High internal phase Pickering emulsions (HIPPEs) have received increasing attention recently due to their unique viscosity and rheological characteristics. Nevertheless, their high viscosity might limit their applications in the transportation field. Developing HIPPEs with adjustable stability, controllable viscosity, and easy preparation remains a challenge. Here, we reported an O/W HIPPEs costabilized by a novel CO₂-switchable nonionic surfactant (NCOEO₃) and hydrophilic silica nanoparticles with low concentrations, facilitated by the adsorption of NCOEO₃ onto the nanoparticles through hydrogen bonding. Upon increasing the NCOEO₃ concentration to 1 mM, the oil volume fraction of the emulsions can be adjusted to 92%. The HIPPEs demonstrate remarkable CO₂ responsiveness due to the reversible transformation of the surfactant structure between nonionic (NCOEO₃) and cationic-nonionic (N⁺COEO₃) forms triggered by CO₂. This responsiveness enables efficient demulsification at room temperature as well as the recycling and recovery of the surfactant within the aqueous phase. More importantly, the inverted highly viscous HIPPEs could be reversibly converted into flowable low viscous HIPPEs through the CO₂ trigger. This research offers an effective method for preparing intelligent HIPPEs with adjustable properties, such as stability, viscosity, and an aqueous recyclable emulsifier, which can meet various practical application needs.

中文翻译：

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CO2 可切换的高内相皮克林乳液，由小分子表面活性剂和亲水性二氧化硅纳米颗粒稳定


高内相皮克林乳液 （HIPPE） 由于其独特的粘度和流变特性，近年来受到了越来越多的关注。然而，它们的高粘度可能会限制它们在运输领域的应用。开发具有可调节稳定性、可控粘度和易于制备的 HIPPE 仍然是一项挑战。在这里，我们报道了一种由新型 CO₂ 可切换非离子表面活性剂 （NCOEO₃） 和低浓度亲水性二氧化硅纳米颗粒共稳定的 O/W HIPPE，这得益于 NCOEO₃ 通过氢键吸附到纳米颗粒上。将 NCOEO₃ 浓度增加到 1 mM 后，乳剂的油体积分数可以调节到 92%。由于 CO₂ 触发了表面活性剂结构在非离子 （NCOEO₃） 和阳离子-非离子 （N⁺COEO₃） 形式的可逆转变，HIPPE 表现出显着的 CO₂ 响应性。这种响应能力能够在室温下进行高效破乳，并在水相中回收和再利用表面活性剂。更重要的是，倒置的高粘度 HIPPE 可以通过 CO₂ 触发器可逆地转化为可流动的低粘度 HIPPE。本研究为制备具有稳定性、粘度等可调性能的智能HIPPEs提供了一种有效的方法，是一种水性可回收乳化剂，可满足各种实际应用需求。