MIT Researchers Discover New Approach to Nanoparticle Assembly

Researchers at MIT have made a significant breakthrough in materials science by discovering that flexible molecular connections can lead to new arrangements of nanoparticles, challenging two decades of conventional wisdom.

Traditionally, scientists believed that rigid molecular connections were essential for controlling how nanoparticles assemble into advanced materials. However, the MIT team found that using highly flexible connectors allows nanoparticles to organize themselves in ways previously thought impossible.

This innovative approach enables the creation of crystal structures that have never been observed before, potentially overcoming a major challenge in materials science and paving the way for substances with precisely engineered properties.

The findings, set to be published in Nature Materials, highlight how the flexibility and electrical charges of molecular connectors influence the structures formed by nanoparticles.

Rethinking Nanoparticle Assembly

Rob Macfarlane, the Richard P. Simmons (1953) Professor in Metallurgy at MIT, noted, “People are interested in nanoparticle superlattices because of the promise of building designer materials where you have more say in what types of structures they can actually build into.” He emphasized that this new approach to nanoparticle assembly is a departure from the long-held belief that rigid connectors are necessary for successful assembly.

The research team included MIT PhD candidate Nicholas Sbalbi, University of Delaware doctoral student Stephen Kronenberger, MIT undergraduate Hana Shinzawa, Matthew Ye PhD ’26, and Arthi Jayaraman, a former professor at the University of Delaware.

Macfarlane explained that the arrangement of a material’s smallest components determines its behavior. “If you know what your building blocks are and how they’re arranged, you can explain what properties materials have,” he said. This principle is crucial for nanoparticles, which can be tailored for various applications, including drug delivery and energy storage.

Challenges in Controlling Nanoparticles

Controlling how nanoparticles connect remains a significant challenge. Researchers must determine not only how many neighboring particles each nanoparticle connects with but also the directions of those connections.

Traditional methods to address this issue involve altering the shapes of nanoparticles or modifying specific surface areas to attract neighboring particles. However, these approaches can be complex and difficult to scale for mass production.

Macfarlane noted that existing methods for defining the stickiness of nanoparticles are often bespoke and limited to specific materials and conditions, making them less practical for broader applications.

Embracing Flexibility in Molecular Bonds

The MIT team decided to explore a different strategy by allowing molecular connectors to remain flexible. Instead of enforcing rigid bonds, they made the connectors flexible enough to reorganize as the nanoparticles come together.

Macfarlane stated, “We thought, ‘Let’s do the exact opposite: make the bonds so flexible it doesn’t matter what direction they’re initially pointing.'” This flexibility allows the connectors to adjust naturally, limiting how many neighbors each particle can bind.

The researchers equipped nanoparticles with flexible ligands that carry electrical charges, which attract each other based on their opposite charges. This attraction facilitates the joining of nanoparticles while allowing for a variety of connections.

Creating Unseen Crystal Structures

Experiments led by Sbalbi demonstrated that by adjusting the sizes of the nanoparticles and the lengths of their flexible molecular chains, the team could control how the particles assembled, leading to previously unseen crystal structures.

These structures, known as superlattices, are formed from organized arrangements of nanoparticles rather than individual atoms. By reducing the number of connections, the researchers created more open arrangements, allowing for greater diversity in the structures formed.

Macfarlane explained, “Without having to predesign where the particles connect or what their shapes are, we can control the number of bonds each particle has.” This flexibility enables the creation of novel lattices that were previously unattainable.

Future Prospects for Customizable Materials

The researchers believe their method could lead to a new era of customizable materials, allowing scientists to select nanoparticles based on their individual properties and arrange them for specific applications.

Macfarlane remarked, “In theory, that should be the case. In reality, it absolutely has not been.” The new approach may help bridge this gap by enabling a wider variety of structures without the complexities of traditional assembly methods.

Potential applications for these advanced materials span across electronics, medicine, and energy technologies, where precisely organized nanoparticles could enhance performance and functionality.

The research received partial support from the National Science Foundation, the Department of Energy, the U.S. Army, and the U.S. Navy.

 

Source: ScienceDaily Engineering