低温煤焦油中正十二烷-甲苯-苯酚的相平衡及分离

低温煤焦油组分的分离对其充分利用具有重要的作用。分别以正十二烷、甲苯和苯酚为模型化合物,采用实验和Aspen Plus模拟两种方法得到了低温煤焦油中脂肪烃-芳烃-酚类三元体系的液液平衡关系,并模拟了N,N-二甲基甲酰胺（DMF）水溶液萃取分离该体系时的典型三元相图。结果表明,Aspen Plus采用UNIF-LL法模拟得到的三元相图与实验测定结果吻合较好。甲苯在正十二烷-甲苯-苯酚体系中作为共溶溶剂,促使三元体系成为均相。根据正十二烷、甲苯和苯酚在DMF中的溶解性差异,结合Hansen溶度参数理论,通过在DMF中添加不同含量的H₂O以调节萃取剂的极性,可使正十二烷和甲苯依次从均相体系中分离。通过对萃取温度、剂油比和萃取剂含水量进行优化,最终在303.15 K,剂油比为1.5时,以DMF对模型油进行单级萃取,可以得到纯度为93.2%的正十二烷;相分离后向萃取相中添加DMF量30%的H₂O,可分离出纯度为93.4%的甲苯。     

Subtle regulation of the micro- and nanostructures of electrospun polystyrene fibers and their application in oil absorption

In this study, we conducted a subtle regulation of micro- and nanostructures of electrospun polystyrene (PS) fibers via tuning the molecular weights of the polymers with different sources, solvent compositions, and solution concentration. The surface morphology and porous structures of as-prepared PS fibers were characterized, and a full and intuitive observation of the porous structures as well as a tentative account of the formation of porous structures was presented. Additionally, the porous PS fibrous mats showed much higher oil absorption capacities than those of commercial polypropylene fibers in the form of a non-woven fabric, which displays a bight future for oil spill cleanups. We believe that such regulation of micro- and nanostructures of the PS fibers will widen the range of their applications in self-cleaning materials, ultra-high sensitivity sensors, tissue engineering, ion exchange materials, etc.     

静电纺丝工艺参数对PMMA／富勒烯纤维形貌的影响

采用甲苯与二甲基甲酰胺（DMF）混合溶液做溶剂,以静电纺丝法制备了含有富勒烯（C60）的聚甲基丙烯酸甲酯（PMMA）纤维,利用扫描电镜观察了纤维的形貌,分析了PMMA的质量分数、溶剂比、纺丝电压、收集距离等对纤维形貌及平均直径的影响。结果表明：PMMA溶液的浓度以及溶剂比对纤维的形貌起着主导作用,当二者变化时,纤维结构变化较大。纤维的平均直径随着PMMA浓废、纺丝电压的增大而增大;当甲苯/DMF体积比增大时,纤维平均直径先增大后减小;纤维形貌受收集距离的影响较小。     

Electrostatic polymer processing of isotactic poly(4-methyl-1-pentene) fibrous membrane

Isotactic poly(4-methyl-1-pentene) (P4M1P) is a widely used polymer in industrial applications and specifically, in medical products. Producing micro- or nanofibers would expand the usefulness of P4M1P to a broad range of medical applications. The choice and quality of solvent for the solution used for electrospinning can have a dramatic effect on the spinnability of fibers and on their morphological appearance. In this study, four solvent systems: cyclohexane, cyclohexane/acetone mixture, cyclohexane/dimethyl formamide (DMF) mixture and cyclohexane/acetone/DMF mixture have been investigated. As demonstrated by FE-SEM, electrospun fibers with different morphologies including round, twisted with a roughened texture, curled and twisted-ribbon shapes were formed. The fiber shape and morphology depended strongly on the type and amount of non-solvent used.     

Electrospinning of polycarbonate urethane biomaterials

Polycarbonate urethane (PCU) nano-fibers were fabricated via electrospinning using N,N- dimethylformamide (DMF) and tetrahydrofuran (THF) as the mixed solvent. The effect of volume ratios of DMF and THF in the mixed solvent on the fiber structures was investigated. The results show that nano-fibers with a narrow diameter distribution and a few defects were obtained when mixed solvent with the appropriate volume ratio of DMF and THF as 1∶1. When the proportion of DMF was more than 75% in the mixed solvent, it was easy to form many beaded fibers. The applied voltage in the electrospinning process has a significant influence on the morphology of fibers. When the electric voltage was set between 22 and 32 kV, the average diameters of the fibers were found between 420 and 570 nm. Scanning electron microscopy (SEM) images showed that fiber diameter and structural morphology of the electrospun PCU membranes are a function of the polymer solution concentration. When the concentration of PCU solution was 6.0 wt-%, a beaded-fiber microstructure was obtained. With increasing the concentration of PCU solutions above 6.0 wt-%, beaded fiber decreased and finally disappeared. However, when the PCU concentration was over 14.0 wt-%, the average diameter of fibers became large, closed to 2 μm, because of the high solution viscosity. The average diameter of nanofibers increased linearly with increasing the volume flow rate of the PCU solution (10.0 wt-%) when the applied voltage was 24 kV. The results show that the morphology of PCU fibers could be controlled by electrospinning parameters, such as solution concentration, electric voltage and flow rate.     

Characterization of nano-structured poly(ε-caprolactone) nonwoven mats via electrospinning

Nano-structured poly(ε-caprolactone) (PCL) nonwoven mats were prepared by electrospinning process. In this study, three types of solution were used. One dissolved in only methylene chloride (MC), the second dissolved in mixture of MC and N,N-dimethylformamide (DMF), the third dissolved in mixture of MC and toluene. MC, toluene and DMF are a good, poor, and nonsolvent for PCL, respectively. For the MC only, electrospun fibers had very regular diameter of about 5500 nm, but electrospinng is not facilitated. For the mixture of MC and DMF, electrospinning is certainly enhanced as well as fiber diameter decreased dramatically as increasing DMF volume fraction. It was due to high electric properties of solution such as dielectric constant and conductivity. Whereas, as increasing toluene volume fraction, electrospinning is strictly restricted due to very high viscosity and low conductivity. As the results, it has regarded that solution properties is one of the important parameter in electrospinning. Properties such as conductivity, surface tension, viscosity and dielectric constant of the PCL solutions prepared from three types of solvent system were studied. The morphology, crystallinity and mechanical properties of electrospun PCL nonwoven mats were characterized by scanning electron microscopy (SEM), wide angle X-ray diffraction (WAXD) and universal testing method (UTM), respectively.     

Effects of solvents on electrospun polymeric fibers: preliminary study on polystyrene

Six solvents [acetic acid, acetonitrile, m‐cresol, toluene, tetrahydrofuran (THF) and dimethylformamide (DMF)] with different properties (eg density, boiling point, solubility parameter, dipole moment and dielectric constant) were used to prepare electrospun polystyrene (PS) fibers. Fiber diameters were found to decrease with increasing density and boiling point of the solvents. A large difference between the solubility parameters of PS and the solvent was responsible for the bead‐on‐string morphology observed. Productivity of the fibers (the numbers of fiber webs per unit area per unit time) increased with increasing dielectric constant and dipole moment of the solvents. Among the solvents studied, DMF was the best solvent that provided PS fibers with highest productivity and optimal morphological characteristics. The beadless, well‐aligned PS fibers with a diameter of ca 0.7 µm were produced from the solution of 10 % (w/v) of PS in DMF at an applied electrostatic field of 15 kV/10 cm, a nitrogen flow rate of 101 ml min^?1 and a rotational speed of the collector of 1500 rev min^?1. Copyright © 2004 Society of Chemical Industry     

Synthesis of ultrafine poly(styrene‐maleic anhydride) and polystyrene fibers by electrospinning

Fiber formation from atactic polystyrene (aPS) and alternating poly(styrene‐maleic anhydride) (PSMA) synthesized by free radical polymerization (AIBN, 90°C, 4 h) were investigated by electrospinning from various solutions. aPS was soluble in dimethylformamide (DMF), tetrahydrofuran (THF), toluene, styrene, and benzene, whereas PSMA was soluble in acetone, DMF, THF, dimethylsulfoxide (DMSO), ethyl acetate, and methanol. aPS fibers could be electrospun from 15 to 20% DMF and 20% THF solutions, but not from styrene nor toluene. PSMA, on the other hand, could be efficiently electrospun into fibers from DMF and DMSO at 20 and 25%, respectively. Few PSMA fibers were, however, produced from acetone, THF, or ethyl acetate solutions. Results showed that solvent properties and polymer–solvent miscibility strongly influenced the fiber formation from electrospinning. The addition of solvents, such as THF, generally improved the fiber uniformity and reduced fiber sizes for both polymers. The nonsolvents, however, had opposing effects on the two polymers, i.e., significantly reducing PSMA fiber diameters to 200 to 300 nm, creating larger and irregularly shaped aPS fibers. The ability to incorporate the styrene monomer and divinylbenzene crosslinker in aPS fibers as well as to hydrolyze PSMA fibers with diluted NaOH solutions demonstrated potential for post‐electrospinning reactions and modification of these ultrafine fibers for reactive support materials. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Processing and characterization of electrospun poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) nanofibrous membranes

Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) nanofibrous membranes were first fabricated via electrospinning from chloroform (CHCl₃) or CHCl₃/dimethylformamide (DMF) polymer solutions. The electrospinning conditions such as the polymer concentration, the solvent composition, and the applied voltage were optimized in order to get smooth and nano-sized fibers. The crystalline structure, the melting behaviors and the mechanical properties of the obtained nanofibrous membranes were characterized. With pure CHCl₃ as the solvent in the electrospinning process, the finest smooth PHBHHx fibers were about 1 μm in diameter. When DMF is added to CHCl₃ as a co-solvent, the conductivity and volatility of the solution increased and reduced, respectively, and the electrospinnability of the polymer solution increased as a result. The averaged diameters of PHBHHx fibers could be reduced down to 300-500 nm when the polymer concentration was kept at 3 wt%, the ratio of DMF/CHCl₃ was maintained at 20/80 (wt%), and the applied voltage was fixed at 15 kV during electrospinning. WAXD and DSC results indicated that the crystallization of the PHBHHx nanofibers was restricted to specific crystalline planes due to the molecular orientation along the axial direction of the fibers. The crystallization behaviors of the electrospun nanofibers were significantly different from that of the cast membranes because of the rapid solidification and the one-dimensional fiber size effect in the electrospinning process. Mechanically, the electrospun PHBHHx nanofibrous membranes were soft but tough, and their elongation at break averaged 240-300% and could be up to 450% in some cases. This study demonstrated how the size of electrospun PHBHHx fibers could be reduced by adding DMF in the solvent and gave a clue of the presence of oriented molecular chain packing in the crystalline phase of the electrospun PHBHHx fibers.     

N,N‐Dimethylformamide Additions to the Solution for the Electrospinning of Poly(ε‐caprolactone) Nanofibers

Summary: Additives that exhibit polyelectrolyte behavior such as N,N‐dimethylformamide (DMF) may improve the electrospinning characteristics of viscoelastic polymer solutions. DMF additions to the solution lead to extensive jet splaying, thereby reducing the fiber diameter significantly. Nanofibrous structures with diameters of the order of 150 nm can be produced by the addition of about 10 vol.‐% DMF to the solvent (chloroform). DMF additions also yield a narrow, unimodal distribution of fibers, compared to the bimodal distribution typically detected in electrospun polymers.

Jet breakdown without (left) and with DMF addition to the solution.     

A novel method for preparing electrospun fibers with nano-/micro-scale porous structures

Electrospun fibers with nano-/micro-scale porous structures were successfully fabricated from polymer solutions that contained suspended micro-/nano-size salt particles of sodium chloride or calcium carbonate, which were subsequently removed through a leaching process after electrospinning. It was found that the size and dispersion of the salt particles had significant effects on the pore size and pore distribution in the resulting electrospun fibers. Using sodium chloride salt particles in the electrospinning process should not induce any residual toxicity in the resulting porous fibers. Therefore, this approach provides a very simple and versatile method in the fabrication of electrospun fibers that have secondary nano-/micro-scale porous structures, which are desirable in many important biomedical applications including tissue engineering and controllable drug release.     

Studies on the electrospun submicron fibers of SIS and its mechanical properties

The submicron fibers were prepared via electrospinning the styrene–isoprene–styrene (SIS) triblock copolymer from a pure solvent of tetrahydrofuran (THF) and a mixed solvent of THF and N, N‐dimethylformamide (DMF). The addition of DMF to THF resulted in a beneficial effect on the fiber formation and the electrospinnability. The obtained results revealed that the fibers were only formed in a narrow solution concentration range of 8–15 wt %; the morphology, diameter, structure, and mechanical performance of as‐spun fibers from PS and SIS solutions were affected by the composition weight ratio and the solution properties; and those from the solution at the intermediate concentration of 10 wt % exhibited a maximum tensile strength and strain at break. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Electrospinning of uniform polystyrene fibers: The effect of solvent conductivity

By means of the electrospinning technique, micron- and nanofibers can be obtained from polymer solutions under a very high electrical field. A special challenge is to produce bead-free uniform fibers since any minor changes in the electrospinning parameters such as slight variations in the polymer solutions and/or electrospinning experimental parameters may result in significant variations in the final nanofiber morphology. Furthermore, it is often not trivial at all to obtain reproducible uniform electrospun nanofibers for the optimized electrospinning conditions. Here we report that the conductivity of the solvent is the key factor for the reproducible electrospinning of uniform polystyrene (PS) fibers from dimethylformamide (DMF) solutions. It is shown that even slight changes in the conductivity of the DMF solutions can greatly affect the morphology of the resulting electrospun PS fibers. Here, we have carried out a thorough and systematic study on the effect of solution conductivity on the electrospinning of bead-free polystyrene (PS) fibers when dimethylformamide (DMF) was used as the solvent. Interestingly, we found out that different grades of solvent as-received (DMF) from various suppliers have slightly different solution conductivities. Consequently, the polymer solutions prepared with the same PS concentration have different conductivities, which are shown to have significant changes on the morphology of the PS fibers resulting in beaded or bead-free uniform fibers when electrospun under the identical electrospinning conditions. Such as, bead-free PS fibers were obtained from PS solutions in the range of 20% (w/v) through 30% (w/v) depending on the DMF grade used. In brief, it was observed that solutions with a higher conductivity yielded bead-free fibers from lower polymer concentrations, which confirms that the solution conductivity plays a very significant role in producing bead-free uniform PS fibers.     

Estimation of dilute solution viscosity parameters of rubber seed oil alkyds

Viscosity measurements were carried out in methyl ethyl ketone (MEK) and dimethyl formamide (DMF) for rubber seed oil alkyds having oil content of 20 (I), 30 (II), 35 (III), 40 (IV), 50 (V), and 60% (VI). Viscosity molecular weights, intrinsic viscosities, and viscosity parameters K and α, characteristic for both polymers and solvents, were determined. Generally, solubility properties were found to depend on molecular weight and polarity of the alkyds and solvent. Intrinsic viscosities of the alkyds were larger in DMF than in MEK, suggesting DMF to be a better solvent than MEK for rubber seed oil alkyds. Molecular weights determined for the alkyds range from 441 for sample III to 1323 for sample V. The viscosity molecular weights are in reasonable agreement with the values determined for samples II–V in MEK and samples I–IV in DMF. The values of Huggin's constant for these alkyds were also determined. Data reported also suggest that rubber seed oil alkyds tend to tolerate relatively basic solvent, such as DMF. Fractionation of the alkyds was considered to be in respect of molecular weight and polarity of the alkyds, and results show that low-molecular-weight species constitute greater proportion of the alkyds. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1987–1992, 1998     

Construction of hierarchical structures by electrospinning or electrospraying

To expand the application of electrospun fibers or electrosprayed beads, micro-nano hierarchical structures of polystyrene (PS) have been constructed through the adjustment of solvent, polymer concentration, environment humidity, electrospinning temperature, etc. Primary structures, such as fibers, beads and bead-on-string structure, as well as secondary structures, such as nanopores, nanopapilla and net-work structure, have been constructed. Solvent plays an important role in the construction of both primary structures and secondary structures. By using N,N-dimethylformamide (DMF), tetrahydrofuran (THF) and mixed solvent of DMF/THF, the micro-nano hierarchical structures can be controlled. Humidity is a key factor to the construction of secondary structures. The obtained fibers or beads have smooth surface at low humidity. While at high humidity, secondary structures tend to appear. For the PS/DMF system, vapor-induced phase separation may be the most pertinent mechanism to explain the formation of secondary structures. While for the PS/THF system, breath figure theory can explain the formation of uniform nanopores properly.     

Molecular size characterization of heavy oil fractions in vacuum and solution by molecular dynamic simulation

Two kinds of heavy oils were fractionated into eight fractions by Liquid-Solid Adsorption Chromatography, respectively, and samples were collected to measure properties. According to the elemental analysis, molecular weight and ¹H-NMR data, average molecular structures of polycyclic aromatic and heavy resin were constructed with improved Brown-Ladner (B-L) method and several corrections. And then, the most stable conformations of polycyclic aromatic and heavy resin in vacuum and toluene solution were obtained by molecular dynamic simulation, and the molecular size was gotten via the radius of gyration analysis. The results showed that the radius of gyration of polycyclic aromatic and heavy resin was 0.55–0.70 nm in vacuum and 0.60–0.90 nm in toluene solution. With molecular weight increasing, the molecular size in vacuum and toluene solution also increased. Due to the swelling behavior of solvent, the alkyl side chains of heavy oil molecule in solution were more stretched. Thus, the molecular size in toluene solution was larger than that in vacuum.     

EXTRACTION OF METAL IONS WITH DZEHPA FROM MIXED AQUEOUS-ORGANIC MEDIA

Extraction of metal ions from the aqueous-organic solution containing dimethyl formamide(DMF), dimethyl sulfoxide(DMSO) and acetonitrile(AN) was investigated by using di-2-ethylhexyl-phosphoric acid(D2EHPA) as an extractant. The organic phase was a binary solution of D2EHPA and n-hexane, or D2EHPA and toluene, while the polar phase was a three component solution of metal salt, non-aqueous solvent and water. The extracted metal ions were Cr(III), Fe(III), Al, Cu, Ni, Co(II), Mg and Ag.

The extraction behaviors may be explained by the solvation ability of non-aqueous solvents, the decrease in distribution of the extractant and extract into the organic phase, and the interaction between the extractant and non-aqueous solvents due to the dissolution of non-aqueous solvents in the organic phase.     

Molecular size characterization of heavy oil fractions in vacuum and solution by molecular dynamic simulation

Two kinds of heavy oils were fractionated into eight fractions by Liquid-Solid Adsorption Chromatography, respectively, and samples were collected to measure properties. According to the elemental analysis, molecular weight and ¹H-NMR data, average molecular structures of polycyclic aromatic and heavy resin were constructed with improved Brown-Ladner (B-L) method and several corrections. And then, the most stable conformations of polycyclic aromatic and heavy resin in vacuum and toluene solution were obtained by molecular dynamic simulation, and the molecular size was gotten via the radius of gyration analysis. The results showed that the radius of gyration of polycyclic aromatic and heavy resin was 0.55–0.70 nm in vacuum and 0.60–0.90 nm in toluene solution. With molecular weight increasing, the molecular size in vacuum and toluene solution also increased. Due to the swelling behavior of solvent, the alkyl side chains of heavy oil molecule in solution were more stretched. Thus, the molecular size in toluene solution was larger than that in vacuum.     

两亲性聚合物分子自组装的研究进展

两亲性聚合物以其同时具有亲水和疏水链段的独特结构,在生物医药、纳米技术等领域有广泛的用途。本文主要介绍了两亲性聚合物通过分子自组装形成聚集体的研究进展,详细论述了几种分子自组装聚集体的制备,包括结构、组成、分子量控制的简单聚集体、半结晶聚集体、交联聚集体以及具有刺激响应性（pH值响应性、温度响应性、pH值/温度双重响应性、氧化还原响应性、溶剂极性响应性等）的智能型聚集体,两亲性聚合物结构的可控性以及如何提高聚集体的稳定性成为国内外专家研究的重点,指出结晶诱导分子自组装及智能型分子自组装是未来研究的热点。     

聚醚砜的静电纺丝研究

采用聚醚砜(PES)的良溶剂二甲基甲酰胺(DMF)和非良溶剂丙酮(AC)为共溶剂体系,研究了溶剂组成、纺丝成形条件对静电纺丝PES纤维的形貌及纤维直径的影响。结果表明:DMF/AC的配比对于静电纺丝PES纤维形貌具有直接的调控作用,随着DMF/AC混合溶剂中AC用量的增加,纤维平均直径变大,纤维毡中串珠数目明显减少,纤维均一性变好;随着纺丝液浓度的升高,纺丝电压的增大,纤维的平均直径变大;接收距离的变化对纤维平均直径影响不大;PES最佳纺丝工艺条件为纺丝溶液质量分数13%,纺丝电压15 kV,接收距离10 cm,mDMF/mAC为8.5/1.5,在此条件下,可以获得纤维平均直径为96 nm的PES纤维毡。