Responsive Emulsions Stabilized by Stimuli-Sensitive Microgels: Emulsions with Special Non-Pickering Properties
Responsive Emulsions Stabilized by Stimuli-Sensitive Microgels: Emulsions with Special Non-Pickering Properties
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DOI：
10.1021/la302331s
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发表时间：
2012-12-18
期刊：
影响因子：
3.9
通讯作者：
Richtering, Walter
中科院分区：
文献类型：
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作者：
Richtering, Walter
最近的研究揭示了微凝胶稳定的响应性乳液的独特性质，并将微凝胶与经典的刚性粒子Pickering稳定剂进行了比较。微凝胶是一种高度膨胀的亲冻性颗粒，在油水界面上变形，仅少量突出到油相中。温度和pH敏感型微凝胶使我们能够制备温度和pH敏感型乳液，从而使我们能够根据需要制备和打破乳液。虽然这种乳液对pH很敏感，但液滴的稳定并不是由于静电斥力，相反，界面的粘弹性似乎决定了液滴的稳定性。由于微凝胶柔软、多孔，在界面上的表现与刚性颗粒截然不同：它们变形并强烈扁平，特别是在水包油乳状液的情况下。对于水包油和油包水乳液，微凝胶主要位于界面的水侧。与刚性固体颗粒不同，微凝胶在油水界面的行为不仅取决于界面张力，还取决于微凝胶的界面张力、膨胀、弹性和变形性之间的平衡，这一点需要考虑。显然，在Pickering乳液中，作为柔软、多孔颗粒的微凝胶与经典的刚性胶体稳定剂有很大的不同，我们建议在使用膨胀微凝胶时避免使用术语Pickering乳液。微凝胶稳定的乳液需要开发新的理论模型来了解其性质。它们为新的复杂应用打开了大门。
Recent studies revealing the unique properties of microgel-stabilized responsive emulsions are discussed, and microgels are compared to classical rigid-particle Pickering stabilizers. Microgels are strongly swollen, lyophilic particles that become deformed at the oil-water interface and protrude only a little into the oil phase. Temperature- and pH-sensitive microgels allow us to prepare temperature- and pH-sensitive emulsions and thus enable us to prepare and break emulsions on demand. Although such emulsions are sensitive to pH, the stabilization of droplets is not due to electrostatic repulsion, instead the viscoelastic properties of the interface seem to dominate droplet stability. Being soft and porous, microgels behave distinctly differently from rigid particles at the interface: they are deformed and strongly flattened especially in the case of oil-in-water emulsions. The microgels are located mainly on the water side of the interface for both oil-in-water and water-in-oil emulsions. In contrast to rigid, solid particles, the behavior of microgels at oil water interfaces does not depend only on the interfacial tension but also on the balance among the interfacial tension, swelling, elasticity, and deformability of the microgel, which needs to be considered. It is obvious that microgels as soft, porous particles are significantly different from classical rigid colloidal stabilizers in Pickering emulsions and we suggest avoiding the term Pickering emulsion when swollen microgels are employed. Microgel-stabilized emulsions require the development of new theoretical models to understand their properties. They open the door to new sophisticated applications.