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 conductivity2,3,4 that are suitable for applications in soft robotics and self-healing electronics5,6,7. 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 attention9,10,11,12. 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).
This is a preview of subscription content
Subscribe to Journal
Get full journal access for 1 year
only $8.25 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
The data that support the plots within this paper and other findings of this study are available from the corresponding author on reasonable request.
Bartlett, M. D. et al. High thermal conductivity in soft elastomers with elongated liquid metal inclusions. Proc. Natl Acad. Sci. USA 114, 2143–2148 (2017).
Fassler, A. & Majidi, C. Liquid-phase metal inclusions for a conductive polymer composite. Adv. Mater. 27, 1928–1932 (2015).
Kramer, R. K., Majidi, C. & Wood, R. J. Masked deposition of gallium–indium alloys for liquid-embedded elastomer conductors. Adv. Funct. Mater. 23, 5292–5296 (2013).
Tabatabai, A., Fassler, A., Usiak, C. & Majidi, C. Liquid-phase gallium–indium alloy electronics with microcontact printing. Langmuir 29, 6194–6200 (2013).
Palleau, E. et al. Self-healing stretchable wires for reconfigurable circuit wiring and 3D microfluidics. Adv. Mater. 25, 1589–1592 (2013).
Blaiszik, B. J. et al. Autonomic restoration of electrical conductivity. Adv. Mater. 24, 398–401 (2012).
Markvicka, E. J., Bartlett, M. D., Huang, X. & Majidi, C. An autonomously electrically self-healing liquid metal–elastomer composite for robust soft-matter robotics and electronics. Nat. Mater. 1, 618–624 (2018).
Kumar, S. K., Benicewicz, B. C., Vaia, R. A. & Winey, K. I. 50th anniversary perspective: are polymer nanocomposites practical for applications? Macromolecules 50, 714–731 (2017).
Finkenauer, L. R. et al. Analysis of the efficiency of surfactant-mediated stabilization reactions of EGaIn nanodroplets. Langmuir 33, 9703–9710 (2017).
Farrell, Z. J. & Tabor, C. Control of gallium oxide growth on liquid metal eutectic gallium/indium nanoparticles via thiolation. Langmuir 34, 234–240 (2018).
Hohman, J. N. et al. Directing substrate morphology via self-assembly: ligand-mediated scission of gallium–indium microspheres to the nanoscale. Nano Lett. 11, 5104–5110 (2011).
Boley, J. W., White, E. L. & Kramer, R. K. Mechanically sintered gallium–indium nanoparticles. Adv. Mater. 27, 2355–2360 (2015).
Dickey, M. D. et al. Eutectic gallium–indium (EGaIn): a liquid metal alloy for the formation of stable structures in microchannels at room temperature. Adv. Funct. Mater. 18, 1097–1104 (2008).
Yan, J. et al. A fatty acid-inspired tetherable initiator for surface-initiated atom transfer radical polymerization. Chem. Mater. 29, 4963–4969 (2017).
Xu, Q. et al. Effect of oxidation on the mechanical properties of liquid gallium and eutectic gallium–indium. Phys. Fluids 24, 063101 (2012).
Konkolewicz, D. et al. SARA ATRP or SET-LRP. End of controversy? Polym. Chem. 5, 4396–4417 (2014).
Chung, J. Y., Nolte, A. J. & Stafford, C. M. Surface wrinkling: a versatile platform for measuring thin-film properties. Adv. Mater. 23, 349–368 (2011).
Brandrup J. et al. (eds) Polymer Handbook 4th edn (Wiley, 1999).
Porter, R. S. & Johnson, J. F. The entanglement concept in polymer systems. Chem. Rev. 66, 1–27 (1966).
Wahlander, M. et al. Tailoring dielectric properties using designed polymer-grafted ZnO nanoparticles in silicone rubber. J. Mater. Chem. A 5, 14241–14258 (2017).
Johnston, I., McCluskey, D., Tan, C. & Tracey, M. Mechanical characterization of bulk Sylgard 184 for microfluidics and microengineering. J. Micromech. Microeng. 24, 035017 (2014).
Spontak, R. J. & Patel, N. P. Thermoplastic elastomers: fundamentals and applications. Curr. Opin. Colloid Interface Sci. 5, 333–340 (2000).
Dufour, B., Koynov, K., Pakula, T. & Matyjaszewski, K. PBA-PMMA 3-arm star block copolymer thermoplastic elastomers. Macromol. Chem. Phys. 209, 1686–1693 (2008).
Yan, J. et al. Matrix-free particle brush system with bimodal molecular weight distribution prepared by SI-ATRP. Macromolecules 48, 8208–8218 (2015).
Dick, K., Dhanasekaran, T., Zhang, Z. & Meisel, D. Size-dependent melting of silica-encapsulated gold nanoparticles. J. Am. Chem. Soc. 124, 2312–2317 (2002).
Wronski, C. R. M. The size dependence of the melting point of small particles of tin. Br. J. Appl. Phys. 18, 1731 (1967).
Yamaguchi, A., Mashima, Y. & Iyoda, T. Reversible size control of liquid-metal nanoparticles under ultrasonication. Angew. Chem. Int. Ed. 54, 12809–12813 (2015).
Rossa, L. & Vögtle, F. in Cyclophanes I Vol. 113 (ed Vögtle, F.) 1–86 (Springer, 1983).
Mansfield, M. L., Douglas, J. F., Irfan, S. & Kang, E.-H. Comparison of approximate methods for calculating the friction coefficient and intrinsic viscosity of nanoparticles and macromolecules. Macromolecules 40, 2575–2589 (2007).
Tsuda, K., Kobayashi, S. & Otsu, T. Vinyl polymerization. CXVI. The effects of several sulfides and oxides on radical polymerization. Bull. Chem. Soc. Jpn 38, 1517–1522 (1965).
The authors acknowledge financial support from the National Science Foundation (DMR 1501324, DMR-1709344 and CMMI-1663305) and the Air Force Office of Scientific Research (AFOSR) Multidisciplinary University Research Initiative (FA9550-18-1-0566; programme manager, K.Goretta). The authors also acknowledge the use of facilities in the Colloids, Surfaces and Polymer Laboratory at Carnegie Mellon, supported by grant no. CMU 678083-769798.
The authors declare no competing interests.
Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
About this article
Cite this article
Yan, J., Malakooti, M.H., Lu, Z. et al. Solution processable liquid metal nanodroplets by surface-initiated atom transfer radical polymerization. Nat. Nanotechnol. 14, 684–690 (2019). https://doi.org/10.1038/s41565-019-0454-6
Nano Research (2022)
npj Flexible Electronics (2021)
Nature Reviews Chemistry (2021)
Nature Nanotechnology (2021)
Nature Nanotechnology (2019)