A general approach to composites containing nonmetallic fillers and liquid gallium

Abstract

We report a versatile method to make liquid metal composites by vigorously mixing gallium (Ga) with non-metallic particles of graphene oxide (G-O), graphite, diamond, and silicon carbide that display either paste or putty-like behavior depending on the volume fraction. Unlike Ga, the putty-like mixtures can be kneaded and rolled on any surface without leaving residue. By changing temperature, these materials can be stiffened, softened, and, for the G-O-containing composite, even made porous. The gallium putty (GalP) containing reduced G-O (rG-O) has excellent electromagnetic interference shielding effectiveness. GalP with diamond filler has excellent thermal conductivity and heat transfer superior to a commercial liquid metal-based thermal paste. Composites can also be formed from eutectic alloys of Ga including Ga-In (EGaIn), Ga-Sn (EGaSn), and Ga-In-Sn (EGaInSn or Galinstan). The versatility of our approach allows a variety of fillers to be incorporated in liquid metals, potentially allowing filler-specific "fit for purpose" materials.

Fig. 1. Synthesis and characterization of a metallic putty made from liquid gallium with a graphene oxide filler.

(A) Left photo shows liquid gallium and GalP (G-O) (3.6 wt % G-O) on glass slides; right photo shows a GalP (G-O) (8.0 wt % G-O) ball with some brown regions on its surface due to the high G-O loading—this GalP (G-O) is easy to crack. (B) GalP (G-O) is highly processable and versatile; it can be readily reshaped to a five-pointed star, a figurine, and a house. Scale bar, 2 cm. (C) Photos showing that GalP (G-O) can be either soft or stiff depending on the temperature: A 5-g piece of soft GalP (G-O) can be sliced easily when T > 31.9°C (left), and the slice can support a 500-g steel block when T < 31.9°C (right). Scale bars, 2 cm. (D) SEM image of GalP (G-O); pink dotted lines indicate some pores generated by the stacking of the G-O sheets. (E) Magnified SEM image and (F) TEM image showing the combination of a G-O sheet with gallium. (G) Viscosity of GalP (G-O) (with different G-O mass loading) under different shear rates. (H) Density of GalP (G-O) as a function of the G-O mass fraction. (I) Tensile strength of GalP (G-O) with different G-O mass fractions. Photos in (A) and (B) were taken at 26°C, and Ga in (A) is liquid due to supercooling. Photo credits: Chunhui Wang, Center for Multidimensional Carbon Materials, Institute for Basic Science.

Fig. 2. Fabrication of various nonmetallic/GLM composites and a porous Ga/rG-O foam.

(A) Illustration of the formation mechanism of GalP; the particle size and Ga oxide layer are two key factors in the formation of GalP. (B) Illustration showing the fabrication of GLM composites by mixing graphite flakes, diamond, or SiC particles with GLM; as long as the particle size is large enough, it is able to be incorporated with GLM. (C) EMI SE of a GalP (SP) composite with thicknesses of 1.6 and 2.0 mm. Inset: Photos showing that GalP (SP) is stretchable. (D) SEM image of a porous Ga/rG-O foam. Inset: Illustration showing the volume expansion of GalP (G-O); the blue background represents the Ga matrix, the yellow sheets represent G-O, the black sheets represent rG-O, and the white dots are the pores formed. (E) Volume expansion of GalP (G-O) with different G-O mass loadings as a function of temperature. Inset: Optical photos showing the volume expansion of a GalP (G-O) (3.6 wt % G-O) ball upon heating. Scale bars, 2.0 cm. (F) EMI SE of porous Ga/rG-O foam with a thickness of 0.5 mm. Inset: Left photo shows the exterior and interior of a Ga/rG-O foam; right photo shows that the Ga/rG-O foam is heat resistant, as it remains stable under a blowtorch. Photos in (B) and (C) were taken at 26°C. GalP (D) and GalP (SP) are soft due to being handheld. Photo credits: Chunhui Wang, Center for Multidimensional Carbon Materials, Institute for Basic Science.

Fig. 3. GalP on various substrates as a UV or electromagnetic shielding coating.

(A) UV-vis spectra of glass/GalP (rG-O), CNF/GalP (rG-O), and PET/GalP (rG-O) film. The transparent glass, CNF, and PET films exhibit complete shielding of UV rays in both the UV-B and UV-A regions, after coating with 1-μm-thick GalP (rG-O) coating. (B) EMI SE of GalP (rG-O) of different thicknesses coated on a commercial A4 paper. (C) SEM image of the cross section of an rG-O/GalP (rG-O) film. Inset: Photo showing the rG-O film with a GalP (rG-O) coating; the composite film is highly flexible and can be rolled up. (D) Tensile strain-stress curves of a rG-O and rG-O/GalP (rG-O) film. Inset: The GalP (rG-O) coating is heat-resistant and has a strong adhesion to the rG-O film; a piece of rG-O/GalP (rG-O) composite film remains unchanged after being burned in an alcohol solution in air. (E) EMI SE of rG-O films at a thickness of 17.2 and 30.0 μm, and 17.2-μm-thick rG-O films with 3.5- and 13.0-μm-thick GalP (rG-O) coatings. (F) Total EMI SE (EMI SE_T) and its absorption (SE_A) and reflection (SE_R) components in ~30.0-μm-thick rG-O film and rG-O/GalP (rG-O) film at 8.0 GHz.

Fig. 4. Thermal performance of GalP.

(A) Thermal diffusivity and conductivity of GalP (rG-O) and GalP (D) parallel and perpendicular to the sheet. (B) Test system configuration for demonstrating the perpendicular heat transfer capability of two bulk GalP (D) and GalP (rG-O) blocks and the corresponding IR images of surface temperature changes. (C) Schematic of the GalP TIM performance measurement system. (D) Temperature change of the stainless steel heater as a function of the heating time and (E) various powers at a steady state. (F) Total thermal resistance of GalP samples. Photo credits: Chunhui Wang, Center for Multidimensional Carbon Materials, Institute for Basic Science.