Solution processable liquid metal nanodroplets by surface-initiated atom transfer radical polymerization

Jiajun Yan; Mohammad H Malakooti; Zhao Lu; Zongyu Wang; Navid Kazem; Chengfeng Pan; Michael R Bockstaller; Carmel Majidi; Krzysztof Matyjaszewski

doi:10.1038/s41565-019-0454-6

Solution processable liquid metal nanodroplets by surface-initiated atom transfer radical polymerization

Nat Nanotechnol. 2019 Jul;14(7):684-690. doi: 10.1038/s41565-019-0454-6. Epub 2019 May 20.

Authors

Jiajun Yan¹, Mohammad H Malakooti², Zhao Lu³, Zongyu Wang¹, Navid Kazem⁴, Chengfeng Pan², Michael R Bockstaller⁵, Carmel Majidi^{6

7}, Krzysztof Matyjaszewski⁸

Affiliations

¹ Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA, USA.
² Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA, USA.
³ Department of Materials Science & Engineering, and Carnegie Mellon University, Pittsburgh, PA, USA.
⁴ Department of Civil and Environmental Engineering, Carnegie Mellon University, Pittsburgh, PA, USA.
⁵ Department of Materials Science & Engineering, and Carnegie Mellon University, Pittsburgh, PA, USA. bockstaller@cmu.edu.
⁶ Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA, USA. cmajidi@andrew.cmu.edu.
⁷ Department of Civil and Environmental Engineering, Carnegie Mellon University, Pittsburgh, PA, USA. cmajidi@andrew.cmu.edu.
⁸ Department of Chemistry, Carnegie Mellon University, Pittsburgh, PA, USA. km3b@andrew.cmu.edu.

PMID: 31110266
DOI: 10.1038/s41565-019-0454-6

Abstract

Eutectic gallium indium (EGaIn) is a liquid metal alloy at room temperature. EGaIn microdroplets can be incorporated into elastomers to fabricate highly stretchable, mechanically robust, soft multifunctional composites with high thermal stability¹ and electrical conductivity^2-4 that are suitable for applications in soft robotics and self-healing electronics^5-7. However, the current methods of preparation rely on mechanical mixing, which may lead to irregularly shaped micrometre-sized droplets and an anisotropic distribution of properties⁸. Therefore, procedures for the stabilization of sub-micrometre-sized droplets of EGaIn and compatibilization in polymer matrices and solvents have attracted significant attention^9-12. Here we report the synthesis of EGaIn nanodroplets stabilized by polymeric ligand encapsulation. We use a surface-initiated atom transfer radical polymerization initiator to covalently functionalize the oxide layer on the surface of the EGaIn nanodroplets¹³ with poly(methyl methacrylate) (PMMA), poly(n-butyl acrylate) (PBMA), poly(2-dimethylamino)ethyl methacrylate) (PDMAEMA) and poly(n-butyl acrylate-block-methyl methacrylate) (PBA-b-PMMA). These nanodroplets are stable in organic solvents, in water or in polymer matrices up to 50 wt% concentration, enabling direct solution-casting into flexible hybrid materials. The liquid metal can be recovered from dispersion by acid treatment. The nanodroplets show good mechanical, thermal and optical properties, with a remarkable suppression of crystallization and melting temperatures (down to -80 °C from 15 °C).