Kinetic modeling of novel solid desiccant based on PVA-LiCl electrospun nanofibrous membrane

A new polymer-based composite desiccant, Polyvinyl alcohol-LiCl nanofibrous membrane (PVA-LiCl NFM), has been prepared by the electrospinning technique. The newly-developed desiccant membrane not only has large moisture adsorption capacity, fast moisture adsorption rate and favorable stability, but also is featured by its low regeneration temperature. In this work, adsorption and desorption kinetic models are explored for PVA-LiCl NFMs, which include the pseudo-first and the pseudo-second order model based on the rate law and a diffusion model based on the Fick's law. The results indicate that the moisture adsorption and desorption kinetics of the PVA-LiCl NFMs follow the pseudo-second-order law very well. As the key parameters in the diffusion model, the equilibrium adsorption capacity and the diffusion coefficient are focused on, and they can be well determined by the Brunauer–Emmett–Teller (BET) model and the radial-basis-functions artificial neural network (RBFANN) model, respectively. Finally, the adsorption and desorption activation energy of the PVA-LiCl NFM with a 0.15 mass ratio of LiCl to PVA are recognized as 24.36 and 26.52 kJ/mol, respectively. The work is of great importance to the better application of the newly-developed desiccant material (PVA-LiCl NFM).     

Surface morphology and mechanical response of randomly oriented electrospun nanofibrous membrane

Electrospinning for the fabrication of fibrous membranes has received great attention due to the simplicity of the technique, ability to effectively control the process and potential for production scale-up. While the optimization of electrospinning parameters for various polymers is widely investigated, the mechanical characterization and modeling of the mechanical response of electrospun membranes remain a major challenge. The present work focuses on the mechanical characterization of electrospun nanofibrous membrane under simple and complex loading conditions. For this purpose, polyvinylidene fluoride (PVDF) is considered for the membrane material. Three types of uniaxial mechanical tests are conducted: monotonic tensile test, cyclic loading test with increasing maximum strain and cyclic-relaxation test. The evolution of fiber re-orientation with deformation is also investigated. Results show that the membrane is initially isotropic in the plane. Moreover, the evolution of membrane Young’s modulus with increasing maximum strain suggests that mechanical deformation induces two interacting phenomena: fiber re-orientation and inter-fiber bond damage.     

Highly sensitive detection of nitroaromatic explosives using an electrospun nanofibrous sensor based on a novel fluorescent conjugated polymer

An electrospun nanofibrous explosive sensor was first constructed based on a newly developed fluorescent conjugated polymer P containing heteroatom polycyclic units. Electrospinning by doping polymer P as a fluorescent probe in a polystyrene supporting matrix afforded a fluorescence nanofibrous film with unique porous structures, and effectively avoided the aggregation of polymer P. The novel explosive sensor exhibited stable fluorescence property, satisfactory reversibility with less than 5% loss of signal intensity after four quenching–regeneration cycles, and good reproducibility among three batches with a relative standard deviation of 2.8%. Such fabricated sensor also showed remarkable sensitivity toward a series of trace nitroaromatic explosive vapors, including picric acid (parts-per-trillion level) and 2,4,6-trinitrotoluene vapor (parts-per-billion level), as well as good selectivity with less than 10% response to typical interferents. Therefore, the present strategy extends the application of different kinds of conjugated polymers for the construction of optical chemosensors.     

Preparation and characterization of antimicrobial polycarbonate nanofibrous membrane

Electrospinning of polycarbonate (PC)/chloroform solution with quaternary ammonium salt (benzyl triethylammonium chloride, BTEAC) was investigated to develop antimicrobial nanofibrous membranes for ultrafiltration. With BTEAC additive, ultrafine PC fibers were continuously generated and densely mounted without the blockage of spinning tip on electrospinning. When small amounts of BTEAC were added to the PC solution, the average diameter was also decreased from several micrometers to submicron range. It was found that the conductivity of the PC solution was a major parameter affecting the morphology and diameter of the electrospun PC fibers as well as the electrospinnability of PC. The nanofibrous membranes electrospun from the PC solution with BTEAC exhibited better excellent antimicrobial activity than those prepared without BTEAC. The PC nanofibrous filter shows a good filtration efficiency to satisfy the criterion of HEPA filter, and the pressure drop of the PC filters are within the normal range. Therefore, PC nanofibrous membrane showed a great potential as a candidate for ultrafiltration, compared to a commercial HEPA filter.     

Preparation and characterization of stable chitosan nanofibrous membrane for lipase immobilization

Nanofibrous membrane with a fiber diameter of 80-150 nm was fabricated from mixed chitosan/poly(vinyl alcohol) (PVA) solution by an electrospinning process. Field emission scanning electron microscope and transmission electron microscope were used to characterize the morphology of the nanofibrous membrane. It was found that chitosan nanofibrous membrane with stabilized morphology could be prepared through removing most of PVA from the nascent one with 0.5 M NaOH aqueous solution. This treatment also resulted in an obvious decrease in fiber diameter. The stabilized chitosan nanofibrous membrane was explored as support for enzyme immobilization due to the characteristics of excellent biocompatibility, high surface/volume ratio, and large porosity. Lipase from Candida rugosa was immobilized on the nanofibrous membrane using glutaraldehyde (GA) as coupling reagent. The properties of the immobilized lipase were assayed and compared with the free one. Results showed that, the observed lipase loading on this nanofibrous membrane was up to 63.6 mg/g and the activity retention of the immobilized lipase was 49.8% under the optimum condition. The pH and thermal stabilities of lipase were improved after it was immobilized on the chitosan nanofibrous membrane. In addition, the experimental results of reusability and storage stability indicated that the residual activities of the immobilized lipase were 46% after 10 cycles and 56.2% after 30 days, which were obviously higher than that of the free one.     

Preparation and biodegradation of electrospun PLLA/keratin nonwoven fibrous membrane

As a kind of natural protein, wool keratin was used to improve the cell affinity of poly(l-lactic acid) (PLLA). After small keratin particles were prepared from keratin solution by spray-drying process, they were blended with PLLA solution. PLLA/keratin nonwoven fibrous membrane was produced by electrospinning the blend solutions. The release rate of keratin from the composite membrane was detected by Fourier transform infrared (FTIR) after PLLA/keratin membranes were degraded in PBS up to 4 weeks. The chemical compositions of the PLLA/keratin surface were examined by X-ray photoelectron spectroscope. Although more than half of the keratin was removed from PLLA/keratin membrane during the first few hours of degradation, some keratin particles were still embedded in the PLLA fibers. Osteoblast cells were used to evaluate the cellular behaviors of the composite membrane. After 7 days culturing, more cells were observed on PLLA/keratin membranes than on pure PLLA membranes. MTT assay and alkaline phosphatase (ALP) activity results suggested that keratin could improve the interactions between osteoblast cells and the polymeric membranes.     

Fabrication of well‐aligned electrospun nanofibrous membrane based on fluorinated polyimide

We have fabricated novel nanofibrous fluorinated polyimide membranes on a specially designed collector, which is composed of conductive aluminum plates and glass insulator materials and can be removed from the apparatus, using an electrospinning method. We describe the structure and water flux properties of the nanofibrous fluorinated polyimide membranes. The electrospun nanofibers were deposited across the plates and uniaxially aligned to the collector. In addition, the multi‐layer stacked nanofibrous membranes, consisting of three‐dimensionally ordered nanopores, were produced. The pure water fluxes for the stacked membranes were measured, using a stirred dead‐end filtration cell, and were linearly decreased with an increasing deposition time, indicating that the nanopores formed in the nanofibrous membrane were further narrowed due to the regularly accumulated nanofibers. Copyright © 2009 John Wiley & Sons, Ltd.     

Effect of thermal treatment on the characteristics of electrospun PVDF−silica composite nanofibrous membrane

Composite nanofibrous membranes were prepared by the electrospinning and the thermal treatment from poly(vinylidene fluoride) (PVDF)-tetramethyl orthosilicate (TMOS) blend solutions. The average diameter of nanofibers was reduced with increasing the concentration of TMOS in the solution due to the decrease of the solution viscosity. The EDX spectra confirmed the presence of TMOS on the external surface of the composite nanofibrous membrane. The porosity of membranes was effectively enhanced by the introduction of electrospinning technique. However, the mechanical properties, thermal stability and hydrophobicity were not markedly amplified. Thus the thermal treatment of the composite membranes was carried out, leading to the enormous enhancement of the mechanical properties and hydrophobicity. In addition, XRD results revealed that the crystal structure of PVDF in the composite membranes transformed from α-phase to β-phase due to the formation of silica particles by the thermal treatment.     

Determination of cerium ion by polymeric membrane and coated graphite electrode based on novel pendant armed macrocycle

Plasticized membranes using 2,3,4:12,13,14-dipyridine-1,3,5,8,11,13,15,18-octaazacycloicosa-2,12-diene (L₁) and 2,3,4:12,13,14-dipyridine-1,5,8,11,15,18-hexamethylacrylate-1,3,5,8,11,13,15,18-octaazacycloicosa-2,12-diene (L₂) have been prepared and explored as Ce(III) selective sensors. Effect of various plasticizers viz. dibutylphthalate (DBP), tri-n-butylphthalate (TBP), o-nitrophenyloctylether (o-NPOE), dioctylphthalate (DOP), benzylacetate (BA) and anion excluders, sodium tetraphenylborate (NaTPB) and potassium tetrakis p-(chlorophenyl) borate was studied in detail and improved performance was observed. Optimum performance was observed for the membrane sensor having a composition of L₂:PVC:o-NPOE:KTpClPB in the ratio of 6:34:58:2 (w/w, mg). The performance of the membrane based on L₂ was compared with polymeric membrane electrode (PME) as well as with coated graphite electrode (CGE). The electrodes exhibit Nernstian slope for Ce(III) ions with limits of detection of 8.3 × 10⁻⁸ mol L⁻¹ for PME and 7.7 × 10⁻⁹ mol L⁻¹ for CGE. The response time for PME and CGE was found to be 12 s and 10 s respectively. The potentiometric responses are independent of the pH of the test solution in the pH range 3.5-7.5 for PME and 2.5-8.5 for CGE. The CGE could be used for a period of 5 months. The practical utility of the CGE has been demonstrated by its usage as an indicator electrode in potentiometric titration of oxalate and fluoride ions with Ce(III) solution. The proposed electrode was also successfully applied to the determination of fluoride ions in mouthwash solution and oxalate ions in real samples.     

Fabrication and invitro evaluation of electrospun gum ghatti-polyvinyl alcohol polymeric blend green nanofibre mat (GG-PVA NFM) as a novel material for polymeric scaffolds in wound healing

The present research is mainly based on the fabrication of biodegradable nanofiber mats (NFM) through the process of electrospinning using a novel combination of Gum Ghatti (GG) and Poly vinyl alcohol (PVA). The prepared NFM was crosslinked (CL-1) using Glutaraldeyde-HCl vapours and was characterized for its tensile strength along other analytical characterizations using FTIR, TGA, DSC and XRD. The mechanical strength of the NFM was found to be sufficiently high than in comparison to noncrosslinked sample and PVA NFM. The internal architecture of the CL-1 by use of atomic force microscopy (AFM) revealed that there was very well formed crosslinks suitable for drug loading as well as cell proliferation. The wound healing properties of the CL-1 in mice animal model indicated the healing within 5 days as compared to the control wound. Moreover, the sample was also analysed for its ability as polymeric scaffold and no toxicity was found onto the locally applied tissue on histological investigations.     

Controlled assembly of superparamagnetic iron oxide nanoparticles on electrospun PU nanofibrous membrane: A novel heat-generating substrate for magnetic hyperthermia application

A facile method of fabricating novel heat-generating membranes composed of electrospun polyurethane (PU) nanofibers decorated with superparamagnetic iron oxide nanoparticles (NPs) is reported. Electrospinning was used to produce polymeric nanofibrous matrix, whereas polyol immersion technique allowed in situ assembly of well-dispersed Fe₃O₄ NPs on the nanofibrous membranes without any surfactant, and without sensitizing and stabilizing reagent. The assembly phenomena can be explained by the hydrogen-bonding interactions between the amide groups in the PU matrix and the hydroxyl groups capped on the surface of the Fe₃O₄ NPs. The prepared nanocomposite fibers showed acceptable magnetization value of 33.12 emu/g, after measuring the magnetic hysteresis loops using SQUID. Moreover, the inductive heating property of electrospun magnetic nanofibrous membranes under an alternating current (AC) magnetic field was investigated. We observed a progressive increase in the heating rate with the increase in the amount of magnetic Fe₃O₄ NPs in/on the membranes. The present electrospun magnetic nanofibrous membrane may be a potential candidate as a novel heat-generating substrate for localized hyperthermia cancer therapy.     

Effects of the relative humidity and water droplet on adhesion of a bio-inspired nano-film

Inspired by geckos' adhesion, the effect of water membrane forming due to the environmental humidity, on the adhesion between a bio-inspired nano-film and a substrate is investigated first. The disjoining pressure is considered, which results in an enhancing adhesion between the nano-film and substrate. When the thickness of water membrane increases, water droplets will form and a repulsive capillary force between the nano-film and substrate is produced. The total adhesion force decreases with an increasing volume of water droplets. The two opposite results in the two different models are consistent well with two seemingly inconsistent experimental observations by Huber et al. (2005) [4] and Sun et al. (2005) [5], respectively, and may be significant for the development of artificial biomimetic attachment systems.     

Sorption and pervaporation properties of sulfonyl‐containing polyimide membrane to aromatic/non‐aromatic hydrocarbon mixtures

Sorption of single‐component vapors of benzene (Bz), n‐hexane (Hx), and cyclohexane (Cx), and of binary liquid mixtures of Bz/Hx and Bz/Cx in a polyimide from 3,3′,4,4′‐diphenylsulfone‐tetracarboxylic dianhydride (DSDA) and 2,8(6)‐dimethyl‐3,7‐diaminobenzothiophene‐5,5‐dioxide (DDBT) were investigated in detail at 333 K. Sorption and desorption of vapors followed the non‐Fickian kinetics and the sorption isotherms were concave to the vapor activity. For the binary liquids, the sorption isotherms of the Bz component were concave to the Bz composition in feed, whereas those of Hx and Cx were convex because of competitive sorption. As a result, the solubility selectivity was much larger than the sorption ratio of pure liquids. The concentration‐averaged diffusion coefficients of Bz (D̄_Bz) and Hx (D̄_Hx) were evaluated using the sorption and pervaporation data of the polyimide membrane toward the binary mixtures. A kind of coupling effect of the coexisting component on D̄ was observed. That is, D̄ of penetrant with smaller molecular size (Hx and Bz for Bz/Hx and Bz/Cx systems, respectively) was reduced by the presence of penetrant with larger molecular size (Bz and Cx, respectively) and vice versa. D̄_Bz was similar to D̄_Hx, but much larger than D̄_Cx. The difference in PV behavior between Bz/Hx and Bz/Cx systems for glassy polymer membranes was understood based on the aforementioned features of sorption and diffusion. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2954–2964, 2000     

Preparation of polymer-supported hydrated ferric oxide based on Donnan membrane effect and its application for arsenic removal

In the present study a novel technique was proposed to prepare a polymer-supported hydrated ferric oxide (D201-HFO) based on Donnan membrane effect by using a strongly basic anion exchanger D201 as the host material and FeCl3-HCl-NaCl solution as the reaction environment. D201-HFO was found to exhibit higher capacity for arsenic removal than a commercial sorbent Purolite ArsenX. Furthermore, it presents favorable adsorption selectivity for arsenic removal from aqueous solution, as well as satis- factory kinetics. Fixed-bed column experiments showed that arsenic sorption on D201-HFO could re- sult in concentration of this toxic metalloid element below 10 μg/L, which was the new maximum con- centration limit set recently by the European Commission and imposed by the US EPA and China. Also, the spent D201-HFO is amenable to efficient regeneration by NaOH-NaCl solution.     

Determination of cobalt ions at nano-level based on newly synthesized pendant armed macrocycle by polymeric membrane and coated graphite electrode

Poly(vinylchloride) (PVC) based membranes of macrocycles 2,3,4:9,10,11-dipyridine-1,3,5,8,10,12-hexaazacyclotetradeca-2,9-diene (L₁) and 2,3,4:9,10,11-dipyridine-1,5,8,12-tetramethylacrylate-1,3,5,8,10,12-hexaazacyclotetradeca-2,9-diene (L₂) with NaTPB and KTpClPB as anion excluders and dibutylphthalate (DBP), benzyl acetate (BA), dioctylphthalate (DOP), o-nitrophenyloctyl ether (o-NPOE) and tri-n-butylphosphate (TBP) as plasticizing solvent mediators were prepared and investigated as Co²⁺ selective electrodes. The best performance was observed with the membranes having the composition L₂:PVC:TBP:NaTPB in the ratio of 6:39:53:2 (w/w; mg). The performance of the membrane based on L₂ was compared with polymeric membrane electrode (PME) and coated graphite electrode (CGE). The PME exhibits detection limit of 4.7 × 10⁻⁸ M with a Nernstian slope of 29.7 mV decade⁻¹ of activity between pH 2.5 and 8.5 whereas CGE exhibits the detection limit of 6.8 × 10⁻⁹ M with a Nernstian slope of 29.5 mV decade⁻¹ of activity between pH 2.0 and 9.0. The response time for PME and CGE was found to be 11 and 8 s, respectively. The CGE has been found to work satisfactorily in partially non-aqueous media up to 35% (v/v) content of methanol, ethanol and 25% (v/v) content of acetonitrile and could be used for a period of 4 months. The CGE was successfully applied for the determination of Co²⁺ in real and pharmaceutical samples and as an indicator electrode in potentiometric titration of cobalt ion.     

Preparation and characterization of electrospun fibers based on poly(L-lactic acid)/cellulose acetate

PLLA/CA mixtures of different compositions were successfully electrospun to obtain composite nanofibrous membranes.The microstructures of the membrances changed from homogeneous to heterogeneous with the addition of CA, which was observed by FE-ESEM.The PLLA/CA fabric membranes were characterized by mechanical testing,DSC and contact angle measurements.The tensile stress of the composite fibrous membranes increased obviously with the increase of CA content.DSC results indicated that the CA component was the main factor for the changes of enthalpies in the composite fibers.Contact angle measurements showed the hydrophilicity of the electrospun nanofiber membranes was improved with the addition of CA.     

Synthesis, water stability and proton conductivity of novel sulfonated polyimides from 4,4′-bis(4-aminophenoxy)biphenyl-3,3′-disulfonic acid

A novel sulfonated diamine monomer, 4,4′-bis(4-aminophenoxy)biphenyl-3,3′-disulfonic acid (BAPBDS) with the high basisity and flexible structure was synthesized by direct sulfonation of 4,4′-bis(4-aminophenoxy)biphenyl (BAPB). Sulfonated polyimides (SPIs) were prepared from 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), BAPBDS and nonsulfonated diamines such as BAPB. The SPI membranes showed much higher water stability at high temperatures than other sulfonated diamine-based SPIs reported so far. Their water vapor sorption isotherm, water uptake (WU), density, dimensional change and proton conductivity σ were investigated. The SPIs showed rather isotropic dimensional changes with WU and the volume increases were slightly smaller than those estimated from the additivity. The SPIs with ion exchange capacities (IECs) of 1.9–2.7 meq/g displayed the similar relationship between σ and WU each other, which was different from those of Nafion 117 and also of the SPIs with the lower IECs. The former SPIs showed reasonably high σ values of 10⁻² S/cm or more even at WU of 25 g/100 g dry polymer under 70% RH at 50 °C, whereas the latter showed the similarly high σ values only in liquid water, but not in the nearly saturated water vapor.     

Fabrication of a novel electrospun molecularly imprinted nanomembrane coupled with high‐performance liquid chromatography for the selective separation and determination of acesulfame

A novel in situ molecularly imprinted sol–gel nanomembrane using nylon 6 as backbone was prepared by the electrospinning technique and coupled on‐line with high‐performance liquid chromatography. The prepared electrospun membrane exhibited extensive selectivity toward acesulfame in the presence of some selected sweeteners in a beverage sample, while the porosity and mechanical stability remained. The prepared electrospun membrane could be applied for 35 consequence extractions without a significant change in extraction recovery, swelling, and flooding. To achieve the best condition and efficiency for on‐line extraction, the effect of influential parameters was investigated. The limit of detection (signal/noise = 3:1) and limit of quantification (signal/noise = 10:1) were 0.6 and 2.0 ng/mL for acesulfame in the beverage samples, respectively. The linearity for the acesulfame was in the range of 2.0–250 ng/mL in beverage samples. The coefficients of determination values were ≥0.997 for all runs. The extraction recoveries of acesulfame in the beverage samples were between 80 and 85%.     

Polymeric membrane and coated graphite samarium(III)-selective electrodes based on isopropyl 2-[(isopropoxycarbothioyl)disulfanyl]ethanethioate

New polymeric membrane (PME) and coated graphite (CGE) samarium(III)-selective electrodes were prepared based on isopropyl 2-[(isopropoxycarbothioyl) disulfanyl]ethanethioate as a suitable neutral ionophore. The electrodes exhibit Nernstian slopes for Sm³⁺ ions over wide concentration ranges (1.0×10⁻⁵ to 1.0×10⁻¹ M for PME and 1.0×10⁻⁶ to 1.0×10⁻¹ M for CGE). The PME and CGE have limits of detection of 3.1×10⁻⁶ and 5.0×10⁻⁷ M, respectively, and response times of about 20 s. The potentiometric responses are independent of the pH of the test solution in the pH range 4.0-7.0. The proposed electrodes revealed good selectivities over a wide variety of other cations including alkali, alkaline earth, transition and heavy metal ions. The electrodes were successfully applied to the recovery of Sm³⁺ ion from tap water samples and also, as an indicator electrode, in potentiometric titration of samarium(III) ions.     

The effect of humidity on the degradation of Nafion membrane

Controlling the activity of water in the reactant streams is critical both to the design of fuel–cell systems and to the useable life of membrane separators. In this study, fuel–cell durability tests were conducted under different levels of relative humidity. The emission rates of various degradation products such as HF, SO₄²⁻ and TFA (trifluoroacetic acid) were determined as a function of water activity. The degradation of the membrane was accelerated as the level of water activity is reduced. The membranes become less conductive, more brittle and rigid after fuel–cell testing. ATR-FTIR investigations showed that the decomposition of the ether group in the middle of side chain corresponds well with the detection of a TFA product. Thermogravimetric analysis also showed a decrease in thermal stability after testing at lower humidity. Formation of cracks was observed in membranes degraded under conditions of low humidity. A model of membrane degradation based on the main chain unzipping process indicates that the mechanism changes with water activity. Finally, the representative reaction pathways in each degradation scheme were postulated.