Stabilization and Carbonization of PAN Nanofiber Mats Electrospun on Metal Substrates

Abstract

Polyacrylonitrile (PAN) nanofiber mats are typical precursors for carbon nanofibers. They can be fixed or even elongated during stabilization and subsequent carbonization to gain straight, mechanically robust carbon nanofibers. These processes necessitate additional equipment or are—if the nanofiber mats are just fixed at the edges—prone to resulting in the specimens breaking, due to an uneven force distribution. Hence, we showed in a previous study that electrospinning PAN on aluminum foils and stabilizing them fixed on these substrates, is a suitable solution to keep the desired morphology after stabilization and incipient carbonization. Here, we report on the influence of different metallic and semiconductor substrates on the physical and chemical properties of the nanofiber mats after stabilization and carbonization at temperatures up to 1200 °C. For stabilization on a metal substrate, an optimum stabilization temperature of slightly above 240 °C was found, approached with a heating rate of 0.25 K/min. Independent from the substrate material, SEM images revealed less defect fibers in the nanofiber mats stabilized and incipiently carbonized on a metal foil. Finally, high-temperature carbonization on different substrates is shown to allow for producing metal/carbon nano-composites.

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

“…Electrospinning on an aluminum substrate, followed by stabilization and carbonization in this configuration (AL-C) or with an additional aluminum support in a sandwich configuration (AL-SW2-C), also helped to avoid a large increase in the fiber diameter. This confirms the previously [25][26][27] suggested solution for the production of relatively straight carbon nanofibers electrospun and heat-treated on aluminum substrates.…”

“…The following spinning parameters were chosen: voltage 80 kV, resulting current 0.1 mA, nozzle diameter 0.9 mm, electrode-substrate distance 240 mm, carriage speed 100 mm/s, substrate speed 0 mm/min, relative humidity 32%, and temperature in the spinning chamber 22 • C. The spinning duration was chosen as 30 min. Spinning and solution parameters were identical to those applied in previous studies [26,27].…”

“…However, these approaches may lead to macroscopic fractures in the nanofiber mats due to the uneven force distribution. This is why previous studies focused on the possibility of stabilizing PAN nanofiber mats, electrospun onto aluminum foils or other substrates, which offer mechanical support during the first stages of heat treatment [25][26][27]. It was found that while stabilizing on a substrate could indeed partially prevent the nanofibers from undesired morphological changes, most substrate parameters did not significantly influence the resulting nanofibers.…”

“…In a previous study [27], 500 • C was found to be ideal for obtaining straight nanofibers without significant morphological changes using aluminum substrates. In addition, morphological changes occur predominantly in the temperature range below 500 • C. Since aluminum with a melting temperature of 650 • C is not suitable for high-temperature carbonization, it is only used to bridge this critical temperature range.…”

Investigation of metallic nanoparticle distribution in PAN/magnetic nanocomposites fabricated with needleless electrospinning technique

“…This process is crucial to prevent melting or fusing of the fibers. Another way to prevent nanofiber contraction during stabilization is electrospinning on metallic substrates [34]. Due to the conductivity of the metallic substrate, the nanofibers adhere to the surface and cannot shrink [35].…”