Synergy between Composite Nanoparticles and Saponin β-Escin to Produce Long-Lasting Foams

A synergy between poly(vinylpyrrolidone) (PVP)-coated silica nanoparticles (CPs) and saponin β-escin was exploited to develop long-lasting foams using low component concentrations. Individually, foams stabilized by either CPs or saponin β-escin suffered from bubble coarsening and bubble coalescence, respectively. In contrast, the successful synergy of CPs and saponin β-escin was shown to provide excellent foamability and foam stability, with no direct interaction between the two components. The CPs aggregated strongly in 0.55 M Na2SO4 and formed a porous stabilizing network, hindering bubble coalescence but not bubble coarsening. However, in foams stabilized by saponin β-escin and CPs, the bubble interface was saturated by the two components, with CPs forming thick liquid lamellae between bubbles, hindering liquid drainage and bubble coalescence, and saponin β-escin (added at 0.01 wt %) saturating the pore space in the CP interfacial network to retard bubble coarsening. Adding saponin β-escin as a co-foaming agent, the foamability and foam lifetime were increased by ∼2.5 and ∼4 times, respectively, compared to CP-stabilized foams.