Controlling internal pore structure of porous carbon nanofibers based on the miscibility between polyacrylonitrile matrix and sacrificial polymers

Porous carbon nanofibers were prepared via electrospinning of polyacrylonitrile (PAN)-based blend solutions and effects of miscibility of the blended polymers on pore structure were investigated. Two sacrificial polymers, poly(vinylidene fluoride) (PVDF) and poly(styrene-co-acrylonitrile) (SAN), were chosen as a sacrificial component to yield porosity after carbonization. The miscibility of PAN with each sacrificial polymer was evaluated both theoretically and empirically. Analyzing solubility parameters revealed that PVDF had higher chemical afľinity with PAN due to dipole-dipole interaction than SAN. Lower value of Flory-Huggins interaction parameter of PAN with PVDF (0.52) than with SAN (1.19) quantitatively confirmed the better miscibility of PAN-PVDF. In dynamic mechanical analysis of PAN/ PVDF blend films, individual loss tangent (tan 5) peaks (i.e., glass transition peak) for PAN and PVDF were observed but they were shifted to each other, indicating partial miscibility. In PAN/SAN films, however, the peak shift of PAN was negligible. These results coincided well with the theoretical analysis. After carbonization, the blend nanofibers exhibited high porosity with different pore structures; elongated shape for PVDF and round shape for SAN system. The pore structure discrepancy in the two systems was ascribed to the miscibility difference of each sacrificial polymer with PAN matrix.