A high molecular-weight polymer not a small molecule or surfactant is superior for dispersing carbon nanotubes in water when processing a waterborne, polymeric nanocomposite. A polymeric dispersant above its entanglement molecular weight creates a brush structure on the nanotube that increases molecular friction on entangles with the matrix, yielding increased adhesion energy, as shown, along with greater toughness and energy dissipation during deformation. A dispersant can thereby be used to tune a nanocomposite's mechanical properties.