Colloids are microparticles in a solution, which means the particles are evenly distributed. Crystals made from colloids are valuable in a wide range of applications such as batteries, fuel cells, sensors, solar cells and catalysts. Scientists have looked for ways to assemble these crystals into larger structures using bonding methods that work in targeted directions. However, this approach is quite difficult. A new strategy exploits the ability to create precise regions with specific chemical and physical properties on the surface of crystal particles. Scientists can use selective interactions between these regions on different particles to direct crystal structure formation.
This strategy is a powerful approach to program particle assembly with desired geometry and properties. The strategy has several key advantages. It avoids the need for costly and complex chemical surface engineering. It can build materials ranging from simple chains to membrane-like structures. It can also easily adjust material properties and structures without having to create a new material from scratch each time.
Colloidal crystals are usually formed from a mixture of large and small particles. The attractive forces between larger particles repel smaller particles. Larger particles squeeze together to form tighter and tighter packings that eventually lead to the formation of crystals. The composition of the smaller particles influences this compression process. Scientists have suggested that it is theoretically possible to use these forces to selectively position non-spherical particles in a crystal lattice by creating surface patches. However, scientists had not realized this possibility. Now the researchers have developed a method to construct hybrid particles composed of distinct polymeric regions. In this process, the adjustment of surface charges on the particles favored the interactions between certain regions. This allowed a specific region of one particle to selectively interact with the same region on neighboring particles. The researchers used these interactions along with particle size and shape to control the bond angles between particles and, therefore, the structural characteristics and properties of the resulting crystals. Researchers observed the simultaneous formation of crystals of different structures in real time using advanced microscopy and computational methods. These interactions are reversible. This approach potentially allows direct reconfiguration of crystal properties and switching between crystal structures.
This work was supported by funding from the Department of Energy’s Office of Science. Partial support for one of the researchers was provided by donors to the American Chemical Society Petroleum Research Fund. The Zeiss Merlin Field Emission SEM was acquired with support from the National Science Foundation.
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