In an attempt to prepare ultrastable aqueous foams composed
entirely of food-grade ingredients, we describe the foamability and foam stability
of aqueous phases containing either calcium carbonate particles (CaCO3
),
sodium stearoyl lactylate surfactant (SSL), or their mixtures. Techniques
including zeta potential measurements, adsorption isotherm determination,
contact angles and optical and cryo-scanning electron microscopy are used to
probe the interaction between particles and surfactant molecules. Aqueous
dispersions of inherently hydrophilic cationic CaCO3
nanoparticles do not foam
to any great extent. By contrast, aqueous dispersions of anionic SSL, which
forms a lamellar phase/vesicles, foam progressively on increasing the
concentration. Despite their foamability being low compared to that of
micelle-forming surfactant sodium dodecyl sulfate, they are much more stable to
collapse with half-lives (of up to 40 days) of around 2 orders of magnitude
higher above the respective aggregation concentrations. We believe that, in addition to surfactant lamellae around bubbles, the
bilayers within vesicles contain surfactant chains in a solidlike state yielding indestructible aggregates that jam the aqueous films
between bubbles, reducing the drainage rate and both bubble coalescence and gas-transfer between bubbles. In mixtures of
particles and surfactant, the adsorption of SSL monomers occurs on particle surfaces, leading to an increase in their
hydrophobicity, promoting particle adsorption to bubble surfaces. Ultrastable foams result with half-lives of around an order of
magnitude higher again at low concentrations and foams which lose only around 30% of their volume within a year at high
concentrations. In the latter case, we evidence a high surface density