The Stabilization of Aqueous PEO‐PPO‐PEO Triblock Copolymer Foam

Foam generated by sparging of aqueous solutions of the block copolymers P85 (PEO₂₆‐PPO₃₉‐PEO₂₆), F88 (PEO₁₀₃‐PPO₄₀‐PEO₁₀₃), F127 (PEO₉₉‐PPO₆₅‐PEO₉₉), and L64 (PEO₁₃‐PPO₃₀‐PEO₁₃), has been characterized by foam volume measurements. Uniform wet foam formed, which, after drainage of the major part of the liquid, transformed to polyhedral dry foam. Conductance jumps across the foam column indicated that structural changes occur at a certain liquid fraction. The dry foams of P85 were less stable than those of F88 and F127. The latter copolymers showed similar foam stability over a period of one hour. The L64 foam was very unstable. It is suggested that the stability of the dry foams is determined by the resistance to rupture of the foam films. Foam stability is discussed in relation to earlier studies on surface rheology and to the thickness of thin foam films. A general relationship for all PEOx‐PPOy‐PEOx block copolymers between the dilatational modulus and the foam stability could not be found. However, the ability to form thick adsorption layers, accompanied by steric repulsive forces across foam films, appears to be a general foam‐stabilizing factor. Surface diffusion coefficients of a fluorescent probe in single‐block copolymers foam films are also reported for a brief discussion on Gibbs‐Marangoni stabilization.

Keywords:

• Block copolymer
• polymeric surfactant
• foam stability
• foamability
• drainage rate
• surface diffusion
• surface rheology
• dilatational rheology
• fluorescence recovery after photobleaching
• FRAP

Acknowledgments

The work was supported by funds from The Foundation of Strategic Research, Colloid and Interface Programme, Sweden. We thank the Institute of Food Reasearch, Norwich, UK for use of the FRAP equipment and Thomas Arnebrant for discussions regarding the foaming experiments. Torbjörn Wärnheim is thanked for valuable comments on the manuscript.