| Feb 04, 2022 |
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(Nanowerk News) Colloids are microparticles in a solution, meaning 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 sought ways to assemble these crystals into larger structures using bonding methods that operate in targeted directions. However, this approach is quite challenging.
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A new strategy exploits the ability to create precise regions with specific chemical and physical properties on the surface of the crystal particles (Nature Materials, “Tunable assembly of hybrid colloids induced by regioselective depletion”). Scientists can use selective interactions between these regions on different particles to direct the formation of the crystal structure.
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| Schematic of a particle with distinct regions (left). The bright-field fluorescent images (center and left) and schematics (inserts) show selective crystallization via pole-to-pole or center-to-center interactions. Scale bars are 5 microns. (Image: David Pine, New York University)
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This strategy is a powerful approach for programming the assembly of particles with desired geometry and properties. The strategy has several key benefits. It avoids the need for costly and complex chemical surface engineering. It can construct materials ranging from simple chains to membrane-like structures. It can also readily tune materials’ properties and structures without having to create a new material from scratch each time.
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Colloidal crystals are commonly formed from a mixture of large and small particles. Attractive forces between the larger particles push the small particles away. The larger particles squeeze together into tighter and tighter packings that eventually lead to crystal formation.
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The composition of the smaller particles influences this squeezing process. Scientists have suggested that it is theoretically possible to use these forces to selectively position non-spherical particles within a crystal lattice by creating surface patches.
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However, scientists had not realized this possibility. Now, researchers have developed a process for building hybrid particles composed of distinct polymer regions. In this process, tuning the surface charges on the particles favored interactions between certain regions. This enabled a specific region of one particle to interact selectively with the same region on neighboring particles.
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The researchers used these interactions along with particle size and shape to control the bonding angles among particles and consequently the structural features and properties of the resulting crystals. The researchers observed the simultaneous formation of crystals with different structures in real time using advanced microscopy and computational methods. These interactions are reversible.
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This approach potentially allows straightforward reconfiguration of crystal properties and switching between crystal structures.
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