Versatile ‘nanocrystal gel’ could enable advances in energy, defense and telecommunications


This graphic shows the material in its gelled state (left) and its ungelled state (right). When the material is heated (right), the chemical bonds between the nanocrystals break and the gel breaks down. As the material (left) cools, chemical bonds form between the nanocrystals and they organize into a network (the gel). Molecular bonds (top) that control gelation as a function of temperature are understood using supercomputer simulations (bottom). Photo credit: Kang, Valenzuela, et al./UT Austin

New applications in energy, defense and telecommunications could get a boost after a team at the University of Texas at Austin developed a new type of “nanocrystal gel” – a gel made up of tiny nanocrystals, each 10,000 times smaller than the width of a human hair are connected in an organized network.

The whole point of the team’s discovery is that this new material is easy to tune. That is, it can be switched between two different states by changing the temperature. This means the material can act as an optical filter, absorbing different frequencies of light depending on whether it is in a gelled state or not. For example, it could be used on the outside of buildings to dynamically control heating or cooling. This type of optical filter also has defense applications, particularly thermal camouflage.

The gels can be tailored for these diverse applications because both the nanocrystals and the molecular linkers that connect them into networks are designer components. Nanocrystals can be chemically tuned to be useful for routing communications through fiber optic networks or keeping spacecraft at a constant temperature on distant planetary bodies. Linkers can be designed to cause gels to switch based on ambient temperature or detection of environmental toxins.

“You could shift an object’s apparent thermal signature by changing the infrared properties of its skin,” said Delia Milliron, professor and chair of the McKetta Department of Chemical Engineering at the Cockrell School of Engineering. “It could also be useful for telecommunications, which all use infrared wavelengths.”

This video demonstrates the tunability of the material as the temperature changes. The sample begins in its ungelled state (referred to as a “dispersion”). As the material cools, the material begins to transform into a nanocrystal gel (referred to as the “sol-to-gel transition”) until the entire sample is in gel form. Next, heat is applied and the nanocrystal gel breaks down again. Photo credit: Cockrell School of Engineering, University of Texas at Austin

The new research is published in the latest issue of the journal scientific advances.

The team, led by graduate students Jiho Kang and Stephanie Valenzuela, conducted this work through the university’s Center for Dynamics and Control of Materials, a National Science Foundation materials research, science and technology center that brings together engineers and scientists from across campus to collaborate on materials Science Research.

The laboratory experiments allowed the team to see how the material changes back and forth between its two states, gel and non-gel (ie free-floating nanocrystals suspended in a liquid), which they triggered by specific temperature changes.

Supercomputer simulations performed at UT’s Texas Advanced Computing Center helped them understand what happens in the gel at the microscopic level when heat is applied. Based on theories from chemistry and physics, the simulations showed the types of chemical bonds that hold the nanocrystals together in a network and how these bonds break when exposed to heat, causing the gel to break down.

This simulation shows 100 nanocrystals at a temperature above the gelation threshold. In doing so, most anocrystals remain in a free-flowing state without sticking together, which is referred to as dispersion. Photo credit: Kang, Valenzuela, et al./UT Austin

This is the second unique nanocrystal gel developed by this team and they continue to track advances in this area. Kang is currently working on developing a nanocrystal gel that can switch between four states, making it even more versatile and useful. This gel would be a mixture of two different types of nanocrystals, each capable of switching between states in response to chemical cues or changes in temperature. Such tunable nanocrystal gels are called “programmable” materials.

Scientists synthesize hafnium-based vacancy-ordered perovskite nanocrystals by hot injection methods

More information:
Jiho Kang et al, Colorimetric Quantification of Linkage in Thermoreversible Nanocrystal Gel Arrays, scientific advances (2022). DOI: 10.1126/sciadv.abm7364.

Provided by the University of Texas at Austin

citation: Versatile “Nanocrystal Gel” Could Enable Advances in Energy, Defense and Telecom (2022 February 18) Retrieved February 20, 2022 from -enable-advances. html

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