Rolle Konrad, Schilling Theresa, Westermeier Fabian, Das Sudatta, Breu Josef, Fytas George
Max-Planck-Institute of Polymer Research, Ackermannweg 10, Mainz 55128, Germany.
Department of Chemistry and Bavarian Polymer Institute, University of Bayreuth, Universitätsstr. 30, Bayreuth 95440, Germany.
Macromolecules. 2021 Mar 9;54(5):2551-2560. doi: 10.1021/acs.macromol.0c02818. Epub 2021 Feb 19.
Studies of glass transition under confinement frequently employ supported polymer thin films, which are known to exhibit different transition temperature close to and far from the interface. Various techniques can selectively probe interfaces, however, often at the expense of sample designs very specific to a single experiment. Here, we show how to translate results on confined thin film to a "nacre-mimetic" clay/polymer Bragg stack, where periodicity allows to limit and tune the number of polymer layers to either one or two. Exceptional lattice coherence multiplies signal manifold, allowing for interface studies with both standard and broadband dynamic measurements. For the monolayer, we not only observe a dramatic increase in (∼ 100 K) but also use X-ray photon correlation spectroscopy (XPCS) to probe platelet dynamics, originating from interfacial slowdown. This is confirmed from the bilayer, which comprises both "bulk-like" and clay/polymer interface contributions, as manifested in two distinct processes. Because the platelet dynamics of monolayers and bilayers are similar, while the segmental dynamics of the latter are found to be much faster, we conclude that XPCS is sensitive to the clay/polymer interface. Thus, large shifts can be engineered and studied once lattice spacing approaches interfacial layer dimensions.
受限条件下玻璃化转变的研究通常采用支撑聚合物薄膜，已知这种薄膜在靠近和远离界面处会表现出不同的转变温度。各种技术可以选择性地探测界面，然而，这往往是以牺牲非常特定于单个实验的样品设计为代价的。在这里，我们展示了如何将受限薄膜的结果转化为“仿珍珠母”粘土/聚合物布拉格堆叠结构，其中周期性允许将聚合物层数限制并调整为一层或两层。出色的晶格相干性使信号多样性增加，从而可以通过标准和宽带动态测量进行界面研究。对于单层，我们不仅观察到（约100K）的显著增加，还使用X射线光子相关光谱（XPCS）来探测源自界面减速的血小板动力学。这从双层结构得到证实，双层结构包含“块状”和粘土/聚合物界面贡献，表现为两个不同的过程。由于单层和双层的血小板动力学相似，而后者的链段动力学要快得多，我们得出结论，XPCS对粘土/聚合物界面敏感。因此，一旦晶格间距接近界面层尺寸，就可以设计和研究大的转变温度变化。
