Liu Yu, Binks Bernard P
Department of Chemistry, University of Hull, Hull HU6 7RX, UK.
Department of Chemistry, University of Hull, Hull HU6 7RX, UK.
J Colloid Interface Sci. 2021 Jul 15;594:204-216. doi: 10.1016/j.jcis.2021.03.021. Epub 2021 Mar 10.
Can a mixture of sucrose ester surfactant in vegetable oil be aerated to yield stable oleofoams? Is foaming achievable from one-phase molecular solutions and/or two-phase crystal dispersions? Does cooling a foam after formation induce surfactant crystallisation and enhance foam stability?
Concentrating on extra virgin olive oil, we first study the effect of aeration temperature and surfactant concentration on foamability and foam stability of mixtures cooled from a one-phase oil solution. Based on this, we introduce a strategy to increase foam stability by rapidly cooling foam prepared at high temperature which induces surfactant crystallisation in situ. Differential scanning calorimetry, X-ray diffraction, infra-red spectroscopy, surface tension and rheology are used to elucidate the mechanisms.
Unlike previous reports, both foamability and foam stability decrease upon decreasing the aeration temperature into the two-phase region containing surfactant crystals. At high temperature in the one-phase region, substantial foaming is achieved (over-run 170%) within minutes of whipping but foams ultimately collapse within a week. We show that surfactant molecules are surface-active at high temperature and that hydrogen bonds form between surfactant and oil molecules. Cooling these foams substantially increases foam stability due to both interfacial and bulk surfactant crystallisation. The generic nature of our findings is demonstrated for a range of vegetable oil foams with a maximum over-run of 330% and the absence of drainage, coalescence and disproportionation being achievable.
植物油中的蔗糖酯表面活性剂混合物能否被充气以产生稳定的油泡沫？从单相分子溶液和/或两相晶体分散体中能否实现发泡？泡沫形成后冷却是否会诱导表面活性剂结晶并增强泡沫稳定性？
我们主要研究特级初榨橄榄油，首先研究充气温度和表面活性剂浓度对从单相油溶液冷却的混合物的发泡性和泡沫稳定性的影响。在此基础上，我们引入了一种策略，即通过快速冷却在高温下制备的泡沫来提高泡沫稳定性，这会原位诱导表面活性剂结晶。使用差示扫描量热法、X射线衍射、红外光谱、表面张力和流变学来阐明其机制。
与之前的报道不同，当充气温度降低到包含表面活性剂晶体的两相区域时，发泡性和泡沫稳定性都会降低。在单相区域的高温下，搅拌几分钟内即可实现大量发泡（膨胀率达170%），但泡沫最终会在一周内坍塌。我们表明，表面活性剂分子在高温下具有表面活性，并且表面活性剂和油分子之间会形成氢键。由于界面和本体表面活性剂结晶，冷却这些泡沫会显著提高泡沫稳定性。我们的研究结果的普遍性在一系列植物油泡沫中得到了证明，其最大膨胀率为330%，并且可以实现不发生排水、聚结和歧化现象。
