The surface dilational viscosity of polypropylene glycol solutions and its influence on water flow and foam behavior

The non-equilibrium interfacial properties of a homologous series of aqueous polypropylene glycol solutions (400–2000 g/mol) were investigated as a function of concentration to understand their role in determining foam behavior. The overflowing cylinder technique was used to generate a continually expanding surface. Static and dynamic surface tensions, as well as the surface velocity of the expanding surface, were characterized. The surface dilational viscosity was compared to water flow rate and foam retention time of the polypropylene glycol solutions reported in the literature. This study suggests that the surface dilational viscosity is a key parameter in the Marangoni effect which retards water drainage, resulting in wetter foam and increased water recovery across flowing foams.