Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States.
Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States.
ACS Nano. 2023 May 23;17(10):9224-9234. doi: 10.1021/acsnano.3c00212. Epub 2023 May 3.
Precise control of nanoparticles at interfaces can be achieved by designing stimuli-responsive surfaces that have tunable interactions with nanoparticles. In this study, we demonstrate that a polymer brush can selectively adsorb nanoparticles according to size by tuning the pH of the buffer solution. Specifically, we developed a facile polymer brush preparation method using a symmetric polystyrene--poly(2-vinylpyridine) (PS--P2VP) block copolymer deposited on a grafted polystyrene layer. This method is based on the assembly of a PS--P2VP thin film oriented with parallel lamellae that remains after exfoliation of the top PS--P2VP layer. We characterized the P2VP brush using X-ray reflectivity and atomic force microscopy. The buffer pH is used to tailor interactions between citrate-coated gold nanoparticles (AuNPs) and the top P2VP block that behaves like a polymer brush. At low pH (∼4.0) the P2VP brushes are strongly stretched and display a high density of attractive sites, whereas at neutral pH (∼6.5) the P2VP brushes are only slightly stretched and have fewer attractive sites. A quartz crystal microbalance with dissipation monitored the adsorption thermodynamics as a function of AuNP diameter (11 and 21 nm) and pH of the buffer. Neutral pH provides limited penetration depth for nanoparticles and promotes size selectivity for 11 nm AuNP adsorption. As a proof of concept, the P2VP brushes were exposed to various mixtures of large and small AuNPs to demonstrate selective capture of the smaller AuNPs. This study shows the potential of creating devices for nanoparticle size separations using pH-sensitive polymer brushes.
通过设计具有可调谐与纳米粒子相互作用的响应性表面，可以实现对纳米粒子在界面处的精确控制。在本研究中，我们证明了通过调节缓冲溶液的 pH 值，聚合物刷可以根据尺寸选择性地吸附纳米粒子。具体而言，我们开发了一种简便的聚合物刷制备方法，使用沉积在接枝聚苯乙烯层上的对称聚苯乙烯-聚（2-乙烯基吡啶）（PS-P2VP）嵌段共聚物。该方法基于具有平行层片取向的 PS-P2VP 薄膜的组装，该薄膜在剥离顶部 PS-P2VP 层后仍然存在。我们使用 X 射线反射率和原子力显微镜对 P2VP 刷进行了表征。缓冲 pH 值用于调整带柠檬酸涂层的金纳米粒子（AuNPs）与表现为聚合物刷的顶部 P2VP 嵌段之间的相互作用。在低 pH（约 4.0）下，P2VP 刷被强烈拉伸并显示出高密度的吸引力位点，而在中性 pH（约 6.5）下，P2VP 刷仅略微拉伸并且吸引力位点较少。石英晶体微天平（QCM-D）监测了作为 AuNP 直径（11 和 21nm）和缓冲液 pH 值函数的吸附热力学。中性 pH 值为纳米粒子提供了有限的穿透深度，并促进了对 11nm AuNP 吸附的尺寸选择性。作为概念验证，将 P2VP 刷暴露于各种大小的 AuNP 混合物中，以证明对较小 AuNP 的选择性捕获。本研究展示了使用 pH 敏感聚合物刷来制造纳米粒子尺寸分离器件的潜力。
