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聚氧乙烯-聚氧丙烯-聚氧乙烯(PEO-PPO-PEO)嵌段共聚物具有分子可设计性、生物相容性和环境响应性等优良特点，在众多领域中得到了广泛应用。了解和掌握嵌段共聚物在选择性溶剂中的聚集体形貌及形成机理是其应用的关键。有关PEO-PPO-PEO在水溶液中的宏观聚集行为已有大量的报道，但对其聚集体形貌的形成及调控机理仍然缺乏深入的研究。分子间弱相互作用是构建特定纳微结构的重要驱动力。利用分子间弱相互作用对PEO-PPO-PEO聚集行为进行调控不仅有助于加深对其聚集体形成机理的理解，也有望提供一种简便的形貌调控手段。基于此，本学位论文通过结合动态光散射、冷冻透射电镜和核磁共振光谱等实验方法与分子动力学模拟手段，研究了小分子化合物对PEO-PPO-PEO嵌段共聚物水溶液中聚集行为的影响，探索了它们之间的各种弱相互作用对聚集体形貌的调控规律，并提出相应的形貌转变机理。研究内容和结果主要包括以下四个方面：(1) 以不同烷基链长度的没食子酸酯为模型小分子，研究了分子间疏水相互作用对PEO-PPO-PEO聚集体形貌的调控及机理。研究结果表明随着没食子酸酯烷基链的增长，其与PPO嵌段间的疏水作用显著增强，从而使它们位于胶团的不同位置。其中，烷基链最短的没食子酸甲酯分布于胶团内核、外壳及外部溶剂中，只能引起胶团尺寸变大而不能导致形貌改变。烷基链较长的没食子酸丙酯的芳香环、酯基及相邻亚甲基位于胶团核-壳界面，其余烷基链位于胶团内核。这种定位致使部分PPO内核暴露于水中，破坏了胶团的稳定性，导致胶团之间发生融合、聚集形成大胶团甚至胶团簇集体。烷基链最长的没食子酸辛酯与PPO嵌段间的强疏水作用使其主要位于胶团PPO内核，其芳香环位于胶团核-壳界面，从而引起胶团发生球形-棒状的形貌转变。 (2) 以具有不同酚羟基数量的苯甲酸丙酯为模型小分子，研究了分子间氢键作用对PEO-PPO-PEO聚集体形貌的影响。研究结果表明没有酚羟基的苯甲酸丙酯与PEO嵌段间无氢键作用，只与PPO嵌段间存在疏水作用，从而完全位于胶团内核，对胶团形貌没有影响。而具有一个酚羟基的对羟基苯甲酸丙酯，酚羟基与PEO嵌段的氢键作用使其芳香环位于胶团的核-壳界面，烷基链位于胶团内核，从而引起胶团发生球形-长蠕虫状-单层囊泡的转变。而具有三个酚羟基的没食子酸丙酯，其与PEO间的氢键作用进一步增强，因而相对于对羟基苯甲酸丙酯其在胶团里的位置更靠近胶团外壳，从而能够诱导大胶团及胶团簇集体的形成。分子动力学模拟表明，虽然小分子与PPO嵌段间的疏水作用要明显强于其与PEO嵌段间的氢键作用，仍可以通过调节氢键作用的强度实现对聚集体形貌的调控。(3) 以正辛醇、正辛胺和正辛酸为代表，进一步考察了具有不同氢键供体的小分子对PEO-PPO-PEO聚集体形貌的调控。虽然三种小分子都能增大P123胶团的尺寸，但正辛醇不能引起胶团形貌的变化，而正辛胺和正辛酸能分别引起胶团发生球形-短蠕虫状和球形-长蠕虫状-单层囊泡的形貌转变。虽然三种小分子与P123嵌段共聚物间的作用位点相同，但作用强度上的差异导致它们位于胶团内的不同位置。其中，正辛酸与PEO、PPO嵌段间的作用最强，其次是辛胺，辛醇与PEO、PPO嵌段间的作用最弱。(4) 离子液体独特的结构蕴含着多重弱相互作用。本学位论文最后考察了阳离子型的表面活性离子液体(SAILs)对水溶液中PEO-PPO-PEO聚集体行为的影响。C8mimBr、C8PyBr和C8MPB对F127嵌段共聚物的CMT没有影响，但会影响胶团的组成。SAILs的加入使F127溶液的浊点升高，且SAILs升高浊点的能力随其烷基链的增长而增强。SAILs对F127胶团的影响与其浓度密切相关，当SAILs浓度较低(CMC)时，SAILs发生聚集，核-壳界面上增强的静电排斥作用使F127胶团分解，F127单体通过不同作用位点与SAILs胶团接触。;Amphiphilic PEO-PPO-PEO block copolymer has wide applications in many fields due to its designable, biocompatible and sensitively responsive properties. Understanding the morphology of block copolymer aggregates in selective solvent and its formation mechanism is crucial to its application. Although the aggregation behaviors of PEO-PPO-PEO block copolymer have been extensively studied, knowledge on mechanism of regulating the aggregates morphology is still lacking. The weak intermolecular interaction is known to be vital to the directional fabrication of nano-micro structure. Therefore, regulating the aggregation behaviors of PEO-PPO-PEO block copolymer by weak intermolecular interaction is not only beneficial to deepen our understanding of the formation mechanism of aggregates, but would provide a simple and effective approach for controlling the aggregates morphology. In this dissertation, the influence of various small molecules on the aggregation behaviors of PEO-PPO-PEO block copolymer in aqueous solution was comprehensively investigated by combining dynamical light scattering, cryo-transmission electron microscopy, nuclear magnetic resonance and molecular dynamics simulations. The effect of various weak interactions between small molecules and PEO-PPO-PEO block copolymers on the morphology was unveiled and the underlying mechanism was provided. The research content and results were mainly composed of four parts that were presented as follow:(1) Using gallates with different alkyl chain lengths as model small molecules, the regulation and mechanism of the intermolecular hydrophobic interaction on the morphology of PEO-PPO-PEO aggregates were studied. The results showed that as the alkyl chain of gallate grows, its hydrophobic interaction with the PPO block was significantly enhanced, so that they were located at different positions of the micelle. Among them, methyl gallate with the shortest alkyl chain was distributed in the core and shell of micelles, as well as in solvent, which could only cause an increase in micellar size but cannot induce the change in morphology. The aromatic ring, ester group and adjacent methylene group of propyl gallate with a longer alkyl chain were located at the core-shell interface of micelles, and the remaining alkyl chains were situated at the core of the micelle. This positioning caused part of the PPO core to be exposed to water, which destroyed the stability of micelles and induced the fusion and aggregated of micelles to form large micelles or even micelle clusters. The strong hydrophobic interaction between the octyl gallate with the longest alkyl chain and the PPO block made it mainly located in the PPO core of the micelle and its aromatic ring situated at the core-shell interface, which brought about the sphere-rod morphological transition of the micelle.(2) Adopting propyl benzoate with different numbers of phenolic hydroxyl groups as model small molecules, the effect of intermolecular hydrogen bonding on the morphology of PEO-PPO-PEO aggregates was studied. The results showed that propyl benzoate without phenolic hydroxyl had no hydrogen bonding interaction with PEO blocks, and only had hydrophobic interaction with PPO blocks, made it completely located in the core of the micelle and had no effect on micellar morphology. For propyl paraben with a phenolic hydroxyl group, the hydrogen bonding interaction between phenolic hydroxyl and PEO blocks caused its aromatic ring to be located at the core-shell interface of micelle and the alkyl chain lied in the core of micelles, thus lead to a morphological transition of sphere-long worm-unilamellar vesicle. Hydrogen bonding interaction between propyl gallate with three phenolic hydroxyl and PEO blocks further enhanced. So compared with propyl paraben, the position of propyl gallate was closer to the micellar shell, which could induce the formation of large micelles and micelle clusters. Molecular dynamics simulations Results showed that although the hydrophobic interaction between small molecules and PPO blocks was significantly stronger than its hydrogen bonding interaction with PEO blocks, the morphologies of aggregates could also be controlled by changing the strength of hydrogen bonding interaction.(3) Taking n-octanol, n-octylamine and n-octanoic acid as the representatives, the regulation of PEO-PPO-PEO aggregate morphology by small molecules with different hydrogen bond donors was further investigated. All three kinds of small molecules could increase the size of P123 micelles, but n-octanol could not cause change in micelle morphologies, while n-octylamine and n-octanoic acid induced morphological transition of spherical-short wormlike and spherical-long wormlike-unilamellar vesicle, respectively. Although the interaction sites between small molecules and P123 block copolymer were same, the difference in interaction intensity made them have different positions within micelle. Thereinto, the interaction between n-octanoic acid and PEO and PPO blocks was the strongest, followed by n-octylamine, and the interaction of n-octanol with PEO and PPO blocks was the weakest.(4) The unique structure of ionic liquid enabled them to bear multiple weak interactions. This dissertation finally investigated the effect of cationic surface active ionic liquids (SAILs) on the aggregation behavior of PEO-PPO-PEO in aqueous solutions. C8mimBr, C8PyBr and C8MPB had no effect on the CMT of F127 block copolymer, but could affect the composition of micelles. Addition of SAILs increased the cloud point of F127 solution, and the ability of SAILs to increase the cloud point enhanced with the growth of its alkyl chain. The effect of SAILs on F127 micelles was closely dependent on their concentration. When the concentration of SAILs is low (CMC), SAILs themselves aggregated, and the enhanced electrostatic repulsion on the core-shell interface of mixed micelles decomposed F127 micelles. F127 monomers had contact with SAILs micelles through different interaction sites.
|罗海燕. 分子间弱相互作用对PEO-PPO-PEO嵌段共聚物聚集体形貌的调控及其机理研究[D]. 中国科学院大学,2020.|
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