Surface and foam properties of polyvinyl alcohol solutions

The surface, film, and foam properties of six polyvinyl alcohols (PVA) with different degrees of hydrolysis (DH) and molecular weights were studied and compared with the properties of nonionic Brij 35 and anionic SLES. Four different foaming methods were employed: the fast foaming method (Bartsch test), intermediate tests (shake test and Ultra Turrax), and slow foaming method (foam rise method) to assess the foamability at various bulk concentrations. The foamability data obtained from different foaming tests, utilizing various surfactant and polymeric concentrations, and differing foaming times, were shown to follow a universal master curve when plotted as relative foamability vs. scaled concentration. A new simple theoretical equation was derived to describe this universal curve, allowing for foamability prediction. The threshold surfactant concentration required to achieve 50% of the maximal foam volume under given conditions (used for scaling the bulk concentration) was found to decrease with foaming time and increase from slow foaming methods to fast foaming methods. When the experimental data are plotted against surface coverage, the results for PVA solutions exhibit intermediate behavior between nonionic surfactants, where a threshold surface coverage of 95% is required to achieve 50% of maximal foamability and anionic surfactants, where 30% surface coverage is sufficient to reach 50% of maximal foamability due to the action of electrostatic repulsion. This intermediate behavior observed in PVA solutions is attributed to the presence of a long-range steric repulsion arising from the adsorption of PVA molecules onto the bubble surfaces. This work advances the foam field by showing that the approach developed in Petkova et al. 2020 can be used for polymeric molecules by deriving a new equation for foamability which is expected to be applicable for wide range of systems.