Liu Senyuan, Sureshkumar Radhakrishna
Department of Biomedical and Chemical Engineering and the Bioinspired Institute, Syracuse University, Syracuse, New York 13244, United States.
Department of Physics, Syracuse University, Syracuse, New York 13244, United States.
Langmuir. 2025 Mar 4;41(8):5083-5096. doi: 10.1021/acs.langmuir.4c04200. Epub 2024 Dec 31.
Copolymer nanovesicles are used extensively in chemical processes and biomedical applications in which they are subjected to dynamic flow environments. Flow-induced vesicle deformation, fragmentation, and reorganization modify the energetic (e.g., polymer-solvent interfacial area) and entropic (e.g., copolymer chain configuration) contributions to the solution free energy. Equilibration of a deformed morphology by flow cessation could reorganize the system into a self-assembled state, which is different from the parent structure through a local free energy minimization pathway. We perform nonequilibrium molecular dynamics simulations to investigate morphology evolution in uniform shear flow of a unilamellar nanovesicle formed by the self-assembly of amphiphilic triblock copolymers in an aqueous solution. Flow strength is characterized by the Weissenberg number , defined as the ratio of the time scale of vesicle shape fluctuations to the inverse shear rate. For < 10, a spherical vesicle deforms into a flow-aligned ellipsoidal bilayer executing tank-treading motion. For > 10, pronounced variations in bilayer thickness and polymer extension manifest along the contour of the elongated vesicle, which breaks up into lamellar fragments. Below a critical strain, the deformed vesicle upon flow cessation returns to its initial spherical morphology. However, for larger strains, structure reorganization after flow stoppage results in the formation of a Novel Equilibrated Shear-Induced Structure (NoESIS) in which two vesicles are connected by a dynamic molecular bridge that can accommodate additional layers of copolymers, leading to a reduction in the polymer-solvent interface area. Mechanisms of morphology hysteresis are explored via an analysis of the thermodynamic markers.
共聚物纳米囊泡广泛应用于化学过程和生物医学应用中，在这些应用中它们会受到动态流动环境的影响。流动诱导的囊泡变形、破碎和重组会改变对溶液自由能的能量贡献（例如聚合物 - 溶剂界面面积）和熵贡献（例如共聚物链构型）。通过停止流动使变形形态达到平衡，可以将系统重新组织成自组装状态，该状态通过局部自由能最小化途径与母体结构不同。我们进行非平衡分子动力学模拟，以研究由两亲性三嵌段共聚物在水溶液中自组装形成的单层纳米囊泡在均匀剪切流中的形态演变。流动强度由魏森贝格数表征，其定义为囊泡形状波动的时间尺度与剪切速率倒数的比值。当魏森贝格数小于10时，球形囊泡会变形为执行罐式行进运动的流动排列的椭球形双层结构。当魏森贝格数大于10时，沿细长囊泡轮廓会出现双层厚度和聚合物伸展的明显变化，囊泡会破碎成层状碎片。在临界应变以下，停止流动后变形的囊泡会恢复到其初始球形形态。然而，对于更大的应变，流动停止后的结构重组会导致形成一种新型平衡剪切诱导结构（NoESIS），其中两个囊泡通过一个动态分子桥连接，该桥可以容纳额外的共聚物层，从而导致聚合物 - 溶剂界面面积减小。通过对热力学标记的分析探索了形态滞后的机制。
