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Templated Metallic Nanostructures on Electrospun Fibers: Synthesis, Mechanical Characterization and Filtration Application
The functionalization of nonwoven electrospun polymeric fibers with metallic nanostructures has enabled the design of novel nanocomposite materials used in a wide range of applications. In particular, designs based on incorporating established antimicrobial species such as copper and silver have potential applications as antimicrobial filtration membranes, leveraging on the convoluted fiber assembly and high surface area–to–volume ratios of the constitutive fibers. Electroless deposition based on spontaneous electrochemical reactions offers a facile and tunable methodology for surface–confined growth of metallic nanostructures on the non–planar substrate architectures presented by nonwoven electrospun fibers.
Firstly, this work explores, in a broad sense, the effects of two different seed catalyst chemistries, palladium and silver, on the evolution of copper nanoparticles on electrospun polyacrylonitrile fibers. Copper nanoparticle coverage and conformity; deposition kinetics; modifications in the surface chemistry of the PAN fibers; and thermal stability of the resultant nanocomposites were examined. Secondly, qualitative and quantitative assessment of the interfacial adhesion between the copper nanostructures and PAN fibers were undertaken by exploiting the elastic mismatch between both phases during tensile deformation. For copper nanocubes on nanofibers, the adhesion energy is estimated to be between 0.48 J/m2 and 1.0 J/m2 using strain and growth based adhesion models.
Macroscopically, the compliant nature of the nonwoven fiber mats makes them susceptible to out-of-plane deformation during water filtration processes which may alter their size exclusion configuration for effective filtration. A bulge testing device is built and implemented to simulate and characterize hydraulic flow – induced deformation in the electrospun PAN fiber mats. The pressure–deflection relationships of the mats show a sub-linear dependence in contrast to classical continuum materials. The macroscopic mat behavior was governed by the properties of the constituent fibers, with an apparent mat bending rigidity dependent on the fiber diameters.
Lastly, the nonwoven fiber mats functionalized with copper nanoparticles were evaluated for use as potential antimicrobial microfiltration membranes. The fiber mats displayed high water flux and high separation efficiency for model 3 μm particles, with separation factors reaching above 99%.