Centeno S P, Nothdurft K, Klymchenko A S, Pich A, Richtering W, Wöll D
DWI Leibniz Institute for Interactive Materials, Forckenbeckstrasse 50, Aachen, 52074, Germany.
Institute of Physical Chemistry, RWTH-Aachen University, Landoltweg 2, Aachen, 52074, Germany.
J Colloid Interface Sci. 2025 Jan 15;678(Pt B):210-220. doi: 10.1016/j.jcis.2024.08.235. Epub 2024 Sep 2.
Polymer microgels are swollen macromolecular networks with a typical size of hundred of nanometers to several microns that show an extraordinary open and responsive architecture to different external stimuli, being therefore important candidates for nanobiotechnology and nanomedical applications such as biocatalysis, sensing and drug delivery. It is therefore crucial to understand the delicate balance of physical-chemical interactions between the polymer backbone and solvent molecules that to a high extent determine their responsivity. In particular, the co-nonsolvency effect of poly(N-isopropylacrylamide) in aqueous alcohols is highly discussed, and there is a disagreement between molecular dynamics (MD) simulations (from literature) of the preferential adsorption of alcohol on the polymer chains and the values obtained by several empirical methods that mostly probe the bulk solvent properties. It is our contention that the most efficacious method for addressing this problem requires a nanoscopic method that can be combined with spectroscopy and record fluorescence spectra and super-resolved fluorescence lifetime images of microgels labeled covalently with the solvatochromic dye Nile Red. By employing this approach, we could simultaneously resolve the structure of sub-micron size objects in the swollen and in the collapsed state and estimate the solvent composition inside of them in - mixtures for two very different polymer architectures. We found an outstanding agreement between the MD simulations and our results that estimate a co-solvent molar fraction excess of approximately 3 with a very flat profile in the lateral direction of the microgel.
聚合物微凝胶是一种膨胀的大分子网络，典型尺寸为几百纳米到几微米，对不同的外部刺激表现出非凡的开放和响应结构，因此是纳米生物技术和纳米医学应用（如生物催化、传感和药物递送）的重要候选材料。因此，了解聚合物主链与溶剂分子之间物理化学相互作用的微妙平衡至关重要，这种平衡在很大程度上决定了它们的响应性。特别是，聚（N-异丙基丙烯酰胺）在醇水溶液中的共非溶剂化效应受到了广泛讨论，文献中的分子动力学（MD）模拟关于醇在聚合物链上的优先吸附结果与几种主要探测本体溶剂性质的经验方法所得值之间存在分歧。我们认为，解决这个问题最有效的方法需要一种纳米级方法，该方法可以与光谱学结合，并记录用溶剂致变色染料尼罗红共价标记的微凝胶的荧光光谱和超分辨荧光寿命图像。通过采用这种方法，我们可以同时解析处于膨胀和收缩状态的亚微米尺寸物体的结构，并估计它们内部在两种非常不同的聚合物结构混合物中的溶剂组成。我们发现MD模拟与我们的结果之间存在显著一致性，我们的结果估计共溶剂摩尔分数过量约为3，在微凝胶的横向方向上具有非常平坦的数据分布。
