(635g) Confined Assembly of Block Copolymer/Nanoparticle Composites: Multi-Axial Electrospinning and Coarse-Grained Molecular Dynamics Simulation

To understand our recent observation of confined self-assembly of block copolymer (BCP)/nanoparticle (NP) composites in electrospun nanofibers, coarse-grained molecular dynamics (MD) simulation of model systems of BCP/NP in cylindrical confinement has been carried out. Two different arrangements of cylindrical confinement were studied to mimic coaxial and triaxial electrospinning where self-assembling materials are placed in the core confined by the sheath, and in the middle layer sandwiched by core and outermost layer, respectively. We considered NPs with selective interactions towards one of the blocks of a model diblock copolymer to represent magnetite nanoparticles in PS-b-PI in experiments. First, symmetric and asymmetric BCP systems with and without NP in the coaxial configuration was investigated. For the symmetric BCP system, non-selective and selective interaction of BCP in the core with the wall gave rise to stacked lamellae along the cylinder axis and concentric rings, respectively, which were observed in coaxial electrospun nanofibers of symmetric PS-b-PI. By placing selective NPs in the matrix or the dispersed domain of asymmetrical BCP systems, we confirmed that it is the PI phase that has the stronger attraction towards both silica wall and magnetite NPs rather than the PS phase, and thus the PI with magnetite is placed next to the wall in our own coaxial experimental results. Secondly, the study of tri-axial systems where BCP/NP is sandwiched by inner and outer walls revealed that the effect of selective wall interactions yields complex morphologies. This tri-axial study also supports the evidence of the microphase segregation of PI towards silica wall. Finally, the tri-axial study was extended to MD simulation result of BCP/homopolymer blend system to verify confined assembly observed in triaxial electrospun fibers. The current study demonstrates that coarse-grained MD simulation can prove to offer a useful guidance in formation of self assembled structures in coaxial and tri-axial electrospinning of BCP/NP.