Current stretchable conductors, often composed of elastomeric composites infused with rigid conductive fillers, suffer from limited stretchability and durability, and declined conductivity with stretching. These limitations hinder their potential applications as essential components such as interconnects, sensors, and actuators in stretchable electronics and soft machines. In this context, an innovative elastomeric composite that incorporates a 3D network of liquid metal (LM), offering exceptional stretchability, durability, and conductivity, is introduced. The mechanics model elucidates how the interconnected 3DLM architecture imparts softness and stretchability to the composites, allowing them to withstand tensile strains of up to 500% without rupture. The relatively low surface‐to‐volume ratio of the 3DLM network limits the reforming of the oxide layer during cyclic stretch, thereby contributing to low permanent strain and enhanced durability. Additionally, the 3D architecture facilitates crack blunting and stress delocalization, elevating fracture resistance, while simultaneously establishing continuous conductive pathways that result in high conductivity. Notably, the conductivity of the 3DLM composite increases with strain during substantial stretching, highlighting its strain‐enhanced conductivity. In comparison to other LM‐based composites featuring 0D LM droplets, the 3DLM composite stands out with superior properties.
A strain-induced electrically conductive liquid metal emulsion for the programmable assembly of soft conductive composites is reported. This emulsion exhibits the shear yielding and shear thinning rheology required for direct ink writing. Examples of complex self-supported 3D printed structures with spanning features are presented to demonstrate the 3D printability of this emulsion. Stretchable liquid metal composites are fabricated by integrating this emulsion into a multi-material printing process with a 3D printable elastomer. The as-printed composites exhibit a low electrical conductivity but can be transformed into highly conductive composites by a single axial strain at low stresses ([Formula: see text] 0.3 MPa), an order of magnitude lower than other mechanical sintering approaches. The effects of axial strain and cyclic loading on the electrical conductivities of these composites are characterized. The electrical conductivity increases with activation strain, with a maximum observed relaxed conductivity of 8.61 × 105S⋅m−1, more than 300% higher than other mechanical sintering approaches. The electrical conductivity of these composites reaches a steady state for each strain after one cycle, remaining stable with low variation ([Formula: see text] standard deviation) over 1000 cycles. The strain sensitivities of these composites are quantitatively analyzed. All samples exhibit strain sensitivities that are lower than a bulk conductor throughout all strains. The printed composites showed low hysteresis at high strains, and high hysteresis at low strains, which may be influenced by the emulsion internal structure. The utility of these composites is shown by employing them as wiring into a single fabrication process for a stretchable array of LEDs.
more » « less- Award ID(s):
- 2047683
- PAR ID:
- 10389353
- Publisher / Repository:
- SAGE Publications
- Date Published:
- Journal Name:
- Journal of Composite Materials
- Volume:
- 57
- Issue:
- 4
- ISSN:
- 0021-9983
- Format(s):
- Medium: X Size: p. 829-839
- Size(s):
- p. 829-839
- Sponsoring Org:
- National Science Foundation
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