Tailoring the Morphologyand Orientation in ImmiscibleBinary Polymer Blends during Melt-Electrospinning

This work constitutes the first comprehensive study on morphology development in melt-electrospun fibers prepared from binary immiscible polymer systems, and in this particular work, we consider a model system composed of polystyrene (PS) and poly(ε-caprolactone) (PCL). The results demonstrate that the levels of alignment and stretching of the dispersed phase in the resulting fibers can be controlled by carefully tuning material properties such as the composition and viscosity ratio of the phases as well as processing parameters such as the applied voltage and drum collector speed. The addition of a PS-<i>b</i>-PCL block copolymer solves the critical issue of process instability caused by morphology coarsening, especially for co-continuous systems, by saturating and stabilizing the PS/PCL interface. As a result, the fibrils formed inside the fibers are more homogeneous and display a smaller diameter, compared to the uncompatibilized system, a topic largely unexplored in fiber-forming processes. By extracting next the PCL phase, highly porous and self-supporting fibers composed of sub-μm, interconnected and intertwined PS fibrils are obtained, with a specific surface 35× higher compared to the initial fibers, an important feature for applications requiring high surface areas and/or textured surfaces such as catalysis, scaffolds for cell culture, filtration, and surface adsorption. Overall, this work exposes for the first time the comprehensive interplay between composition, interface, viscosity ratio, and processing parameters in an elongational flow-field type of environment associated with the formation of polymer microfibers.