Tailoring multiporous carbon nanomaterials via electrospun polyacrylonitrile block copolymers: Effects of composition and processing on morphology and porosity

This study presents a method for producing multiporous carbon nanomaterials using high-molecular-weight polyacrylonitrile-b-poly(butyl acrylate) (PAN-b-PBA) block copolymers synthesised via atom transfer radical polymerisation (ATRP). The precursors were processed into nanoparticles or nanofibers by electrospinning. The resulting multiporous structure arises from both the microscale morphology of the electrospun materials and the mesoporous architecture templated by the block copolymer, where the sacrificial degradation of the PBA segment during carbonisation creates additional porosity. This study examines the effects of varying PAN and PBA block lengths, as well as processing parameters, particularly solution ageing, on fibre and particle morphology and porosity. High-molecular-weight PAN-Br is essential for obtaining a spinnable solution capable of forming nanofiber precursors, whereas low-molecular-weight precursors tend to form nanoparticles via electrospray. The results indicate that ageing the electrospinning solution increases the fibre diameter and transitions the structure from smooth-porous to rough-porous, likely due to physical crosslinking and both interand intra-molecular interactions in the concentrated solutions. This transformation was also observed in films cast from the aged solutions. Additionally, a higher PBA content promotes phase separation, enhancing the porosity of both the precursor and carbonised fibres, and yielding materials with increased surface areas. This investigation highlights the critical role of the solution parameters and processing conditions in controlling the structure and properties of carbon nanofibers, offering insights into the tailored design of multi-porous carbon nanomaterials with specific morphologies.