Aqueous and Oil Foams Stabilized by Surfactant Crystals: New Concepts and Perspectives

Abstract

Surfactant crystals can stabilize liquid foams. The crystals are adsorbed at bubble surfaces, slowing down coarsening and coalescence. Excess crystals in the liquid channels between bubbles arrest drainage, leading to ultrastable foams. The melting of crystals upon raising the temperature allows thermoresponsive foams to be designed. In the case of oil foams, the stabilization by crystals received substantial renewed interest in the last 5 years due to their potential applications, particularly in the food industry. For aqueous foams, several reports exist on foams stabilized by crystals. However, these two kinds of liquid foams possess similarities in terms of stabilization mechanisms and the design of surfactant crystal systems. This field will certainly grow in the coming years, and it will contribute to the engineering of new soft materials not only for food but also for cosmetics, pharmaceuticals, and biomedical applications.

Application of X-ray Microcomputed Tomography for the Static and Dynamic Characterization of the Microstructure of Oleofoams

“…In fact, adsorbed fat crystals at air/oil interfaces can prevent air diffusion and hence disproportionation of air bubbles. 1 , 2 …”

“…Oleofoams are an emerging type of soft matter with remarkable potential for application in pharmaceuticals, cosmetic, care, and food products. 1 , 2 They comprise an oil continuous phase and a dispersed gas phase that is stabilized by adsorbed solid particles or molecular surfactants. In contrast to aqueous foams, their production is more challenging, due to the limited availability of suitable stabilizers for air/oil interfaces.…”

“… 3 , 4 Nevertheless, over the last 5 years, some publications appeared, which describe the use of fat crystals to produce oleofoams with a high air volume fraction and outstanding thermodynamic stability, up to several months. 1 , 2 …”

Back to the future: Fatty acids, the green genie to design smart soft materials

“…For non‐aqueous systems, the low‐surface tension makes the adsorption of hydrocarbon‐based surfactants energetically unfavorable. One way to produce and stabilize non‐aqueous foams is to use surfactant crystalline particles, which can adsorb at the air‐liquid surface (Fameau & Binks, 2021). Fatty acids crystalline particles are efficient non‐aqueous foam stabilizers (Binks et al, 2016; Fameau et al, 2021).…”

“…At sufficient concentration, they can lead to the formation of gels by the immobilization of the liquid in a three‐dimensional network, due to the interactions between particles (Marangoni, 2012). These surfactant crystalline particles have also been recently shown to be an efficient foam stabilizer by adsorbing at bubbles surface leading to foams with unusual properties (Fameau et al, 2021; Fameau & Binks, 2021). They also have been used as solid smart particles to design liquid marbles (Mahmoudi Salehabad et al, 2019).…”