Jiménez-Ángeles Felipe, Kwon Ha-Kyung, Sadman Kazi, Wu Thomas, Shull Kenneth R, Olvera de la Cruz Monica
Department of Materials Science and Engineering, Department of Chemistry, Department of Chemical and Biological Engineering, and Department of Physics, Northwestern University, Evanston, Illinois 60208, United States.
ACS Cent Sci. 2019 Apr 24;5(4):688-699. doi: 10.1021/acscentsci.9b00084. Epub 2019 Mar 25.
Quantitatively understanding the self-assembly of amphiphilic macromolecules at liquid-liquid interfaces is a fundamental scientific concern due to its relevance to a broad range of applications including bottom-up nanopatterning, protein encapsulation, oil recovery, drug delivery, and other technologies. Elucidating the mechanisms that drive assembly of amphiphilic macromolecules at liquid-liquid interfaces is challenging due to the combination of hydrophobic, hydrophilic, and Coulomb interactions, which require consideration of the dielectric mismatch, solvation effects, ionic correlations, and entropic factors. Here we investigate the self-assembly of a model block copolymer with various charge fractions at the chloroform-water interface. We analyze the adsorption and conformation of poly(styrene)--poly(2-vinylpyridine) (PS--P2VP) and of the homopolymer poly(2-vinylpyridine) (P2VP) with varying charge fraction, which is controlled via a quaternization reaction and distributed randomly along the backbone. Interfacial tension measurements show that the polymer adsorption increases only marginally at low charge fractions (<5%) but increases more significantly at higher charge fractions for the copolymer, while the corresponding randomly charged P2VP homopolymer analogues display much more sensitivity to the presence of charged groups. Molecular dynamics (MD) simulations of the experimental systems reveal that the diblock copolymer (PS--P2VP) interfacial activity could be mediated by the formation of a rich set of complex interfacial copolymer aggregates. Circular domains to elongated stripes are observed in the simulations at the water-chloroform interface as the charge fraction increases. These structures are shown to resemble the spherical and cylindrical helicoid structures observed in bulk chloroform as the charge fraction increases. The self-assembly of charge-containing copolymers is found to be driven by the association of the charged component in the hydrophilic block, with the hydrophobic segments extending away from the hydrophilic cores into the chloroform phase.
定量理解两亲性大分子在液 - 液界面的自组装是一个基本的科学问题，因为它与广泛的应用相关，包括自下而上的纳米图案化、蛋白质封装、石油开采、药物递送及其他技术。由于疏水、亲水和库仑相互作用的综合影响，阐明驱动两亲性大分子在液 - 液界面组装的机制具有挑战性，这需要考虑介电失配、溶剂化效应、离子相关性和熵因素。在此，我们研究了一种具有不同电荷分数的模型嵌段共聚物在氯仿 - 水界面的自组装。我们分析了聚（苯乙烯） - 聚（2 - 乙烯基吡啶）（PS - P2VP）和均聚物聚（2 - 乙烯基吡啶）（P2VP）在不同电荷分数下的吸附和构象，电荷分数通过季铵化反应控制并沿主链随机分布。界面张力测量表明，对于共聚物，在低电荷分数（<5%）时聚合物吸附仅略有增加，但在较高电荷分数时增加更为显著，而相应的随机带电的P2VP均聚物类似物对带电基团的存在表现出更高的敏感性。对实验系统的分子动力学（MD）模拟表明，二嵌段共聚物（PS - P2VP）的界面活性可通过形成一系列丰富的复杂界面共聚物聚集体来介导。随着电荷分数增加，在水 - 氯仿界面的模拟中观察到从圆形域到细长条纹的转变。这些结构显示出与随着电荷分数增加在本体氯仿中观察到的球形和圆柱形螺旋结构相似。发现含电荷共聚物的自组装是由亲水性嵌段中带电组分的缔合驱动的，疏水链段从亲水性核延伸到氯仿相中。
