Polyimide Nanofiber Membrane Research Articles

Ultrathin inorganic-nanoshell encapsulation: TiO2 coated polyimide nanofiber membrane enabled by layer-by-layer deposition for advanced and safe high-power LIB separator

Separators with superior thermal stability, excellent electrolyte uptake and high ionic conductivity are imperative for developing high-power lithium ion batteries (LIBs). Yet it is not easy to build a separator possessing excellent performances in every aspect. For addressing this issue, herein, a novel in-situ growth-bonded titania (TiO2) nanolayer is coated on the polyimide (PI) nanofiber membrane via a novel layer-by-layer deposition (LBLD) strategy. Despite the tiny TiO2 content (2.2%), the resulting hybrid nano-fabric demonstrates improved performance and great potential for high-power LIBs. Benefited from the advantages of LBLD, the TiO2 nanolayer coated on PI nanofibers is ultrathin with neither sacrificing the porosity nor increasing the total thickness, which indicates that the strategy reported herein is a tremendous progress in comparison with conventional coating methods. After coated by the TiO2 nanolayer, the nanofibrous PI membranes exhibit superb heating-endurance, great flame-retardance, excellent wettability and high Li ion transmission, which would enhance the security of LIBs. More importantly, a unique bonding nanostructure is introduced into the nanofibrous PI membrane accompanied by TiO2 nanolayer, leading to strong interactions among PI nanofibers and promoted mechanical performance, which would improve the operability of the separators in LIBs assembly. The electrochemical tests show that cells assembled with the TiO2 coated PI separators have better high-rates performance, higher discharge capacity and great long-term running stability even at 120 °C. These characters suggest that the TiO2 coated PI membrane might play an important role in the forthcoming advanced power LIBs.

High temperature carbon nanotube – Nanofiber hybrid filters

Novel hybrid filters composed of aligned carbon nanotube (CNT) sheets, sandwiched between electrospun polyimide (PI) nanofiber membranes serving as the supporting layers, were fabricated for the capture of fine particles. The CNT sheets and PI nanofiber membranes were thermally bonded together by melting electrospun polyetherimide (PEI) nanofibers. Two different kinds of filter structures were prepared, where multiple layers of aligned CNT sheets were either stacked together on top of each other or separated from each other by a PEI layer. The filtration performance tests showed that the filtration efficiency increased with increasing number of CNT sheets. The maximum filtration efficiency reached 99.99% at 5.3 cm/s face velocity for 0.3 μm particles by the 4-layer CNT filter, while the pressure drop was only 120 Pa. In mechanical testing, the CNT sheets also reinforced the hybrid filters, even though the PI nanofiber membrane already had relatively high mechanical properties. The tensile strength of the 4-layer CNT hybrid filters was 9 MPa, reaching the highest tier of strength reported for nanofiber membranes. In addition to high efficiency and low pressure drop, the hybrid all-nanofiber filters are also targeted for use in hot gas filtration applications where temperatures reach 200–250 °C.

Graphite oxide dopping polyimide nanofiber membrane via electrospinning for high performance lithium-ion batteries

Abstract The battery separator is an important component of the battery which is related to the safety of the battery. However, there are many flaws of traditional lithium ion battery separator made by polyolefin , especially thermal stability and wettability . It was necessary, therefore, to invent a battery that heat resistance and electrolyte wettability. Here, we use the polyimide (PI) as a base material and graphene oxide (GO) as a reinforcing material, and get the nanofiber membrane through electrospinning technology, with the feature of three dimensional porous. Results show that as prepared PI nanofiber membrane possesses excellent thermal stability (no shrinkage even up to 200 °C), and admirable electrolyte absorption rate (2200%), which further significantly improves the ionic conductivity (2.04041 mS/cm). In addition, cells assembled with PI nanofiber membrane deliver outstanding cycling performance and C-rate discharge capability compared with 2400 separator in the same conditions. It is indicates that as-fabricated PI nanofiber separator has the potential of becoming a more mature technology offering better performance.

High-performance polyimide nanofiber membranes prepared by electrospinning

Polyimide (PI) nanofiber membranes were successfully prepared from a PI/N-methyl-2-pyrrolidone (NMP) solution via electrospinning. This technique simply and facilely produced efficient high-performance PI fibers. The morphology, surface wettability, thermal stability, mechanical properties, and filtration performance of the as-prepared PI nanofiber membranes were characterized in detail. The membranes exhibited smooth and hydrophobic surfaces. The nanofibers were well distributed in the membranes with fiber diameters in the range of 140–400 nm. All the PI nanofiber membranes showed excellent thermostability, and their initial decomposition temperature ( Td) and heat resistance temperature ( THRI) exceeded 544.4°C and 198.8°C, respectively. The PI nanofiber membranes also possessed reasonable mechanical properties with a tensile strength and a Young’s modulus reaching 10.5 and 927.6 MPa, respectively. Regarding the filtration performance, the developed nanofiber membranes achieved the best filtration efficiency of 90.4%. Such electrospun PI nanofiber membranes can be a promising candidate for hot gas filtration.

Rapid formation of polyimide nanofiber membranes via hot-press treatment and their performance as Li-ion battery separators.

We describe a new strategy to prepare thermally- and electrochemically-stable polyimide (PI) nanofiber membranes by the hot-press treatment of polyamic acid (PAA) nanofiber sheets in situ and examine their performance as Li-ion battery separators. Typical thermal imidization of PAA to PI membranes using sequential high temperature treatments in an oven takes a long time, but our method readily completes this conversion process at a mild temperature in 30 min while generating a high probability of inter-nanofiber imidization. Along with the improved electrolyte uptake capability and uniform distribution of the pore size and porosity caused by the dense and compact arrangements, the hot-press-induced PI membrane exhibits relatively thin sheets and a much greater mechanical strength than the membrane prepared by the thermal treatment. Subsequently, these PI-based membranes are installed in Li-ion full coin cells as battery separators whose C-rate (charging and discharging) performances are comparable to a commercial polyethylene (PE) separator. In addition, the highly improved thermal stabilities of these PI separators over PE separators are observed during thermal shrinkage and hot-box tests. Overall, our strategy can allow for the manufacture of diverse PI-based membranes with minimal preparation time and cost that can be utilized in high power portable devices requiring thermal and electrochemical stability.

A novel TFC forward osmosis (FO) membrane supported by polyimide (PI) microporous nanofiber membrane

A novel interfacial polymerization (IP) procedure on polyimide (PI) microporous nanofiber membrane support with mean pore size 1.27μm was reported. Using m-phenylenediamine (MPD) as aqueous phase monomer, trimesoyl chloride (TMC) as organic phase monomer, ethanol as aqueous phase co-solvent, thin-film composite (TFC) forward osmosis (FO) membrane was fabricated by two IP procedures. The first IP procedure with the unconventional order (ie, the membrane was immersed in the TMC organic phase first, then in the co-solvent ethanol-water MPD aqueous phase) was used to diminish the pore size of PI microporous nanofiber membrane support for the formation of the polyamide layer. The secondary IP procedure was employed to form the relatively dense polyamide layer with conventional order (ie, the membrane was immersed in the co-solvent ethanol-water MPD aqueous phase first, then in the TMC organic phase). The experimental results showed that higher ethanol concentration led to the relatively higher pure water permeability in RO process and osmotic water flux in FO process, whereas NaCl rejection in RO process decreased and reverse salt flux increased. The specific salt flux (Js/Jv) of TFC FO PI nanofiber membrane (PIN-2-4) could be as low as 0.095g/L in FO mode. These results could be attributed to influence of the addition of ethanol into aqueous phase on the surface morphology, hydrophilicity and polyamide layer structure.

Solution Blow Spun High Performance Co-Polyimide Nanofibers

Solution blow spinning (SBS) is an innovative nanofiber fabricating method with high productivity. 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) / p-phenylenediamine (PDA) / 4,4'-oxydianiline (ODA) co-polyimide nanofiber membrane was efficiently produced by SBS followed by imidization from precursor polyamic acid (PAA) nanofiber membrane in the paper. The morphologies and structures of the obtained PAA and PI nanofiber membrane were examined by SEM and FT-IR. The effect of thermal imidization temperature on the tensile property was investigated. The thermal stability of polyimide nanofiber membrane was also characterized by TGA.

Electrically conductive polyaniline/polyimide microfiber membrane prepared via a combination of solution blowing and subsequent in situ polymerization growth

Dodecylbenzene sulfonic acid (DBSA) doped-polyaniline (PANI) coated conductive polyimide (PI) microfiber membrane was prepared by chemical oxidation polymerization. PI nanofiber membrane was prepared by solution blowing. Fourier transform infrared spectra (FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM) proved that the successful preparation of composite microfiber membrane with core-shell structures. At the same time, the PANI had an effect of protection on PI nanofiber, which was detected by thermal gravimetric analysis (TGA). The orthogonal experiments were designed to determine the optimal reaction conditions for the conductivity of PANI/PI microfiber membranes as following: ANI concentration (0.15 mol L−1), APS concentration (0.1 mol L−1) and DBSA concentration (0.3 mol L−1). The conductivity of PANI/PI microfiber membranes could arrive to 3.83 × 10−2 S cm−1. Moreover, the PANI/PI microfiber membranes had a superior hexavalent chromium (Cr (VI)) adsorption performance. The factors affecting the performance of hexavalent chromium (Cr (VI)) removal from the aqueous solutions were investigated.

Crosslinked Polyimide Nanofiber Membrane Prepared via Ammonia Pretreatment and Its Application as a Superior Thermally Stable Separator for Li-Ion Batteries

Polyimide (PI) nanofiber membrane with crosslinked morphology has been prepared by ammonia pretreatment of the electrospun poly(amic acid) precursor followed by an imidization process. The ammonia-induced crosslinking offers an obvious benefit for converting the loose and weak PI nonwoven to compact and robust fabric membrane. This promotes the tensile strength from 10.8 MPa to 37.5 MPa and shifts the onset deformation temperature from 328°C to 380°C. Crosslinking also chemically welds the nanofibers together, which greatly reduces the risk of robust fabric membrane disassembling into the loose nonwovens during long-term battery cycling, and consequently improves the stability of PI nanofiber membrane as separator. The cell assembled with the crosslinked PI nanofiber membrane as separator displays outstanding cycling stability and rate capability with 80% capacity retention up to 5 C (130 mAh/g) and could work steadily at 120°C with no capacity fading. The separator perfectly retains its crosslinked feature without lithium deposition after 100 battery cycles. These characteristics make the crosslinked PI nanofiber membrane advanced separator for high-performance Li-ion batteries.

Icephobicity of Penguins Spheniscus Humboldti and an Artificial Replica of Penguin Feather with Air-Infused Hierarchical Rough Structures

Although penguins live in the world’s coldest environment, frost and ice are seldom found on their feathers. That is to say, their feathers exhibit excellent antifrosting or anti-icing properties. We found that their air-infused microscale and nanoscale hierarchical rough structures endow the body feathers of penguins Spheniscus humboldti with hydrophobicity (water CA ≈ 147°) and antiadhesion characteristics (water adhesive force ≈ 23.4 μN), even for supercooled water microdroplets. A polyimide nanofiber membrane with novel microstructures was prepared on an asymmetric electrode by electrospinning, acting as an artificial replica of a penguin’s body feather. The unique microstructure of the polyimide nanofiber membrane results in a density gradient of the surface chemical substance, which is crucial to the formation of gradient changes of the contact angle and adhesive force. With decrease of the density of the surface chemical substance (i.e., with increase of the distance between adjacent fibers), the s...

Synthesis and filtration properties of polyimide nanofiber membrane/carbon woven fabric sandwiched hot gas filters for removal of PM 2.5 particles

In this work, hot gas filters composed of polyimide nanofiber membrane sandwiched between carbon woven fabrics are fabricated to capture fine particles of PM 2.5 level. Polyimide (PI) nanofibers with an average diameter of 190nm are electrospun on supporting carbon fabrics as filtration layers. The filtration performance tests show that the maximum filtration efficiency reaches 99.99% for PM 2.5, while the maximum pressure drop is only 251.86Pa after continuously testing for 25min under a constant flow rate of 20L/min. As the areal density of the PI nanofiber membrane increases, the filtration efficiency increases first and then levels off when the areal density reaches 11.64g/m2. In regeneration performance test with back air flush at a pressure of 500KPa, the composite filter maintains a filtration efficiency of 99.99% and a pressure drop of about 410Pa. After heat treatment at 260 and 300°C, the composite filter shows a relatively high filtration efficiency while the tensile strength of the carbon fabric does not change significantly.

Acetone-activated polyimide electrospun nanofiber membrane for thin-film microextraction and thermal desorption-gas chromatography–mass spectrometric analysis of phenols in environmental water

In this work, a polyimide nanofiber membrane was electrospun and applied as sorbent for thin film microextraction (TFME). After TFME of phenols in water samples, direct thermal desorption of the sorbent at 300°C followed by gas chromatography-mass spectrometric (TD–GC–MS) analysis was carried out. The extraction efficiency of TFME was enhanced by 6–12 times for phenols after activation with acetone. The positive effect of acetone activation was correlated to the increased hydrophilicity of the membrane. Extraction parameters, including mass of nanofiber membrane, pH value, NaCl concentration and extraction time, were optimized. Under optimal conditions, the LODs and LOQs for analysis of phenols in spiked purified water were 0.0006–0.008 and 0.002–0.025μgL−1, respectively. The linearity range was more than two orders of magnitude (R>0.99). The RSDs of intra-batch and inter-batch were 4.3–7.4% and 2.7–10.6% (n=3). Finally the method was applied to real samples, including tap water, sea water, and waste water. These results indicate that the polyimide nanofiber membrane is a promising candidate as TFME sorbent for determination of polar analytes in water samples coupled with TD–GC–MS.

Electrospun polyimide nanofiber membranes for high flux and low fouling microfiltration applications

A newly developed electrospun polyimide nanofiber mat/membrane along with three commercial 0.22µm microfiltration membranes have been investigated for applications within a renewable biorefinery to complete solid–liquid clarification at two locations: (1) following enzymatic hydrolysis (pre-fermentation) and (2) post-ethanol fermentation. Performance was assessed by evaluating process flux, reversible and irreversible fouling, and the ability to completely remove insoluble solids. Lignin (the primary insoluble solid following enzymatic hydrolysis of a biomass feedstock), yeast cells, and cell debris (following fermentation to ethanol), along with soluble phenolic compounds, all being very hydrophobic in nature, caused extensive fouling, which led to permanent irreversible flux decline for the three commercial membranes. In addition, all three commercial membranes showed a small amount of insoluble solids in the permeate, indicating incomplete removal of the insoluble solids. In contrast, the polyimide nanofiber membrane showed virtually no irreversible fouling and complete retention of insoluble solids, suggesting the tremendous potential for biorefinery applications.

Electrically Conductive Polyaniline/Polyimide Nanofiber Membranes Prepared via a Combination of Electrospinning and Subsequent In situ Polymerization Growth

Highly aligned polyimide (PI) nanofiber membranes have been prepared by electrospinning equipped with a high speed rotating collector. As the electrospun polyimide nanofiber membranes possess large surface area, they can be used as the template for in situ growth of polyaniline (PANi) by using FeCl₃ as the oxidant. It is found that PANi nanoparticles can be uniformly distributed on the surface of highly aligned PI nanofibers due to the low oxidization/reduction potential of FeCl₃ and the active nucleation sites of the functionalized PI nanofibers. The as-prepared PANi/PI composite membranes not only possess excellent thermal and mechanical properties but also show good electrical conductivity, pH sensitivity and significantly improved electromagnetic impedance properties. This is a facile method for fabricating high-performance and multifunctional composites that can find potential applications in electrical and aerospace fields.

Preparation of polyimide nanofiber membrane with gradient wettability by electrospinning

Radial polyimide(PI) nanofiber membrane was prepared on an asymmetric electrode by electrospinning.The morphology and arragement of the nanofiber on the PI membrane were observed by environmental scanning electron microscope(ESEM).The wettability was characterized by the apparent contact angle and the surface adhesive effect was characterized by the high-sensitivity microelectromechanical balance system.The effect of the microstructures on the contact angle and adhesive force was analyzed.The experimental results show that the PI nanofibers exhibit novel gradient microstructures.Particularly,the PI nanofibers were in a radial pattern from dense to sparse along the direction of triangular electrode to curved electrode.The diameter of the PI nanofibers was uniform and their surfaces were smooth.The distance between the adjacent fibers was from a few microns to tens of microns.The unique gradient microstructure of PI nanofiber membrane results in the gradient density of the surface chemical substance and they are crucial to the gradient changes of the contact angle and adhesive force.

Elastic wave velocities of lunar samples at high pressures and their geophysical implications: Kanamori, H., Nur, A., and Chung, D., Wones, D., Simmons, G. Science, Vol 167, No 3918 (30 January 70) p726 (2217)

A newly developed electrospun polyimide nanofiber mat/membrane along with three commercial 0.22 µm microfiltration membranes have been investigated for applications within a renewable biorefinery to complete solid–liquid clarification at two locations: (1) following enzymatic hydrolysis (pre-fermentation) and (2) post-ethanol fermentation. Performance was assessed by evaluating process flux, reversible and irreversible fouling, and the ability to completely remove insoluble solids. Lignin (the primary insoluble solid following enzymatic hydrolysis of a biomass feedstock), yeast cells, and cell debris (following fermentation to ethanol), along with soluble phenolic compounds, all being very hydrophobic in nature, caused extensive fouling, which led to permanent irreversible flux decline for the three commercial membranes. In addition, all three commercial membranes showed a small amount of insoluble solids in the permeate, indicating incomplete removal of the insoluble solids. In contrast, the polyimide nanofiber membrane showed virtually no irreversible fouling and complete retention of insoluble solids, suggesting the tremendous potential for biorefinery applications.