Abstract
Electrospun polymer fibers can be used as templates for the stabilization of metallic nanostructures, but metallic species and polymer macromolecules generally exhibit weak interfacial adhesion. We have investigated the adhesion of model copper nanocubes on chemically treated aligned electrospun polyacrylonitrile (PAN) fibers based on the introduction of interfacial shear strains through mechanical deformation. The composite structures were subjected to distinct macroscopic tensile strain levels of 7%, 11%, and 14%. The fibers exhibited peculiar deformation behaviors that underscored their disparate strain transfer mechanisms depending on fiber size; nanofibers exhibited multiple necking phenomena, while microfiber deformation proceeded through localized dilatation that resulted in craze (and microcrack) formation. The copper nanocubes exhibited strong adhesion on both fibrous structures at all strain levels tested. Raman spectroscopy suggests chemisorption as the main adhesion mechanism. The interfacial adhesion energy of Cu on these treated PAN nanofibers was estimated using the Gibbs–Wulff–Kaischew shape theory giving a first order approximation of about 1 J/m2. A lower bound for the system’s adhesion strength, based on limited measurements of interfacial separation between PAN and Cu using mechanically applied strain, is 0.48 J/m2.
Highlights
The filamentary polymer architectures traditionally engendered by the electrospinning process have enabled the development of functional material systems and devices that are underpinned by design manipulations at micron and nanometric scales
An estimate of the adhesion energy was made based on microstructural evidence for nanocube delamination at an applied global strain of 11% as provided by Figure 8, and the following input parameters: nanocube length of 146 ± 10 nm, reported PAN nanofiber modulus of 3 GPa [44], copper modulus of 117 GPa [45], Poisson ratio of 0.3, and a measured crack length, 2a = 83 ± 4 nm
Ascertaining the integrity of interfacial adhesion is pivotal for a sustained functional performance
Summary
The filamentary polymer architectures traditionally engendered by the electrospinning process have enabled the development of functional material systems and devices that are underpinned by design manipulations at micron and nanometric scales. For applications in which the electrospun structures are subjected to mechanical strain (i.e., when being used as water filters where flow causes non-woven membranes to flex) poorly adhered nanoparticles can cause the structure to lose efficacy and lead to potential release of nanoparticles into the environment. Creating both the structure with well adhered nanoparticles of metal and developing a quantitative assessment of the adhesion of said structures will enable improved design for reliability in these systems. We make an approximation of the adhesion energy of the copper nanocubes on the fibers using geometric relationships based on the Gibbs–Wulff–Kaischew model and energy release rates during crack propagation
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