Actuation of shape-memory colloidal fibres of Janus ellipsoids

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Many natural micrometre-scale assemblies can be actuated to control their optical, transport and mechanical properties, yet such functionality is lacking in colloidal structures synthesized thus far. Here, we show with experiments and computer simulations that Janus ellipsoids can self-assemble into self-limiting one-dimensional fibres with shape-memory properties, and that the fibrillar assemblies can be actuated on application of an external alternating-current electric field. Actuation of the fibres occurs through a sliding mechanism that permits the rapid and reversible elongation and contraction of the Janus-ellipsoid chains by ~36% and that on long timescales leads to the generation of long, uniform self-assembled fibres. Colloidal-scale actuation might be useful in microrobotics and in applications of shape-memory materials.

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Figure 1: Janus-ellipsoid self-assembly at different NaCl concentrations.
Figure 2: Phase diagram and mechanism of Janus-ellipsoid self-assembly.
Figure 3: Electric-field-assisted assembly of Janus ellipsoids.
Figure 4: Actuation of Janus-ellipsoid fibres by using a.c. electric fields.
Figure 5: Changes in Janus-fibre length due to an a.c. electric field.


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This material is based on work supported by the US Army Research Office under Grant Award No. W911NF-10-1-0518 and by the Assistant Secretary of Defense for Research and Engineering, US Department of Defense [DOD/ASD(R&E)] under Award No. N00244-09-1-0062.

Author information

A.A.S. and M.J.S. conceived the research and designed the experiments. A.A.S. synthesized the particles, developed the imaging methods and created the assembly devices. A.A.S. and W.Z. performed the experiments. B.S. and S.C.G. designed the computer simulations. B.S. performed the simulations and produced the computer-generated renderings. A.A.S., B.S., S.C.G. and M.J.S. analysed the data and wrote the manuscript. All authors reviewed and approved the manuscript.

Correspondence to Aayush A. Shah or Benjamin Schultz or Michael J. Solomon.

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Shah, A., Schultz, B., Zhang, W. et al. Actuation of shape-memory colloidal fibres of Janus ellipsoids. Nature Mater 14, 117–124 (2015) doi:10.1038/nmat4111

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