Superhydrophobic Surfaces Formed Using Layer-by-Layer\nSelf-Assembly with Aminated Multiwall Carbon Nanotubes

Abstract

A convenient and simple route to functionalized multiwall carbon nanotubes (MWNTs) using the reaction of the\namine (NH) groups of polyethyleneimine (PEI) with MWNTs in <i>N</i>,<i>N</i>-dimethylformamide (DMF) at 50 °C is described.\nThe product functionalized MWNTs (MWNT-NH-PEI) contain 6−8% by weight PEI based on elemental analysis,\nthermal gravimetric analysis, and titration. The products form stable emulsions in water below pH 9 and can be\nderivatized to form alkylated MWNTs that are dispersible in organic media. Such MWNT-NH-PEI nanoparticles can\nalso be used in covalent or ionic layer-by-layer assembly to form nanocomposite thin films on functionalized polyethylene\n(PE) films and powders. Such nanocomposite films were analyzed by contact angle analysis, atomic force microscopy\n(AFM), and confocal Raman microscopy. These analyses show that these superhydrophilic surfaces have micro/nanoroughness with a roughly uniform distribution of MWNT nanoparticles. Superhydrophobic PE films can be\nformed either from ionic layer-by-layer self-assembly of MWNT-NH-PEIs and poly(acrylic acid) or from covalent\nlayer-by-layer self-assembly of MWNT-NH-PEIs and Gantrez if the final graft is acrylated with a mixed anhydride\nprepared from ethyl chloroformate and octadecanoic acid. The resulting octadecylated surface produced by five\ncovalent layer-by-layer deposition steps has a water contact angle of 165° and a sliding angle of less than 5°. The\ncorresponding surface produced by five ionic layer-by-layer deposition steps has a water contact angle of 155° but\nexhibits water pinning. The ionically assembled nanocomposite graft is labile under acidic conditions. The covalently\nassembled graft is more chemically robust.