Impact of zinc salt counterion on poly(ethylene oxide) solution viscosity, conductivity, and ability to generate electrospun MOF/nanofiber composites

Abstract

The effect of seeding poly(ethylene oxide), PEO, aqueous solutions with zinc acetate (ZA) and zinc chloride (ZC) on solution properties (e.g., viscosity and electrical conductivity) and the ability to electrospin nanofibers was investigated. The impacts of the type of Zn counterion and overall salt concentration on solution viscosity and electrical conductivity were correlated to the ability to electrospin nanofibers, as well as the resulting fiber morphology. In dilute PEO solutions, Zn salt addition reduced the PEO hydrodynamic radius ( R h ) and viscosity likely as a result of PEO chain envelopment of Zn cations, while in semi-dilute entangled regimes, Zn salt addition increased R h and viscosity likely due to interactions a single Zn cation with multiple polymer chains. The addition of Zn salts had limited effects on the overlap concentration ( c* ), but increased the entanglement concentration ( c e ), and the presence of either ZA or ZC enabled electrospinning of bead-free fibers at lower PEO concentrations (than without salt) because of the increased electrical conductivity of the solution. However, increasing the ZA concentration in solution had limited effect on fiber diameter and morphology, while raising the ZC concentration in solution resulted in the fusion of fibers into webs and films likely due to charge carryover. The resulting salt-doped PEO nanofibers were used as a template to synthesize a zeolitic imidazolate framework, ZIF-8, through a vapor-deposition approach exploiting the embedded Zn as nucleation sites for heterogeneous growth in a ‘Fiber-first’ strategy. • Aqueous poly(ethylene oxide) solutions were seeded with zinc salts. • Zinc salts, notably Zn acetate, reduced polymer concentration required to spin bead-free fibers. • Zinc chloride, especially at higher loadings, led to electrospun fused webs instead of fibers. • Zinc counterion type impacted solution conductivity and affected bead-free fiber development. • Zinc salt seeding enabled the vapor-phase growth of the zeolitic imidazolate framework ZIF-8.