Metallic Supports Accelerate Carbonization and Improve Morphological Stability of Polyacrylonitrile Nanofibers during Heat Treatment

Abstract

Electrospun poly(acrylonitrile) (PAN) nanofibers are typical precursors of carbon nanofibers. During stabilization and carbonization, however, the morphology of pristine PAN nanofibers is not retained if the as-spun nanofiber mats are treated without an external mechanical force, since internal stress tends to relax, causing the whole mats to shrink significantly, while the individual fibers thicken and curl. Stretching the nanofiber mats during thermal treatment, in contrast, can result in fractures due to inhomogeneous stress. Previous studies have shown that stabilization and carbonization of PAN nanofibers electrospun on an aluminum substrate are efficient methods to retain the fiber mat dimensions without macroscopic cracks during heat treatment. In this work, we studied different procedures of mechanical fixation via metallic substrates during thermal treatment. The influence of the metallic substrate material as well as different methods of double-sided covering of the fibers, i.e. sandwiching, were investigated. The results revealed that sandwich configurations with double-sided metallic supports not only facilitate optimal preservation of the original fiber morphology but also significantly accelerate the carbonization process. It was found that unlike regularly carbonized nanofibers, the metal supports allow complete deoxygenation at low treatment temperature and that the obtained carbon nanofibers exhibit increased crystallinity.

Magnetic Carbon Nanofiber Mats for Prospective Single Photon Avalanche Diode (SPAD) Sensing Applications

“…In CLSM micrographs, the color change looks different, from light gray ( Figure 3 a) to brown ( Figure 3 b) after stabilization, and carbonized nanofiber mats ( Figure 3 c) look gray with the light brown again (see Figure 3 e,f). Interestingly, the color brown remains visible during carbonization at 600 °C, which is atypical compared to previous studies [ 15 , 83 ]. The reason for this is probably that the Fe 3 O 4 particles in the sample carbonized at 600 °C are visible, which is not the case when pure PAN is carbonized and normally represents light gray color of the surfaces of the nanofiber mat in CLSM image [ 15 , 83 ].…”

“…Interestingly, the color brown remains visible during carbonization at 600 °C, which is atypical compared to previous studies [ 15 , 83 ]. The reason for this is probably that the Fe 3 O 4 particles in the sample carbonized at 600 °C are visible, which is not the case when pure PAN is carbonized and normally represents light gray color of the surfaces of the nanofiber mat in CLSM image [ 15 , 83 ]. This assumption is confirmed in further CLSM images, because even at higher carbonization temperatures like 800 °C and 1000 °C, the Fe 3 O 4 particles are still faintly visible as light brown dots.…”

“…Polyacrylonitrile (PAN) polymer is often used to prepare nanofiber mats [ 12 ] as it exhibits water-resistant properties and is applicable in many defined areas requiring this property, such as water purification, filtration, or medical areas [ 13 , 14 ]. In addition, PAN is often used for the production of carbon nanofibers, as it is known to have a high carbon yield [ 15 , 16 ]. Carbon nanofibers exhibit high electrical conductivity, low density, as well as high specific strength.…”

“…In our previous study by Döpke et al, PAN/magnetite nanofiber mats were prepared and the magnetic properties were investigated [ 2 ]. Here, networks of magnetic nanofibers with beads that can be used to transport data in the form of domain walls moving along them and combined with objects that could be used to store data and transport [ 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 …”

The Possibility of Reuse of Nanofiber Mats by Machine Washing at Different Temperatures

“…Electrospinning technology provides an easy way to produce nanofiber mats [8,9] for various purposes, from a wide range of biobased and synthetic polymers [10][11][12] and admixtures of particles [13,14], etc. Using electrospinning technology, nanofiber mats can be produced easily and cost-effectively for use in electronics [15], battery storage [13,16], medical and biotech-nology [17], water and air filtration [18], protective clothing [19,20], tissue engineering [21] and other applications.…”