Revisiting the calcination-induced multi-layer hollowing of electrospun solid fibers
The process of transforming solid electrospun fibers into coaxial hollow structures (wire-in-tubes) by controlled calcination has led to a variety of novel nano/microstructures with high aspect ratios and extended open channels. The governing mechanism of the calcination-induced structural evolution, however, remains controversial. Herein, we present our interpretation of the structural transformation from solid electrospun fibers into wire-in-tubes (single- and double-layer tubes) in a TiO2–VxOy system. We believe that the structural evolution is the result of a delamination of the crystalline crust from the underneath amorphous layer due to the different degrees of volume contraction, where the lock-up of the crystalline crust and the fluidity of the remaining organics plays vital roles. By tuning the calcination parameters, including the atmosphere, temperature and heating rate, the structural features of the hollow product fibers can be modulated.