Kennedy Chris L, Sayasilpi Daphne, Schall Peter, Meijer Janne-Mieke
Department of Applied Physics, Eindhoven University of Technology, Groene Loper 19, 5600 MB Eindhoven, The Netherlands.
Institute for Complex Molecular Systems, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands.
J Phys Condens Matter. 2022 Mar 21;34(21). doi: 10.1088/1361-648X/ac5866.
The structure of self-assembled materials is determined by the shape and interactions of the building blocks. Here, we investigate the self-assembly of colloidal 'superballs', i.e. cubes with rounded corners, by temperature-tunable critical Casimir forces to obtain insight into the coupling of a cubic shape and short range attractions. The critical Casimir force is a completely reversible and controllable attraction that arises in a near-critical solvent mixture. Using confocal microscopy and particle tracking, we follow the self-assembly dynamics and structural transition in a quasi-2D system. At low attraction, we observe the formation of small clusters with square symmetry. When the attraction is increased, a transition to a rhombic Λ-lattice is observed. We explain our findings by the change in contact area at faces and corners of the building blocks combined with the increase in attraction strength and range of the critical Casimir force. Our results show that the coupling between the rounded cubic shape and short-range attraction plays a crucial role for the superstructures that form and provide new insights for the active assembly control of micro and nanocubes.
自组装材料的结构由构建单元的形状和相互作用决定。在此，我们通过温度可调的临界卡西米尔力研究胶体“超级球”（即圆角立方体）的自组装，以深入了解立方形状与短程吸引力的耦合。临界卡西米尔力是在近临界溶剂混合物中产生的一种完全可逆且可控的吸引力。利用共聚焦显微镜和粒子追踪技术，我们追踪了准二维系统中的自组装动力学和结构转变。在低吸引力下，我们观察到形成了具有方形对称性的小聚集体。当吸引力增加时，会观察到向菱形Λ晶格的转变。我们通过构建单元面和角处接触面积的变化，结合临界卡西米尔力吸引力强度和范围的增加来解释我们的发现。我们的结果表明，圆角立方形状与短程吸引力之间的耦合对形成的超结构起着关键作用，并为微纳米立方体的主动组装控制提供了新的见解。
