By Josh Perry, Editor
[email protected]

Chemists and engineers from Carnegie Mellon University (Pittsburgh, Pa.) developed a new method for creating stretchable polymer composites that demonstrate enhanced electrical and thermal properties, according to a report from the school.

New research creates polymers with enhanced thermal and electrical properties.
(Carnegie Mellon University)

Researchers incorporated eutectic gallium indium (EGaIn), which is a metal alloy that is a liquid at room temperature, into an elastomer to produce a soft, stretchable composite with high thermal stability and electrical conductivity.

The final product used a combination of techniques developed by Carnegie Mellon researchers, including a process for building rubber composites with nanoparticles of liquid metal and atom transfer radical polymerization (ATRP), which allows precise tailoring of polymers to produce specific properties.

Scientists “used ATRP to attach monomer brushes to the surface of EGaIn nanodroplets. The brushes were able to link together, forming strong bonds to the droplets. As a result, the liquid metal uniformly dispersed throughout the elastomer, resulting in a material with high elasticity and high thermal conductivity.”

The research was recently published in Nature Nanotechnology. The abstract read:

“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 stability and electrical conductivity that are suitable for applications in soft robotics and self-healing electronics.

“However, the current methods of preparation rely on mechanical mixing, which may lead to irregularly shaped micrometre-sized droplets and an anisotropic distribution of properties. Therefore, procedures for the stabilization of sub-micrometre-sized droplets of EGaIn and compatibilization in polymer matrices and solvents have attracted significant attention.

“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 nanodroplets 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).”