Water effect on the gelation behavior of polyacrylonitrile/dimethyl sulfoxide solution

The gelation behavior of polyacrylonitrile (PAN)/dimethyl sulfoxide (DMSO) solution containing different amounts of water has been investigated using various methods. The ternary phase diagram of PAN/DMSO/water system indicated that water enhanced the temperature at which phase separation of PAN/DMSO solution occurred. Intrinsic viscosities [η] of dilute PAN/DMSO solution and PAN/DMSO/water solution at varied temperatures were measured to examine the influence of water on the phase behavior of PAN/DMSO solution. The presence of water in the solution gave rise to elevated critical temperature T_c. The gelation temperature T_g obtained by measuring the loss tangent tan δ at different oscillation frequencies in a cooling process was found to increase with increased water content in the solution. The critical relaxation exponent n value, however, changed little with varied concentration. During the aging process, the gelation rate of PAN/DMSO solution increases with the water level. The n values of the PAN/DMSO solutions with 2 wt% and 4 wt% water were a little larger than that of the solution without water, which may be explained by the turbid gel resulted from phase separation. The n values obtained in the aging process were larger than those obtained in the cooling process for the same three solutions, ascribed to the weaker gel with less cross-linking points formed in long time. Water led to the formation of denser gel structure. The coarser gel surface can also be attributed to the phase separation promoted by water.     

Viscometric measurement of the thermodynamics of PAN terpolymer/DMSO/water system and effect of fiber‐forming conditions on the morphology of PAN precursor

The thermodynamics of polyacrylonitrile (PAN) terpolymer/dimethyl sulphoxide (DMSO)/water system was investigated by viscometric method. Fourier transform infrared (FTIR) measurement of the temperature dependence of polymer/solvent interaction was performed in the range of 25–80 °C, which was in good agreement with viscometric results. Meanwhile, the upper critical solution temperature (UCST) for PAN terpolymer/DMSO/water system, which is proved to be stable one, was determined from the temperature dependence of the expansion factor α_η 3 . The morphology of PAN precursor prepared by dry‐jet‐wet spinning with different fiber‐forming conditions was examined with a scanning electron microscope (SEM). Judging from SEM photographs, not only the number and size of microvoids of PAN precursor gradually increase, with increasing the temperature of coagulation bath, but also the cross‐section shape of PAN precursor changes from nephroid shape to elliptical shape or circular shape. Therefore, PAN precursor with different microstructures can be fabricated at different quenching‐depths, suggesting that the final microstructure of the PAN precursor greatly depends on the phase separation in the fiber‐forming process. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1997–2011, 2008     

Enthalpic effect of polyacrylonitrile on the concentrated solutions in dimethyl sulfoxide: Strong thixotropic behavior and formation of bound solvents

The effect of dipole–dipole interaction by nitrile groups of PAN on the bound state of solvent molecules and the concentrated solution properties in DMSO was investigated. Variation of a solution viscosity exhibited three overlap concentrations, C1*, C2*, and C3*, at 2.7, 8.6, and 16.3 wt%, respectively, representing the transition of concentration regions in the order of dilute, unentangled‐semi dilute, entangled‐semi dilute, and concentrated regions. The two‐dimensional mapping of FT‐IR analysis and dielectric measurement confirmed that the intermolecular interaction of PAN was suddenly enhanced at the C*s, inducing polarization to DMSO. In the ice‐melting process of PAN solutions, two different melting peaks (T_m2 and T_m3) of DMSO newly appeared at each C2* and C3*, suggesting the different types of bound solvents. In the concentrated solutions, the saturated dielectric constant and the strongly delayed evaporation of the solvent even at the boiling point of DMSO along with strong thixotropic behavior were indicative of the stronger confinement state of bound DMSO than in the semidilute solutions. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1080–1089     

Viscoelastic behavior of polyacrylonitrile/dimethyl sulfoxide concentrated solution with water

The spinnability and polydispersity of polyacrylonitrile/dimethyl sulfoxide (PAN/DMSO)/H₂O spinning solutions with conventional PAN molecular weight and comparative high PAN concentration have been investigated using a cone‐plate rheometer. It is observed from the measurements that, the viscosities of the solutions decreased with the rising of shear rate, and then stabilized to almost the same value, regardless of the PAN concentration. The chain orientation in the fiber formed under constant shear rate cannot be changed considerably even after long relaxation of more than 900s. For dynamic experiments, a steady increase of both G′ and G″ with escalating oscillation frequency was seen for all samples. Higher viscous‐elastic modulus at higher H₂O content was found, too. It is also concluded from the log G′ ? log G″ plot and the gel point that the PAN/DMSO/H₂O system with regular PAN molecular weight behaves very close to a mono‐disperse system, thus very suitable for gel spinning and for preparation of high performance PAN precursor fiber. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1437–1442, 2009     

Poly(acrylonitrile) ultrafiltration membranes. II. Membrane morphology and permeation characteristics

The rheology and phase‐boundary characteristics of various solutions comprising three polyacrylonitrile (PAN) grades dissolved in solutions of N,N‐dimethylformamide + salt (LiCl, ZnCl₂, or AlCl₃) additives were correlated with the resulting membrane morphology as determined by microscopy and permeability measurements. The phase separation characteristics of the dope solution were not markedly affected by the PAN molecular weight (MW); however, they were affected by the salt additive. For higher MW grades, the effect of salt addition can also be masked by the increased self‐association tendency of the polymer chains. PAN‐B and ‐C membranes were clearly less asymmetric in structure than the lower MW PAN‐A–based membranes. This is attributed to the higher viscosity/lower diffusivity of the PAN‐B and ‐C solutions, which results in slower solvent–nonsolvent exchange during the phase inversion process. Two factors reduce the incidence of surface defects (increased bubble points): (a) higher solution viscosity dampens surface perturbations during phase inversion, and (b) phase inversion pathways resulting in more homogenous morphology lead to membranes with higher bubble points. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2074–2085, 2005     

Morphology control of polyacrylonitrile (PAN) fibers by phase separation technique

Based on the constructed theoretical ternary phase diagrams of water/dimethyl sulfoxide (DMSO)/polyacrylonitrile (PAN) terpolymer system, the phase separation behavior for PAN fibers preparation was investigated. Theoretical ternary phase diagrams were determined by the extended Flory‐Huggins theory. To investigate the temperature dependence of theoretical ternary phase diagrams, all binary interaction parameters at different temperatures were determined accurately and thoroughly revisited. From numerical calculations, it was found that a small quantity of water was needed to induce phase demixing. Meanwhile, the cloud point data of the system for more dilute PAN terpolymer solutions were determined by cloud point titration, and the cloud point data for more concentrated PAN terpolymer solutions were calculated by Boom's linearized cloud point (LCP) curve correlation. Furthermore, the morphology of PAN fibers was investigated by using scanning electron microscopy (SEM). With increasing the concentration of PAN terpolymer solutions as well as the quenching depth, the morphology of PAN fibers turns from large open channels to small bead‐like structures, accompanying with a reduction of the porosity of PAN fibers. Judging from our investigation, it was clear that the final morphology of PAN fibers was mainly determined by phase separation in fiber‐forming process. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 261–275, 2009     

Specific swelling behaviors of alkali‐metal poly(styrene sulfonate) gels in aqueous solvent mixtures

Counterion‐ and solvent‐specific swelling behaviors were investigated for alkali‐metal poly(styrene sulfonate) (PSSM) gels having different degrees of sulfonation in aqueous organic solvent mixtures [water plus methanol, ethanol, 2‐propyl alcohol, t‐butyl alcohol, dimethyl sulfoxide (DMSO), acetone, acetonitrile, tetrahydrofuran, or dioxane]. With an increasing organic solvent concentration, most gel systems, except for DMSO, showed a volume phase transition. The transition abruptly occurred without significant deswelling in the lower solvent concentration region. Such swelling behavior contrasted with that of other common charged gel systems, including alkali‐metal polyacrylate (PAAM) gels, which showed gel collapse after gradual deswelling with an increasing organic solvent concentration. The dielectric constant at the critical transition point (D_cr) for most mixed solvent systems decreased in the order of PSSK ≥ PSSCs ≥ PSSNa > PSSLi; that is, larger counterion systems were favorable for the transition. The counterion specificity also contrasted with our previous results for PAAM gels: PAANa > PAAK > PAALi ～ PAACs. On the other hand, the solvent specificity for the PSSM gels was similar to that for the PAAM gels; the higher the dielectric constant was of the organic solvent, the higher the D_cr value was at which the transition occurred. These specificities were examined on the basis of the solvation properties of the counterions and polymer charged groups and the solvent properties such as the Gutmann–Mayer donor number and acceptor number. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1166–1175, 2007     

同质编织管增强型聚丙烯腈中空纤维膜研究

利用二维编织技术将聚丙烯腈(PAN)纤维编织成中空编织管,以聚丙烯腈为成膜聚合物,以聚乙二醇为成孔剂,配制铸膜液,采用同心圆纺丝法制备同质编织管增强型聚丙烯腈中空纤维膜.研究结果表明,所得同质编织管增强型聚丙烯腈中空纤维膜的表面分离层具有类似于非对称膜的结构,铸膜液可渗入编织管纤维束中;随着编织管编织节距的增大,同质编织管增强型聚丙烯腈中空纤维膜表面分离层厚度减小,同时膜的平均孔径增大,膜的纯水通量随之增大;铸膜液渗入编织管纤维束的现象未影响膜的通透性能;编织管的断裂强度最大可达100 MPa以上.通过水浴振荡、超声波水浴振荡及等力拉伸3种方法测试了同质编织管增强型中空纤维膜和异质编织管增强型中空纤维膜中编织管与表面分离层之间的界面结合性能,结果表明前者的界面结合性能优于后者.     

Microporous polyethersulfone membranes prepared under the combined precipitation conditions with non‐solvent additives

Using diethylene glycol (DegOH) as non‐solvent additive (NSA) and N, N‐dimethylacetamide (DMAc) as solvent (S), polyethersulfone (PES) flat sheet membranes were prepared via immersion precipitation combined with the vapor induced phase separation (VIPS) process. Light transmittance was used to follow the precipitation rate during the immersion process as well as during the VIPS stage. As the addition of the NSA, the viscosity of casting solutions increased, which led to a slow precipitation rate. Though the precipitation rate decreased, the instantaneous demixing type was maintained. High flux membranes were obtained only at a high mass ratio of NSA/S; producing membranes had cellular pores on the top surface and sponge‐like structure on cross section. The VIPS process prior to immersion precipitation was important for the formation of cellular pore on the surface. With the increase in exposure time, the liquid–liquid phase separation took place on the surface of casting solution; nucleation and growth induced the formation of cellular pore on the top surface. Coagulation bath temperature also had large effect on the precipitation rate; high temperature on coagulation bath mainly accelerated the transfer of solvent and non‐solvent. Higher flux membrane with a porous skin layer could be obtained at a high coagulation bath temperature, but at the same time the mechanism properties were weakened. Copyright © 2007 John Wiley & Sons, Ltd.     

Electrochemistry and Spectroscopy of Sulfate Complexes of (Tetraphenylporphyrinato)manganese

The electrochemical and spectroscopic properties of [Mn₂(tpp)₂(SO₄)] (H₂tpp=tetraphenylporphyrin=5,10,15,20‐tetraphenyl‐21H,23H‐porphine) were studied to characterize the stability of this compound as a function of solvent, redox state, and sulfate concentration. In non‐coordinating solvents such as 1,2‐dichloroethane, the dimer was stable, and two cyclic voltammetric waves were observed in the region for Mn^III reduction. These waves correspond to reduction of the dimer to [Mn^II(tpp)] and [Mn^III(tpp)(OSO₃)]^?, and reduction of [Mn^III(tpp)(OSO₃)]^? to [Mn^II(tpp)(OSO₃)]^2?, respectively. In the coordinating solvent DMSO, [Mn₂(tpp)₂(SO₄)] was unstable and dissociated to form [Mn^III(tpp)(DMSO)₂]⁺. A single voltammetric wave was observed for Mn^III reduction in this solvent, corresponding to formation of [Mn^II(tpp)(DMSO)]. In non‐coordinating solvent systems, addition of sulfate (as the bis(triphenylphosphoranylidene)ammonium (PPN⁺) salt) resulted in dimer dissociation, yielding [Mn^III(tpp)(OSO₃)]^?. Reduction of this monomer produced [Mn^II(tpp)(OSO₃)]^2?. In DMSO, addition of SO led to displacement of solvent molecules forming [Mn^III(tpp)(OSO₃)]^?. Reduction of this species in DMSO led to [Mn^II(tpp)(DMSO)].     

Solvent concentrations of dimethylsulfoxide-water and 1-propanol-water solutions inside and outside poly (N-isopropylacrylamide) gel

The volumes of poly (N-isopropylacrylamide) (NIPA) gel in both dimethylsulfoxide (DMSO)-water and 1-propanol-water solutions were measured at 25°C. The solvent concentrations inside and outside the NIPA gel were also measured. The gel was swollen in water, shrunk according to increase in concentration of organic solvent, and reswollen in pure organic solvent. This phenomenon is typical reentrant swelling behavior. The DMSO concentrations inside the gel were almost equal to those outside the gel in the whole concentration range. On the other hand, the 1-propanol concentrations between inside and outside the gel were much different from each other in the shrunk state, though they were almost the same in the swollen state.     

采用静电纺丝/非溶剂致相分离制备聚丙烯腈多孔超细纤维的研究

以聚丙烯腈/二甲基亚砜/N,N'-二甲基甲酰胺三元体系为纺丝液、3℃水浴为接收介质,通过静电纺丝制备了具有纳米孔结构的静电纺聚丙烯腈多孔超细纤维.探讨了溶剂比例、接收介质、聚丙烯腈浓度、纺丝电压及接收距离等因素对纤维直径和表面孔隙率的影响.结果表明最佳制备条件为混合溶剂质量比1∶1、纺丝电压16 kV、聚丙烯腈浓度15 wt%、接收距离5 cm、纺丝速率0.7 mL/h、环境温度25℃、相对湿度40%～70%.在此条件下得到的聚丙烯腈多孔超细纤维直径在420～490 nm,平均直径468 nm,表面孔隙率3.4%,纤维内部形成大量孔径为8～30 nm的孔结构,且孔径分布均匀,孔形状相对一致.N2吸附脱附测试表明,聚丙烯腈多孔纤维的BET比表面积达43.86 m2/g,是相同直径无孔聚丙烯腈纤维比表面积理论值的6倍.通过研究聚丙烯腈/(二甲基亚砜+N,N'-二甲基甲酰胺)/水的三元相图,提出非溶剂致相分离是主要成孔机理.     

Structural changes in thermal-induced polyacrylonitrile gel under uniaxial drawing

The influences of uniaxial drawing on the different structural scales in thermal-induced polyacrylonitrile (PAN) gel were studied. The results of atomic force microscopy (AFM) and swelling tests indicated that the drawn PAN gels had more compact structure with less solvent contained. Besides, some microphase separations occurred in the highly drawn gel and caused the gel to become more porous, as verified by the results from differential scanning calorimetry (DSC). The wide-angle X-ray diffraction (WAXD) results confirmed that drawing induces chain orientation and partial crystallization in the thermal-induced PAN gels, and higher draw ratio generated greater structural changes in the gels. It was also found from the tensile stress relaxation of the gels that the crosslinks in the gel increased with the draw ratio. In Fourier transform infrared (FTIR) spectra, the blue shift in wave numbers of two absorption peaks (3200-3700 cm⁻¹ and around 2244 cm⁻¹), and a gradually disappearing peak at 1036 cm⁻¹ all indicated the weakening hydrogen bonding between the PAN molecular chains and dimethyl sulfoxide (DMSO) molecules during the drawing process.     

Characterization of Klason lignin samples isolated from beech and aspen using microbore column size‐exclusion chromatography

The present study is focused on the separation and characterization of lignin samples isolated by Klason method from European beech (Fagus sylvatica) broadleaf hardwood and European aspen (Populus tremula) broadleaf softwood by size‐exclusion chromatography. The separation was carried out using dimethylformamide as major component of the mobile phase and a 3 mm id microbore column packed with hydroxyethyl methacrylate gel, calibrated with polystyrene standards. The influence of mobile phase composition and sample solvent composition on the chromatographic behavior and molar mass distributions was investigated.     

Preparation of porous polylactide microspheres by emulsion‐solvent evaporation based on solution induced phase separation

Porous polylactide (PLA) microspheres were fabricated by an emulsion‐solvent evaporation method based on solution induced phase separation. Scanning electron microscopy (SEM) observations confirmed the porous structure of the microspheres with good connectivity. The pore size was in the range of decade micrometers. Besides large cavities as similarly existed on non‐porous microspheres, small pores were found on surfaces of the porous microspheres. The apparent density of the porous microspheres was much smaller than that of non‐porous microspheres. Fabrication conditions such as stirring rate, good solvent/non‐solvent ratio, PLA concentration and dispersant (polyvinyl alcohol, PVA) concentration had an important influence on both the particle size and size distribution and the pore size within the microspheres. A larger pore size was achieved at a slower stirring rate, lower good solvent/non‐solvent ratio or lower PLA concentration due to longer coalescence time. Copyright © 2005 John Wiley & Sons, Ltd.     

溶剂对相分离法制备聚偏氟乙烯微孔膜性质的影响

研究了用相转换法制备聚偏氟乙烯（PVDF）微孔膜时溶剂对成膜性质的影响.用浊点法测定了二甲基亚砜、N,N-二甲基甲酰胺、N,N-二甲基乙酰胺、N-甲基吡咯烷酮、磷酸三甲酯等五种溶剂配制的质量分数为wPVDF=0.12的铸膜液在30℃时的相分离点,显微镜拍照法测定了这些铸膜液与水接触时相分离前沿推进速率,泡点法测定了膜孔径,并测定了气体通量.结果表明,二甲基亚砜、磷酸三甲酯、N,N-二甲基乙酰胺是适于制作聚偏氟乙烯微孔膜的溶剂.     

Synthesis of poly(o‐phenylenediamine) nanofiber with novel structure and properties

The poly(o‐phenylenediamine) (PoPD) was synthesized from the monomer o‐phenylenediamine in various organic solvent medium viz. dimethyl sulfoxide (DMSO), N,N‐dimethyl formamide (DMF) and methanol using ammonium per sulfate as a radical initiator. The structure just like polyaniline derivative with free ?NH functional groups of the synthesized polymers confirmed by various standard characterizations was explained from the proposed polymerization mechanism. All the synthesized polymers were completely soluble in common organic solvent like DMSO and DMF because of the presence of polar free ?NH functional groups in its structure. The formation of polymer nanofiber by reverse salting‐out process was confirmed, and the synthesized polymer in DMSO medium was the best polymer in terms of nano‐morphology as well as conducting properties. Interestingly, the average DC conductivity of undoped polymer film was recorded as 2.21 × 10^?6 Scm^?1 because of induced doping through self charge separation. Moreover, the conductivity of the polymer film was further increased to 1.16 × 10^?3 Scm^?1 after doping by sulfuric acid. Copyright © 2016 John Wiley & Sons, Ltd.     

Theory and simulation of polymerization‐induced phase separation in polymeric media

A rigorous model of polymerization‐induced phase separation (PIPS), based on the non‐linear Cahn‐Hilliard (C‐H) and Flory‐Huggins (F‐H) theories combined with a second‐order polymerization reaction equation, has been formulated and its solutions characterized. The model describes phase separation in system consisting of a non‐reactive polymer and a monomer that undergoes condensation polymerization. The model consists of a balance equation for the low molecular weight polymerization regime and another balance equation for the high molecular weight entangled regime. The model equations are solved, and the solutions are characterized to identify the dynamical and morphological phenomena of the PIPS process. The extent of phase separation increases significantly with time during the early stage of phase separation, and slows down in the intermediate stage. The various types of phase‐separated morphologies are fully characterized using a novel morphological characterization techniques, known as the intensity and scale of segregation. Both the dynamical and morphological features of the PIPS method are sensitive to the magnitudes of the dimensionless diffusion coefficient D* and the dimensionless reaction rate constant K*. The scale of segregation and the droplet size decreases as D* and K* increase. On the other hand, the intensity of segregation increases with K*, but decreases with D*. The present results extend the present knowledge of the PIPS process by taking into account the effects arising from the presence of a non‐reactive polymer.     

Diffusion Mechanism of As‐spun Polyacrylonitrile Fiber in a Dimethyl Sulfoxide‐Water Coagulation Bath

In this paper, the diffusion mechanism of as‐spun PAN fiber was investigated in dimethyl sulfoxide‐water by determining the dynamic compositions of the fibers and the diffusion coefficients of solvent and nonsolvent during coagulation. The diffusion process could be divided into two stages. Results showed that the first stage of the diffusion process was the most important during the whole process, which was fundamental to further study on the formation mechanism. Also, compared with wet spinning, the dry‐jet wet spinning method had the advantage of mild coagulating at a high jet‐stretch. At high concentrations, the diffusion coefficients increased and the ratio of solvent diffusion coefficient to nonsolvent diffusion coefficient decreased; an increasing temperature resulted in the increase of both diffusion coefficients with a decrease in their ratios. To some extent, for the PAN‐DMSO‐water system, the more the ratios D_s*/D_n* tended to 1, the more the cross‐section shapes of as‐spun PAN fiber tended to be circular.     

Preparation of non‐spherical particles from amphiphilic block copolymers

Simple self‐assembly techniques to fabricate non‐spherical polymer particles, where surface composition and shape can be tuned through temperature and the choice of non‐solvents was developed. A series of amphiphilic polystyrene‐b‐poly(2‐ethyl‐2‐oxazoline) block copolymers were prepared and through solvent exchange techniques using varying non‐solvent composition a range of non‐spherical particles were formed. Faceted phase separated particles approximately 300 nm in diameter were obtained when self‐assembled from tetrahydrofuran (THF) into water compared with unique large multivesicular particles of 1200 nm size being obtained when assembled from THF into ethanol (EtOH). A range of intermediate structures were also prepared from a three part solvent system THF/water/EtOH. These techniques present new tools to engineer the self‐assembly of non‐spherical polymer particles. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 750–757