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Nat Commun. 2017 Sep 28;8(1):721. doi: 10.1038/s41467-017-00538-z.

Shaping micro-clusters via inverse jamming and topographic close-packing of microbombs.

Author information

1
Materials Architecturing Research Center, Korea Institute of Science and Technology, Seoul, 136-791, Republic of Korea.
2
Department of Materials Science and Engineering, Yonsei University, Seoul, 120-749, Republic of Korea.
3
Department of Materials Science and Engineering, University of Pennsylvania, 3231 Walnut Street, Philadelphia, PA, 19104, USA.
4
3D New Devices Research Section, Electronics and Telecommunications Research Institute, Daejeon, 305-700, Republic of Korea.
5
Nanomaterials Science and Engineering, University of Science and Technology, Daejeon, 305-350, Republic of Korea.
6
Department of Materials Science and Engineering, University of Pennsylvania, 3231 Walnut Street, Philadelphia, PA, 19104, USA. shuyang@seas.upenn.edu.
7
Materials Architecturing Research Center, Korea Institute of Science and Technology, Seoul, 136-791, Republic of Korea. koo@kist.re.kr.
8
Nanomaterials Science and Engineering, University of Science and Technology, Daejeon, 305-350, Republic of Korea. koo@kist.re.kr.
9
KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul, 02841, Republic of Korea. koo@kist.re.kr.

Abstract

Designing topographic clusters is of significant interest, yet it remains challenging as they often lack mobility or deformability. Here we exploit the huge volumetric expansion (up to 3000%) of a new type of building block, thermally expandable microbombs. They consist of a viscoelastic polymeric shell and a volatile gas core, which, within structural confinement, create micro-clusters via inverse jamming and topographical close-packing. Upon heating, microbombs anchored in rigid confinement underwent balloon-like blowing up, allowing for dense clusters via soft interplay between viscoelastic shells. Importantly, the confinement is unyielding against the internal pressure of the microbombs, thereby enabling self-assembled clusters, which can be coupled with topographic inscription to introduce structural hierarchy on the clusters. Our strategy provides densely packed yet ultralight clusters with a variety of complex shapes, cleavages, curvatures, and hierarchy. In turn, these clusters will enrich our ability to explore the assemblies of the ever-increasing range of microparticle systems.Self-assembled systems are normally composed of incompressible building blocks, which constrain their space filling efficiency. Yu et al. show programmable, densely packed clusters using thermally expandable soft microparticles, whereby the self-assembling process is realized via a jamming transition.

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