Oleofoams are dispersions of gas bubbles in a continuous oil phase and can be stabilized by crystals of fatty acids or waxes adsorbing at the oil-air interface. Because excess crystals in the continuous phase form an oleogel, an effect of the bulk rheology of the continuous phase is also expected. Here, we evaluate the contributions of bulk and interfacial rheology below and above the melting point of a wax forming an oleogel in sunflower oil. We study the dissolution behaviour of single bubbles using microscopy on a temperature-controlled stage. We compare the behaviour of a bubble embedded in an oleofoam, which owes its stability to both bulk and interfacial rheology, to that of a bubble extracted from the oleofoam and resuspended in oil, for which the interfacial dilatational rheology alone provides stability. We find that below the melting point of the wax, bubbles in the oleofoam are stable whereas bubbles that are only coated with wax crystals dissolve. Both systems dissolve when heated above the melting point of the wax. These findings are rationalized through independent bulk rheological measurements of the oleogel at different temperatures, as well as measurements of the dilatational rheological properties of a wax-coated oil-air interface.

中文翻译：

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蜡基油泡沫中气泡的稳定性：分离大量油凝胶流变学和界面流变学的影响

油泡沫是连续油相中气泡的分散体，可以通过吸附在油-气界面上的脂肪酸或蜡晶体来稳定。由于连续相中过量的晶体形成油凝胶，因此也预期连续相的体积流变学的影响。在这里，我们评估了在向日葵油中形成油凝胶的蜡的熔点以下和以上的体积和界面流变学的贡献。我们在温控台上使用显微镜研究单个气泡的溶解行为。我们将嵌入在油泡沫中的气泡的行为（其稳定性归功于本体和界面流变学）与从油泡沫中提取并重新悬浮在油中的气泡的行为进行比较，仅凭界面膨胀流变学即可提供稳定性。我们发现在蜡的熔点以下，油泡沫中的气泡是稳定的，而仅涂有蜡晶体的气泡会溶解。当加热到蜡的熔点以上时，两种系统都会溶解。通过在不同温度下对油凝胶进行独立的整体流变测量，以及对涂蜡油-空气界面的膨胀流变特性的测量，这些发现得以合理化。