rus
DOI: https://doi.org/10.22184/1993-8578.2022.15.2.118.127
Electroforming is a versatile and flexible method for producing ultrathin fibers. Fibers produced by electroforming are used in many industries due to the high ratio of fiber length to its area. Electroforming has found especially great application in the production of filter materials based on ultrathin synthetic fibers.
Electroforming is a versatile and flexible method for producing ultrathin fibers. Fibers produced by electroforming are used in many industries due to the high ratio of fiber length to its area. Electroforming has found especially great application in the production of filter materials based on ultrathin synthetic fibers.
Теги: electroforming membrane nanofibers nanomaterials nanotechnology synthetic fibers мембрана нановолокна наноматериалы нанотехнологии синтетические волокна электроформование
INTRODUCTION
Nowadays, the process of formation of the sixth technological mode is under way [1–3], which core is based on new technologies and new materials [4]. A prominent place among new materials is occupied by fibrous materials produced by various technologies. However, electroforming is a promising method for obtaining qualitatively new fibres. This method of formation is primarily designed for production of synthetic fibres.
Electrostatic fibre formation, also known as electroforming (EF), belongs to the field of nanotechnology due to morphology and scale of the structures created. Electroforming is a very promising and unique technology for nanomaterials, in particular for production of nanofibres.
Recently there has been a great deal of interest in this method of producing fibres, although it has a long history. The basic principles of this method of formation were invented almost a century ago. Different sources hold different views on this date. The development of EF as a separate technology is generally considered to have begun with the work of Anton Formhals in the 1930s. But in the work of Beuys [5] in 1887, there was already a mention of the technology of drawing fibres from a liquid by means of electrostatic force, which was already known in the middle of the 18th century. The first patents in this field belong to Cooley and Morton, registered in 1900 and 1902 respectively, which probably formed the basis of Formhals’ work [6]. Over the next 120 years, EF technology was developed and refined by a number of engineers and became a promising technology for the production of cheap synthetic fibres, yarns and textiles.
This technology attracts a new wave of interest due to the work of J. Doshi, D.H. Renecker in 1995, wherein the authors introduced the term "electroforming" [7]. Currently, EF is among the most promising technologies for the production of polymeric, ceramic and carbon nanofibres/microfibres applied in medicine, pharmaceuticals, water treatment, filtration, electronics, energy harvesting and storage, sensors and a wide range of other equally important fields.
Production of nanofibres
The significant impetus that has led to the development of the most prominent and modern technologies has been driven by recent discoveries in the field of nanoscience. Moving to the nanoscale level of structural ordering of matter has revealed the large-scale dependence of the properties of well-known materials. These materials include zero-dimensional nanoparticles or quantum dots; one-dimensional nanowires, rods, fibres and tubes; and two-dimensional nanosheets (graphene, borophene, phosphorus, g-C3N4, etc.) [8].
Among the nanomaterials listed, nanofibres stand out. The exceptionally high surface area to volume ratio along with high porosity, simplicity and flexibility in designing properties make nanofibres an attractive candidate for a number of applications. To date, nanofibres have been derived from a variety of materials, including natural and synthetic polymers, carbon-based nanomaterials, and semiconductor and composite materials.
Along with the development of manufacturing technologies, tremendous efforts have been focused on exploring the potential applications of nanofibres, including energy generation and storage [9, 10], water and air purification [11, 12], and healthcare and biomedical engineering [13, 14]. Nanofibres can be produced by a variety of technologies. They all have their pros and cons; they are based on different principles, but the aim is to produce fibres with the highest possible precision and reproducibility.
From some points of view, EF can be regarded as a variant of electrostatic spraying. It is a process which produces continuous polymer fibres in the micron to submicron diameter range under the action of an external electric field applied to the liquid polymer [15]. The process of forming thin fibres is based on the uniaxial stretching and elongation of an electrified viscoelastic polymer jet formed by a viscous solution or melt, due to electrostatic repulsion between surface charges and solvent evaporation.
Electroforming technology itself is one of the most established and has been known for just over a century. But the tools for a comprehensive study of its products have only recently been developed, and an understanding of the parameters that are critical or have only a minor influence on the process, along with the potential of the technology, is still undergoing detailed study.
Materials used in electroforming
Both natural and synthetic polymers are often used in production of nanofibres. Thanks to the concept of "green chemistry", which is currently gaining popularity, water is the most commonly used solvent and still the cheapest. Many of the water-soluble polymers are non-toxic, biocompatible and already used in the food industry. This makes the concept of green chemistry fully applicable to large-scale industrial production. The use of water-soluble natural polymers makes it easy to modify nanofibres for various applications: from biocompatible wound dressings to special substrates for the vertical growth of moulds, fungi or plants.
Producing ceramic and carbon fibres by electroforming
Electroforming enables production of ceramic, carbon and composite fibres, depending on the nature and conditions of the treatment used.
When producing ceramic fibres obtained by electroforming, the most commonly used method is a post-press heat treatment, in the form of calcination (in air or oxygen) and pyrolysis (usually in argon or other inert gas or vacuum), as well as a non-thermal plasma treatment which is a new and promising application.
Production of ceramic fibres cannot be made directly by electroforming. In this approach precursor fibres are produced by injecting a suspension of nano- or submicron size powders into a polymer solution. After EF, a heat treatment must be applied to remove the polymer binder, which acts as an obligatory agent for fibre formation, but it also causes bonding/sintering of the ceramic component along with retaining the fibrous morphology [16]. Despite its apparent simplicity, the physical approach has not been widely adopted due to its limitations. The most important of these relate to the requirements to the particles used, the particle size must be much smaller than the desired diameter of the final fibre at high concentration in order to ensure fusion of particles during heat treatment. The higher the concentration of the particles, the more densely they will be arranged in the fibre and the higher the probability that they will fuse and retain their fibrous morphology during heat treatment. On the other hand, the concentration of ceramic powder directly affects the viscosity of the EF solution so as to increase it. This leads to an increase of the diameter of the formed fibres, thus introducing another limitation.
The economic aspect should also be mentioned: powders with smaller particle sizes are much more expensive or have to be milled, which also requires expensive equipment.
Compared to the physical approach, the chemical approach is more complex, but provides a higher level of technical flexibility and allows finer tuning of the final properties of the fibres. Synthesis of complex ceramic materials (complex oxides, non-oxide structures) by the chemical method is often accomplised by the gel technology. In this case, one or more individual ceramic precursors are replaced by a sequential gel synthesis.
As the polymer-ceramic precursor composites have already been prepared, the next step after electroforming – post-pressure processing – is necessary and common to both approaches. The removal of the polymer matrix to form ceramic fibres takes place.
For this purpose a heat treatment is usually used. Some of the ceramic precursors (alkoxides and metal halides) are highly reactive and are converted into ceramics (by hydrolysis with air humidity) already in the EF process [17]. The formed ceramics are often amorphous, so the resulting polymer-ceramic composites still require high-temperature treatment for crystallisation of the ceramics as well. Heat treatment includes both calcination and pyrolysis; depending on the temperature and atmosphere applied, the effect can vary greatly. Quenching at low temperatures in some polymers (PVS, PAN) [16] can initiate intra- and inter-fibre transformations such as polymer cross-linking and fibre fusion or network formation, respectively. Tempering at high temperatures (>>300 °C) results in pre-oxidation of the polymer, followed by complete oxidation and removal (burnout) together with formation of ceramic, crystallisation, sintering and fusion of ceramic grains and the subsequent formation of fibres.
On the other hand, pyrolysis – heat treatment in an inert atmosphere or vacuum – results in carbonisation of the polymer base of fibres and other organic components with retained shape and formation of carbon-based fibrous materials [18]. This effect has been applied to produce a wide range of carbon fibres used as catalysts, electrodes for gas separation reactions, fuel cells, supercapacitors [19], hydrogen storage [9], filters with nanoparticles, sorbents for removing precious metals from sewage and sea water and a number of other promising applications [20].
The most commonly used polymer for obtaining carbon fibres by electroforming is polyacrylonitrile [18], but due to its high price there are works aimed at replacing it with polyvinyls [21], as well as their composites and blends with lignin [22]. Addition of small amounts of ceramic precursors (mainly metal salts) to the polymer solution leads to the formation of nanoparticles inside and/or outside the fibre during pyrolysis. Fine-tuning of the heat treatment conditions makes it possible to use the formed nanoparticles as germs for the synthesis of carbon nanotubes.
Applications of nanofibres
Over the last three decades, EF nanofibres have gained a wide range of applications. Every year the number of fields where fibres, and nanofibres in particular, are used is increasing rapidly. The membrane produced by electroforming is a multilayer mat of nanofibres lying in a chaotic pattern (Fig.1).
Biologically, almost all human tissues and organs are based on nanofibrous forms or structures, including bone, dentin, cartilage and skin. They are all characterised by well-organised hierarchical fibrous structures, in particular the extracellular matrix [16]. This allows the use of synthetic fibre frameworks to replace or regenerate damaged tissues or organ parts.
In the industrial field nanofibres are widely used in various types of advanced materials and composites, filtration, special and unique clothing, electronic devices, transparent/flexible solar cells and screens.
Filtration and microfiltration /nanofiltration
As filter channels and structural elements must match the scale of particles or droplets to be captured by the filter, one direct way to develop highly efficient and effective filter media is to use nanometre-sized fibres in the filter structure.
Carbon, polymer or ceramic nanofibres are suitable for the adsorption of valuable or toxic substances thanks to their large surface area [11].
In water treatment systems nanofibre membranes are used for filtration and membrane distillation [23]. The nanofibre membranes used in this technology make it possible to desalinate seawater at high capacity and autonomously using solar energy only.
Military industry and advanced composites (composites for armour and structural parts).
Polymer and ceramic matrix composites reinforced with fibres can be used as new lightweight materials for instruments, aircraft or armour plates for personal use and vehicles. Due to very small fibre diameters and large contact area, the impact energy dissipation can be far more effective for the same material size. This makes it possible to reduce the weight of the armor while maintaining the protective capacity [24].
Works are also carried out to create flexible materials with increased strength, modulus of elasticity and impact resistance. This is due to the low crystallinity of the nanofibres resulting from the rapid solidification of the ultra-thin jets.
Semiconductor materials such as TiO2, SnO2, ZnO, WO3, MoO3 are used to detect trace concentrations of gaseous compounds. In principle, the higher specific surface area and porosity of the sensitive material can lead to higher sensor sensitivity. In addition, one-dimensional materials can offer the additional advantage of allowing rapid mass transfer of target molecules around the interaction region, as well as overcoming charge carrier barriers. Ceramic nanofibres have been successfully applied as sensitive interfaces for detection of a great number of gases with increased detection limits, the well known examples include NO2, CO, H2O, NH3, CH3OH, C2H5OH, O2, H2 and toluene [17].
Many new active packaging materials attract the ever increasing attention in the food industry. Active packaging can inhibit growth of microorganisms on food surfaces, improve the nutritional and sensory quality of food, extend the shelf life of certain food products and reduce the environmental impact of packaging [25]. Active packaging technologies can be based on synthetic or natural materials and some of them contain active ingredients such as antioxidants, antimicrobials, vitamins, flavourings or colourings. Functional electroplating mats can be used as tools to develop nanocomposite fabrics from a wide range of plastics with improved characteristics for packaging applications.
Application of nanofibres in the food industry is not limited to the aforementioned areas. It has been shown that nanofibre mats may have potential for applications in the vertical cultivation of products such as fungi, with the possibility of developing the properties of the final product or even vice versa, if it can demonstrate antifungal functionality [26].
Polymeric membranes also have potential for such applications as electrostatic charge dissipation, corrosion protection, electromagnetic protection, photovoltaic devices, fabrication of microelectronic devices or machines such as Schottky transitions, sensors and actuators, etc., since the rate of electrochemical reactions is proportional to the electrode surface area.
Conductive nanofibre membranes are also quite suitable for use as porous electrodes in the development of high-performance batteries and fuel cells with polymer electrolyte membranes due to their high porosity and inherently large total surface area. Polymer batteries have been developed for cellular phones to replace conventional bulky lithium batteries [27]. Insulating mats made of polymer fibres can be used as separators in the same batteries or supercapacitors.
Carbon and ceramic fibres are promising materials for water splitting, hydrogen storage, membranes for fuel cells of various designs, electrodes in supercapacitors and dye-sensitive solar cells [9].
CONCLUSIONS
It is evident that EF is a versatile technology capable of creating unique materials with a variety of properties. In spite of the significant scope of research carried out, the high level of applied technical improvements and the wide range of applications where electroformed nanofibres are already used, still there are some challenges:
Safety of technical personnel. The use of high voltage power supplies requires safety training and increased caution when working with equipment. Improved process automation and failsafe components/modules can provide the necessary safety.
Lack of reliable prediction models. There are only a few papers devoted to theoretical prediction of EF outcomes, but they are not universal and cannot include all influential parameters to predict the results of their EF.
When nanofibres are used in composites, there is still a problem of fibre dispersion within the matrix.
It is worth noting that the materials produced by electroforming technology cannot currently be used as structural materials, due to limitations in the reproducibility of geometric dimensions and, as a consequence, mechanical characteristics. The main area belongs to the functional materials.
Despite the existing challenges, electroformed fibre technology is of great interest and has the potential for producing materials with unique properties.
PEER REVIEW INFO
Editorial board thanks the anonymous reviewer(s) for their contribution to the peer review of this work. It is also grateful for their consent to publish papers on the journal’s website and SEL eLibrary eLIBRARY.RU.
Declaration of Competing Interest. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Nowadays, the process of formation of the sixth technological mode is under way [1–3], which core is based on new technologies and new materials [4]. A prominent place among new materials is occupied by fibrous materials produced by various technologies. However, electroforming is a promising method for obtaining qualitatively new fibres. This method of formation is primarily designed for production of synthetic fibres.
Electrostatic fibre formation, also known as electroforming (EF), belongs to the field of nanotechnology due to morphology and scale of the structures created. Electroforming is a very promising and unique technology for nanomaterials, in particular for production of nanofibres.
Recently there has been a great deal of interest in this method of producing fibres, although it has a long history. The basic principles of this method of formation were invented almost a century ago. Different sources hold different views on this date. The development of EF as a separate technology is generally considered to have begun with the work of Anton Formhals in the 1930s. But in the work of Beuys [5] in 1887, there was already a mention of the technology of drawing fibres from a liquid by means of electrostatic force, which was already known in the middle of the 18th century. The first patents in this field belong to Cooley and Morton, registered in 1900 and 1902 respectively, which probably formed the basis of Formhals’ work [6]. Over the next 120 years, EF technology was developed and refined by a number of engineers and became a promising technology for the production of cheap synthetic fibres, yarns and textiles.
This technology attracts a new wave of interest due to the work of J. Doshi, D.H. Renecker in 1995, wherein the authors introduced the term "electroforming" [7]. Currently, EF is among the most promising technologies for the production of polymeric, ceramic and carbon nanofibres/microfibres applied in medicine, pharmaceuticals, water treatment, filtration, electronics, energy harvesting and storage, sensors and a wide range of other equally important fields.
Production of nanofibres
The significant impetus that has led to the development of the most prominent and modern technologies has been driven by recent discoveries in the field of nanoscience. Moving to the nanoscale level of structural ordering of matter has revealed the large-scale dependence of the properties of well-known materials. These materials include zero-dimensional nanoparticles or quantum dots; one-dimensional nanowires, rods, fibres and tubes; and two-dimensional nanosheets (graphene, borophene, phosphorus, g-C3N4, etc.) [8].
Among the nanomaterials listed, nanofibres stand out. The exceptionally high surface area to volume ratio along with high porosity, simplicity and flexibility in designing properties make nanofibres an attractive candidate for a number of applications. To date, nanofibres have been derived from a variety of materials, including natural and synthetic polymers, carbon-based nanomaterials, and semiconductor and composite materials.
Along with the development of manufacturing technologies, tremendous efforts have been focused on exploring the potential applications of nanofibres, including energy generation and storage [9, 10], water and air purification [11, 12], and healthcare and biomedical engineering [13, 14]. Nanofibres can be produced by a variety of technologies. They all have their pros and cons; they are based on different principles, but the aim is to produce fibres with the highest possible precision and reproducibility.
From some points of view, EF can be regarded as a variant of electrostatic spraying. It is a process which produces continuous polymer fibres in the micron to submicron diameter range under the action of an external electric field applied to the liquid polymer [15]. The process of forming thin fibres is based on the uniaxial stretching and elongation of an electrified viscoelastic polymer jet formed by a viscous solution or melt, due to electrostatic repulsion between surface charges and solvent evaporation.
Electroforming technology itself is one of the most established and has been known for just over a century. But the tools for a comprehensive study of its products have only recently been developed, and an understanding of the parameters that are critical or have only a minor influence on the process, along with the potential of the technology, is still undergoing detailed study.
Materials used in electroforming
Both natural and synthetic polymers are often used in production of nanofibres. Thanks to the concept of "green chemistry", which is currently gaining popularity, water is the most commonly used solvent and still the cheapest. Many of the water-soluble polymers are non-toxic, biocompatible and already used in the food industry. This makes the concept of green chemistry fully applicable to large-scale industrial production. The use of water-soluble natural polymers makes it easy to modify nanofibres for various applications: from biocompatible wound dressings to special substrates for the vertical growth of moulds, fungi or plants.
Producing ceramic and carbon fibres by electroforming
Electroforming enables production of ceramic, carbon and composite fibres, depending on the nature and conditions of the treatment used.
When producing ceramic fibres obtained by electroforming, the most commonly used method is a post-press heat treatment, in the form of calcination (in air or oxygen) and pyrolysis (usually in argon or other inert gas or vacuum), as well as a non-thermal plasma treatment which is a new and promising application.
Production of ceramic fibres cannot be made directly by electroforming. In this approach precursor fibres are produced by injecting a suspension of nano- or submicron size powders into a polymer solution. After EF, a heat treatment must be applied to remove the polymer binder, which acts as an obligatory agent for fibre formation, but it also causes bonding/sintering of the ceramic component along with retaining the fibrous morphology [16]. Despite its apparent simplicity, the physical approach has not been widely adopted due to its limitations. The most important of these relate to the requirements to the particles used, the particle size must be much smaller than the desired diameter of the final fibre at high concentration in order to ensure fusion of particles during heat treatment. The higher the concentration of the particles, the more densely they will be arranged in the fibre and the higher the probability that they will fuse and retain their fibrous morphology during heat treatment. On the other hand, the concentration of ceramic powder directly affects the viscosity of the EF solution so as to increase it. This leads to an increase of the diameter of the formed fibres, thus introducing another limitation.
The economic aspect should also be mentioned: powders with smaller particle sizes are much more expensive or have to be milled, which also requires expensive equipment.
Compared to the physical approach, the chemical approach is more complex, but provides a higher level of technical flexibility and allows finer tuning of the final properties of the fibres. Synthesis of complex ceramic materials (complex oxides, non-oxide structures) by the chemical method is often accomplised by the gel technology. In this case, one or more individual ceramic precursors are replaced by a sequential gel synthesis.
As the polymer-ceramic precursor composites have already been prepared, the next step after electroforming – post-pressure processing – is necessary and common to both approaches. The removal of the polymer matrix to form ceramic fibres takes place.
For this purpose a heat treatment is usually used. Some of the ceramic precursors (alkoxides and metal halides) are highly reactive and are converted into ceramics (by hydrolysis with air humidity) already in the EF process [17]. The formed ceramics are often amorphous, so the resulting polymer-ceramic composites still require high-temperature treatment for crystallisation of the ceramics as well. Heat treatment includes both calcination and pyrolysis; depending on the temperature and atmosphere applied, the effect can vary greatly. Quenching at low temperatures in some polymers (PVS, PAN) [16] can initiate intra- and inter-fibre transformations such as polymer cross-linking and fibre fusion or network formation, respectively. Tempering at high temperatures (>>300 °C) results in pre-oxidation of the polymer, followed by complete oxidation and removal (burnout) together with formation of ceramic, crystallisation, sintering and fusion of ceramic grains and the subsequent formation of fibres.
On the other hand, pyrolysis – heat treatment in an inert atmosphere or vacuum – results in carbonisation of the polymer base of fibres and other organic components with retained shape and formation of carbon-based fibrous materials [18]. This effect has been applied to produce a wide range of carbon fibres used as catalysts, electrodes for gas separation reactions, fuel cells, supercapacitors [19], hydrogen storage [9], filters with nanoparticles, sorbents for removing precious metals from sewage and sea water and a number of other promising applications [20].
The most commonly used polymer for obtaining carbon fibres by electroforming is polyacrylonitrile [18], but due to its high price there are works aimed at replacing it with polyvinyls [21], as well as their composites and blends with lignin [22]. Addition of small amounts of ceramic precursors (mainly metal salts) to the polymer solution leads to the formation of nanoparticles inside and/or outside the fibre during pyrolysis. Fine-tuning of the heat treatment conditions makes it possible to use the formed nanoparticles as germs for the synthesis of carbon nanotubes.
Applications of nanofibres
Over the last three decades, EF nanofibres have gained a wide range of applications. Every year the number of fields where fibres, and nanofibres in particular, are used is increasing rapidly. The membrane produced by electroforming is a multilayer mat of nanofibres lying in a chaotic pattern (Fig.1).
Biologically, almost all human tissues and organs are based on nanofibrous forms or structures, including bone, dentin, cartilage and skin. They are all characterised by well-organised hierarchical fibrous structures, in particular the extracellular matrix [16]. This allows the use of synthetic fibre frameworks to replace or regenerate damaged tissues or organ parts.
In the industrial field nanofibres are widely used in various types of advanced materials and composites, filtration, special and unique clothing, electronic devices, transparent/flexible solar cells and screens.
Filtration and microfiltration /nanofiltration
As filter channels and structural elements must match the scale of particles or droplets to be captured by the filter, one direct way to develop highly efficient and effective filter media is to use nanometre-sized fibres in the filter structure.
Carbon, polymer or ceramic nanofibres are suitable for the adsorption of valuable or toxic substances thanks to their large surface area [11].
In water treatment systems nanofibre membranes are used for filtration and membrane distillation [23]. The nanofibre membranes used in this technology make it possible to desalinate seawater at high capacity and autonomously using solar energy only.
Military industry and advanced composites (composites for armour and structural parts).
Polymer and ceramic matrix composites reinforced with fibres can be used as new lightweight materials for instruments, aircraft or armour plates for personal use and vehicles. Due to very small fibre diameters and large contact area, the impact energy dissipation can be far more effective for the same material size. This makes it possible to reduce the weight of the armor while maintaining the protective capacity [24].
Works are also carried out to create flexible materials with increased strength, modulus of elasticity and impact resistance. This is due to the low crystallinity of the nanofibres resulting from the rapid solidification of the ultra-thin jets.
Semiconductor materials such as TiO2, SnO2, ZnO, WO3, MoO3 are used to detect trace concentrations of gaseous compounds. In principle, the higher specific surface area and porosity of the sensitive material can lead to higher sensor sensitivity. In addition, one-dimensional materials can offer the additional advantage of allowing rapid mass transfer of target molecules around the interaction region, as well as overcoming charge carrier barriers. Ceramic nanofibres have been successfully applied as sensitive interfaces for detection of a great number of gases with increased detection limits, the well known examples include NO2, CO, H2O, NH3, CH3OH, C2H5OH, O2, H2 and toluene [17].
Many new active packaging materials attract the ever increasing attention in the food industry. Active packaging can inhibit growth of microorganisms on food surfaces, improve the nutritional and sensory quality of food, extend the shelf life of certain food products and reduce the environmental impact of packaging [25]. Active packaging technologies can be based on synthetic or natural materials and some of them contain active ingredients such as antioxidants, antimicrobials, vitamins, flavourings or colourings. Functional electroplating mats can be used as tools to develop nanocomposite fabrics from a wide range of plastics with improved characteristics for packaging applications.
Application of nanofibres in the food industry is not limited to the aforementioned areas. It has been shown that nanofibre mats may have potential for applications in the vertical cultivation of products such as fungi, with the possibility of developing the properties of the final product or even vice versa, if it can demonstrate antifungal functionality [26].
Polymeric membranes also have potential for such applications as electrostatic charge dissipation, corrosion protection, electromagnetic protection, photovoltaic devices, fabrication of microelectronic devices or machines such as Schottky transitions, sensors and actuators, etc., since the rate of electrochemical reactions is proportional to the electrode surface area.
Conductive nanofibre membranes are also quite suitable for use as porous electrodes in the development of high-performance batteries and fuel cells with polymer electrolyte membranes due to their high porosity and inherently large total surface area. Polymer batteries have been developed for cellular phones to replace conventional bulky lithium batteries [27]. Insulating mats made of polymer fibres can be used as separators in the same batteries or supercapacitors.
Carbon and ceramic fibres are promising materials for water splitting, hydrogen storage, membranes for fuel cells of various designs, electrodes in supercapacitors and dye-sensitive solar cells [9].
CONCLUSIONS
It is evident that EF is a versatile technology capable of creating unique materials with a variety of properties. In spite of the significant scope of research carried out, the high level of applied technical improvements and the wide range of applications where electroformed nanofibres are already used, still there are some challenges:
Safety of technical personnel. The use of high voltage power supplies requires safety training and increased caution when working with equipment. Improved process automation and failsafe components/modules can provide the necessary safety.
Lack of reliable prediction models. There are only a few papers devoted to theoretical prediction of EF outcomes, but they are not universal and cannot include all influential parameters to predict the results of their EF.
When nanofibres are used in composites, there is still a problem of fibre dispersion within the matrix.
It is worth noting that the materials produced by electroforming technology cannot currently be used as structural materials, due to limitations in the reproducibility of geometric dimensions and, as a consequence, mechanical characteristics. The main area belongs to the functional materials.
Despite the existing challenges, electroformed fibre technology is of great interest and has the potential for producing materials with unique properties.
PEER REVIEW INFO
Editorial board thanks the anonymous reviewer(s) for their contribution to the peer review of this work. It is also grateful for their consent to publish papers on the journal’s website and SEL eLibrary eLIBRARY.RU.
Declaration of Competing Interest. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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