Influence of solvent and nanoparticles on the morphology and gas separation properties of copolyimide membranes

In this study, the effect of solvent type and nanoparticles of silica and zeolite 4A on the gas separation properties of polyimide (PI) membranes were investigated. Gas separation of the membranes based on pure solvents of dimethylformamide (DMF), n-methyl-2-pirrolidone (NMP), dimethylacetamide (DMAc), and dimethylsulfoxide (DMSO) were studied. The prepared PI membranes using DMAc and DMSO showed the highest selectivity and permeability, respectively. In this regard, the influence of their mixing on transport properties of the PI was evaluated. The prepared membrane using the mixture of DMSO/DMAc with the volume ratio of 1:3 showed the best gas separation performance in comparison to the Robeson's upper bound. Incorporation of 20 wt% of silica and zeolite 4A nanoparticles into the PI membrane indicated that the selectivity of CO₂/CH₄ increased from 39.4 to 57.6 and 68.5, respectively. Besides, gas transport properties of the PI-based mixed matrix membranes were satisfactory predicted by modified Maxwell model. Furthermore, characteristic parameters of the encapsulated particles by interfacial layer were determined.     

Stress enhanced gold dispersion by solvent induced crystallization in BPA-PC membranes

In this paper the embedding of gold clusters in crystallizing bisphenol-A polycarbonate is treated as diffusion with drift in inhomogeneous and changing in time medium. Initially the gold is deposited on the polymer surface, which is subsequently exposed to acetone vapour. The polymer undergoes significant crystallization, induced by diffusing agent, while gold clusters become embedded in its bulk. The paper presents a model of gold dispersion based on Smoluchowski equation. It identifies the driving force of dispersion with the gradient of stress field generated during crystallization. Numerical results of the model are found to be in good agreement with available experimental data obtained by XPS depth profiling technique.     

Comparison of solvent removal methods of microporous polypropylene tubular membranes via thermally induced phase separation using a novel solvent: Camphene

A novel solvent, camphene, was used to prepare microporous polypropylene tubular membranes via thermally induced phase separation (TIPS). In this process, camphene was removed by either sublimation or extraction. The effect of the solvent-removal on the structure and properties of the resulting membrane was studied. Microscopic observation and wide angle X-ray scattering indicate that the morphology and crystalline structure difference is minor. Thermal analysis and tensile tests reveal that the crystallinity and breaking strength of the tubular membrane from the extracting method are slightly higher than those for the sublimating method. Porosity measurements show that the sublimation method can yield membranes with slightly higher porosity than the extraction method. Furthermore, permeation results indicate that membranes from extraction have a smaller permeation rate and higher retention. Therefore solvent-extraction can produce a denser membrane structure than sublimation can.     

Influence of pH and ionic strength on transmission of plasmid DNA through ultrafiltration membranes

One of the simple, robust and scalable methods for purification of plasmid DNA is by membrane filtration. Utilizing manipulation of pH, ionic strength, and membrane pore size, the process is designed to completely retain the plasmid DNA. The performed study shows that despite electrostatic repulsion and a significant size difference between plasmid and membrane pore, the circular double-stranded DNA plasmid is able to penetrate through UF membranes. Experiments demonstrate that the tertiary structure of DNA changes easily and is dramatically affected by variations in ionic strength and pH. The penetration is probably due to stretching of the plasmid by hydrodynamic shear. In contrast to previous reports, the transmitted DNA copies kept their integrity and infectious ability.     

Influence of solvent on ion conductivity of polybenzimidazole proton exchange membranes for vanadium redox flow batteries

Polybenzimidazole(PBI) is a kind of proton transport membrane material, and its ion conductivity is a key factor affecting its application in vanadium redox flow batteries(VRFBs). The casting solvent of PBI has a significant influence on the acid doping level of PBI membranes which is closely related to ionic conductivity. In this paper, 3,3′-diaminobenzidine(DABz) and 4,4′-Dicarboxydiphenylether(DCDPE) were used as raw materials by solution condensation to prepare the PBI with ether bond groups. The chemical structure of PBI was determined by1~H NMR and FT-IR, and the prepared PBI had good solubility which can be dissolved in a variety of solvents. The PBI proton exchange membranes were prepared by solution coating with 5 different solvents of N,N-dimethylformamide(DMF), N,N-dimethylacetamide(DMAc), dimethyl sulfoxide(DMSO), 1-methyl-2-pyrrolidone(NMP), methane sulfonic acid(MSA). The effects of different solvents on the ion conductivity and physicochemical properties were discussed in detail. The results showed that the PBI membrane prepared by using MSA as solvent(the PBI + MSA membrane) exhibits high water uptake, acid doping level and low vanadium ion permeability. The VRFB assembled with the PBI + MSA membrane exhibited higher coulombic efficiency(CE) 99.87% and voltage efficiency(VE) 84.50% than that of the commercial Nafion115 membrane at100 m A·cm~(-2), and after 480 cycles, the EE value can still be maintained at 83.73%. The self-discharge time of a single battery was recorded to be as long as 1000 h. All experimental data indicated that MSA is the best solvent for casting PBI membrane.     

Experimental analysis and simulation of the gas transport in dense Hyflon AD60X membranes: Influence of residual solvent

The present paper discusses the tendency of solution-cast Hyflon^® AD membranes to retain unexpectedly high amounts of solvent, the possible reasons of this phenomenon and its effect on the membrane performance. Dense membranes, prepared by solution-casting and subsequent evaporation, showed large differences in their thermal, mechanical and transport properties, depending on the residual solvent content. Complete solvent removal required heating under vacuum up to well above the glass transition temperature. Analysis of the permeability, diffusion and solubility coefficients of six permanent gases showed that plasticization by the residual solvent reduces the permselectivity and increases the permeability.Data of solution-cast membranes after complete solvent removal compare well with those of a melt-pressed sample. Experimental gas transport parameters were confronted with simulated data, obtained by the Gusev-Suter Transition-State Theory (TST) method and by molecular dynamics (MD) simulations. ¹H High Resolution Magic Angle Spinning Nuclear Magnetic Resonance spectroscopic analysis of the residual solvent in the polymer matrix did not reveal a particular interaction between polymer and solvent, suggesting that the solvent retention is mainly diffusion controlled.     

耐溶剂纳滤膜的制备与应用研究进展

有机溶剂纳滤(organic solvent nanofiltration,OSN)是近年来快速发展起来的一项新型纳滤膜分离技术,具有广阔的应用前景。耐溶剂纳滤(solvent-resistant NF,SRNF)膜的制备是OSN技术发展的关键,也是目前的研究热点之一。本文侧重阐述了SRNF膜在制备及应用方面的进展,着重介绍了相转化法、界面聚合法、自组装法及有机-无机杂化法等SRNF膜制备方法。相转化法是目前国内外SRNF膜制备研究常用的方法,但该法所制备的膜皮层较厚,通量明显偏小;界面聚合法SRNF膜制备的相关研究目前较少,但由于其皮层非常薄,因此是SRNF膜制备发展的一大趋势;自组装膜有较好的耐溶剂性能;加入无机物可以提高耐有机溶剂性,有机-无机杂化法的膜制备是SRNF膜制备的趋势之一。同时简单介绍了SRNF膜的应用,并对未来SRNF膜研究的方向提出了建议。     

Influence of solvent type on the ability and properties of the boehmite nanoparticles embedded emulsion polyvinyl chloride nanocomposite ultrafiltration membranes

Iranian Polymer Journal - The effects of two different solvents of dimethylacetamide (DMAc) and N-methyl-2-pyrrolidone (NMP) were investigated on the properties and performance of the neat and...     

Effects of solvent on microstructure and proton conductivity of organic-inorganic hybrid membranes

Effects of solvent on the microscopic structure and proton conductivity of organic-inorganic hybrids containing heteropolyacid are reported. The organic-inorganic hybrids were prepared by sol-gel synthesis of 1,8-bis(triethoxysilyl)octane (TES-Oct) in the presence of phosphotungstic acid (PWA). The proton conductivity of the membranes prepared under different solvents exhibited greater values in the order methanol < 1-butanol < 2-propanol < ethanol < 1-propanol < 2-butanol. The conductivity strongly correlated to the amount of incorporated PWA in the membranes, which was determined by titration of the solutions containing PWA leaked from the membrane. Small-angle X-ray scattering (SAXS), atomic force microscopy (AFM) and thermogravimetric analysis (TGA) were employed to reveal the relationship between the proton conductivity and microscopic structure of the TES-Oct/PWA membranes. It was found that there is an optimal condition for the formation of the condensed domain structure, indicating the important role of the structures in the membrane conductivity.     

溶剂流动方式对药物提取过程的影响

以大黄为实验材料 ,利用半连续提取设备 ,分别采用简单提取和循环提取的方式 ,研究了溶剂流速对提取率和提取液浓度的影响。结果表明简单提取的速度快 ,极限提取率高 ,提取液浓度在初期很高 ,并随提取率增加而下降 ;循环提取溶剂用量和提取液浓度易控制 ,收率受级平衡限制而较低 ;适当增大溶剂流速可缩短提取时间 ,但会增加前者的溶剂消耗 ;在简单提取中引入回流对后期的提取有一定促进作用 ,回流的时间和回流强度值得研究。将简单提取和循环提取适当组合能够在保证效率的基础上使收率和提取液浓度有较大提高。     

Influence of residual solvent on the gas transport properties of dense Hyflon® AD 60X gas separation membranes

The solvent retention by dense Hyflon AD 60X membranes were studied. The effect of the residual solvent on the transport properties of the membranes was evaluated. The permeability, diffusion coefficient and solubility of six permanent gases in membranes prepared under different conditions were determined and compared with the results of simulation studies.     

Zirconia aerogels and xerogels: Influence of solvent and acid on structural properties

High-surface-area zirconia aerogels with meso- to macroporosity have been prepared by an acid-catalyzed alkoxide-sol-gel route with tetrabutoxyzirconium(IV) and subsequent high-temperature supercritical drying at 578 K. The effect of solvent (ethanol, propanol, butanol, t-amylalcohol), amount of nitric acid, calcination temperature, and drying method was studied by nitrogen physisorption, X-ray diffraction, Fourier transform Raman and diffuse reflectance infrared Fourier transform spectrosopy, scanning electron microscopy, thermal analysis, and temperature-programmed desorption of NH₃. After calcination in air at 573 or 773 K, the aerogels possess specific surface areas of up to 270 or 180 m² · g^–1, respectively. The use of ethanol as solvent resulted in the highest specific surface areas and pore volumes (up to 1.5 cm³ · g^–1) among all samples studied, whereas bulky t-amylalcohol caused a shift of the maxima of the broad pore size distributions from 30 to 70 nm. With the corresponding xerogels, prepared via the same wet-chemical procedure but evaporatively dried at ambient temperature, butanol resulted in a maximum at 3 nm and t-amylalcohol in a bimodal pore size distribution with maxima at 3 and 15 nm. The variation of the acid-to-alkoxide ratio in the range 0.08–0.12 at a hydrolysis level of 4 did not significantly influence the structural properties of aerogels and related xerogels. In contrast to the aerogels, the xerogels had significantly lower specific surface areas and prominent microporosity. All uncalcined aerogels contained crystalline ZrO₂, whereas the corresponding uncalcined xerogels were X-ray amorphous and crystallized only during calcination at 573 K. Both aerogels and xerogels possessed Brønsted-type and Lewis-type acid sites. With the xerogels, the density of acid sites on the surface was significantly lower. This behaviour is attributed to the higher amounts of organic residues which persisted in and on the xerogels up to 773 K and thus blocked the acid sites partially.     

蛭石层状膜的制备及有机溶剂纳滤性能

受全球能源形势与环境问题影响,新型膜分离技术尤其是二维层状膜在分离领域展现出广阔的应用前景。然而,目前使用的二维纳米材料化学环境相对复杂,且膜制备成本高昂,限制了其工业化推广。天然蛭石廉价易得,剥离简单,表面只含有硅羟基且其含量易于调控,可精确调控所制备层状膜层间亲疏水性,实现有机溶剂的高效渗透和极性与非极性溶剂的高效分离。研究发现：蛭石层状膜展现出优异的极性溶剂分子传递能力,而非极性溶剂则相对较低,其中乙腈分子渗透性高达1650L/（m²·h·bar)（1bar=0.1MPa）,甲苯分子渗透性仅为37.8L/（m²·h·bar),乙腈与甲苯的分离因子高达43.6,展现出优异的分子分离性能。本文所制备蛭石层状膜具有1.36nm的规则平直层间传递通道,对分子动力学直径大于层间距的结晶紫（1.5nm）、亮蓝（1.6nm）、酸性黄14（1.9nm）等染料分子的截留率均大于90%,截留性能优良。同时,蛭石层状膜具有良好的压力循环稳定性及抗污染能力, 展现出巨大的分离应用潜力。     

Photo/pH dual-responsive behavior of azopyridine-containing copolymer vesicles

The amphiphilic diblock copolymer composed of poly(ethylene oxide) as the hydrophilic chain and polymethacrylate with azopyridine moieties in the side groups as the hydrophobic chain self-assembled to vesicles in the mixture of THF/water. The dual photo- and pH-responsive behavior of the copolymeric vesicles was investigated by UV–Vis absorption spectra and optical microscope. It was found that the trans–cis photoisomerization of azopyridine in the vesicles was influenced by the water content in the mixture and the intensity of light irradiation. Regard to the pH-responsive behavior, the copolymer vesicles dissociated into solution gradually triggered by acid, while they reformed in a basic environment. Furthermore, the UV light irradiation accelerated the process of pH-induced dissociation of the vesicles.     

Characterization of solvent induced crystalline and amorphous homoharringtonine

The morphologies of homoharringtonine were conveniently controlled by solvent treatment and the morphologies of homoharringtonine were characterized by XRD and SEM. Crystalline homoharringtonine was simply made by dissolving homoharringtonine in a special polar solvent containing a small amount of water (methanol/water= 98/2, v/v). On the other hand, amorphous homoharringtonine was made by dissolving homoharringtonine in relatively non-polar solvent (methylene chloride/methanol=98/2, v/v). Amorphous homoharringtonine, with a fine particle size, was obtained by dissolving in methylene chloride/methanol (98/2, v/v), following by spray drying. Also, residual solvents, methanol and methylene chloride, were easily removed to less than concentration limit in ICH (International Conference on Harmonisation) guidance by spray drying and successive drying in a vacuum oven. Amorphous homoharringtonine was more soluble in water than crystalline homoharringtonine, and the water content of amorphous homoharringtonine was less changeable than crystalline homoharringtonine at given humidity (95 RH%) during storage. This information is very useful for production and quality control of pharmaceuticals in the commercialization step.     

Characterization of Na ion-sensitive solvent polymeric membranes based on a neutral carrier

The states in the surface and the bulk phases of Na ion-sensitive polymeric membranes based on a synthetic carrier were investigated using SEM, IR, ¹³C-NMR, and GC. The ¹³C-NMR study revealed that conformation change of the carrier took place when the carrier was incorporated into the membrane phase. From SEM, IR, and ¹³C-NMR experiments with a deteriorated membrane, the conformation change of the carrier was proposed as one of the deterioration factors other than the decrease in the diffusion coefficient of the carrier in the membrane phase.     

Studies on syntheses and permeabilities of special polymer membranes: 38. Formation mechanism of finger-like cavities in membranes from cellulose nitrate and single solvent

The relationship between the permeation characteristics of an aqueous polymer solution and the asymmetric structure of cellulose nitrate membranes was investigated under various conditions. The conditions and mechanism of the formation of finger-like cavities in cellulose nitrate membranes are discussed in some detail.     

Influence of the dilute‐solution properties of cellulose acetate in solvent mixtures on the morphology and pervaporation performance of their membranes

The pervaporation performance of cellulose acetate (CA) membranes prepared from acetone (AC), acetone/tetrahydrofuran (AC/THF), acetone/chloroform (AC/CF), and acetone/cyclohexane (AC/CYH) was studied for separating MeOH/MTBE (methyl tert‐butyl ether) mixture with 5 (wt) % MeOH. The dilute‐solution properties and Huggins constant (K_H) of CA dissolved in AC and AC/solvent mixtures with 15 vol % of the second solvent (tetrahydrofuran, chloroform, or cyclohexane) were examined. J and α of the CA membranes were affected by the types of solvent mixtures used to prepare the casting solutions. Under the same conditions, the membrane with AC/CYH had the highest J value and the lowest α value, and it was followed by the membranes with AC/CF, AC/THF, and AC. The increasing value of J and decreasing value of α for the CA membranes from different solvent mixtures were in good agreement with the increasing value of K_H of CA in corresponding solvent mixtures. Furthermore, differences in the morphology from scanning electron microscopy images of the cross sections or from atomic force microscopy photographs of the surfaces of the membranes existed, and they provided proof of the different pervaporation performances of the CA membranes prepared from AC and AC/solvent mixtures. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97:1891–1898, 2005     

Influence of the solvent viscosity on surface graft-polymerization reactions

Solvent viscosity was found to be a predominant parameter to control free-radical surface graft polymerization. Poly(ethylene-alt-tetrafluoroethylene) foils were lithographically exposed to 92 eV photons in order to create patterns of radicals at their surface, which react with the oxygen of the ambient air to produce peroxides. Glycidyl methacrylate was then radically polymerized from these peroxide initiators. We discovered that increasing the viscosity of the grafting solution by addition of polyethylene glycol boosts the grafting reaction, leading to an order of magnitude increase in the height of the grafted layer. Further increasing the viscosity leads to thinner layers of grafted material. The increase of the grafted layer thickness in the low viscosity range is interpreted to be due to a diminution of the termination rate while for higher viscosity, the reduction of the initiation rate causes the observed decrease of the grafted thickness. This interpretation is in agreement with observed morphological and structural differences of nanostructures grafted at different viscosities. We conclude that viscosity is an essential and very easily controllable parameter for surface graft-reactions.     

Polyaniline membranes for nanofiltration of solvent from dewaxed lube oil

Polyaniline nanofiltration membranes were synthesized to examine a potential candidate for application of solvent recovery from lube oil. An integrally skinned polyaniline membrane was cast on a woven polyester fabric and then was chemically crosslinked with glutaraldehyde in order to further increase the membranes resistant in a methyl ethyl ketone and toluene mixture. Subsequently, membrane performance was tested under different operational conditions. The operation pressure was fixed at 35 bar and was held constant for all of the tests. The membrane demonstrated a permeate flux of 10 l/(m² h) and oil rejection of 69%.

Abbreviations: PANi: Polyaniline; PI: polyimide; MEK: methyl ethyl ketone; GA: glutaraldehyde; NMP: N-methyl-2-pyrrolidone; 4MP: 4-methylpiperidine; SEM: Scanning Electron Microscope; OSN: organic solvent nanofiltration; MWCO: molecular weight cut-off.