Layer-by-layer, ultrasonic spray assembled 2D and 3D chemically crosslinked carbon nanotubes and graphene
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Two- and three-dimensional assemblies of carbon nanomaterials such as carbon nanotubes and graphene are necessary to harness their remarkable physicochemical properties in many clean energy, electronics, and biomedical applications. Herein we report a facile, economical, and versatile method for layer-by-layer fabrication of chemically-crosslinked carbon nanomaterial assemblies by ultrasonic spray coating combined with radical-initiated crosslinking reaction. The chemical, surface, and mechanical properties of the carbon nanomaterial coatings were characterized by Raman spectroscopy, atomic force microscopy, scanning- and transmission-electron microscopy, and nano-dynamic mechanical analysis. Our results indicate that the macroscopic 2D assemblies of crosslinked carbon nanotubes or graphene nanoparticles have surface uniformity, are chemically-crosslinked, and are mechanically robust. We further provide proof-of-concept demonstration of fabricating free-standing, porous, 3D single-walled carbon nanotube structures. Taken together, the results opens avenues toward adapting our method to enable 3D printing or additive manufacturing of all-carbon nanomaterial structures.
I. INTRODUCTION
Carbon nanomaterials such as carbon nanotubes and graphene possess interesting and sometimes unique physicochemical properties1 suitable for energy,2 electromagnetic,3 and biomedical4 applications. Manufacturing large macroscopic two- and three-dimensional assemblies of these nanomaterials are required for many of these applications including sensor development,5,6 solar cells,7 electromagnetic shielding,8,9 fuel cells,10 and scaffolding.11 Spray coating, chemical vapor deposition, and vacuum filtration have been explored as methods to deposit two- and three-dimensional assemblies of carbon nanomaterials. However, none of these current technologies have been demonstrated to facilitate layer-by-layer additive manufacturing of three dimensional all-carbon nanomaterial structures or parts.12–16 Among these methods, spray coating is one of the most inexpensive and flexible manufacturing methods for creating thick surface coatings of carbon nanomaterials. Unlike other coating modalities, spray coating does not require a flat substrate, impose specific substrate chemistries for chemical growth of the nanomaterial, or exert high pressures and temperatures on the substrates.17–19 The layer-by-layer approach of spray coating allows for fine control of coating thickness. Also, recent advances in Contributing Editor: Mauricio Terrones a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.472
spray coating have significantly improved surface homogeneity20 and the mechanical properties of spray coated carbon nanomaterial coatings.21 Spray coating has been previously used to fabricate large surface area graphene22 and carbon nanotube20,23 films. The two main methods of spray coating include airbrush spraying techniques and ultrasonic spray coating. Airbrush spray coating involves application of an a
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