Foamability of PEO-PPO-PEO triblock copolymers (P85 and F108) and role of the foam films

The foamability of two commercial PEO-PPO-PEO triblock copolymers (Synperon ic P85 and F108, ICI) was studied and compared to the properties of single foam films. The volume of a steady-state foam column created with a combine d pneumatic-mechanical device is used as a measure of the copolymers foamab ility. Experiments were carried out at bulk copolymer concentrations corres ponding to full surface coverage, i.e. constant area per molecule, under eq uilibrium conditions. The foamability of F108 solutions was higher than tha t of P85 although the surface activity of both copolymers was similar. The foam volume increases with increasing the bulk copolymer concentration. Hig her electrolyte concentration or lower pH caused the foam volume to diminis h. A pronounced parallelism between the properties of dynamic foams and sin gle microscopic foam films was observed: when thicker single foam films wer e formed (from F108 solutions) the steady-state foam column was higher. The resemblance is especially striking with respect to the factors governing e lectrostatic stabilization (electrolyte concentration and pH) and the trans ition to steric stabilization. Apparently the foamability is determined by the durability of the topmost layer of bubbles as only there foam films or their local elements can attain thickness similar to the equilibrium ones.