Theoretical and experimental studies on the fabrication of cylindrical-electrode-assisted solution blowing spinning nanofibers

Cylindrical-electrode-assisted solution blowing spinning (CSBS) is a novel technique of fabricating nanofibers. In this paper, a combination of numerical simulation, theoretical analysis, and experiment is used to study the influences of CSBS airflow field and electric field on the fabrication of CSBS nanofibers for the first time. The effects of air pressure and injection speed on the morphology of CSBS fiber are studied. The research results show that the increase in air pressure will increase the centerline velocity and the centerline turbulence intensity within the effective stretching distance of the airflow. The increase in centerline velocity will result in a decrease in the diameter of CSBS fibers. There is a negative correlation between jet diameter and surface charge density of CSBS jet. The increase in air pressure will increase the stretching of the jet by the air flow, which will make the jet more likely to become thinner again because of the charge repulsion. Increasing air pressure will reduce the porosity of the nonwoven. As the injection speed increases, the diameter of CSBS fiber increases, and the porosity of the nonwoven decreases first and then increases. This work provides theoretical and experimental bases for the controllable preparation of CSBS nanofibers.

Potential carbon nanomaterials as additives for state-of-the-art Nafion electrolyte in proton-exchange membrane fuel cells: a concise review

Proton-exchange membrane fuel cells (PEMFCs) have received great attention as a potential alternative energy device for internal combustion engines due to their high conversion efficiency compared to other fuel cells. The main hindrance for the wide commercial adoption of PEMFCs is the high cost, low proton conductivity, and high fuel permeability of the state-of-the-art Nafion membrane. Typically, to improve the Nafion membrane, a wide range of strategies have been developed, in which efforts on the incorporation of carbon nanomaterial (CN)-based fillers are highly imperative. Even though many research endeavors have been achieved in relation to CN-based fillers applicable for Nafion, still their collective summary has rarely been reported. This review aims to outline the mechanisms involved in proton conduction in proton-exchange membranes (PEMs) and the significant requirements of PEMs for PEMFCs. This review also emphasizes the improvements achieved in the proton conductivity, fuel barrier properties, and PEMFC performance of Nafion membranes by incorporating carbon nanotubes, graphene oxide, and fullerene as additives.

Fabrication and evaluation of electrospun biomimetic sulphonated PEEK nanofibrous scaffold for human skin cell proliferation and wound regeneration potential

Regeneration of skin wound is a challenging process since functional and architectural restoration of the damaged skin tissue is an arduous task. The use of springing up biomaterials with nano-topographic and bio-mimicking characteristics resembling natural skin's extra cellular matrix (ECM) would be a favorable approach to regenerate such an injured skin tissue. In this study an attempt has been carried out to design and develop sulphonated polyether ether ketone (SPEEK) nanofibrous scaffold to explore its role on skin cell proliferation potential. 2 h-SPEEK portrayed the highest proliferative potential for HaCaT keratinocytes and fibroblasts. It was aimed for the tailored release of bio-actives from the spatiotemporally designed Aloe vera incorporated 2 h-SPEEK nanoscaffold to accelerate the skin wound regeneration. FTIR, EDX and XRD analyses revealed the effective incorporation of Aloe vera in the electrospun nanofibers. SEM analysis revealed the nano-topographical morphology with highly porous, dense and interconnected fibrous structures mimicking the skin ECM. The regulated delivery of Aloe vera demonstrated the biocompatibility of the nanofibrous scaffold in skin keratinocytes (HaCaT) and fibroblasts (3T3) cells through in vitro analysis proving its non-toxic properties. Further, the fabricated nanoscaffolds exhibited excellent anti-microbial efficacy towards the tested human skin pathogenic microbes. The results of in vivo studies in Wistar rat model exhibited scar-less wound healing with complete wound closure. Thus, this nanofiber based drug delivery system implicitly acts as a skin like ECM, bio-mimicking the topographical and chemical cues of the natural skin tissues paving way for a complete regeneration and integration of the injured area strengthening the functional restoration of insulted cells around the wound area.

Highly conductive mechanically robust high Mw polyfluorene anion exchange membrane for alkaline fuel cell and water electrolysis application

New, high molecular weight poly-(fluorene-alt-tetrafluorophenylene) anion exchange membranes were synthesized by a Pd-catalyzed C–H activation method.

Proton Conductivity through Polybenzimidazole Composite Membranes Containing Silica Nanofiber Mats

The quest for sustainable and more efficient energy-converting devices has been the focus of researchers' efforts in the past decades. In this study, SiO2 nanofiber mats were fabricated through an electrospinning process and later functionalized using silane chemistry to introduce different polar groups -OH (neutral), -SO3H (acidic) and -NH2 (basic). The modified nanofiber mats were embedded in PBI to fabricate mixed matrix membranes. The incorporation of these nanofiber mats in the PBI matrix showed an improvement in the chemical and thermal stability of the composite membranes. Proton conduction measurements show that PBI composite membranes containing nanofiber mats with basic groups showed higher proton conductivities, reaching values as high as 4 mS·cm-1 at 200 °C.

Proton-Conducting Poly-γ-glutamic Acid Nanofiber Embedded Sulfonated Poly(ether sulfone) for Proton Exchange Membranes

Development and fabrication of novel proton exchange membranes (PEMs) with excellent performance have a great significance to the commercial application of PEM fuel cell. Inspired from the proton-conducting mechanism, γ-poly(glutamic acid) (γ-PGA) nanofibers (NFs) are first fabricated by solution blowing with the help of polylactic acid (PLA) and designed to form amino acid arrays as efficient proton channels for PEMs. The NFs with 50% γ-PGA exhibit a high proton conductivity of 0.572 S cm^-1 at 80 °C/50% relative humidity (RH), and 1.28 S cm^-1 at 40 °C/90% RH. Density functional theory is carried out to explain the mechanisms of proton hopping in γ-PGA, and the activation energy barriers from NH to COO^- for trans and cis conformations under anhydrous conditions are only 0.64 and 0.62 eV, respectively. Then the γ-PGA/PLA NFs are incorporated into sulfonated poly(ether sulfone) to prepare PEMs, which show remarkable performance compared with the Nafion membrane. The composite membrane with 30 wt % NFs exhibits the highest proton conductivity (0.261 S cm^-1 at 80 °C/100% RH). The direct methanol fuel cells with this membrane show a maximum power density (202.3 mW cm^-2) among all of the PEMs, showing great application potential in the field of PEMs.

Effects of cylindrical-electrode-assisted solution blowing spinning process parameters on polymer nanofiber morphology and microstructure

Cylindrical-electrode-assisted solution blowing spinning (CSBS) is a novel method for preparing polymer nanofibers by using air-stretch and electrostatic simultaneously, which can fabricate thinner and more uniform nanofibers than the traditional solution blowing spinning (SBS). In this work, the effects of processing parameters including length of cylinder (LC), needle to cylinder distance (NCD) and left face of cylinder to collector distance (CCD) on the CSBS nanofiber diameter were investigated. The results are as follows: when the NCD decreased, the fiber diameter decreased; when the LC increased, the fiber diameter decreased; the CCD didn’t significantly affect the fiber diameter. Moreover, an orthogonal experimental design was utilized to investigate the effect of injection rate, air pressure, NCD, LC, diameter of cylinder (DC), voltage and CCD on the fiber diameter and porosity of various surface layers of nanofiber web (P1, P2, and P3). The results showed that the varied range of each properties (average diameter, standard deviation of the diameter, P1, P2, and P3) was 539.121-904.149 nm, 127.903-303.253, 71.464-85.1415%, 60.32725-75.46625%, 48.23925-70.08875%, respectively. We also found the order of the influence of the above-mentioned seven process parameters on each above properties of the nanofiber web, and the corresponding optimal spinning process parameters were listed. It is well known that the fiber diameter affects the mechanical properties of nanofibers, and porosity of nano-fiber webs is an important parameter in tissue engineering, bioengineering, and filtration. The effects of CSBS process parameters on nanofiber morphology and microstructure were investigated for the first time. The conclusion of the paper can help researchers to produce high quality CSBS nanofiber and promote the wider application of this novel technology.

Self-Assembly DBS Nanofibrils on Solution-Blown Nanofibers as Hierarchical Ion-Conducting Pathway for Direct Methanol Fuel Cells

In this work, we reported a novel proton exchange membrane (PEM) with an ion-conducting pathway. The hierarchical nanofiber structure was prepared via in situ self-assembling 1,3:2,4-dibenzylidene-d-sorbitol (DBS) supramolecular fibrils on solution-blown, sulfonated poly (ether sulfone) (SPES) nanofiber, after which the composite PEM was prepared by incorporating hierarchical nanofiber into the chitosan polymer matrix. Then, the effects of incorporating the hierarchical nanofiber structure on the thermal stability, water uptake, dimensional stability, proton conductivity, and methanol permeability of the composite membranes were investigated. The results show that incorporation of hierarchical nanofiber improves the water uptake, proton conductivity, and methanol permeability of the membranes. Furthermore, the composite membrane with 50% hierarchical nanofibers exhibited the highest proton conductivity of 0.115 S cm-1 (80 °C), which was 69.12% higher than the values of pure chitosan membrane. The self-assembly allows us to generate hierarchical nanofiber among the interfiber voids, and this structure can provide potential benefits for the preparation of high-performance PEMs.

Composite Proton-Exchange Membrane with Highly Improved Proton Conductivity Prepared by in Situ Crystallization of Porous Organic Cage

Porous organic cage, a kind of newly emerging soluble crystalline porous material, is introduced to proton-exchange membrane by in situ crystallization. The crystallized Cage 3 with intrinsic water-meditated three-dimensional interconnected proton pathways working together with Nafion matrix generates a composite membrane with highly improved proton conductivity. Different from inorganic crystalline porous materials, like metal-organic frameworks, the organic porous material shows better compatibility with Nafion matrix due to the absence of inorganic elements. In addition, Cage 3 can absorb water up to 20.1 wt %, which effectively facilitates proton conduction under both high- and low-humidity conditions. Meanwhile, the selectivity of Nafion-Cage 3 composite membrane is also elevated upon the loading of Cage 3. The proton conductivity is evidently enhanced without obvious increased methanol permeability. At 90 °C and 95% RH, the proton conductivity of NC3-5 reaches 0.27 S·cm^-1, highly improved compared to 0.08 S·cm^-1 of recast Nafion under the same condition. This study offers a new strategy for modifying proton-exchange membrane with crystalline porous materials.

Preparation of Solution Blown Polyamic Acid Nanofibers and Their Imidization into Polyimide Nanofiber Mats

Solution blow spinning (SBS) is an innovative process for spinning micro/nanofibers. In this paper, polyamic acid (PAA) nanofibers were fabricated via a SBS apparatus and then imidized into polyimide (PI) nanofibers via thermal process. The morphology and diameter distributions of PAA nanofibers were determined by scanning electron microscope (SEM) and Image Tool software, the processing parameters, including PAA concentration, solution feeding rate, gas pressure, nozzle size, and receiving distance were investigated in details. The fourier transform infrared spectroscopy (FTIR) was used to characterize the chemical changes in the nanofibers after thermal imidization. The results showed that the solution concentration exhibited a notable correlation with spinnability, and the formation of bead defects in PAA nanofibers. Solution feeding rate, gas pressure, nozzle size, and receiving distance affected nanofiber production efficiency and diameter distribution. The average diameters of fibers produced ranged from 129.6 to 197.7 nm by varying SBS parameters. Precisely, PAA nanofibers with good morphology were obtained and the average diameter of nanofibers was 178.2 nm with optimum process parameter. After thermal imidization, the PI nanofibers exhibited obvious adhesion morphology among interconnected fibers, with an increased average diameter of 209.1 nm. The tensile strength of resultant PI nanofiber mat was 12.95 MPa.

Understanding methods of preparation and characterization of pore-filling polymer composites for proton exchange membranes: a beginner’s guide

Composite membranes based on porous support membranes filled with a proton-conducting polymer appear to be a promising approach to develop novel proton exchange membranes (PEMs). It allows optimization of the properties of the filler and the matrix separately, e.g. for maximal conductivity of the former and maximal physical strength of the latter. In addition, the confinement itself can alter the properties of the filling ionomer, e.g. toward higher conductivity and selectivity due to alignment and restricted swelling. This article reviews the literature on PEMs prepared by filling of submicron and nanometric size pores with Nafion and other proton-conductive polymers. PEMs based on alternating perfluorinated and non-perfluorinated polymer systems and incorporation of fillers are briefly discussed too, as they share some structure/transport relationships with the pore-filling PEMs. We also review here the background knowledge on structural and transport properties of Nafion and proton-conducting polymers in general, as well as experimental methods concerned with preparation and characterization of pore-filling membranes. Such information will be useful for preparing next-generation composite membranes, which will allow maximal utilization of beneficial characteristics of polymeric proton conductors and understanding the complicated structure/transport relationships in the pore-filling composite PEMs.

Proton conducting electrospun sulfonated polyether ether ketone graphene oxide composite membranes

A series of novel composite membranes, based on sulfonated poly(ether ketone) (SPEEK) with a graphene oxide (GO) layer, were prepared.

A Review of the Fundamental Principles and Applications of Solution Blow Spinning

Solution blow spinning (SBS) is a technique that can be used to deposit fibers in situ at low cost for a variety of applications, which include biomedical materials and flexible electronics. This review is intended to provide an overview of the basic principles and applications of SBS. We first describe a method for creating a spinnable polymer solution and stable polymer solution jet by manipulating parameters such as polymer concentration and gas pressure. This method is based on fundamental insights, theoretical models, and empirical studies. We then discuss the unique bundled morphology and mechanical properties of fiber mats produced by SBS, and how they compare with electrospun fiber mats. Applications of SBS in biomedical engineering are highlighted, showing enhanced cell infiltration and proliferation versus electrospun fiber scaffolds and in situ deposition of biodegradable polymers. We also discuss the impact of SBS in applications involving textiles and electronics, including ceramic fibers and conductive composite materials. Strategies for future research are presented that take advantage of direct and rapid polymer deposition via cost-effective methods.

A review on non-electro nanofibre spinning techniques

A large surface area, scalable porosity, and versatility have made nanofibres one of the most widely investigated morphologies among the nanomaterials.

Direct polymerization of novel functional sulfonated poly(arylene ether ketone sulfone)/sulfonated poly(vinyl alcohol) with high selectivity for fuel cells

The acid–base pairs (–SO₃H⋯H₂N–) formed between –SO₃H and –NH₂ can promote protons transport.

Sulfonated nanocrystal cellulose/sulfophenylated poly(ether ether ketone ketone) composites for proton exchange membranes

The suggested proton transport path in the composite membranes.

Effect of pore-directing agents and silanol groups in mesoporous silica nanoparticles as Nafion fillers on the performance of DMFCs

Pore-directing agents in SBA-15 and MSN mesopores could resist methanol crossover, while only P123 inside SBA-15 could assist proton transferring. But, highest proton conductivity was obtained on membranes with extracted MSN of high silanol contents.

Microphase separated sepiolite-based nanocomposite blends of fully sulfonated poly(ether ketone)/non-sulfonated poly(ether sulfone) as proton exchange membranes from dual electrospun mats

In this study, nanocomposite blends of fully sulfonated poly(ether ketone) (PEK) and non-sulfonated poly(ether sulfone) (PES) were prepared from a dual electrospinning process.

Solution-blown core–shell hydrogel nanofibers for bovine serum albumin affinity adsorption

In this work, nylon 6 core–chitosan/poly(vinyl alcohol) (PVA) shell hydrogel nanofibers (NCNFs) were fabricated by coaxial solution blowing for BSA adsorbing.

Phosphotungstic acid embedded sulfonated poly(arylene ether ketone sulfone) copolymers with amino groups for proton exchange membranes

The acid–base interaction between HPW and the amino groups can immobilize HPW to maintain high proton conductivity at medium-high temperature in the composite membranes.