Gas Sensors Based on Electrospun Nanofibers

Nanofibers fabricated via electrospinning have specific surface approximately one to two orders of the magnitude larger than flat films, making them excellent candidates for potential applications in sensors. This review is an attempt to give an overview on gas sensors using electrospun nanofibers comprising polyelectrolytes, conducting polymer composites, and semiconductors based on various sensing techniques such as acoustic wave, resistive, photoelectric, and optical techniques. The results of sensing experiments indicate that the nanofiber-based sensors showed much higher sensitivity and quicker responses to target gases, compared with sensors based on flat films

Electro-spinning/netting: A strategy for the fabrication of three-dimensional polymer nano-fiber/nets.

Since 2006, a rapid development has been achieved in a subject area, so called electro-spinning/netting (ESN), which comprises the conventional electrospinning process and a unique electro-netting process. Electro-netting overcomes the bottleneck problem of electrospinning technique and provides a versatile method for generating spider-web-like nano-nets with ultrafine fiber diameter less than 20 nm. Nano-nets, supported by the conventional electrospun nanofibers in the nano-fiber/nets (NFN) membranes, exhibit numerious attractive characteristics such as extremely small diameter, high porosity, and Steiner tree network geometry, which make NFN membranes optimal candidates for many significant applications. The progress made during the last few years in the field of ESN is highlighted in this review, with particular emphasis on results obtained in the author's research units. After a brief description of the development of the electrospinning and ESN techniques, several fundamental properties of NFN nanomaterials are addressed. Subsequently, the used polymers and the state-of-the-art strategies for the controllable fabrication of NFN membranes are highlighted in terms of the ESN process. Additionally, we highlight some potential applications associated with the remarkable features of NFN nanostructure. Our discussion is concluded with some personal perspectives on the future development in which this wonderful technique could be pursued

Colorimetric nanofibers as optical sensors

Sensors play a major role in many applications today, ranging from biomedicine to safety equipment, where they detect and warn us about changes in the environment. Nanofibers, characterized by high porosity, flexibility, and a large specific surface area, are the ideal material for ultrasensitive, fastresponding, and user-friendly sensor design. Indeed, a large specific surface area increases the sensitivity and response time of the sensor as the contact area with the analyte is enlarged. Thanks to the flexibility of membranes, nanofibrous sensors cannot only be applied in high-end analyte detection, but also in personal, daily use. Many different nanofibrous sensors have already been designed; albeit, the most straightforward and easiest-to-interpret sensor response is a visual change in color, which is of particular interest in the case of warning signals. Recently, many researchers have focused on the design of so-called colorimetric nanofibers, which typically involve the incorporation of a colorimetric functionality into the nanofibrous matrix. Many different strategies have been used and explored for colorimetric nanofibrous sensor design, which are outlined in this feature article. The many examples and applications demonstrate the value of colorimetric nanofibers for advanced optical sensor design, and could provide directions for future research in this area

Development of Conductive Electrospun Fabric Systems for Smart Textiles

Electrospinning (ES) is a simple, cost-effective and versatile method for the production of nanofibrous materials. However, the production of intrinsically conductive polymers (ICPs) nan-ofibres by electrospinning still represents an important challenge – often due to poor solubility and high crystallinity of the rigid backbone. This dissertation reports the development of conductive fibres produced by electrospinning of two ICPs: polyaniline (PANI) and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS). These were electrospun and studied in terms of their electrical conductivity. In both cases, polyvynilpyrrolidone (PVP) was used as a carrier polymer in the ES process. PANI was synthesised from the aniline monomer and the influence of the oxidant-to-mon-omer ratio on its conductivity was studied. Pellets of pressed PANI powders resulted in an average conductivity of 20.64 S.cm-1. The chemical addition of a tert-butyloxycarbonyl (t-Boc) group to the structure of PANI allowed the dissolution in dimethylformamide (DMF). The soluble PVP/t-Boc-PANI was electrospun into fibres with an average fibre diameter of 180 nm with a maximum conductivity of 5.1810-3 S.cm-1. Electrospinning of PVP/PEDOT:PSS allowed the production of non-woven mats with an average fibre diameter of 1.5 μm with a conductivity of 4.010-8 S.cm-1. A thorough study of the UV crosslinking of PVP is enclosed

Development of Amino Functionalized Graphene Based Polymer Nanofibers for Gas Sensors

RÉSUMÉ: Ces dernières années, la préparation d'architectures nanostructurées a été une stratégie importante pour améliorer les performances de détection de gaz. Ces matériaux ont un rapport surface / volume extrêmement élevé et ont des structures avec une nanoporosité élevée, ce qui augmente l’adsorption des gaz. Parmi ces nanomatériaux, le graphène fonctionnalisé a suscité un intérêt considérable pour l’application en détection du fait de sa conductivité variable, ce qui le rend disponible pour les phénomènes de transport d'électrons à très grande mobilité électrique en présence de gaz oxydants et réducteurs. De plus, la polyaniline (PANI) est facilement synthétisée et la structure de sa chaîne moléculaire peut être modifiée de manière pratique par copolymérisation ou dérivations structurelles. Grace à ses propriétés électriques, électrochimiques et optiques uniques, elle peut également être utilisée comme détecteur efficace pour la surveillance de composés organiques et inorganiques.----------ABSTRACT: In recent years, the preparation of nanostructured architectures has been an important strategy for improving gas sensing performance. These materials have an extremely high surface-to-volume ratio and high nanoporous structures, which increases the adsorption of gases. Among these nanomaterials, functionalized graphene has generated considerable interest in sensing applications owing to its variable conductivity, which makes it available for electron transport phenomena with very high electrical mobility in the presence of oxidizing and reducing gases. Additionally, polyaniline (PANI) is easily synthesized and its molecular chain structure can be modified conveniently by copolymerization or structural derivations. Due to its unique electrical, electrochemical, and optical properties, it can also be utilized as efficient sensors for monitoring organic and inorganic compounds

Development of Graphene-Based Polymer Nanocomposites for Electrical Conductors and Supercapacitors

L’électrofilage est une méthode pratique et avantageuse pour obtenir des nanofibres de polymères avec des diamètres contrôlés de l'ordre de quelques dizaines de nanomètres à quelques micromètres. Les mats de fibres non-tissées résultants ont des surfaces spécifiques élevées de l'ordre de 1 à 100 m2/g. La combinaison de ces propriétés avec la conductivité électrique intrinsèquement élevée de certains polymères conducteurs donne lieu à des mats de fibres conducteurs qui sont très prometteurs pour diverses applications dans divers domaines dont : l’électronique, le magnétique, le biomédical, mais encore des applications en optique et dans le domaine des capteurs. Une nouvelle classe de polymère connue sous le nom de polymères intrinsèquement conducteurs (PIC) a été découverte en 1960. Les PIC sont de nature intrinsèquement conducteurs en raison de la présence d'un système d'électrons π conjugué dans leur structure. Les PIC possèdent des bonnes propriétés électroniques, des faibles potentiels d'ionisation et une électroaffinité élevée. La polyaniline (PANi) est l'un des PIC les plus étudiés. Elle est unique en raison de la facilité de sa synthèse, de sa stabilité environnementale et de la simplicité de sa chimie de dopage/dédopage. En revanche, elle est relativement difficile à mettre en forme par rapport à la plupart des autres polymères conventionnels, ce qui est typique des PIC. En effet, la polyaniline a un squelette assez rigide en raison de son aromaticité élevée. Ainsi, l'élasticité des solutions de PANi est généralement insuffisante pour qu'elles puissent être électrofilées pour en faire des nanofibres. En outre, la PANi a une mauvaise solubilité dans la plupart des solvants communs, ce qui rend son électrofilabilité encore plus difficile. Cependant, si les limitations de solubilité et de rigidité suscitées pouvaient être résolues, la PANi pourrait être électrofilée en mats de fibres conductrices pouvant être utilisés dans une large gamme d'applications telles que les capteurs chimio-résistants, les surfaces hydrophobes réversibles et les substrats pour la fonctionnalisation. Le but ultime de la première partie de cette thèse est de préparer des nanofibres de PANi électrofilées avec du graphène intégré pour une utilisation potentielle comme capteurs pour la détection de gaz et de pathogènes. À cette fin, deux stratégies ont été utilisées pour obtenir les nanofibres électrofilées de PANi: Mélanger de la PANi dopée avec des polymères isolants et facilement électrofilables comme le poly(oxyde d’éthylène) ou PEO. Cependant, la présence du polymère isolant réduit la conductivité des fibres en raison de la diminution des composés conducteurs dans le mélange. Une bonne stratégie pour compenser l'addition du polymère isolant et améliorer les propriétés électriques globales des fibres électrofilées, est d’y incorporer des nanocharges conductrices à base de carbone. À cet effet, le graphène a été sélectionné. Depuis sa découverte en 2004, le graphène a suscité un intérêt considérable en recherche. Il est constitué d’un simple feuillet d’une seule épaisseur en deux dimensions, lui-même composé d'atomes de carbone organisés en une structure cristalline en nid d'abeilles. Il possède une surface, une résistance ainsi qu’une conductivité thermique et électrique exceptionnellement élevées. Par conséquent, compte tenu des excellentes propriétés du graphène et de la PANi, des nanofibres de PANi contenant des nanocharges de graphène comme agent de remplissage peuvent être obtenues. Ainsi, des nanofibres conductrices de PANi dopée avec de l'acide camphre-10-sulfonique (ACS), mélangée à du PEO et remplie avec du graphène fonctionnalisé ester succinimidyle de l'acide 1-pyrènebutanoïque ou (G-PBASE) ont été préparées par électrofilage. La microscopie électronique à balayage (MEB), la microscopie électronique à transmission (MET), la spectroscopie de photoélectrons par rayons X (XPS), laspectroscopie infrarouge à transformée de Fourier (FTIR) et l’analyse thermogravimétrique (TGA) ont été utilisées pour caractériser la morphologie des fibres de PANi/PEO/G-PBASE ainsi que leurs propriétés. Les observations montrent que les fibres électrofilées sont fortement interconnectées et possèdent une surface relativement lisse. Le diamètre moyen des fibres est d'environ 220 nm. La conductivité électrique des fibres de PANi/PEO et PANi/PEO/G-PBASE à température ambiante a également été étudiée. Les fibres composites nanostructurées PANi/PEO/G-PBASE avec une faible charge de G-PBASE (5 % en poids par rapport à la PANi) a montré une augmentation de la conductivité électrique de deux ordres de grandeur et une amélioration d’un ordre de grandeur de la stabilité thermique en comparaison avec les nanofibres de PANi/PEO. Utiliser la technique d'électrofilage coaxial pour préparer des nanofibres structurées en coeur-enveloppe avec la PANi au centre de la fibre et un polymère facilement électrofilable tel que le poly(méthacrylate de méthyle) (PMMA). Par la suite, l’enveloppe externe a été retirée par extraction-solvant pour obtenir des nanofibres de PANi pures. La méthode d'électrofilage coaxial constitue une alternative et un moyen efficace pour l’obtention de fibres de polymères non-électrofilables. Dans cette technique, deux solutions différentes sont électrofilées simultanément à travers une filière composée de deux capillaires coaxiaux pour produire des nanofibres structurées en coeur-enveloppe avec le polymère non-électrofilable au centre de la fibre. Par conséquent, des nanofibres coeur-enveloppe de PANi/PMMA contenant du G-PBASE sont préparées par électrofilage coaxial, avec la PANi et le G-PBASE étant au coeur des fibres et le PMMA l'enveloppe externe, respectivement. Les nanofibres de PANi/G-PBASE/PMMA obtenues possèdent des diamètres de ~420 nm. En outre, des nanofibres de pure PANi et de PANi/G-PBASE ont été obtenues par extraction-solvant de l’enveloppe de PMMA, ce qui a réduit le diamètre des fibres à 230 nm. La morphologie des nanofibres a été analysée par MEB et MET. La structure coeur-enveloppe et l'existence de feuillets de graphène dans la couche centrale des fibres ont été confirmées par les images en MET, obtenues avant et après extraction-solvant du PMMA. La conductivité électrique des fibres obtenues à température ambiante a été étudiée par la méthode de la sonde à quatre points. Les nanofibres de PANi/G-PBASE ont montré une conductivité électrique de 30,25 S/cm, laquelle est trois fois plus élevée que celle des nanofibres de PANi pure. Dans la deuxième partie de cette thèse, nous investiguons l'ajout de graphène à du polyacrylonitrile (PAN) renforcé par des nanofibres de carbone (NFC). L’objectif étant d'améliorer la surface spécifique et la capacitance des fibres obtenues, en vue d’applications où une densité de haute énergie est requise, tel que dans les supercondensateurs. Récemment, beaucoup de recherches ont été menées sur des matériaux à base de PAN et NFC pour des applications de stockage d'énergie. Cependant, la faible conductivité et densité de puissance des NFC représentent un obstacle à leur utilisation potentielle dans les supercondensateurs. Par conséquent, dans cette étude, des NFC électrofilées en structure coeur-enveloppe et additionnées de différentes quantités de graphène fonctionnalisé de façon non covalente ont été préparées. La technique employée à cet effet est l'électrofilage à une seule buse en utilisant une solution biphasée de polyacrylonitrile et de polyvinylpyrrolidone (PAN/PVP), avec comme solvant du N,N-diméthylformamide (DMF). La concentration en graphène varie de 0% à 15% en poids (par rapport au PAN). Les nanofibres électrofilées structurées en coeur-enveloppe ont d'abord été stabilisées à 250 °C dans l'air puis, par la suite carbonisées à 850 °C dans une atmosphère sous azote pour produire les NFC. Les fibres ultra-minces résultantes ont des diamètres moyens de l'ordre de 60 à 80 nm. La morphologie et la microstructure des nanofibres ont été caractérisées par SEM, TEM, spectroscopie Raman, XPS et BET pour l'adsorption d'azote à 77 K. Après incorporation des nanofeuillets de graphène, les résultats ont montré une augmentation de la surface spécifique et du volume des pores des mats de fibres allant jusqu’à 627 m2 g-1 et 0,35 cm3 g-1, respectivement. La performance électrochimique des nanocomposites NFC/graphène a été étudiée dans une solution de KOH (6M). Les analyses électrochimiques de ces mêmes nanofibres révèlent une capacitance spécifique maximale de 265 F g-1, après ajout de 10% en poids de nanofeuillets de graphène. ----------- Electrospinning is a convenient method to produce polymer nanofibers with controlled diameters on the order of tens of nanometers to micrometers. The resulting non-woven fiber mats have high specific surface areas of around 1−100 m2/g. Combining these properties with the high electrical conductivity of intrinsically conductive polymers yields conductive electrospun fiber mats that are very promising for a variety of applications such as electronic, magnetic, biomedical, sensor and optical fields. A new class of polymer known as intrinsically conducting polymers (ICPs) were discovered in 1960. ICPs are intrinsically conducting in nature due to the presence of a conjugated π electron system in their structure. ICPs possess electronic properties, low ionization potentials and a high electroaffinity. Polyaniline (PANi) is one of the most studied ICPs and it is unique due to its ease of synthesis, environmental stability, and simple doping/dedoping chemistry, yet it is relatively hard to process compared to most other polymers. As is common among ICPs, it has a fairly rigid backbone due to its high aromaticity. Thus, the elasticity of its solutions is generally insufficient for it to be electrospun directly into fibers. Moreover, PANi has poor solubility in common solvents, which further complicates it electrospinnability. However, if aforementioned processing limitations of PANi can addressed and it can be electrospun into conductive fiber mats, it can be used for a variety of applications such as chemoresistive sensors, reversible hydrophobic surfaces and substrates for functionalization. The ultimate purpose of first part of this thesis is to fabricate electrospun PANi nanofibers embedded with graphene for potential sensor applications such as gas and pathogen detection. To this end, two strategies were utilized to electrospin PANi nanofibers: 1) Blending doped-PANi with insulating polymers which are easily electrospinnable such as polyethylene oxide (PEO). However, the presence of the insulator polymer will decrease the fibers conductivity due to a reduction of the conducting component in the blend and a good strategy to compensate for the addition of insulating polymer and to improve the overall electrical properties of the electrospun fibers blend is to incorporate carbon-based conductive nanofillers into the fibers and in this work graphene was selected. Since the discovery of graphene in 2004, it has attracted tremendous research interest. Graphene is a single-atom-thick, two-dimensional sheet of sp2-hybrized carbon atoms arranged in a honeycomb crystal structure with exceptionally high strength, surface area, thermal conductivity, and electronic conductivity. Therefore, considering the excellent properties of graphene and PANi, highly conductive PANi nanofibers with graphene as nanofiller can be obtained. To this end, conducting nanofibers of PANi doped with camphor-10-sulfonic acid (HCSA), blended with PEO, and filled with 1-pyrenebutanoic acid, succinimidyl ester functionalized graphene (G-PBASE) have been fabricated using electrospinning. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transforms infrared (FTIR) and thermal gravimetric analyzer (TGA) were utilized to characterize the PANi/PEO/G-PBASE fibers morphology and properties. The observations show that electrospun fibers are highly interconnected and possess a relatively smooth surface. The average diameter of fibers was ~ 220 nm. The electrical conductivity of PANi/PEO and PANi/PEO/G-PBASE at room temperature was also studied. The unique nanostructured composite of PANi/PEO/G-PBASE with small loading of G-PBASE (5 wt.% relative to PANi) showed two order of magnitude enhancement in the electrical conductivity and one order of magnitude enhancement in thermal stability in comparison to PANi/PEO nanofibers. 2) Utilizing coaxial electrospinning technique to produce core−shell structured nanofiber with PANi at the core layer and an easily electrospinnable polymer such as poly(methyl methacrylate) (PMMA) at shell segment. Subsequently, the shell segment was removed by solvent etching to produce pure PANi nanofibers. The coaxial electrospinning method provides an alternative and effective way for fabrication of unspinnable polymer with unique core−shell structured fibers. In this technique, two dissimilar solutions are spun simultaneously through a spinneret composed of two coaxial capillaries to produce core−shell structured nanofibers with unspinable polymer at the core section. Therefore, Core−shell structured PANi/PMMA nanofibers embedded with G-PBASE are produced by a coaxial electrospinning setup. PANi/G-PBASE and PMMA solutions were used as core and shell layer respectively. The as-prepared PANi/G-PBASE/PMMA nanofibers possessed diameters in the range of ~420 nm. Moreover, neat PANi/G-PBASE and PANi nanofibers were obtained by solvent etching of PMMA shell which reduced the fiber diameter to 230 nm. The morphology of the nanofibers was investigated by SEM and TEM. The core−shell structure and the existence of graphene sheets in the core layer were confirmed by TEM images obtained before and after solvent etching of PMMA. The electrical conductivity of the fibers at room temperature was investigated by four-point probe method. The PANi/G-PBASE nanofibers exhibited electrical conductivity as high as of 30.25 S/cm which was 3 times higher than that of neat PANi nanofibers. The second part of this thesis investigates the addition of graphene to polyacrylonitrile (PAN)-based carbon nanofibers (CNFs) in order to improve their surface area and capacitance for applications where high-energy density is required such as in supercapacitors. Recently, a lot of research has been conducted on PAN-based CNFs for energy storage applications. However, CNFs low conductivity and power density is an obstacle for their potential application in supercapacitors. Therefore, in this study core–shell structured CNFs embedded with various amounts of non-covalently functionalized graphene were fabricated by single-nozzle electrospinning technique using phase-separated solution of polyacrylonitrile and polyvinylpyrrolidone (PAN/PVP) in N,N-dimethylformamide (DMF). The concentration of graphene varied from 0 wt% to 15 wt% (relative to PAN). These core-shell structured electrospun nanofibers were first stabilized at 250 °C in air and consecutively carbonized at 850 °C in nitrogen atmosphere to produce CNFs. The resulting ultra-fine fibers have average fiber diameters in the range of 60-80 nm. The morphology and microstructure of the nanofibers were characterized by SEM, TEM, Raman spectroscopy, XPS and BET nitrogen adsorption at 77 K. The result showed that the specific surface area and pore volume of nanofiber mats increased to 627 m2 g−1 and 0.35 cm3 g−1 respectively by embedding graphene nanosheets. The electrochemical performance of as-synthesized CNF/G nanocomposites was investigated in 6M KOH electrolyte by cyclic voltammetry and galvanostatic charge/discharge. Electrochemical measurements of CNF/G nanofibers exhibited a maximum specific capacitance of 265 F g−1 after addition of 10 wt% graphene nanosheets

Functional applications of electrospun nanofibers

With the rapid development of nanoscience and nanotechnology over the last two decades, great progress has been made not only in preparation and characterization of nanomaterials, but also in their functional applications. As an important one-dimensional nanomaterial, nanofibers have extremely high specific surface area because of their small diameters, and nanofiber membranes are highly porous with excellent pore interconnectivity. These unique characteristics plus the functionalities from the polymers themselves impart nanofibers with many desirable properties for advanced applications

A class of multifunctional smart energy materials

Funding Information: S. Goswami would like to thank to Lisboa2020 Programme, Centro 2020 programme, Portugal 2020, European Union, through the European Social Fund who supported LISBOA-05-3559-FSE-000007 and CENTRO-04-3559-FSE-000094 operations as well as to Fundação para a Ciência e Tecnologia (FCT) and Agência Nacional de Inovação (ANI). Publisher Copyright: © 2022 The AuthorsPolymer material provides significant advantages over the conventional inorganic material-based electronics due to its attractive features including miniaturized dimension and feasible improvisations in physical properties through molecular design and chemical synthesis. In particular, conjugate polymers are of great interest because of their ability to control the energy gap and electronegativity through molecular design that has made possible the synthesis of conducting polymers with a range of ionization potentials and electron affinities. Polyaniline (PANI) is one of the most popular conjugated polymers that has been widely explored so far for its multifunctionality in diverse potential applications. This review is focusing on the recent advances of PANI for smart energy applications including supercapacitors, batteries, solar cells and nanogenerators and the development in its synthesis, design, and fabrication processes. A details investigation on the different types of chemical process has been discussed to fabricate PANI in nanostructures, film, and composites form. The paper includes several studies which are advantageous for understanding: the unique chemical and physical properties of this polymer; and the easily tunable electrical properties along with its redox behavior; and different processes to develop nanostructures, film, or bulk form of PANI that are useful to derive its applicability in smart objects or devices.publishersversionpublishe

The Electrospun Ceramic Hollow Nanofibers

Hollow nanofibers are largely gaining interest from the scientific community for diverse applications in the fields of sensing, energy, health, and environment. The main reasons are: their extensive surface area that increases the possibilities of engineering, their larger accessible active area, their porosity, and their sensitivity. In particular, semiconductor ceramic hollow nanofibers show greater space charge modulation depth, higher electronic transport properties, and shorter ion or electron diffusion length (e.g., for an enhanced charging–discharging rate). In this review, we discuss and introduce the latest developments of ceramic hollow nanofiber materials in terms of synthesis approaches. Particularly, electrospinning derivatives will be highlighted. The electrospun ceramic hollow nanofibers will be reviewed with respect to their most widely studied components, i.e., metal oxides. These nanostructures have been mainly suggested for energy and environmental remediation. Despite the various advantages of such one dimensional (1D) nanostructures, their fabrication strategies need to be improved to increase their practical use. The domain of nanofabrication is still advancing, and its predictable shortcomings and bottlenecks must be identified and addressed. Inconsistency of the hollow nanostructure with regard to their composition and dimensions could be one of such challenges. Moreover, their poor scalability hinders their wide applicability for commercialization and industrial use

White paper on the future of plasma science and technology in plastics and textiles

This is the peer reviewed version of the following article: “Uros, C., Walsh, J., Cernák, M., Labay, C., Canal, J.M., Canal, C. (2019) White paper on the future of plasma science and technology in plastics and textiles. Plasma processes and polymers, 16 1 which has been published in final form at [doi: 10.1002/ppap.201700228]. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving."This white paper considers the future of plasma science and technology related to the manufacturing and modifications of plastics and textiles, summarizing existing efforts and the current state‐of‐art for major topics related to plasma processing techniques. It draws on the frontier of plasma technologies in order to see beyond and identify the grand challenges which we face in the following 5–10 years. To progress and move the frontier forward, the paper highlights the major enabling technologies and topics related to the design of surfaces, coatings and materials with non‐equilibrium plasmas. The aim is to progress the field of plastics and textile production using advanced plasma processing as the key enabling technology which is environmentally friendly, cost efficient, and offers high‐speed processingPeer ReviewedPostprint (author's final draft