Soft shape-programmable surfaces by fast electromagnetic actuation of liquid metal networks

Abstract

Low modulus materials that can shape-morph into different three-dimensional (3D) configurations in response to external stimuli have wide-ranging applications in flexible/stretchable electronics, surgical instruments, soft machines and soft robotics. This paper reports a shape-programmable system that exploits liquid metal microfluidic networks embedded in an elastomer matrix, with electromagnetic forms of actuation, to achieve a unique set of properties. Specifically, this materials structure is capable of fast, continuous morphing into a diverse set of continuous, complex 3D surfaces starting from a two-dimensional (2D) planar configuration, with fully reversible operation. Computational, multi-physics modeling methods and advanced 3D imaging techniques enable rapid, real-time transformations between target shapes. The liquid-solid phase transition of the liquid metal allows for shape fixation and reprogramming on demand. An unusual vibration insensitive, dynamic 3D display screen serves as an application example of this type of morphable surface.

Fig. 1. Programmable surfaces enabled by electromagnetic actuation of liquid metal networks.

a Schematic illustration of the fabrication process. Soft microfluidic channels filled with liquid metal serve as conducting ribbons bonded onto a thin elastomeric membrane (~5 µm) to form the programmable surface. b Optical image of the programmable surface before and after filling with liquid metal. The elastomeric membrane is optically transparent in regions not occupied by liquid metal. Scale bar, 5 mm for the surface, 500 µm for the exploded view illustration of the microchannels. Optical images of the surface in the initial flat configuration (c) and at maximum deformation (d). Various 3D shapes can be obtained through the action of Lorentz forces by controlling the electric currents passing through each liquid metal ribbon. Scale bar, 5 mm. FEA (e) and 3D Digital Image Correlation (3D-DIC; f) results of the surface in d. g Scaling law results for the maximum deformation of an isolated liquid metal ribbon as a function of ribbon geometries, material properties, magnetic field strength, and applied current. h Plots of the maximum surface deformation as a function of the scaling law parameters with different ribbon numbers (2-by-2, 4-by-4, and 8-by-8).

Fig. 2. 3D shapes transformed from the programmable surface.

a FEA predictions and experimental results (3D-DIC and optical images) of four representative 3D shapes transformed from the programmable surface featuring an orthogonal and symmetric ribbon layout (45°/−45°) in a non-uniform magnetic field associated with a single permanent block magnet. b FEA predictions and experimental results (3D DIC and optical images) of four representative 3D shapes transformed from the programmable surface featuring a non-orthogonal and asymmetric ribbon layout (0°/45°) in the same magnetic field as in a. Scale bars, 5 mm.

Fig. 3. Target shape programming and shape fixation.

Various target shapes realized by the programmable surfaces with 45°/−45° (a) and 0°/45° (b) ribbon layouts, respectively. c Shape fixation and reprogramming utilizing liquid metal phase transition. d Experimental results of the different force–displacement response of a surface that incorporates a 4-by-4 array of gallium ribbons in solid and liquid states. e Load bearing capability of the surface with gallium ribbons in solid and liquid states. Scale bars, 5 mm.

Fig. 4. 4D programmability.

a A dynamic shape changing sequence associated with dropping a ball onto a test membrane under the action of gravity, as captured by 3D-DIC. b Experimental results (3D-DIC and optical images) of the programmable surface reproducing the dynamic physical process in a, but without the ball. Scale bars, 5 mm.

Fig. 5. Noise canceling capability.

a Optical (top) and 3D-DIC images (bottom) of the programmable surface with the letter “N” projected onto it (left) and bulging upwards due to external vibrational noise (right). b Optical (top) and 3D-DIC images (bottom) of the programmable surface actuated with different current intensities to find the optima to cancel the noise effect. c The maximum displacement on the surface as a function of time at different phases of noise cancellation. Scale bars, 5 mm.

Fig. 6. Applications of the 4D programmable surface as an unusual type of dynamic 3D display system.

Schematic illustration (a) and optical image (b) of the programmable surface serving as a projection screen. c Schematic illustrations and selected frames from Supplementary Movie 10 of a moving ball projected onto the surface as the shape of the surface morphs to create an illusion of actual physical interactions due to surface modulation, gravity, and inertial effects. Scale bars, 5 mm.