Self-Organized Colloidal Assemblies in Confined Spaces:Formation Mechanism, Internal Structure and Resulting Optical Properties

从结晶过程，到复合材料，再到构成复杂组织的活细胞，单个构建块自发组织成有序结构在自然界中广泛使用，并在所有长度尺度上都能找到。理解构建模块、环境条件和最终结构之间的关系对于控制材料性能至关重要。本文提出了球形聚合物胶体粒子在密闭空间中自组织的实验-理论联合研究。这种粒子可以很容易地以高精度合成，并作为简单的纳米级构建块来研究自组装过程中的结构-性能关系。如果这些粒子的大小足够均匀，它们就会自组装成一个紧密排列的面心立方晶格。这些所谓的胶体晶体表现出强烈的结构色彩。施加在自组织粒子上的限制因素可以显著地改变组装过程，并可能导致完全不同的胶体晶体。特别有趣的限制是乳状液滴，它通过引入边界和曲率来防止周期性结构的形成。在初步实验中，我们观察到具有惊人结构精度和几何形状的球形组件，这使我们能够以前所未有的细节研究约束对最终结构的影响。迄今为止，唯一可用来描述球形约束下组装的模型依赖于具有硬边界的非相互作用球体的熵最大化。虽然我们观察到的结构遵循该模型预测的一般趋势，但形成结构的细节表明比预期的更丰富的相行为。我们预计，装配动力学以及界面的柔软性和可变形性在装配过程中也起着至关重要的作用。在这个建议中，我们的目标是建立一个约束自组装机制的连贯模型，以获得对外部约束下胶体颗粒自组织产生的大量结构细节的预测能力，并可靠地以均匀的方式使用基于液滴的微流体产生这种颗粒。为了实现这一目标，我们将结合实验、理论和计算工作，将实验观察到的组装结构与粒子模拟和自由能量最小化计算相关联，这些计算基于密度和熵、表面张力、界面的可变形性及其与胶体粒子的相互作用。最后，我们将研究组装的上层结构的光学性质，作为可以通过自组织球形胶体组件的内部结构定制的功能性质的一个例子。

The spontaneous organization of individual building blocks into ordered structures is extensively used in nature and found at all length scales, from crystallization processes, via composite materials, to living cells constituting complex tissue. Understanding the relationship between building blocks, environmental conditions, and resulting structure is of fundamental importance for controlling materials properties. Here we propose a joint experimental-theoretical investigation of the self-organization of spherical polymer colloidal particles in confined spaces. Such particles can easily be synthesized with high precision and serve as simple, nanoscale building blocks to study structure-property relationships in self-assembly processes. If sufficiently uniform in size, these particles self-assemble in a close-packed face-centered cubic lattice. These so-called colloidal crystals exhibit intense structural colors.Confining elements imposed upon the self-organizing particles can significantly alter the assembly process and may lead to entirely different colloidal crystals. Especially interesting confinements are emulsion droplets that prevent the formation of periodic structures by introducing boundaries and curvature. In preliminary experiments, we observed spherical assemblies with astonishing structural precision and geometry that enable us to investigate the effect of confinement on the resulting structure in unprecedented details. To date, the only model available to describe the assembly in spherical confinement relies on entropy maximization of non-interacting spheres with hard boundaries. While our observed structures follow the general trends predicted by this model, details of the formed structures indicate a richer phase behavior than expected. We anticipate that the kinetics of the assembly as well as the softness and deformability of the interface play a crucial role in the assembly process as well. Within this proposal we aim to establish a coherent model for the mechanism of confined self-assembly, to gain predictive power over the great many structural details arising from the self-organization of colloidal particles under external confinements and to reliably produce such particles in a uniform fashion using droplet-based microfluidics. Towards this aim, we will combine experimental, theoretical, and computational efforts to correlate experimentally observed assembly structures with particle simulations and free energy-minimization computations based on density and entropy as well as surface tension, deformability of the interface and its interaction with the colloidal particles. Finally, we will investigate the resulting optical properties of the assembled superstructures as an example of a functional property that can be tailored via the internal structure of the self-organized spherical colloidal assemblies.