RELATIONSHIP BETWEEN FOAM STABILITY AND SURFACE ELASTICITY FORCES - FATTY-ACID SOLUTIONS

The stability of wet foams of fatty acid solutions (n-pentanoic to n-decanoic acid) in 0.005 N HCl was studied. Retention time values, being a measure of the stability of foams under steady-state conditions, equilibrium surface tension - concentration isotherms sigma-(log c0), values of the surface dilational modulus, and effective elasticity forces E(eff) were determined. The mechanism of foam formation is discussed and the importance of dynamic effects in foam stability is stressed. It is shown that stabilizing forces are connected with actual non-equilibrium coverages of interfaces, and changes in foamability can be correlated with values of the effective elasticity forces. Reasons why the foamability of solutions of the higher members of a homologous series of fatty acids starts to decrease even though their surface activity is successively increasing are also explained.