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Transforming Circles Into Squares: Researchers Reconfigure Material Topology on the Microscale

Researchers encoded patterns and designs into the materials by making tiny, invisible tweaks to the geometry of the triangular lattice. Credit score: Picture courtesy of Shucong Li/Bolei Deng/Harvard SEAS

Reconfigurable supplies can do wonderful issues. Flat sheets transform into a face. An extruded cube transforms into dozens of different shapes. However there’s one factor a reconfigurable materials has but to have the ability to change: its underlying topology. A reconfigurable materials with 100 cells will all the time have 100 cells, even when these cells are stretched or squashed.

Now, researchers from the Harvard John A. Paulson College of Engineering and Utilized Sciences (SEAS) have developed a technique to vary a mobile materials’s basic topology at the microscale. The analysis is printed in Nature

“Creating mobile buildings able to dynamically altering their topology will open new alternatives in growing energetic supplies with data encryption, selective particle trapping, in addition to tunable mechanical, chemical and acoustic properties,” stated Joanna Aizenberg, the Amy Smith Berylson Professor of Supplies Science at SEAS and Professor of Chemistry & Chemical Biology and senior creator of the paper.

Triangles Material Topology

Researchers developed a technique to vary a mobile materials’s basic topology at the microscale, paving the method for energetic supplies with tunable mechanical, chemical and acoustic properties. Credit score: Photographs courtesy of Shucong Li/Bolei Deng/Harvard SEAS

The researchers harnessed the similar physics that clumps our hair collectively when it will get moist — capillary pressure. Capillary pressure works effectively on delicate, compliant materials, like our hair, however struggles with stiff mobile buildings that require the bending, stretching or folding of partitions, particularly round robust, related nodes. Capillary pressure can also be momentary, with supplies tending to return to their unique configuration after drying.

With a view to develop a long-lasting but reversible methodology to remodel the topology of stiff mobile microstructures, the researchers developed a two-tiered dynamic technique. They started with a stiff, polymeric mobile microstructure with a triangular lattice topology, and uncovered it to droplets of a unstable solvent chosen to swell and soften the polymer at the molecular scale. This made the materials quickly extra versatile and on this versatile state, the capillary forces imposed by the evaporating liquid drew the edges of the triangles collectively, altering their connections with each other and remodeling them into hexagons. Then, as the solvent quickly evaporated, the materials dried and was trapped in its new configuration, regaining its stiffness. The entire course of took a matter of seconds.

“When you consider functions, it’s actually essential to not lose a cloth’s mechanical properties after the transformation course of,” stated Shucong Li, a graduate scholar in the Aizenberg Lab and co-first creator of the paper. “Right here, we confirmed that we are able to begin with a stiff materials and finish with a stiff materials via the strategy of quickly softening it at the reconfiguration stage.”

Video of the meeting of the microstructures. The triangle lattice is uncovered to a liquid which swells and softens the polymer. On this versatile state, the capillary forces imposed by the evaporating liquid drew the edges of the triangles collectively, altering their connections with each other and remodeling them into hexagons. Credit score: Video courtesy of Shucong Li/Bolei Deng/Harvard SEAS

The brand new topology of the materials is so sturdy it will possibly stand up to warmth or be submerged in some liquids for days with out disassembling. Its robustness truly posed an issue for the researchers who had hoped to make the transformation reversible.

To return to the unique topology, the researchers developed a way that mixes two liquids. The primary quickly swells the lattice, which peels aside the adhered partitions of the hexagons and permits the lattice to return to its unique triangular construction. The second, much less unstable liquid delays the emergence of capillary forces till the first liquid has evaporated and the materials has regained its stiffness. On this method, the buildings will be assembled and disassembled repeatedly and trapped in any in-between configuration.

Video of the disassembly of the microstructures. The primary quickly swells the lattice, which peels aside the adhered partitions. The second, much less unstable liquid delays the emergence of capillary forces till the first liquid has evaporated and the materials has regained its stiffness. Credit score: Video courtesy of Shucong Li/Bolei Deng/Harvard SEAS

“With a view to lengthen our method to arbitrary lattices, it was essential to develop a generalized theoretical mannequin that connects mobile geometries, materials stiffness and capillary forces,” stated Bolei Deng, co-first creator of the paper and graduate scholar in the lab of Katia Bertoldi, the William and Ami Kuan Danoff Professor of Utilized Mechanics at SEAS.  

Guided by this mannequin, the researchers demonstrated programmed reversible topological transformations of assorted lattice geometries and responsive supplies, together with turning a lattice of circles into squares.

The researchers explored numerous functions for the examine.  For instance, the staff encoded patterns and designs into the materials by making tiny, invisible tweaks to the geometry of the triangular lattice.  

“You possibly can think about this getting used for data encryption in the future, as a result of you may’t see the sample in the materials when it’s in its unassembled state,” stated Li.

The researchers additionally demonstrated extremely native transformation, assembling and disassembling areas of the lattice with a tiny drop of liquid. This methodology might be used to tune the friction and wetting properties of a cloth, change its acoustic properties and mechanical resilience, and even lure particles and fuel bubbles.

“Our technique might be utilized to a spread of functions,” stated Bertoldi, who can also be a co-author of the paper. “We are able to apply this methodology to completely different supplies, together with responsive supplies, completely different geometries and completely different scales, even the nanoscale the place topology performs a key position in designing tunable photonic meta-surfaces. The design area for that is large.”

Reference: “Liquid-induced topological transformations of mobile microstructures” by Shucong Li, Bolei Deng, Alison Grinthal, Alyssha Schneider-Yamamura, Jinliang Kang, Reese S. Martens, Cathy T. Zhang, Jian Li, Siqin Yu, Katia Bertoldi and Joanna Aizenberg, 14 April 2021, Nature.
DOI: 10.1038/s41586-021-03404-7

This analysis was co-authored by Alison Grinthal, Alyssha Schneider-Yamamura, Jinliang Kang, Reese S. Martens, Cathy T. Zhang, Jian Li, and Siqin Yu.

It was supported by the Nationwide Science Basis via the Designing Supplies to Revolutionize and Engineer our Future (DMREF) program below award no. DMR-1922321, the Harvard College Supplies Analysis Science and Engineering Heart (MRSEC) below award no. DMR-18 2011754, and by the US Division of Power (DOE), Workplace of Science, Primary Power Sciences (BES) below award quantity DE-SC0005247.

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