DMF), N,N-dimethylacetamide Research Articles

Isobaric vapor–liquid equilibrium for binary system of N, N-dimethyl formamide + N, N-dimethyl acetamide and quaternary system of sec-butyl alcohol + sec-butyl acetate + N, N-dimethyl formamide + N, N-dimethyl acetamide at 101.3 kPa

Isobaric vapor–liquid equilibrium (VLE) for the binary system N, N-dimethyl formamide (DMF) + N, N-dimethyl acetamide (DMAC) and the quaternary system sec-butyl alcohol (SBA) + sec-butyl acetate (SBAC) + DMF + DMAC were determined at 101.3 kPa using a vapor–liquid equilibrium still. The thermodynamic consistency test for the experimental data was checked by Van Ness point test. The binary VLE data were correlated with the NRTL, UNIQUAC and Wilson activity coefficient models respectively. And the VLE data of the quaternary system predicted by the correlated binary interaction parameters agree well with the experimental data. And the mixture of DMF (3) and DMAC (4) can eliminate the pseudo-azeotrope of sec-butyl alcohol (1) + sec-butyl acetate (2). Thus, the mixture of DMF and DMAC is appropriate for separation of the pseudo-azotrope of SBA and SBAC by extractive distillation.

Impact of solvents and process conditions on the formation of polyethersulfone membranes and its fouling behavior in lake water filtration

BACKGROUND: The existence of natural organic colloids causes membrane fouling, which decreases the flux rate. Hence, membrane modification and lake water pretreatment were carried out to improve membrane performance. In this study, important preparation parameters such as solvents (N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO) and N-methyl-2-pyrrolidone (NMP)), coagulant bath temperature (CBT) (10, 20 and 30 °C) and coagulant (sodium dodecyl sulfate SDS): 0.5, 1.0 and 1.5 g L−1) were optimized for the fabrication of high flux polyethersulfone (PES) membrane. Cloisite was used for the pretreatment of lake water. RESULTS: The highest water permeability and pore radius of 393.03 × 10−9 m s−1 kPa−1 and 4.43 nm, respectively, were observed for the PES/DMAc membrane combination at coagulant bath temperature of 10 °C and non-solvent containing 1.5 g L−1 SDS solution. Morphology analysis also displayed large pore size and macrovoid formation for such combination. Pretreated lake water had highest natural organic matter (NOM) rejection of 93% for PES/DMF membrane made at a coagulant bath temperature of 20 °C and non-solvent containing water. CONCLUSION: High flux PES membrane formation is achieved through the DMAc solvent with SDS as non-solvent solution at lower coagulation bath temperature. Pretreated lake water showed an increase of membrane flux and fouling resistance. © 2015 Society of Chemical Industry.

Measurement and correlation of the solubility of rivaroxaban (form I) in binary mixtures of ethyl acetate with tetrahydrofuran, N,N-dimethylformamide, and N,N-dimethylacetamide from T = (278.15 to 318.15) K

In this work, the solubility of rivaroxaban (form I) in binary solvent mixtures of ethyl acetate (EA) with N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA) and tetrahydrofuran (THF) was firstly experimentally measured over the temperature range from (278.15 to 318.15)K. Then the measured solubility data were correlated with such semiempirical thermodynamic models as Jouyban–Acree (JA) equation and Buchowski (λh) equation. The crystal form of the residual solids in equilibrium with liquids was identified by powder X-ray diffraction (PXRD). The melting temperature and fusion enthalpy were determined using differential scanning calorimetry (DSC). The results show that, the solubility of rivaroxaban generally increases with the temperature and decreases with the increase in the content of EA in the binary solvent mixtures. Furthermore, when λh equation is used to correlate the solubility of rivaroxaban with the temperature in each solvent mixture, the average relative deviation (ARD) between the experimental and calculated values is about 0.0671, while it is about 0.0905 when JA equation is employed to correlate the solubility with the temperature and the composition of solvent mixtures simultaneously.

Synthesis and Characterization of Fluorinated Polyimide Derived from 3,3′‐Diisopropyl‐4,4′‐diaminodiphenyl‐3′′,4′′‐difluorophenylmethane

AbstractA novel aromatic diamine monomer, 3,3′‐diisopropyl‐4,4′‐diaminodiphenyl‐3′′,4′′‐difluorophenylmethane (PAFM), was successfully synthesized by coupling of 2‐isopropylaniline and 3,4‐difluorobenzaldehyde. The aromatic diamine was adopted to synthesize a series of fluorinated polyimides by polycondensation with various dianhydrides: pyromellitic dianhydride (PMDA), 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA), 4,4′‐oxydiphthalic anhydride (ODPA) and 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride (BTDA) via the conventional one‐step method. These polyimides presented excellent solubility in common organic solvents, such as N,N‐dimethylformamide (DMF), N,N‐dimethyl acetamide (DMAc), dimethyl sulfoxide (DMSO), N‐methyl‐2‐pyrrolidone (NMP), chloroform (CHCl3), tetrahydrofuran (THF) and so on. The glass transition temperatures (Tg) of fluorinated polyimides were in the range of 260–306°C and the temperature at 10% weight loss in the range of 474–502°C. Their films showed the cut‐off wavelengths of 330–361 nm and higher than 80% transparency in a wavelength range of 385–463 nm. Moreover, polymer films exhibited low dielectric properties in the range of 2.76–2.96 at 1 MHz, as well as prominent mechanical properties with tensile strengths of 66.7–97.4 MPa, a tensile modulus of 1.7–2.1 GPa and elongation at break of 7.2%–12.9%. The polymer films also showed outstanding hydrophobicity with the contact angle in the range of 91.2°–97.9°.

Synthesis and characterization of novel highly soluble and optical transparent polyimides containing tert-butyl and morpholinyl moieties

A series of novel organo-soluble and optical transparent polyimides were synthesized via conventional one-step polycondensation from a novel diamine, 3,3′-diterbutyl-4,4′-diaminodiphenyl-4″-morpholinophenylmethane (TAMPM) and various commercial aromatic dianhydrides. The structures of monomer and polymers were confirmed by FT-IR and NMR. The solubility, thermal stability, optical transparency, dielectric and hydrophobic properties of polyimides were investigated. The results showed polymers presented excellent solubility in common organic solvents, such as N,N-dimethylformamide (DMF), N,N-dimethyl acetamide (DMAc), dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), chloroform (CHCl3), tetrahydrofuran (THF) and dichloromethane (CH2Cl2). The polymers exhibited prominent thermal stability and high optical transparency with the glass transition temperature (T g) in the range of 311–355 °C, and the cutoff wavelengths in the range of 287–344 nm. Furthermore, all of the polymers also presented low dielectric constants in the range of 2.85–3.16 at 1 MHz, and outstanding hydrophobic properties with the contact angle in the rang of 85.1–94.2 o.

Novel Non‐Coplanar and Tertbutyl‐Substituted Polyimides: Solubility, Optical, Thermal and Dielectric Properties

AbstractA novel aromatic diamine monomer bearing tertbutyl and 4‐tertbutylphenyl groups, 3,3′‐ditertbutyl‐4,4′‐diaminodiphenyl‐4′′‐tertbutylphenylmethane (TADBP), was prepared and characterized. A series of non‐coplanar polyimides (PIs) were synthesized via a conventional one‐step polycondensation from TADBP and various aromatic dianhydrides including pyromellitic dianhydride (PMDA), 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA), 4,4′‐oxydiphthalic anhydride (OPDA), 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride (BTDA) and 4,4′‐(hexafluoroisopropylidene)dipthalic anhydride (6FDA). All PIs exhibit excellent solubility in common organic solvents such as N,N‐dimethylformamide (DMF), N,N‐dimethylacetamide (DMAc), N‐methyl‐2‐pyrrolidone (NMP), dimethyl sulfoxide (DMSO), chloroform (CHCl3), tetrahydrofuran (THF), and so on. Furthermore, the obtained transparent, strong and flexible polyimide films present good thermal stability and outstanding optical properties. Their glass transition temperatures (Tgs) are in the range of 298 to 347°C, and 10% weight loss temperatures are in excess of 490°C with more than 53% char yield at 800°C in nitrogen. All the polyimides can be cast into transparent and flexible films with tensile strength of 80.5–101 MPa, elongation at break of 8.4%–10.5%, and Young's modulus of 2.3–2.8 GPa. Meanwhile, the PIs show the cutoff wavelengths of 302–356 nm, as well as low moisture absorption (0.30% –0.55%) and low dielectric constant (2.78–3.12 at 1 MHz).

Kinetic solvent effects on the reactions of the cumyloxyl radical with tertiary amides. Control over the hydrogen atom transfer reactivity and selectivity through solvent polarity and hydrogen bonding.

A laser flash photolysis study on the role of solvent effects on hydrogen atom transfer (HAT) from the C-H bonds of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), N-formylpyrrolidine (FPRD), and N-acetylpyrrolidine (APRD) to the cumyloxyl radical (CumO(•)) was carried out. From large to very large increases in the HAT rate constant (kH) were measured on going from MeOH and TFE to isooctane (kH(isooctane)/kH(MeOH) = 5-12; kH(isooctane)/kH(TFE) > 80). This behavior was explained in terms of the increase in the extent of charge separation in the amides determined by polar solvents through solvent-amide dipole-dipole interactions and hydrogen bonding, where the latter interactions appear to play a major role with strong HBD solvents such as TFE. These interactions increase the electron deficiency of the amide C-H bonds, deactivating these bonds toward HAT to an electrophilic radical such as CumO(•), indicating that changes in solvent polarity and hydrogen bonding can provide a convenient method for deactivation of the C-H bond of amides toward HAT. With DMF, a solvent-induced change in HAT selectivity was observed, suggesting that solvent effects can be successfully employed to control the reaction selectivity in HAT-based procedures for the functionalization of C-H bonds.

Towards non-toxic solvents for membrane preparation: a review

Solvents are used in every chemical process and affect its overall safety, environmental, and economic impact. Membrane processes have attracted increasing interest as sustainable alternatives to traditional technologies, being characterized by reduced energy consumption and use of chemicals. However, the most important membrane preparation techniques are often based on the use of toxic solvents, which reduces the benefit to the environment. Due to the influence of solvent properties such as viscosity, dielectric constant, polarity, and boiling point on the final features and the indispensable prerequisite of dissolving the selected polymer (at room or high temperature, depending on the technique), one of the most difficult but most interesting challenges for membrane scientists is replacing these solvents, such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), N-methyl-2-pyrrolidone (NMP), and tetrahydrofuran (THF), with safer alternatives. In this review, the most relevant steps towards the use of non-toxic solvents in membrane preparation are reported, focusing particular attention on the non-solvent induced and temperature induced phase separation (NIPS and TIPS) techniques. Supercritical CO2 (ScCO2) and ionic liquids (ILs) are promising examples of benign solvents, and their use in membrane preparation will also be described. The total replacement of toxic diluents with greener alternatives still remains at the beginning stages. However, in several cases, membranes prepared using less/non-toxic solvents achieved performance comparable to those produced with classical toxic solvents. This review offers valid support for membrane scientists who wish to reduce the environmental impact of solvent use and increase membrane processes sustainability.

Probing molecular interactions of ionic liquid in industrially important solvents by means of conductometric and spectroscopic approach

Qualitative and quantitative analysis of molecular interaction prevailing in ionic liquid-organic solvent media, probed by electrical conductances and FT-IR measurements have been reported. Conductometric studies of 1-ethyl-3-methylimidazolium bromide [EMIm]Br in acetonitrile (AN), methanol (MeOH), N,N-dimethyl formamide (DMF), N,N-dimethyl acetamide (DMA) and dimethyl sulphoxide (DMSO) at 298.15K reveals high molecular interaction contributed mainly by ion–dipole interaction as evident from the FT-IR measurements. The extent of interaction is expressed in terms of the association constant (KA) and shows the ion–dipole interaction to be a function of viscosity. The interaction obtained is highest in case of DMSO in comparison to the other solvents. The greater share of the conductance of [EMIm]Br in different solvents comes from the Br− ion than the [EMIm]+ ion as evident from their ionic conductance values which is estimated from the appropriate division of the limiting molar conductivity value of tetrabutylammonium tetraphenylborate [Bu4NBPh4] as the “reference electrolyte” method.

Densities and volumetric properties of binary mixtures of N,N-dimethylformamide/N,N-dimethylacetamide with some alkyl acrylates at temperatures from 288.15 K to 318.15 K

The densities, ρ of binary mixtures of N,N-dimethylformamide (DMF)/N,N-dimethylacetamide (DMA) with methyl acrylate (MA), ethyl acrylate (EA) and butyl acrylate (BA), including those of pure liquids, over the entire composition range were measured at temperatures (288.15, 293.15, 298.15, 303.15, 308.15, 313.15, and 318.15)K and atmospheric pressure. From the experimental results, the excess molar volume, VmE, partial molar volumes, V¯m,1°∞ and V¯m,2°∞ and excess partial molar volumes, V¯m,1°E,∞ and V¯m,2°E,∞ at infinite dilution were calculated. The VmE values were found to be negative over the whole composition range for all the mixtures and at each temperature studied indicating the presence of specific interactions between DMF/DMA and acrylate molecules in the mixtures. It is observed that VmE values depend upon the size of alkyl group in acrylate molecules and the interactions between DMF/DMA and acrylate molecules decrease with increase in size of alkyl group. Also, the DMA-acrylate interactions are found stronger than DMF-acrylate interactions in these mixtures.

Synthesis and characterization of highly soluble and optically transparent polyimides derived from novel fluorinated pyridine-containing aromatic diamine

A novel fluorinated pyridine-containing aromatic diamine monomer, 4-phenyl-2,6-bis[2-(4-amino-2-trifluoromethyphenoxy)phenyl]pyridine ( o, p-6FPAPP), was prepared in a three-step synthetic route. This aromatic diamine was then employed to synthesize a series of fluorinated pyridine-containing polyimides (PIs) by polycondensation with various aromatic dianhydrides via the conventional two-step method. The inherent viscosities of the resulting poly(amic acid)s (PAAs) and PIs were in the range of 0.71–0.89 and 0.62–0.84 dL/g; all the PIs obtained by chemical imidization were readily soluble in common organic solvents such as N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF) and so on. Meanwhile, transparent, strong and flexible PI films were obtained, which had good thermal stability, with the glass transition temperature ( Tg) of 195.2°C–232.7°C, the temperature at 10% weight loss of 530.2°C–546.0°C in nitrogen atmosphere, and good optical transparency with the cutoff wavelengths of 354–382 nm, as well as outstanding mechanical properties with tensile strengths of 96.4–105.8 MPa, tensile modulus of 1.57–1.88 GPa and elongations at break of 9.5%–13.4%. The PI films were also found to possess low water uptake of 0.52%–0.67%.

Solubility of CO2 in amide-based Brønsted acidic ionic liquids

Several hydrophilic amide-based Brønsted acidic ionic liquids (BAILs) were prepared by simple acid-base neutralization reaction of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and N-methylpyrrolidone (NMP) with trifluoroacetic acid (TFA) or tetrafluoroboric acid (FBA). The solubility data of CO2 in these BAILs were determined at T=(303.15, 313.15, and 323.15)K and subatmospheric pressure using isochoric saturation method. With the same cation, CO2 solubility in TFA-based BAILs was higher than that in FBA-based ones. From the variation of solubility, expressed as Henry’s law constants, with temperature, the standard Gibbs free energy, enthalpy, and entropy changes of CO2 solvation were calculated. The solubilities of CO2 in these BAILs were apparently increased with increasing the molar volume of BAIL except for [DMFH][TFA].

Solvent-Dependent Formation of Cd(II) Coordination Polymers Based on a C2-Symmetric Tricarboxylate Linker

Three novel solvent-dependent Cd(II) coordination architectures [Cd3(BPT)2(DMF)2]·2H2O [1], [Cd3(BPT)2(DMA)2] [2], and [(CH3CH2)2NH2]·[Cd(BPT)]·2H2O [3] were obtained by the hydrothermal reaction of a C2-symmetric tricarboxylate linker, biphenyl-3,4′,5-tricarboxylic acid (H3BPT), with cadmium nitrate in the mixed solvents of water with N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), diethylformamide (DEF), respectively. Single-crystal X-ray diffraction analyses reveal that complex 1 is a three-dimensional (3D) network containing infinite Cd–O–Cd chains with the solvent DMF molecule bridging the neighboring Cd1 and Cd2 centers. Though complex 2 also has a 3D network containing infinite metal-carboxylate chains, the solvent DMA molecule only coordinates to one of the Cd(II) centers as a terminated solvent molecule. Complex 3 possesses a two-dimensional (2D) (6, 3) honeycomb type net formed by the mononuclear metal ion and the BPT ligand, which are further stacked in ABAB fashion through π–π intera...

Investigations on ionic conduction in amides + glycerol binary mixtures

The ionic conductivity of amides (N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), formamide (FA)), glycerol (Gly) and binary mixtures of amides with Gly (amides+Gly) over the entire composition range were investigated at 1MHz radio frequency in the temperature range of 15–60°C. The Arrhenius behaviour of ionic conductivity of the amides and amides+Gly mixtures of amide-rich concentration confirms the static-type (direct current) ionic conduction mechanism at 1MHz. The Gly and amides+Gly mixtures of Gly-rich concentration have the static to alternating current transport of ions at 1MHz, and show the non-Arrhenius behaviour of their ionic conductivity. The values of conductivity activation energy of these binary mixtures were evaluated and the same were compared with their viscosity activation energy. The dependence of ionic conductivity on the static permittivity, viscosity and also the behavior of hydrogen-bonded interactions between amides and Gly molecules were explored.

Dielectric behaviour of some amides and formamides dissolved in nonpolar solvents under static electric field

Structural and associational aspects of polar amides (j) like formamide, acetamide, N-methyl acetamide (NMA), N,N-dimethyl formamide (DMF), N,N-dimethyl acetamide (DMA) and acetanilide dissolved in the nonpolar solvent (i) benzene or 1,4-dioxan have been estimated from the measured static relative permittivity e0ij and high-frequency permittivity e∞ij at different weight fractions wjs of polar solute at 35°C under static electric field using Debye model of polar liquid molecule. The static dipole moments μss are compared with μjs reported from conductivity method and theoretical μtheos to get exact μcal. μtheos of the molecules are predicted from the available bond angles and bond moments where difference in electron affinity exists between two adjacent atoms of a polar group due to inductive, mesomeric and electromeric effects in them. Solute–solute molecular association for NMA in benzene and solute–solvent association for other amides are ascertained to arrive at their conformational structures.

SYNTHESIS AND PROPERTIES OF POLY(ARYL ETHER KETONE)S CONTAINING PENDANT ARYL ESTER GROUPS

A series of novel poly(aryl ether ketone) s containing pendant aryl ester groups(PEK-COO-Ar) were prepared from poly(aryl ether ketone)s containing pendant carboxyl acid groups(PEK-A) and phenol in the presence of 1,1,2,2-tetrachloroethane and by using p-toluenesulfonic acid as a catalyst.The PEK-A was synthesized from trimellitic anhydride chloride(TMAc),terephthaloyl chloride(TPC) and 1,4-bis(4-phenoxybenzoyl)benzene(p-EKKE) by low temperature solution poly-condensation.By changing the molar ratio of TMAc and TPC a series of PEK-A polymers were prepared.The PEK-COO-Ars were characterized by Fourier transform infrared spectroscopy(FTIR),wide-angle X-ray diffraction(WAXD),thermal gravimetric analysis(TGA) and differential scanning calorimetry(DSC).The results showed that the glass transition temperature(Tg) of the PEK-COO-Ar was in the range of 195 ～ 219℃ and the decomposition temperature(Td) at 5% weight loss was from 416℃ to 447℃ and the melting temperature(Tm) was between 325℃ and 345℃.The Tg of the PEK-COO-Ar increased by increasing the mole ratio of aryl ester groups in the polymer,while the Td deceased.The polymers were readily soluble in N-methly-2-pyrrodine,chloroacetic acid and concentrated sulfuric acid at room temperature.They were swelling or soluble in the strong polar aprotic solvent such as N,N-dimethylformamide(DMF),N,N-dimethylacetamide(DMAc) and dimethyl sulfoxide(DMSO) by heating.The polymers converted to amorphous when the molar ratio of TPC to TMAc was less than 1.The polymers had good mechanical properties after being isothermally crystallization.The tensile strength,elongation at break and elastic modulus of S2’(TPC/TMAc = 60/40) and S3’(TPC/TMAc = 50/50) were 112.1 MPa,27%,2.9 GPa and 130.3 MPa,24.2%,2.4 GPa,respectively.

Synthesis and characterization of highly soluble poly(ether imide)s containing indane moieties in the main chain

AbstractA new indane containing unsymmetrical diamine monomer (3) was synthesized. This diamine monomer leads to a number of novel semifluorinated poly (ether imide)s when reacted with different commercially available dianhydrides like benzene‐1,2,4,5‐tetracarboxylic dianhydride (PMDA), benzophenone‐3,3′, 4,4′‐tetracarboxylic dianhydride (BTDA), 4,4′‐(hexafluoro‐isopropylidene)diphthalic anhydride (6FDA), 4,4′‐oxydiphthalic anhydride (ODPA), and 4,4′‐(4,4′‐Isopropylidenediphenoxy)bis(phthalic anhydride) (BPADA) by thermal imidization route. All the poly(ether imide)s showed excellent solubility in several organic solvents such as N‐methylpyrrolidone (NMP), N,N‐dimethylformamide (DMF), N,N‐dimethylacetamide (DMAc), tetrahydrofuran (THF), chloroform (CHCl3) and dichloromethane (DCM) at room temperature. These light yellow poly (ether imide)s showed very low water absorption (0.19–0.30%) and very good optical transparency. Wide angle X‐ray diffraction measurements revealed that these polymers were amorphous in nature. The polymers exhibited high thermal stability up to 526°C in nitrogen with 5% weight loss, and high glass transition temperature up to 265°C. The polymers exhibited high tensile strength up to 85 MPa, modulus up to 2.5 GPa and elongation at break up to 38%, depending on the exact polymer structure. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Molecular Structure and Liquid-Crystalline Characteristics of Chitosan Phenylcarbamate

Chitosan phenylcarbamate (CtsPC) samples were synthesized to have different degrees of substitution (DS) ranging from approximately 2.7 to approximately 3.7, and the lyotropic liquid crystallinity was mainly characterized by spectrophotometry. The products of DS>2.8 formed a cholesteric type of mesophase in concentrated solutions of >44 wt % with polar aprotic solvents such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and dimethyl sulfoxide (DMSO), and some of the solutions imparted vivid colorations because of selective visible light reflection. The cholesteric helical pitch increased with increasing temperature and with decreasing polymer concentration, but the helical sense remained left-handed under the adopted measurement conditions. It was also found that the helical pitch increased in proportion to the increment of DS, whereas an average degree of phenylcarbamoyl polyaddition in the side chains (DPs) rather affected the pitch distribution measuring an orderliness in the cholesteric structure. With a small increase in DPs (e.g., from 1.01 to 1.04), the cholesteric orderliness decreased and the temperature sensitivity of the pitch turned sluggish. Wide-angle X-ray diffractometry was also used for evaluating the distance and azimuth difference between adjacent nematic thin layers in the cholesteric mesophase.

DIFFERENT INFLUENCES OF SOLVENTS ON PVDF CASTING SOLUTION PHASE INVERSION AND MEMBRANE SKIN-SUBLAYER STRUCTURE

Poly(vinyldiene fluoride) (PVDF) asymmetrical membranes using three solvents N,N-dimethylforamide(DMF),N,N-dimethylacetamide(DMAc), and dimethylsulfoxide(DMSO) were prepared by phase inversion process.The thermodynamic properties of the casting solutions and the kinetic diffusion during membrane-forming processes were investigated via cloud point determination and light transmittance measurements.It was found that the thermodynamic stability of the casting solutions was enhanced gradually from DMSO/PVDF/water,DMF/PVDF/water to DMAc/PVDF/water,the delayed demixing due to the decrease of kinetic diffusion rates was easier to occur as the solvents were changed from DMF,DMAc to DMSO.The characterization of membranes showed that membranes containing a macrovoid structure were fabricated with higher porosity and lower crystallinity when DMSO and DMAc were used as solvent,but the honeycomb-structure membranes with higher crystallinity and lower porosity were prepared from DMF solvent,which indicated that the three membranes morphologies and properties were not controlled by the thermodynamic property or kinetic process uniformly.As a result,based on the theory of "the predominance on the growth of preformed nucleus" and the macrovoid development,the influences of the three solvents on the phase separation behavior of PVDF casting solutions,PVDF aggregate structure and membrane structure were discussed by the membrane formation mechanism of skin-sublayer two step precipitation.The results showed that for the three membrane-forming systems using DMF,DMAc and DMSO as solvent respectively,the delayed solid-liquid demixing took place in the skin layer under the control of the thermodynamics of casting solutions,and the dense skin layer formed with spherical particles.The delayed time was controlled by the kinetic diffusion.Mutual diffusion coefficient of solvent and non-solvent (D_m) increased gradually in the order of DMSO,DMAc,DMF,therefore,the delayed time decreased following the sequence of DMSO,DMAc,DMF.The phase transformation behaviors of the sublayers of the three membrane-forming systems were dominated by the liquid-liquid demixing controlled by the kinetic diffusion processes.For the systems with DMSO as solvent,the instantaneous liquid-liquid demixing happened in the sublayer, and crystallization had little effect on the kinetic diffusion.It was found in the light transmission that the demixing time was short, and curve variation was steep.Correspondingly,the membrane formed with a fingerlike macrovoid structure and a small amount of crystal spherulite in the sublayer,thus the membrane displayed the lower crystallinity and the higher membrane thickness,higher porosities and higher gas fluxes.For the systems with DMAc as solvent,the instantaneous liquid-liquid demixing happened in the sublayer.Compared to the DMSO system,crystallization had a great influence on the kinetic diffusion,leading to the longer demixing time and the flat curve variation in the light transmission drawing.Accordingly,the membrane was fabricated with an amount of crystal spherulite and the concurrent structure of macrovoid and spongy-like pores in the sublayer,and the membrane displayed the high crystallinity and the low membrane thickness,porosities and gas fluxes.For the system with DMF as solvent,compared to the DMSO and DMAc systems,the delayed liquid-liquid demixing initiated in the sublayer, and the crystallization had a greatest effect on the kinetic precipitation process, resulting in the longer demixing time and the flatter curve variation in the light transmission drawing.Finally,the membrane with a honeycomb-structure sublayer was prepared with the higher crystallinity and the smaller thickness,porosities and gas fluxes.

Influence of dispersion solvent for catalyst ink containing sulfonated poly(ether ether ketone) on cathode behaviour in a direct methanol fuel cell

Electrode properties are key determinants of the performance of the membrane-electrode assembly (MEA) in fuel cells. In this study, the influence of dispersion solvent for the catalyst ink on cathode properties and also on the cell performance is investigated. Cathodes containing sulfonated poly(ether ether ketone) (sPEEK) as an electrode binder are prepared with different dispersion solvents such as N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), and N-methyl-2-pyrrolidone (NMP). When DMF is used as a casting solvent, the sPEEK membrane exhibits a particular low proton conductivity. The high boiling points of DMSO and NMP as dispersion solvents for the cathode lead to a reduction in the pore volume of the cathode and, consequently, cause poor transport of oxygen at the cathode. A MEA based on a cathode using DMAc as a dispersion solvent gives the highest performance due to the high proton conductivity and good morphology of the cathode.