Nanocarbon/polymer brush materials: synthesis, characterization and application.

Abstract

Nanocarbon materials, specifically graphitic carbon nanofibers (GCNFs) and ultra-dispersed nanodiamond (UDD) particles, have attracted tremendous attention due to their specific nanometer scale structures and unique thermal, mechanical and electrical properties. However, surface-functionalization of GCNFs and UDD particles is necessary to enhance dispersion properties for various applications. In this work, a “grafting from” strategy is successfully employed for synthesis of organic polymer brushes from the surface of GCNFs and UDD particles via the in situ atom transfer radical polymerization (ATRP) technique to prepare nanocarbon/polymer brush materials. Polymerization of (meth)acrylate monomers occurs at GCNFs surface sites covalently derivatized with ATRP initiators to form hydrophobic GCNF-poly(n-butyl acrylate), GCNF-poly(iso-butyl methacrylate), GCNF-poly(tert-butyl acrylate), and GCNF-poly(glycidyl methacrylate) polymer brushes. Acid hydrolysis of the GCNF-poly(tert-butyl acrylate) polymer brush gives a hydrophilic GCNF-poly(acrylic acid) polymer brush. Because of the unique atomic structure of GCNFs, a high surface density of ca. 3 polymer chains/10 nm2 on GCNFs is achieved. Similarly, polymerization of methacrylate monomers on UDD surface gives hydrophobic UDD-poly(iso-butyl methacrylate), UDD-poly(tert-butyl methacrylate), UDD-poly(octodecyl methacrylate), and UDD-poly(glycidyl methacrylate) polymer brushes whereas hydrophilic UDD-poly(methacrylic acid) polymer brush is obtained by acid hydrolysis of a UDD-poly(tert-butyl methacrylate) polymer brush. Surface density of a representative UDD/polymer brush is ca. 5 polymer chains/100 nm2. Carbon nanofiber/interdigitated array circuits fabricated with GCNF/polymer brushes have been evaluated as solid-state gas sensing materials. Analyte vapor detection is observed with chemoselectivities and maximum response sensitivities ranging over five orders of magnitude. Epoxy/nanocarbon nanocomposites are fabricated by incorporating UDD-poly(glycidyl methacrylate) polymer brushes and reactivated GCNF-3,4’-oxydianiline nanofibers in epoxy matrices. Uniform dispersion of UDD particles in epoxy has been achieved and a ca. 302 % increase in hardness is obtained at ca. 13.7 wt% UDD loading in the nanocomposites. Epoxy/nanofiber nanocomposite adhesives are used to bond PMMA or Al specimens and ca. 39 % shear strength increase and ca. 33 % tensile strength enhancement are achieved in PMMA-PMMA joints, respectively.