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The initiative has the potential to disrupt the creation of materials for an array of uses, such as robotics and high-performance computing

A team of researchers, which includes participants from the University of Michigan, has introduced a novel observational method that is attuned to the movements of the inherent quantum fluctuations within materials, referred to as phonons.

This endeavor will assist scientists and engineers in crafting metamaterials—substances endowed with unusual characteristics that are seldom found in the natural world—that can be reconfigured and are composed of solutions with nanoparticles that aggregate into larger formations, as noted by the researchers. These materials hold extensive applications, ranging from shock absorption to guiding acoustic and optical energy in advanced computing devices.

“This paves the way for a new area of research wherein nanoscale components—along with their fundamental optical, electromagnetic, and chemical traits—can be integrated into mechanical metamaterials, fostering the emergence of technologies across diverse domains, from robotics and mechanical engineering to information technology,” stated Xiaoming Mao, U-M physics professor and co-author of the recent study.

Phonons are natural occurrences that can be understood as discrete wave packets traversing the components of materials, whether these are atoms, particles, or 3D-printed joints, causing vibrations and facilitating energy transfer. This description arises from quantum mechanics and reflects common attributes seen in various contexts, including heat transfer, sound propagation, and even seismic waves generated by earthquakes.

Certain materials, both synthetic and natural, are engineered to guide phonons along designated paths, imparting specific mechanical properties. Two tangible instances of this are materials employed in structures designed to endure seismic waves during earthquakes and the development of the robust yet lightweight frameworks of deep-sea sponges that allow these organisms to resist the extreme pressures found in deep-water settings.

“Utilizing the liquid-phase electron microscopy method developed in our laboratory at Illinois, this new research represents the first instance where we’ve successfully observed phonon dynamics in nanoparticle assemblies, functioning as a novel variety of mechanical metamaterials,” remarked Qian Chen, a professor of materials science and engineering at the University of Illinois.

Published in the journal Nature Materials, the study merges nanoparticle assembly with principles of mechanical metamaterials, thereby enabling the engineering of mechanical traits through architectural design. This project stems from a four-year collaboration involving Chen, who directed the materials science and experimental facets, Mao at U-M, who spearheaded the theoretical and mechanical metamaterial segments, and Wenxiao Pan, assistant professor of mechanical engineering at the University of Wisconsin who spearheaded the simulation aspect.

“The design of metamaterials is a highly active domain,” Chen commented. “Most of the research has concentrated on the macroscale, where it is simpler to manage geometry and structure as well as assess and model phonon properties.”

However, Chen and her team operate at the nanoscale, where both engineering and theoretical methods of phonon manipulation present significant challenges. To overcome these obstacles, the group employed precise theoretical modeling alongside experimental approaches, observational techniques, and machine learning-enhanced simulations to formulate a new paradigm for metamaterials design.

In the laboratory, using liquid-phase electron microscopy, the team scrutinized the vibrational paths of gold nanoparticles to establish the phonon band structures, which were then correlated to a discrete mechanical framework to extract nanoscale springs.

“This research also highlights the capacity of machine learning to further the exploration of complex particle systems, enabling the monitoring of their self-assembly routes governed by intricate dynamics,” Pan stated. “It opens fresh pathways for data-driven inverse design of reconfigurable colloidal metamaterials utilizing machine learning and artificial intelligence.”

The Office of Naval Research, National Science Foundation, Defense Established Program to Stimulate Competitive Research, and Army Research Office funded this investigation.

“We believe we are positioned at a compelling intersection of disciplines, collaboration, and the necessity for innovation in materials science,” Chen concluded. “With nanoparticle assembly, we can engineer structures with meticulously controlled geometry, and then utilize mechanical metamaterials to refine the theoretical framework in material design.”

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