School of Chemistry & Chemical Engineering, State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University , 800 Dongchuan Road, Shanghai, China 200240.
Institute of Theoretical Chemistry, State Key Laboratory of Supramolecular Structure and Materials, Jilin University , Changchun, China 130021.
Langmuir. 2017 Sep 26;33(38):10084-10093. doi: 10.1021/acs.langmuir.7b02411. Epub 2017 Sep 12.
Asymmetric vesicles are valuable for understanding and mimicking cell and practical biomedicine applications. Recently, a very straightforward methodology for fabricating asymmetric polymersome was developed by Lodge's group through the coassembly of polystyrene-b-poly(ethylene oxide) (PS-b-PEO) and polybutadiene-b-poly(ethylene oxide) (PB-b-PEO) block copolymers at the interface of a polystyrene/polybutadiene/chloroform (PS/PB/CHCl) emulsion. However, the in-depth microscopic mechanism for the formation of asymmetric polymersomes remains unclear. To address this issue, in this article, the coassembly process for the formation of the asymmetric polymersomes in Asano's experimental system was systematically investigated by employing a dissipative particle dynamics (DPD) simulation. Our results definitely demonstrate the formation of the asymmetric polymersomes such as that in the experiments and that the bilayer formed through the folding and crossing of the PEO blocks. Besides, from the microscopic view, three stages can be discerned in the formation process: (1) the formation of micelles, (2) the micelle diffusion to the interface, and (3) the micelle rearrangement at the interface to form an asymmetric polymersome. Meanwhile, the incompatibility among PS, PB, and PEO is proven to be the main driving force for asymmetric polymersome formation. Moreover, the effects of the order of addition of copolymers and the volume fraction of PEO blocks on the structure of the asymmetric polymersomes are also investigated. We find that the formation process is affected severely by the order of addition, and adding PS-b-PEO first can make the asymmetric bilayer more perfect. Not only that, but perfect asymmetric polymersomes can be formed only when the volume fraction of PEO (f) is greater than 0.55. We believe the present work can extend the knowledge of the self-assembly of asymmetric polymersomes, especially with respect to the self-assembly mechanism.
不对称囊泡对于理解和模拟细胞以及实际生物医学应用具有重要价值。最近，Lodge 小组通过聚苯乙烯-聚（环氧乙烷）（PS-b-PEO）和聚丁二烯-聚（环氧乙烷）（PB-b-PEO）嵌段共聚物在聚苯乙烯/聚丁二烯/氯仿（PS/PB/CHCl）乳液界面的共组装，开发了一种非常简单的制备不对称聚合物囊泡的方法。然而，对于不对称聚合物囊泡形成的深入微观机制仍不清楚。为了解决这个问题，在本文中，通过耗散粒子动力学（DPD）模拟，系统地研究了 Asano 实验体系中不对称聚合物囊泡形成的共组装过程。我们的结果明确地证明了不对称聚合物囊泡的形成，如实验中那样，通过 PEO 链段的折叠和交叉形成双层结构。此外，从微观角度来看，可以在形成过程中区分出三个阶段：（1）胶束的形成，（2）胶束向界面的扩散，以及（3）界面处胶束的重新排列以形成不对称聚合物囊泡。同时，PS、PB 和 PEO 之间的不相容性被证明是不对称聚合物囊泡形成的主要驱动力。此外，还研究了共聚物添加顺序和 PEO 链段体积分数对不对称聚合物囊泡结构的影响。我们发现形成过程受到添加顺序的严重影响，先添加 PS-b-PEO 可以使不对称双层更加完美。不仅如此，只有当 PEO（f）的体积分数大于 0.55 时，才能形成完美的不对称聚合物囊泡。我们相信本工作可以扩展对不对称聚合物囊泡自组装的认识，特别是对自组装机制的认识。
