Dispersion Behavior and Aqueous Foams in Mixtures of a Vesicle-Forming Surfactant and Edible Nanoparticles

Abstract

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 of discrete surfactant-coated particles at bubble surfaces, rendering them stable to coalescence and disproportionation.

Aqueous Foams in the Presence of Surfactant Crystals

“…This is in line with reports on ultra-stable foams in which an armoured layer of solid particles imparts excellent stability to both spherical and non-spherical bubbles. 25,52,53 The same conclusions were drawn from foam studies in series 4 for 15 mM SDS as a function of salt concentration (Figures S13-S16).…”

Egg white protein microgels as aqueous Pickering foam stabilizers: Bubble stability and interfacial properties

“…For cryo-SEM analysis, fresh foams stabilized by EWPM were imaged via an FEI Nova 450 SEM (Eindhoven, The Netherlands), as described by other researchers (Binks, Campbell, Mashinchi, & Piatko, 2015). Briefly, samples were prepared by mounting a small volume of fresh foam onto a copper holder and then placed in liquid nitrogen (-208 ) where the sample was frozen.…”

A gemini surfactant-containing system with abundant self-assembly morphology and rheological behaviors tunable by photoinduction

“…Surfactants can self-assemble into various ordered structures including spherical micelles, 1 vesicles, 2,3 rod or worm-like micelles, [4][5][6][7] as well as liquid crystals. 8,9 These surfactant assemblies with various morphologies have attracted widespread attention because of their wide application in colloids, templates, and so matter materials.…”