Latent orientation in the skin layer of electrospun isotactic polystyrene ultrafine fibers

Isotactic polystyrene was electrospun into ultrafine fibers from the chloroform or tetrahydrofuran solutions. Tubular or ribbon-like fibers with many small pores were obtained from the chloroform solution. Densely stacked lamellae were formed by annealing them. On the other hand, fibers with many small dents on the skin layer were obtained from the tetrahydrofuran solution. The skin layer changed into the densely stacked lamellae by annealing, while the interior was not crystallized under the utilized annealing condition. These results suggested that the skin layer of the as-spun fiber should contain a finite amount of highly-oriented molecular chains, while the interior may be unoriented. Despite the annealing, the orientation of the chains in the skin layer has been preserved and worked as the nuclei for the densely stacked lamellae.