In this study, cellulose nanofibrils (CNF) were used to induce depletion stabilization of oil-in-water Pickering emulsions formed by interfacial adsorption of another type of nanocellulose, namely, cellulose nanocrystals (CNC). This depletion effect triggered solely by the non-adsorbing CNF was achieved in a novel system that contained spherical droplets and the high-aspect cellulose nanorods. By exploiting the synergies between the two nanocelluloses, green emulsions were prepared either by sequential or by one-step, simultaneous addition. A battery of techniques to unveil the properties of the emulsions (droplet size and morphology by AFM and confocal microscopy, stability and creaming by light backscattering and rheological behavior) and related surface interactions (quartz crystal microgravimetry), were applied for a comprehensive evaluation of the emulsification phenomena. Three regimes of concentration-dependent depletion stabilization were established, including (1) creaming of non-flocculated droplets at low CNF concentration; (2) flocculation at intermediate CNF content and, (3) stabilization of the emulsions with characteristic micron-sized droplets at the highest CNF concentrations used. Remarkably, the latter regime was achieved at CNF concentrations as low as 0.1%. Above a critical stabilization concentration, the emulsion droplet size became independent of CNF content, following depletion and gelation mechanisms. The universality of the findings was tested with a natural oil, sunflower oil, as well as a paraffinic alkane. Overall, we unveiled the depletion interactions in Pickering emulsions induced by the long, flexible cellulose nanofibrils, opening the way to green, edible Pickering emulsions for foodstuff, cosmetic and other related formulations. This is mainly by combining the shape-anisotropy and amphiphilicity of nanocelluloses extracted from plant cell walls.

中文翻译：

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通过将纤维素纳米原纤维和纳米晶体相结合来进行乳化剂乳化：相行为和耗竭稳定性

在这项研究中，使用纤维素纳米原纤维（CNF）来诱导通过界面吸附另一种纳米纤维素，即纤维素纳米晶体（CNC）形成的水包油Pickering乳液的耗竭稳定。在包含球形液滴和高纵横比纤维素纳米棒的新型系统中，仅由非吸附CNF引发的这种耗尽效应得以实现。通过利用两种纳米纤维素之间的协同作用，通过顺序或一步同时添加来制备绿色乳液。揭示乳剂特性的一系列技术（通过AFM和共聚焦显微镜观察的液滴尺寸和形态，通过光反向散射和流变行为获得的稳定性和乳化性）以及相关的表面相互作用（石英晶体微重力法），被应用于乳化现象的综合评价。建立了三种浓度依赖性耗尽稳定化机制，其中包括：（1）在低CNF浓度下对非絮凝液滴的乳化；（2）在中等CNF含量下絮凝，以及（3）在使用的最高CNF浓度下用特征性的微米级液滴稳定乳液。值得注意的是，后一种方案是在低至0.1％的CNF浓度下实现的。在临界稳定浓度以上时，乳液的液滴尺寸变得不依赖于CNF含量，这取决于消耗和胶凝机理。研究结果的普遍性用天然油，葵花籽油以及链烷烃进行了测试。总体而言，我们揭示了由于长时间，柔性纤维素纳米原纤维，为食品，化妆品和其他相关配方的绿色可食用Pickering乳液开辟了道路。这主要是通过结合从植物细胞壁中提取的纳米纤维素的形状各向异性和两亲性来实现的。