Phase separation of microemulsions plays an important role in many applications such as oil recovery, nanomaterials synthesis, and chemical reactions. However, reversible switching from ionic liquid-based microemulsions to complete oil–water phase separation has not been reported so far. In this work, we developed a novel class of stimuli-responsive microemulsions composed of CO₂-responsive ionic liquids, n-pentanol and water. The microstructures and phase behavior of the microemulsion systems before and after the bubbling of CO₂ were investigated by electrical conductivity, dynamic light scattering, small-angle X-ray scattering, cryogenic transmission electron microscopy, and optical microscopy. It was found that these microemulsions could be reversibly switched from W/O monophase to complete oil–water phase separation upon alternate bubbling and removal of CO₂ at atmospheric pressure. Furthermore, ¹³C NMR spectroscopy was used to understand the CO₂-driven reversible phase separation of the microemulsions. The results suggest that the mechanism behind the reversible phase separation involved the reversible formation of bicarbonate and carbamate from the reaction between CO₂ and the anions of the ionic liquids in the presence of water, which resulted in the increase of ionic strength (or vice versa) in the mixture. Using the microemulsions as microreactors, the phase separation protocol was applied in the Knoevenagel reaction for an efficient coupling of a chemical reaction, product separation, and recycling of the microemulsions.

中文翻译：

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通过CO ₂切换离子液体基微乳液的油水相分离

微乳液的相分离在许多应用中起着重要作用，例如采油，纳米材料合成和化学反应。但是，到目前为止，尚未报道从离子液体基微乳液可逆转换到完全的油水相分离。在这项工作中，我们开发了一类新型的刺激响应性微乳液，由CO ₂响应性离子液体，正戊醇和水组成。CO ₂鼓泡前后微乳液体系的微观结构和相行为通过电导率，动态光散射，小角X射线散射，低温透射电子显微镜和光学显微镜进行了研究。人们发现，在大气压下交替鼓泡并除去CO ₂时，这些微乳状液可以从W / O单相可逆地转换为完全的油水相分离。此外，使用¹³ C NMR光谱了解微乳液的CO ₂驱动可逆相分离。结果表明，可逆相分离的机理涉及CO ₂之间的反应可逆地形成碳酸氢盐和氨基甲酸酯。和离子液体在水存在下的阴离子，导致混合物中离子强度的增加（反之亦然）。使用微乳液作为微反应器，将相分离方案应用于Knoevenagel反应中，以有效耦合化学反应，产物分离和微乳液的回收。