Adsorption of Stearic Acid by Carbon

The equations used in the calculations are based on the assumption that the adsorbed molecules are dipoles and are adsorbed in an oriented condition. That the values check is evidence that the proposed theory of dispersion is correct and that the dispersing agent is in an oriented condition on the surface of the filler particle. It is possible to calculate that the center of the dipole axis is 4.2 A˚ngströms from the filler surface. Since this value is but 20 per cent of the length of the stearic acid molecule, the carboxyl group is the chief contributor to its dipole moment. This would imply that the length of the hydrocarbon chain is probably not critical so far as the dispersing properties of a fatty acid are concerned. The mechanism of the successful dispersion of fillers other than carbon black should be essentially the same. The whole theory throws much light on the essential part that the naturally occurring fatty acids and added stearic acid play in the dispersion of carbon black in rubber and explains why the addition of small amounts of stearic acid to rubber, especially to rubbers deficient in the naturally occurring dispersing agents, tends to produce a better and more uniform product.