(5bi) Self-Assembled Structures within Electrospun Nanofibers

We have fabricated poly(styrene-b-isoprene) (PS-b-PI) nanofibers using the electrospinning process. The goal of this investigation was to understand how the electrospinning processing conditions and various annealing treatments affected the development of the self-assembled structures within the fibers. SEM, SAXS and TEM techniques were used to analyze the fiber morphology and the internal structure. We found that the as-spun fibers exhibited microphase separation, but lacked long-range order. This is possibly due to the strong elongational force and short residence time inherent in the electrospinning process. In an attempt to get more ordered structures, we thermally annealed the nanofibers. To be able to heat them above the glass transition temperature (T_g), we developed a co-axial electrospinning set-up where we encased the PS-b-PI within a thermally stable sheath. Upon annealing at temperatures above the T_g, we observed the formation of interesting self-assembled structures similar to those recently reported in the literature for block copolymers formed under cylindrical confinement. In anticipation of making nanofibers for sensor applications, we modeled diblock copolymer / nanoparticle composites with molecular dynamics simulations. Specifically, we studied the effects of shear flow on the self-assembled structures.