(357a) From Multilayer Films to Nanoscale Fibers: Probing the Connection Between Assembly and Mechanics

Forced assembly via layer multiplication offers the unique opportunity to directly probe the relationship between structural development and deformation behavior under confined conditions. Several multilayer polymeric films have been investigated, including an elastomeric block copolymer (BCP) layered against a rigid thermoplastic, and a semicrystalline polymer layered with high glass transition temperature polyme. Confinement of the cylindrical BCP systems extruded below the order-disorder transition (ODT) resulted in a layer thickness-dependent shift from crazing to shear banding under deformation due to a combination of microdomain orientation, interfacial effects, and thin layer yielding. Microstructure development of a spherical BCP processed above the ODT was shown to vary with confining layer due to interfacial interactions and layer thickness. For the semicrystalline multilayer films, the deformation behavior was observed to shift from axial alignment of the crystalline fraction in the thicker layers to non-uniform mechanics and micronecking mechanisms in the thinner layers.   

More recently, innovations in multilayer coextrusion technology via the combination of horizontal and vertical layering steps have translated to the fabrication of melt-extruded polymeric rectangular fiber mats and composites.  Distinct advantages of this modular approach over other traditional fiber processing techniques include scalability, environmentally-friendly conditions, and the ability to obtain cross-sectional dimensions on the nanoscale.  Specifically, we have manufactured biologically-relevant, high surface poly(caprolactone) (PCL) fiber constructs and achieved tunable fiber dimensions and variations in PCL chain orientation and mechanics via uniform fiber drawing. Surface functionalization of these PCL fibers has also been demonstrated, providing a pathway for functional fiber substrates.  PCL blends have also been manufactured to tailored degradation pathways.  PCL fiber blends and scaffolds are currently being explored. It is envisioned that these materials will impact a range of applications in health care technology.