Studies on Pigment Dispersion in Water. V.

The Adsorption of Non-ionic Surfactant onto Wet Oxidized Carbon Black

Abstract

The influence of the characteristic properties of carbon black on the adsorption (at 25°C) of non-ionic surfactants from aqueous solution on wet oxidized carbon black was studied.
Polyoxyethylene octyl phenyl ether (OP-n) and polyoxyetylene nonyl phenyl ether (NP-n) in which n indicates the mole number of ethylene oxide were used as the surfactants. The wet oxidization of carbon black (furnace type) was carried out with nitric acid.
Measurements were made on the characteristic properties of these carbon blacks such as the surface area, the specific gravity, the bulk, the pH, the functional groups on the surface, the amount of the total oxygen, the liquid adsorption and the hydrophilicity.
The results obtained were as follow :
In proportion to oxidizing condition, the amount of the total acidic groups (carboxyls and phenolic hydroxyls), that of a strong acidic groups (carboxyls), the total oxygen and the hydrophilicity increased, and the pH value decreased. However, the amount of a weak acidic groups (phenolic hydroxyls) increased by less oxidization (1 N-HNO₃, 50°C), and decreased by more oxidizing condition. The linear relationship was observed between the amount of the total oxygen and the hydrophilicity.
Adsorption of non-ionic surfactants on these carbon blacks followed the Langmuir's isotherm. The amount of adsorption of surfactants on carbon blacks decreased with increase of the total oxygen. In the case of the same lipophilic group of surfactants, the amount of adsorption decreased with increase of n.
The area occupied per a molecule of surfactant calculated from the amount of saturated adsorption was much greater than the value on gas-liquid interface. The area occupied per a molecule was linearly proportional to the hydrophilicity.