Poster, Materials Research Society (MRS), Boston: 26.11.2007 - 30.11.2007
Arrays of polymer nanofibers and microfibers are a versatile platform for a broad range of applications, since polymers combine advantageous mechanical properties, low specific weight, biocompatibility, and durability with outstanding chemical resistivity. For example, arrays consisting of ferroelectric polymer fibers could be used as actuator arrays or as sensor arrays for mechanical excitations. Molding the polymers into ordered porous templates is a potentially attractive access to ordered fiber arrays. The fibers are automatically aligned as their arrangement is determined by that of the template pores. Moreover, oriented crystallization of ferroelectric polymers in the two-dimensional confinement of the pores may enable well-defined polarization switching, which is associated with rotations about C-C bonds in the polymer backbone. Up to now, the release of the fiber arrays requires the destruction of the templates by wet-chemical etching with acids and bases. However, the consumption of templates prevents the up-scaling of template-based methods. The use of bases and acids requires specific precautions regarding work safety and environmental compatibility. An alternative approach to the release of the fibers is their mechanical extraction from the templates that remain thus intact and can be recycled. However, the occurrence of shear forces in the course of the extraction may result in the breakage of a significant portion of the fibers. We have systematically investigated how the occurrence of breakage depends on the mechanical properties of the molded polymer. To this end, we selected polystyrene as a linear stiff model polymer and poly(vinylidene difluoride) (PVDF) as a linear ductile model polymer for ferroelectric PVDF copolymers. Moreover, we studied the extraction of fibers consisting of cross-linked resins with stiff and ductile properties. As mold, we selected macroporous silicon with a pore diameter of 1 µm, various pore depths and non-polar, silanized pore walls. Whereas stiff fibers exhibited a strong tendency to breakage, independent of whether they consisted of linear or cross-linked polymers, fibers consisting of ductile polymers could be extracted even if they had high aspect ratios because of their ability to dissipate the shear forces. Extended, highly ordered arrays of fibers consisting of the ductile cross-linked resin could easily be obtained due to its robust nature. However, mechanical extraction also yields extended, highly ordered arrays of fibers consisting of functional fluoropolymers. Therefore, this non-destructive process enables the fabrication of fiber arrays from recyclable templates and is therefore a promising access to actuator and sensor arrays based on ferroelectric polymer fibers. Mechanical extraction may pave the way to the up-scaling of template-based approaches to the preparation of fiber arrays.