Bochenek Steffen, Scotti Andrea, Richtering Walter
Institute of Physical Chemistry, RWTH Aachen University, Landoltweg 2, 52056 Aachen, Germany.
Soft Matter. 2021 Jan 28;17(4):976-988. doi: 10.1039/d0sm01774d. Epub 2020 Dec 7.
The formation of smart emulsions or foams whose stability can be controlled on-demand by switching external parameters is of great interest for basic research and applications. An emerging group of smart stabilizers are microgels, which are nano- and micro-sized, three-dimensional polymer networks that are swollen by a good solvent. In the last decades, the influence of various external stimuli on the two-dimensional phase behavior of microgels at air- and oil-water interfaces has been studied. However, the impact of the top-phase itself has been barely considered. Here, we present data that directly address the influence of the top-phase on the microgel properties at interfaces. The dimensions of pNIPAM microgels are measured after deposition from two interfaces, i.e., air- and decane-water. While the total in-plane size of the microgel increases with increasing interfacial tension, the portions or fractions of the microgels situated in the aqueous phase are not affected. We correlate the area microgels occupy to the surface tensions of the interfaces, which allows to estimate an elastic modulus. In comparison to nanoindentation measurements, we observe a larger elastic modulus for the microgels. By combining compression, deposition, and visualization, we show that the two-dimensional phase behavior of the microgel monolayers is not altered, although the microgels have a larger total in-plane size at higher interfacial tension.
能够通过切换外部参数按需控制稳定性的智能乳液或泡沫的形成，对于基础研究和应用而言具有极大的吸引力。一类新兴的智能稳定剂是微凝胶，它是纳米级和微米级的三维聚合物网络，能被良溶剂溶胀。在过去几十年里，人们研究了各种外部刺激对微凝胶在空气 - 水界面和油 - 水界面二维相行为的影响。然而，顶层相本身的影响几乎未被考虑。在此，我们展示了直接探讨顶层相对界面处微凝胶性质影响的数据。聚N - 异丙基丙烯酰胺（pNIPAM）微凝胶的尺寸是在从空气 - 水和癸烷 - 水这两个界面沉积后测量的。虽然微凝胶的总平面内尺寸随着界面张力的增加而增大，但位于水相中的微凝胶部分或比例并未受到影响。我们将微凝胶占据的面积与界面的表面张力相关联，这使得能够估算弹性模量。与纳米压痕测量结果相比，我们观察到微凝胶具有更大的弹性模量。通过结合压缩、沉积和可视化，我们表明微凝胶单层的二维相行为并未改变，尽管微凝胶在较高界面张力下具有更大的总平面内尺寸。
