Substrate induced coagulation (SIC) of nano-disperse carbon black in non-aqueous media: the dispersibility and stability of carbon black in N-methyl-2-pyrrolidinone

Dispersions of carbon black in water and N-methyl-2-pyrrolidinone were investigated with respect to their stability in order to find conditions for the substrate induced coagulation (SIC) process. The SIC process is a dip coating process based on enhanced adsorption of particles or coagulation of dispersions on surfaces which are conditioned with flocculants. Efficient SIC coating requires careful adjustment of the stability of the dispersion; “over-stabilised” dispersions will not show sufficient interaction with the conditioned surfaces. Zeta potentials of carbon black particles in aqueous and non-aqueous solutions were calculated from electrophoretic mobilities determined by phase analysis light scattering (PALS) and the electroacoustic method. The electrophoretic mobilities of carbon black in NMP decreased in magnitude on addition of bis-2-ethylhexyl sodium sulfosuccinate (AOT), which is the opposite effect to that observed in water. This is attributed to the AOT behaving as a normal electrolyte in NMP, with no evidence of the surfactant behaviour that it displays in water.