Abstract
The stability of concentrated aqueous dispersions of carbon black has been investigated using rheological measurements. The dispersions are stabilised by a series of Synperonic NPE non-ionic surfactants. These materials contain nonyl phenol, 13 units of propylene oxide and between 27 and 175 ethylene oxide units. The adsorption of the surfactants onto carbon black was studied. The adsorption isotherms revealed that the weight of surfactant adsorbing per unit area was approximately constant (or the number of molecules of surfactant adsorbing decreases with increase of the molecular weight of the polyethylene oxide chain). All the surfactants studied stabilised the carbon dispersions. However, those stabilised by the higher molecular weight surfactants showed higher viscosities and elastic moduli than those stabilised by the lower molecular weight materials. With these surfactants it was possible to prepare dispersions with a phase volume of carbon up to 55%. From the elastic and viscous properties of these dispersions it was possible to estimate the thickness of the adsorbed surfactant layer. This agreed closely with that obtained from light scattering. Critical flocculation temperature of the surfactant-stabilised dispersions corresponded to the 0 temperature of the polyethylene oxide, indicating that the mechanism for stabilisation of carbon black is steric in nature.
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