School of Chemistry and Chemical Engineering, Yangzhou University, Jiangsu Province, China.
School of Chemistry and Chemical Engineering, Yangzhou University, Jiangsu Province, China.
J Colloid Interface Sci. 2021 Mar;585:205-216. doi: 10.1016/j.jcis.2020.11.062. Epub 2020 Nov 20.
Reverse Janus emulsion, with droplets composed by "two rooms" of water phases, is a novel multiple emulsion attributed to excellent integration capability and biocompatibility. However, significant instability compared with normal Janus emulsions renders the stability issue of great importance. Moreover, the ultra-low aqueous-aqueous inner interfacial tension, the anisotropic nature of the droplets with distinct lobe composition, and the random orientation in the continuous phase endow the complicated and various demulsification mechanisms.
Reverse Janus emulsion of (W+W)/O, employing typical salt-alcohol aqueous two-phase system (ATPS) as inner phases, is prepared in batch scale by conventional one-step vortex mixing. The demulsification process is detected by multiple light scattering technique, which provides real-time, in-situ, and quantitative information of emulsion evolution. Moreover, the fusion pattern of the anisotropic droplets is illustrated by the combination with light microscopy and size distribution measurement.
Coalescence and sedimentation are found to be two main demulsification processes. Two salt "body" lobes of the "snowman" shaped Janus droplets combine first resulting in an intermediate Cerberus topology with two alcohol "heads" on one salt "body". Subsequently, two "head" lobes coalesce resulting in a larger Janus droplet. Ultimately, the Gibbs free energy leads to a final state with three separated liquids. In addition, the variation in lobe viscosity, density, and properties of interfacial film greatly affect the demulsification rate and fusion pattern. A critical alcohol/surfactant mass ratio of 2 is found, beyond which a completely different fusion pattern occurs. Two alcohol "body" lobes combine first resulting in an intermediate Cerberus topology with two salt "heads" on one alcohol "body". Subsequently, two "head" lobes coalesce resulting in a larger Janus droplet. The findings are instructive in the stability of aqueous based multiple emulsions with advanced morphologies and meanwhile, promote the future application of this novel emulsion in food science, pharmacy, and biomimetic compartmentalization.
由“两个房间”水相组成的反向 Janus 乳液是一种新型的多重乳液，具有优异的集成能力和生物相容性。然而，与正常的 Janus 乳液相比，它的不稳定性显著，这使得稳定性问题变得非常重要。此外，超低的水-水内界面张力、具有明显叶瓣组成的各向异性液滴以及在连续相中随机取向，赋予了复杂多样的破乳机制。
采用典型的盐-醇双水相体系（ATPS）作为内相，通过常规的一步涡旋混合批量制备（W+W）/O 型反向 Janus 乳液。采用多重光散射技术检测破乳过程，实时、原位、定量地提供乳液演变的信息。此外，结合光显微镜和粒径分布测量，说明了各向异性液滴的融合模式。
聚结和沉降被发现是两种主要的破乳过程。“雪人”形状的 Janus 液滴的两个盐“体”叶瓣首先结合，形成具有两个醇“头”的中间 Cerberus 拓扑结构，位于一个盐“体”上。随后，两个“头”叶瓣聚结，形成一个更大的 Janus 液滴。最终，吉布斯自由能导致最终状态为三个分离的液体。此外，叶瓣粘度、密度和界面膜性质的变化极大地影响破乳速率和融合模式。发现临界醇/表面活性剂质量比为 2，超过该值则会发生完全不同的融合模式。两个醇“体”叶瓣首先结合，形成具有两个盐“头”的中间 Cerberus 拓扑结构，位于一个醇“体”上。随后，两个“头”叶瓣聚结，形成一个更大的 Janus 液滴。这些发现对具有先进形态的水基多重乳液的稳定性具有指导意义，同时也促进了这种新型乳液在食品科学、药学和仿生分区化领域的未来应用。
