各向异性核壳和中空微凝胶的界面组装
Interfacial assembly of anisotropic core-shell and hollow microgels
摘要：
微凝胶是一种具有亚微米尺寸的交联聚合物，是理想的软模型体系。虽然球形微凝胶已被广泛研究，但各向异性微凝胶却几乎没有研究。在这项研究中，我们比较了各向异性核壳和中空微凝胶的界面变形和组装。核-壳微凝胶由覆盖有薄二氧化硅层的赤铁矿的椭圆形核和由PNiPAM制成的薄壳组成。在无机核的两步蚀刻程序之后获得中空微凝胶。利用LB槽结合原子力显微镜研究了这些微凝胶在油水界面上的行为。首先，实验和耗散粒子动力学模拟研究了各向异性微凝胶的结构对它们在界面处的扩散的影响。在此基础上，重点讨论了局部壳层厚度对界面横向和纵向变形的影响，以及核壳结构与空心结构的区别。分析了压缩等温线的形状以及不同压缩下微凝胶的尺寸、有序性和取向。由于它们的各向异性的形状和刚度，两个各向异性的微凝胶被发现表现出显着的毛细管相互作用与优先的侧到侧的组件，导致稳定的微凝胶簇在低界面覆盖率。这种毛细管相互作用被发现减少的情况下，更可变形的中空各向异性微凝胶。因此，各向异性的中空微凝胶被发现在高表面压力下分布更均匀的刚性核-壳微凝胶相比。我们的研究结果强调了界面组装的胶体设计，各向异性和柔软性之间的复杂相互作用，从而提供了创造更复杂的有序界面的机会。
英文摘要：
Microgels, cross-linked polymers with submicrometer size, are ideal soft model systems. While spherical microgels have been studied extensively, anisotropic microgels have been hardly investigated. In this study, we compare the interfacial deformation and assembly of anisotropic core-shell and hollow microgels. The core-shell microgel consists of an elliptical core of hematite covered with a thin silica layer and a thin shell made of PNiPAM. The hollow microgels were obtained after a two step etching procedure of the inorganic core. The behavior of these microgels at the oil-water interface was investigated in a Langmuir Blodgett trough combined with ex-situ AFM. First, the influence of the architecture of anisotropic microgels on their spreading at the interface was investigated experimentally and by dissipative particle dynamic simulations. Hereby, the importance of the local shell thickness on the lateral and longitudinal interfacial deformation was highlighted as well as the differences between the core-shell and hollow architectures. The shape of the compression isotherms as well as the dimensions, ordering and orientation of the microgels at the different compressions were analysed. Due to their anisotropic shape and stiffness, both anisotropic microgels were found to exhibit significant capillary interactions with a preferential side-to-side assembly leading to stable microgel clusters at low interfacial coverage. Such capillary interactions were found to decrease in the case of the more deformable hollow anisotropic microgels. Consequently, anisotropic hollow microgels were found to distribute more evenly at high surface pressure compared to stiffer core-shell microgels. Our findings emphasize the complex interplay between the colloid design, anisotropy and softness on the interfacial assembly and the opportunities it thus offers to create more complex ordered interfaces.
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