results of particle measurements and viscosity measurement illuminated that a large number of the nano-apatite particles with an average dimension of 297.86 nm and viscosity of 0.8872 cP in DMF suspension could be dispersed up to 91.28 nm by the DMF dispersant and the DMF dispersant could minimize agglomeration between the apatite ultra-fine nano-powders. DMF is a more effective and appropriate dispersant to disperse the apatite nano-fillers than chloroform, tetrahydrofuran, acetone and ethanol, when the nano-apatite/PLA composite biomaterials were prepared.     

Kinetics of the thermal decomposition reaction of diethylketone cyclic triperoxide in acetone–toluene and acetone–1‐propanol binary solvent mixtures

The thermal decomposition reaction of diethylketone triperoxide (DEKT) ca. 0.02 M was studied in binary mixtures of acetone–toluene and acetone–1‐propanol at 150 °C. Products of DEKT thermolysis in solution, detected by GC analysis, were diethylketone, bibenzyl and butane. The reactions were explored by GC at different solvent compositions and in each case the reactions followed a pseudo first order kinetic law, up to at least 90% peroxide conversion. The rate coefficient value of the reaction is affected by the solvent properties, showing an increase in the k_obs values with increases in the polarity of the solvent mixture in acetone–toluene systems. Changes in the rate coefficient values are probably caused by the presence of the apolar toluene solvent, which dominates the preferential solvation around the DEKT molecule through non‐specific interactions. In acetone–1‐propanol mixtures the solvation effect is slightly dominated by the specific interactions between the 1‐propanol and a polar intermediate specie represented by the biradical, initially formed. The rate coefficient value increases ca. 6% in the mixture with 0.1 mole fraction of 1‐propanol in comparison with the value in pure acetone; but no more changes in rate coefficient values are observed when the amount of the alcohol increases. The critical state of the reaction (intermediate biradical) is preferentially solvated by the 1‐propanol instead of acetone, but in mixtures of different composition, it is not possible to detect any effect on the reactivity for homolytic rupture of the O? O bond. Copyright © 2008 John Wiley & Sons, Ltd.     

Electrospun nanofibers of NiO/SiO2 composite

Composite nanofibers with a weight ratio of 30%NiO-70%SiO₂ and diameters ranging from 80 to 100 nm were successfully prepared by electrospinning a precursor mixture of polyvinyl alcohol (PVA)/silica/nickel acetate followed by calcination treatment of the electrospun polymer/inorganic composite fibers. The resulting NiO/SiO₂ composite nanofibers were characterized by TG-DTA, FT-IR spectroscopy, X-ray diffraction and scanning electron microscopy . The results revealed that the crystalline phase of NiO nanoparticles were formed at a temperature higher than 600 °C. The SEM results show that the morphology of the fibers is affected greatly by the calcination temperature.     

Preparation of poly(?-caprolactone)-based polyurethane nanofibers containing silver nanoparticles

In this study, poly(?-caprolactone)-based polyurethane (PCL-PU) nanofibers containing Ag nanoparticles for use in antimicrobial nanofilter applications were prepared by electrospinning 8 wt% PCL-PU solutions containing different amounts of AgNO₃ in a mixed solvent consisting of DMF/THF (7/3 w/w). The average diameter of the pure PCL-PU nanofibers was 560 nm and decreased with increasing concentration of AgNO₃. The PCL-PU nanofiber mats electrospun with AgNO₃ exhibited higher tensile strength, tensile modulus, and lower elongation than the pure PCL-PU nanofiber mats. Small Ag nanoparticles were produced by the reduction of Ag⁺ ions in the PCL-PU solutions. The average size and number of the Ag nanoparticles in the PCL-PU nanofibers were considerably increased after being annealed at 100 °C for 24 h. They were all sphere-shaped and evenly distributed in the PCL-PU nanofibers, indicating that the PCL-PU chains stabilized the Ag nanoparticles well.     

Solvatochromic Studies of Fluorescein Dianion in N,N-Dimethylformamide/Water and Dimethylsulphoxide/Water Mixtures

Abstract

The absorption, excitation and fluorescence spectra of the fluorescein dianion (FL^2?) in N, N-Dimethylformamide (DMF)/water (H₂O) and Dimethylsulphoxide (DMSO)/H₂O solvent mixtures have been investigated. It is found that the absorption λ_max and emission maxima EX, _nax are both hypsochromic shifted when the H₂O content in the solvent mixtures increases. However, the shoulder peaks λ_s remain constant at 483. 5nm within the range of H₂O mole fraction, x= 0 to 0. 518 in a DMF/H₂O solvent mixture and at 484. 4nm within the range, x=0 to 0. 304, in a DMSO/H₂O mixture. Further increases in H₂O content, cause a hypsochromic shift in λ_s. The molar energies for the electronic transition from the ground state (S₀) to S₁, the first excited singlet state, (E_T(1)) and to S₂, the 2nd excited singlet state, (E_T(2)) of FL^2?in the solvent mixtures are also plotted against x. Linear straight lines and intersection points are observed at x=0. 73 for E_T(1) and at x=0. 51 for E_T(2) in the DMF/H₂O mixture and at x=0. 71 for E_T(1) and at x=0. 31 &; 0. 69 for E_T(2) in the DMSO/H₂O mixture. Hydrogen-bonding stabilization effects are used to explain the above observations. The variation in relative fluorescence quantum yields of S₁ and S₂ of FL^2? with x in the aprotic solvent-H₂O mixtures to FL^2? in pure aprotic solvent are determined and discussed.     

β-Phase of poly(vinylidene fluoride) formation in poly(vinylidene fluoride)/poly(methyl methacrylate) blend from solutions

The effect of single and mixed solvent on the crystallization behavior of the PVDF/PMMA blend from solutions was investigated. The films cast from the good solvent N,N-dimethylformamide (DMF) dominantly yielded the β-phase crystal with the highest crystallinity of PVDF. Those deposited from the methyl ethyl ketone (MEK) and tetrahydrofuran (THF) exhibited a mixture of α- and some extra β-phase crystals and presented the low crystallinity of PVDF. The crystallization behavior and morphology of the films cast from the mixed solvent (THF/DMF) revealed an enormous dependence on the DMF content. The increased DMF content in the mixed solvent enhanced the interactions between polymers and solvents, and favored the β-crystal of PVDF formation but hindered the α-phase of PVDF formation. Thus, the total crystallinity of PVDF in the blend film was decreased with the DMF content increasing, because of the decreased α-phase of PVDF. In addition, the morphological feature revealed that the voids between the PVDF spherulites were eliminated remarkably by blending with PMMA. The average size of the connected spherulite on top surface of the film can grow into larger as DMF content increased.     

8-羟基喹哪啶-丙烯酸-镓(Ⅲ)与甲基丙烯酸甲酯共聚物的光致发光研究

制备了8-羟基喹哪啶、丙烯酸与镓(Ⅲ)的三元配合物,将此配合物与甲基丙烯酸甲酯共聚后得到一种含镓(Ⅲ)的共聚物,这种共聚物易溶于氯仿、丙酮等普通低沸点溶剂,具有良好的成膜性能。通过红外光谱、元素分析、紫外光谱等方法对三元配合物和共聚物的组成进行了表征。三元配合物和共聚物的荧光光谱测试,表明共聚物在496 nm处能发出较强的荧光。     

丝素蛋白在甲醇-水混合溶剂中构象变化的光谱学研究

应用圆二色谱、内源荧光和外源荧光探针研究了丝素蛋白在甲醇-水混合溶剂中的构象变化及机理。结果显示,在浓度低于30%(V/V)的甲醇-水混合溶剂中,处于无规卷曲状态的丝素蛋白可以通过疏水相互作用形成小的疏水区域,随着甲醇浓度的增加,丝素蛋白发生由无规卷曲向β-折叠的构象转变,削弱了疏水侧链的相互作用。分析表明,丝素蛋白的构象变化与溶剂体系的微观结构密切相关,其稳定性主要由肽键单元与混合溶剂中的分子簇之间的相互作用决定。低浓度的甲醇-水混合溶剂保持水固有的氢键结构,对丝素蛋白肽键单元的溶剂化和丝素蛋白构象的影响较小,而随着甲醇浓度的增加,溶剂结构出现由四面体结构的水分子簇向链状结构的甲醇分子簇的转变,丝素蛋白通过形成分子内氢键减少肽键单元与溶剂分子的接触,从而引发丝素蛋白的构象转变。     

Sonochemical synthesis of polyaniline nanofibers

Conventionally, micro-sized irregular polyaniline (PANI) particles were synthesized by dropwise addition of the ammonium persulfate (APS) solution into the aniline (ANI) solution with mechanical stirring. By replacing the mechanical stirring with an ultrasonic irradiation, PANI nanofibers in diameters of approximately 50 nm and lengths of 200 nm to several micrometers were prepared. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) showed that at the early stage of polymerization, the polymers formed in both the mechanical stirred and ultrasonicated systems are in the form of nanofiber. However, with continuing of the reaction, these primary nanofibers grow and agglomerate into irregular shaped PANI particles in the mechanical stirred system, while in the case of the ultrasonic irradiation, the growth and agglomeration are effectively prevented, preserving thus the PANI nanofibers in the final product. By increasing the APS/ANI molar ratio from 0.5 to 2.5, the aspect ratios of the PANI nanofibers decreased. The PANI nanofibers exhibit higher solubility than the irregular shaped PANI particles. Although the yield, as well as the conductivity of the ultrasonic synthesized PANI nanofibers, was slightly lower than the irregular shaped PANI particles, the ultrasonic synthesis approach is one of the facile and scalable approaches in synthesizing PANI nanofibers in comparison with other ones without use of templates (e.g., the interfacial polymerization and rapid mixing polymerization). UV-Vis and Fourier transformed infrared (FTIR) spectra indicated ultrasound had no significant effect on the chemical structure of the PANI.     

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.     

Effect of process parameters on the recovery of lactose in an antisolvent acetone/acetone-ethanol mixture: A comparative study based on sonication medium

Recovery of lactose from the whey using sonocrystallization was studied experimentally. The effect of sonication medium and irradiation power levels was evaluated using three different ultrasonic equipments. Effects of various parameters such as sonication time, pH of the medium, antisolvent (acetone and acetone-ethanol mixture) and concentration of lactose were determined. The optimal parametric conditions were analyzed using differential scanning calorimetry, thermogravimetric analysis, particle size distribution, and zeta potential measurements. Overall, the highest lactose recovery was obtained using a mixture of acetone and ethanol as antisolvent in bath sonication as well as atomization process.