Pickering emulsions by combining cellulose nanofibrils and nanocrystals: phase behavior and depletion stabilization
Pickering emulsions by combining cellulose nanofibrils and nanocrystals: phase behavior and depletion stabilization
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DOI：
10.1039/c8gc00134k
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发表时间：
2018-04-07
期刊：
影响因子：
9.8
通讯作者：
Rojas, Orlando J.
中科院分区：
文献类型：
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作者：
Bai, Long;Huan, Siqi;Rojas, Orlando J.
在这项研究中，纤维素纳米纤维(CNF)被用来诱导由另一种类型的纳米纤维素(即纤维素纳米晶)界面吸附形成的水包油Pickering乳状液的耗尽稳定化。这种由非吸附CNF单独触发的耗尽效应是在一个包含球形液滴和高纵横比纤维素纳米棒的新系统中实现的。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的方法制备了绿色乳液。用一系列技术揭示了乳液的性质(原子力显微镜和共聚焦显微镜下的液滴大小和形态，光后向散射和流变性的稳定性和乳化性)以及相关的表面相互作用(石英晶体微重法)，以综合评价乳化现象。建立了三个依赖于浓度的耗尽稳定区域，包括(1)在低CNF浓度下非絮凝液滴的乳状化；(2)在中等CNF浓度下的絮凝；(3)在最高CNF浓度下使用特征微米级液滴的乳状液稳定。值得注意的是，后者是在CNF浓度低至0.1%时实现的。在临界稳定浓度以上，乳液液滴大小与CNF含量无关，遵循耗尽和凝胶化机制。这些发现的普适性是用天然油、葵花籽油和石蜡烷烃测试的。总体而言，我们揭示了Pickering乳液中由长而灵活的纤维素纳米纤维引起的耗尽相互作用，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的形状各向异性和两亲性来实现的。
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.