Adsorption kinetics and nanostructure development during layer by layer assembly of graphene nanoplatelets and amorphous carbon nanospheres

Nanostructure evolution and adsorption kinetics during carbon nanoparticle layer by layer (LbL) assembly are investigated for thin film coating applications that require high through-plane electrical conductivity. Two types of nanoparticles are evaluated: 5-10 nm thick stacks of graphene sheets (graphene nanoplatelets) and 20 nm diameter amorphous carbon spheres. Electrostatic interactions between the carbon nanoparticles and a cationic polyacrylamide binder are systematically altered by varying the carbon nanoparticle suspending media composition and quantified with electrophoretic mobility zeta potential (ζ) measurements. Suspension pH is used to control the nanoparticle surface charge density through dissociation of hydrolyzed surface groups while the addition of alcohol is used to enhance electrostatic interactions by altering the dielectric constant of the medium. Alcohol and pH are found to have opposing effects with respect to the packing density and through-plane conductivity of the polyelectrolyte-nanoparticle structures formed. Such behavior is ascribed to steric effects associated with the heterogeneous dispersion of weakly acidic functional groups on the hydrolyzed carbon nanoparticles surface; whose dissociation regulates electrostatic interaction with the cationic polyelectrolyte binder during LbL assembly. Complete dissociation of these groups in the absence of alcohol yields more densely packed polyelectrolyte-nanoparticle structures with as much as 40% reduction in through-plane conductivity.