The confinement of colloidal particles at liquid interfaces offers many opportunities for materials design. Adsorption is driven by a reduction of the total free energy as the contact area between the two liquids is partially replaced by the particle. From an application point of view, particle-stabilized interfaces form emulsions and foams with superior stability. Liquid interfaces also effectively confine colloidal particles in two dimensions and therefore provide ideal model systems to fundamentally study particle interactions, dynamics, and self-assembly. With progress in the synthesis of nanomaterials, more and more complex and functional particles are available for such studies. In this Account, we focus on poly(N-isopropylacrylamide) nanogels and microgels. These are cross-linked polymeric particles that swell and soften by uptaking large amounts of water. The incorporated water can be partially expelled, causing a volume phase transition into a collapsed state when the temperature is increased above approximately 32 °C. Soft microgels adsorbed to liquid interfaces significantly deform under the influence of interfacial tension and assume cross sections exceeding their bulk dimensions. In particular, a pronounced corona forms around the microgel core, consisting of dangling chains at the microgel periphery. These polymer chains expand at the interface and strongly affect the interparticle interactions. The particle deformability therefore leads to a significantly more complex interfacial phase behavior that provides a rich playground to explore structure formation processes. We first discuss the characteristic "fried-egg" or core-corona morphology of individual microgels adsorbed to a liquid interface and comment on the dependence of this interfacial morphology on their physicochemical properties. We introduce different theoretical models to describe their interfacial morphology. In a second part, we introduce how ensembles of microgels interact and self-assemble at liquid interfaces. The core-corona morphology and the possibility to force these elements into overlap upon compression results in a complex phase behavior with a phase transition between microgels with extended and collapsed coronae. We discuss the influence of the internal particle architecture, also including core-shell microgels with rigid cores, on the phase behavior. Finally, we present new routes for the realization of more complex structures, resulting from multiple deposition protocols and from engineering the interaction potential of the individual particles.

中文翻译：

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流体界面处的聚N-异丙基丙烯酰胺纳米凝胶和微凝胶。

胶体颗粒在液体界面处的封闭为材料设计提供了许多机会。由于两种液体之间的接触面积被颗粒部分取代，因此总自由能的减少推动了吸附。从应用的角度来看，颗粒稳定的界面形成具有优异稳定性的乳液和泡沫。液体界面还可以有效地将胶体颗粒限制在二维范围内，因此提供了理想的模型系统，可以从根本上研究颗粒的相互作用，动力学和自组装。随着纳米材料合成的进展，越来越多的复杂和功能性颗粒可用于此类研究。在此帐户中，我们重点研究聚（N-异丙基丙烯酰胺）纳米凝胶和微凝胶。这些是通过吸收大量水而溶胀和软化的交联聚合物颗粒。当温度升高到大约32°C以上时，混入的水可能会部分排出，导致体积相转变为塌陷状态。吸附在液体界面上的软微凝胶在界面张力的影响下会发生明显变形，并呈现出超过其整体尺寸的横截面。特别地，在微凝胶核心周围形成明显的电晕，其由在微凝胶外围的悬空链组成。这些聚合物链在界面处膨胀并强烈影响粒子间的相互作用。因此，粒子的可变形性导致界面相行为明显更为复杂，从而为探索结构形成过程提供了一个丰富的场所。我们首先讨论吸附到液体界面的单个微凝胶的特征“煎蛋”或“核心电晕”形态，并评论这种界面形态对其物理化学性质的依赖性。我们介绍了不同的理论模型来描述它们的界面形态。在第二部分中，我们介绍微凝胶团如何在液体界面相互作用和自组装。核芯电晕的形态以及在压缩时迫使这些元素重叠的可能性会导致复杂的相行为，并在具有扩展和塌陷电晕的微凝胶之间发生相变。我们讨论了内部颗粒结构（包括具有刚性核的核壳微凝胶）对相行为的影响。最后，