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   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Making the structure of 'fire ice' with nanoparticles    
    The structure harnesses a strange physical phenomenon and could enable   
   engineers to manipulate light in new ways.    
      
     Date:   
         May 25, 2023   
     Source:   
         University of Michigan   
     Summary:   
         Cage structures made with nanoparticles could be a route   
         toward making organized nanostructures with mixed materials,   
         and researchers have shown how to achieve this through computer   
         simulations.   
      
      
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   FULL STORY   
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   Cage structures made with nanoparticles could be a route toward making   
   organized nanostructures with mixed materials, and researchers at the   
   University of Michigan have shown how to achieve this through computer   
   simulations.   
      
   The finding could open new avenues for photonic materials that manipulate   
   light in ways that natural crystals can't. It also showcased an unusual   
   effect that the team is calling entropy compartmentalization.   
      
   "We are developing new ways to structure matter across scales, discovering   
   the possibilities and what forces we can use," said Sharon Glotzer,   
   the Anthony C.   
      
   Lembke Department Chair of Chemical Engineering, who led the study   
   published today in Nature Chemistry. "Entropic forces can stabilize even   
   more complex crystals than we thought."  While entropy is often explained   
   as disorder in a system, it more accurately reflects the system's tendency   
   to maximize its possible states. Often, this ends up as disorder in the   
   colloquial sense. Oxygen molecules don't huddle together in a corner --   
   they spread out to fill a room. But if you put them in the right size box,   
   they will naturally order themselves into a recognizable structure.   
      
   Nanoparticles do the same thing. Previously, Glotzer's team had shown   
   that bipyramid particles -- like two short, three-sided pyramids stuck   
   together at their bases -- will form structures resembling that of fire   
   ice if you put them into a sufficiently small box. Fire ice is made of   
   water molecules that form cages around methane, and it can burn and melt   
   at the same time. This substance is found in abundance under the ocean   
   floor and is an example of a clathrate.   
      
   Clathrate structures are under investigation for a range of applications,   
   such as trapping and removing carbon dioxide from the atmosphere.   
      
   Unlike water clathrates, earlier nanoparticle clathrate structures had no   
   gaps to fill with other materials that might provide new and interesting   
   possibilities for altering the structure's properties. The team wanted   
   to change that.   
      
   "This time, we investigated what happens if we change the shape of   
   the particle. We reasoned that if we truncate the particle a little,   
   it would create space in the cage made by the bipyramid particles,"   
   said Sangmin Lee, a recent doctoral graduate in chemical engineering   
   and first author of the paper.   
      
   He took the three central corners off each bipyramid and discovered the   
   sweet spot where spaces appeared in the structure but the sides of the   
   pyramids were still intact enough that they didn't start organizing in a   
   different way. The spaces filled in with more truncated bipyramids when   
   they were the only particle in the system. When a second shape was added,   
   that shape became the trapped guest particle.   
      
   Glotzer has ideas for how to create selectively sticky sides that would   
   enable different materials to act as cage and guest particles, but in   
   this case, there was no glue holding the bipyramids together. Instead,   
   the structure was completely stabilized by entropy.   
      
   "What's really fascinating, looking at the simulations, is that the host   
   network is almost frozen. The host particles move, but they all move   
   together like a single, rigid object, which is exactly what happens   
   with water clathrates," Glotzer said. "But the guest particles are   
   spinning around like crazy -- like the system dumped all the entropy   
   into the guest particles."  This was the system with the most degrees of   
   freedom that the truncated bipyramids could build in a limited space,   
   but nearly all the freedom belonged to the guest particles. Methane in   
   water clathrates rotates too, the researchers say. What's more, when   
   they removed the guest particles, the structure threw bipyramids that   
   had been part of the networked cage structure into the cage interiors --   
   it was more important to have spinning particles available to maximize   
   the entropy than to have complete cages.   
      
   "Entropy compartmentalization. Isn't that cool? I bet that happens in   
   other systems too -- not just clathrates," Glotzer said.   
      
   Thi Vo, a former postdoctoral researcher in chemical engineering at U-M   
   and now an assistant professor of chemical and biomolecular engineering   
   at the Johns Hopkins University, contributed to the study.   
      
   This study was funded by the Department of Energy and Office of Naval   
   Research, with computing resources provided by the National Science   
   Foundation's Extreme Science and Engineering Discovery Environment and   
   the University of Michigan.   
      
   Glotzer is also the John Werner Cahn Distinguished University Professor   
   of Engineering, the Stuart W. Churchill Collegiate Professor of Chemical   
   Engineering, and a professor of materials science and engineering,   
   macromolecular science and engineering, and physics.   
      
       * RELATED_TOPICS   
             o Matter_&_Energy   
                   # Civil_Engineering # Nature_of_Water # Materials_Science   
                   # Organic_Chemistry   
             o Computers_&_Math   
                   # Computer_Science # Computers_and_Internet # Robotics #   
                   Artificial_Intelligence   
       * RELATED_TERMS   
             o Nanoparticle o Computer_simulation o 3D_computer_graphics   
             o Virtual_reality o Electron_microscope o Supercomputer o   
             Nanotechnology o Triboelectric_effect   
      
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   Story Source: Materials provided by University_of_Michigan. Note:   
   Content may be edited for style and length.   
      
      
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   Related Multimedia:   
       * Cage_network_structure_illustration   
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   Journal Reference:   
      1. Sangmin Lee, Thi Vo, Sharon C. Glotzer. Entropy compartmentalization   
         stabilizes open host-guest colloidal clathrates. Nature Chemistry,   
         2023; DOI: 10.1038/s41557-023-01200-6   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/05/230525141429.htm   
      
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