Surface-confined synthesis of silver nanoparticle composite coating on electrospun polyimide nanofibers

Abstract

A methodology for fabricating hierarchical nanostructures by surface-confined synthesis of silver nanoparticles on electrospun polyimide nanofibers is reported. Through surface-confined imide cleavage at the dianhydride domain via immersion in an aqueous KOH solution, potassium polyamate coatings of accurately defined thickness are formed (at a rate of 25 nm h -1). By utilizing the ion-exchange capability of the polyamate resin, silver ions are introduced through immersion in an aqueous AgNO 3 solution. Subsequent reduction of the metal ion species leads to the formation of nanoparticles at the fiber surface. Two modes of reduction, chemical and thermal, are investigated in the report, each leading to distinct morphologies of the nanoparticle coatings. Via thermal reduction, a composite surface layer consisting of monodisperse silver nanoparticles (average diameter 5.2 nm) embedded in a re-imidized polyimide matrix is achieved. In the case of chemical reduction, the reduction process occurs preferentially at the surface of the fiber, leading to the formation of silver nanoparticles anchored at the surface, though not embedded, in a polyamic acid matrix. By regulating the modification depth, control of the particle density on the fiber surface is established. In both reduction approaches, the polyimide nanofiber core exhibits maintained integrity. Hierarchical nanostructures based on electrospun polyimide nanofibers with silver nanoparticle composite coatings are fabricated and characterized. By alkaline-induced imide cleavage confined at the surface of the nanofibers, a precursor matrix of defined depth and capability of ion exchange is generated. After silver cation exchange and thermal or chemical reduction, nanoparticle coatings with defined dispersion and morphology are generated at the fiber surface. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.