Interfacially stabilized nonaqueous lipid-based foams, which we name here oleofoams, are rarely encountered as opposed to the large number of aqueous foams stabilized by molecular or particulate emulsifiers. There is no case well described in the literature with a convincing characterization of the interfacial contribution to oleofoam stability. Methods for filling this gap are described here, which reach out to a large part of the lipid phase diagram. We bring here complete evidence that lipidic crystals made of a high fraction of fully soluble monoglyceride (MG) in oil do not only adsorb at the oil-air interface but also can easily form a jammed, closely packed layer of crystals around the bubbles of a foam produced by whipping (Pickering effect). Very fine bubbles, soft textures, or firmer ones such as for shaving foams could be obtained, with a high air fraction (up to 75%), which is unprecedented. A thin, jammed layer of crystals on bubbles can cause bubbles to retain nonspherical shapes in the absence of bulk effects for times much longer than the characteristic capillary relaxation time for bare bubbles, which is actual evidence for Pickering-type interfacial stabilization. By comparing to foams obtained by depressurization, we show that whipping is necessary for bubble wrapping with a layer of crystals. The origin of high stability against Ostwald ripening at long times is also discussed. Furthermore, we show that these Pickering whipped foams have rheological properties dominated by interfacial or film contributions, which is of high interest for food and cosmetics applications because of their high moduli. This system can be considered to be a model of the crystallization behavior of MG in oil, which is similar to that in many fats. Our methods are very general in the context of lipid-based foaming, in particular, from food materials, and were used in patent applications.

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The coupled mechanisms of extensional coalescence and subsequent shape relaxation can lead to catastrophic destabilization of moderately concentrated emulsions. We demonstrate that application of local extensional flow through the use of small lateral channels allows controlled, systematic investigation of both single drop pair and propagating (avalanche) coalescence through a chain of drops. Drop-drop collisions and separations were controlled independently, and did not significantly disturb the primary flow. The probability of the first coalescence event was controlled by bulk flow parameters, allowing for systematic investigation of these phenomena. Simulations with COMSOLÒ were used in order to quantify and thus validate various assumptions relating to the flow characteristics of our setup. For the configurations tested, the droplet pair separation speed increased linearly with the lateral channel infusion rate. Flows were laminar and collision conditions remained stable until a first coalescence event between a pair of drops was triggered by the superposed local extensional flow field close to the lateral channels. Results are described in terms of coalescence probability versus separation capillary number (Ca sep ). For all systems tested, an upper limit value Ca * sep was observed, above which coalescence did not occur. The probability and length of upstream coalescence propagation induced by the drop shape relaxation following the initial, triggered event are reported. Drop-drop contact times were varied by injecting fluid using different combinations of lateral channels. Ca * sep shifted to a higher value for a given system as the lubricating film drained for a longer time, which, in addition, increased the probability and length of an avalanche of events. The present results demonstrate how microfluidic tools can be used for systematically mapping the most probable behavior of complex systems with respect to coalescence under well controlled hydrodynamic conditions. In general we observe that larger drops, slower separation and higher surfactant concentration favour extensional coalescence and its propagation, in agreement with earlier published experimental studies.

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