Smart Non-Aqueous Foams from Oleogel based on Lipid Materials

International audienceRecently, responsive aqueous foams, which can be manipulated using external fields, have been obtained from various systems such as surfactants, particles or polymers [Fameau, 2013]. Here, we present a novel class of responsive foams obtained from oleogel based on lipid materials. These non-aqueous foams are stabilized by lipid crystals dispersed in sunflower oil (Figure 1). The presence of lipid crystals in oil both entraps bulk liquid oil leading to oleogel and protects the air bubbles against coalescence and coarsening.In the first step; we studied the oleogel properties as a function of both the lipid chain length and its concentration. By using WAXS, DSC, microscopy and rheological measurements, we determined the structure of the lipid crystals, their thermodynamic and rheological properties as a function of the temperature. We demonstrated that the crystals can reversibly be formed and melted by tuning the temperature which in turn depends on the lipid chain length and its concentration in the oil. In the second step, we investigated the foamability and foam stability of these lipid crystals dispersed in oil with temperature. We correlated the evolution of these properties with the formation and melting of the crystals. Foamability was directly linked to the concentration of lipid crystals. Foam could not be produced above the melting temperature of the crystals, since no crystal was present in the oil to stabilize the air bubbles. Below the melting temperature, foams were stable for months due to the layer of crystals surrounding the bubbles protecting them against coalescence and coarsening. However, above the melting temperature, crystals melted and bubbles disappeared instantaneously. The formation and melting of the crystals inside the foam are reversible. The foam can then be easily stabilized and destabilized on demand by simply melting the crystals surrounding the bubbles upon heating. To our knowledge, such foams obtained from oleogel are the first example of responsive non-aqueous foams. These systems obtained from lipids can find application in a wide range of industrial applications in pharmaceutical and cosmetic