Widmann Tobias, Kreuzer Lucas P, Hohn Nuri, Bießmann Lorenz, Wang Kun, Rinner Stephan, Moulin Jean-François, Schmid Andreas J, Hannappel Yvonne, Wrede Oliver, Kühnhammer Matthias, Hellweg Thomas, von Klitzing Regine, Müller-Buschbaum Peter
Lehrstuhl für Funktionelle Materialien, Physik Department , Technische Universität München , James-Franck-Straße 1 , 85748 Garching , Germany.
Helmholtz-Zentrum Geesthacht at Heinz Maier-Leibnitz Zentrum , Lichtenbergstraße 1 , 85747 Garching , Germany.
Langmuir. 2019 Dec 10;35(49):16341-16352. doi: 10.1021/acs.langmuir.9b03104. Epub 2019 Nov 26.
The investigation of the response kinetics of smart colloidal microgel films is crucial for their optimization to enable advanced applications. We study the classical thermoresponsive microgel model system -isopropylacrylamide cross-linked with ,'-methylenebisacrylamide. Without the typically used polyelectrolyte coating of the substrate, thin microgel films are prepared in a single spin-coating step. Atomic force microscopy measurements reveal an extremely dense packing, resulting in a homogeneous compact thin film of microgel particles. The hydration kinetics of these films in HO and DO atmospheres as well as the kinetics of the solvent exchange between both water species are investigated with in situ time-of-flight neutron reflectometry (TOF-NR) and in situ Fourier-transform infrared (FTIR) spectroscopy. With accounting for a nonconstant humid atmosphere, the intrinsic diffusion dynamics of water molecules into the thin microgel film are modeled and the specific time constant τ and the effective Flory-Huggins interaction parameter χ are determined. Comparing the results in HO and DO atmospheres, TOF-NR and FTIR spectroscopy results show an increased affinity of the microgel films toward HO as compared to DO. From the FTIR spectroscopy data, we further identify different kinetics of intermolecular processes and order them according to their temporal evolution.
研究智能胶体微凝胶薄膜的响应动力学对于优化其性能以实现先进应用至关重要。我们研究了经典的热响应性微凝胶模型体系——由N,N'-亚甲基双丙烯酰胺交联的异丙基丙烯酰胺。在没有通常使用的基底聚电解质涂层的情况下，通过单次旋涂步骤制备了微凝胶薄膜。原子力显微镜测量揭示了极其致密的堆积，形成了由微凝胶颗粒组成的均匀致密薄膜。利用原位飞行时间中子反射仪（TOF-NR）和原位傅里叶变换红外（FTIR）光谱研究了这些薄膜在H₂O和D₂O气氛中的水合动力学以及两种水物种之间的溶剂交换动力学。考虑到非恒定的潮湿气氛，对水分子进入微凝胶薄膜的本征扩散动力学进行了建模，并确定了特定的时间常数τ和有效的弗洛里-哈金斯相互作用参数χ。比较在H₂O和D₂O气氛中的结果，TOF-NR和FTIR光谱结果表明，与D₂O相比，微凝胶薄膜对H₂O的亲和力增加。从FTIR光谱数据中，我们进一步确定了分子间过程的不同动力学，并根据它们的时间演化对其进行排序。
