PRIMARY ADSORPTION DURING FOAM FORMATION.

Foam formation as distinct from foam stability was investigated in respect to the effect of detergent concentration. It was shown that foam volume increases with increasing concentration in much the same way as does the surface tension lowering of the solutions, and similarly gives a marked change in slope of the curve in the region of the critical concentration. Direct determinations of the composition of the surface film adsorbed on the bubbles of a foam indicated that adsorption is much more rapid below than above the critical concentration, and also provided further evidence that adsorbed films for pure detergents are highly expanded but may be condensed by relatively small amounts of an impurity. It is suggested that both foam stability and foam formation depend on the formation of an adsorbed surface film and thus on the thermodynamics of colloidal solutions. The adsorbed film involved in foam stability represents true equilibria whereas foam formation is a dynamic process and thus also may depend on the kinetics of the processes involved in reaching such equilibria. Author