(555f) Effect of Cylindrical Confinement on Self-Assembly of Block Copolymers within Co-Axial Electrospun Fibers

Recently there have been many experimental and computational studies on the effect of cylindrical confinement on the self-assembled structures of block copolymers. In such studies, nanorods are formed by introducing copolymer melts inside cylindrical membrane pores with diameters of ~100nm and lengths of ~1μm. A variety of interesting structures such as helices and concentric rings have been reported; moreover, these structures have been shown to depend on the pore diameter or the interaction between the copolymer and the pore wall. One limitation to the use of nanorods in applications is that their lengths are relatively short. Recently, we have reported on the fabrication of poly(styrene-b-isoprene) (PS-b-PI) diblock copolymer nanofibers using the electrospinning process. Although phase separated structures have been obtained in electrospun fibers of both asymmetric and symmetric block copolymers, we were unable to induce long-range structural order because annealing the nanofibers above the glass transition temperature (T_g) resulted in melting and therefore loss of the fiber integrity. To overcome this limitation of thermal treatment, we extended the electrospinning process to fabricate co-axial nanofibers where a PS-b-PI core is enveloped by a silica sheath. With this thermally stable sheath, we can anneal at temperatures well above the T_g. Using transmission electron microscopy, we observed PS-b-PI self-assembled structures that, we believe, are strongly affected by cylindrical confinement. A comparison was made between the structures of the co-axial nanofibers and nanorods. The effects of PI volume fraction and molecular weight on confined assembly of electrospun fibers will also be presented.