Network topologies dictate electromechanical coupling in liquid metal–elastomer composites

Zolfaghari, Navid; Khandagale, Pratik; Ford, Michael J.; Dayal, Kaushik; Majidi, Carmel

doi:10.1039/d0sm01094d

Cited by 48 publications

(54 citation statements)

References 36 publications

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“…Moreover, the low q scattering curve of the microfiber at 0% strain shows a q −3.5 scattering, which shifts to q −3.0 at 300% strain, indicating the loss of fiber density after stretching as LM particles start to flow. All the above observations coincide with the recent computation results from Zolfaghari et al ( 54 ) who explained the reduced electromechanical coupling of LM-embedded elastomers to mainly two principal contributions: One is the hydrostatic pressure–controlled opening of the narrow, neck-like connections among LM droplets, and the other one, probably the primary contribution, is the stretching out of the original highly tortuous serpentine conductive path, which does not prominently alter their length and average cross-sectional area to preserve the end-to-end conductance ( G = σ A / l ; where σ is the intrinsic conductivity of LM, A is the cross-sectional area, and l is the conductive length). A schematic mechanism for the strain-insensitive conductance of LM sheath-core microfiber is presented in fig.…”

Section: Resultssupporting

confidence: 93%

Conductance-stable liquid metal sheath-core microfibers for stretchy smart fabrics and self-powered sensing

et al. 2021

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Highly conductive and stretchy fibers are crucial components for smart fabrics and wearable electronics. However, most of the existing fiber conductors are strain sensitive with deteriorated conductance upon stretching, and thus, a compromised strategy via introducing merely geometric distortion of conductive path is often used for stable conductance. Here, we report a coaxial wet-spinning process for continuously fabricating intrinsically stretchable, highly conductive yet conductance-stable, liquid metal sheath-core microfibers. The microfiber can be stretched up to 1170%, and upon fully activating the conductive path, a very high conductivity of 4.35 × 104 S/m and resistance change of only 4% at 200% strain are realized, arising from both stretch-induced channel opening and stretching out of tortuous serpentine conductive path of the percolating liquid metal network. Moreover, the microfibers can be easily woven into an everyday glove or fabric, acting as excellent joule heaters, electrothermochromic displays, and self-powered wearable sensors to monitor human activities.

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Section: Resultssupporting

confidence: 93%

Conductance-stable liquid metal sheath-core microfibers for stretchy smart fabrics and self-powered sensing

et al. 2021

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“…[ 10,11,17,21 ] This coupling is likely a function of the morphology of the percolation network, [ 11 ] and we are involved in ongoing work on modeling and characterizing the droplet morphology as it relates to electromechanical coupling. [ 36 ]…”

Section: Figurementioning

confidence: 99%

Controlled Assembly of Liquid Metal Inclusions as a General Approach for Multifunctional Composites

et al. 2020

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functionality of LM composites relies on assembly and interactions between the matrix and filler. [11,23,24] To date, most of these LM composites have utilized silicone rubbers, where the functionality imparted by the matrix is limited to mechanical compliance and deformability, although a few meaningful exceptions exist (e.g., where the LM catalyzes/initiates poly mer ization). [19,21,25,26] Synthetic polymers can be designed with properties like stimuli responsivity, self-healing, processability, shape-morphing, and dynamic compliance and could be combined with LM to permit novel functionalities and processing capabilities. [27] The combination of finely tuned polymer synthesis with LM composite engineering will enable advanced applications like soft prosthetics, self-healing artificial skins, and 3D electronic materials. To achieve electrical conductivity, LM droplets within a composite must coalesce, for example, through an applied pressure (termed "mechanical sintering"). [28] Notably, the curing conditions and precursor composition dictate the network topology and resulting mechanical properties of the silicone matrix, which appear to influence whether an applied pressure forms percolation pathways for a LM composite. For example, LM composites using a commercially available silicone formulation (Sylgard 184, 10:1 weight ratio of Part A and Part B) can be electrically conductive after application of localized pressure [28] that coalesces LM droplets. However, permanent electrical conductivity has not been observed in LM composites that use a different commercially available silicone formulation (Ecoflex 00-30, 1:1 weight ratio of Part A and Part B), which is softer and more deformable than Sylgard 184. [8,20,29] This difference poses a limitation in generality of functionality for LM composites. Progress in LM composite engineering depends on a framework for materials synthesis that overcomes this limitation and enables integration of electrically conductive networks of LM in a wider range of media. Importantly, progress toward multifunctionality should include a focus on the properties of the matrix material. For LM composites, our group and others have demonstrated LM incorporation in functional matrix materials like hydrogels and shape-morphing polymers, but the predominate choice of matrix material has been silicone rubbers. [19,21,25,26] The development of an approach to achieve electrical conductivity by incorporating LM in functional polymer networks will facilitate Soft composites that use droplets of gallium-based liquid metal (LM) as the dispersion phase have the potential for transformative impact in multifunctional material engineering. However, it is unclear whether percolation pathways of LM can support high electrical conductivity in a wide range of matrix materials. This issue is addressed through an approach to LM composite synthesis that focuses on the interrelated effects of matrix curing/solidification and droplet formation. The combined influence of LM concentration, particle size, and ...

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“…For traditional conductive materials, the relative increase in electrical resistance can be predicted by the Pouillet's law: Δ Ω / Ω 0 = λ 2 − 1 (λ is the stretched times). [ 38 ] The inset figure is the change of normalized electrical resistance of our composite at different strains compared with Pouillet's law. The stress−strain curve of the SBS&LM@MUA composite shows that increasing LM will reduce the strength of SBS&LM@MUA composite (Figure 4f).…”

Section: Resultsmentioning

confidence: 99%

Highly Stretchable and Biocompatible Liquid Metal‐Elastomer Conductors for Self‐Healing Electronics

Mou

Tang

et al. 2020

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Wearable and implantable devices are more versatile than traditional rigid devices. One important class of these devices is wearable sensors, which can maximize performance, minimize the risk of injury, help track movements, or serve as biomechanical and biochemical markers. Wearable devices require biocompatible and stretchable conductors with high conductivity. [1-5] Traditional materials cannot meet all these requirements. There are two ways to make flexible conductors: one is to use intrinsically Highly stretchable, conductive, biocompatible conductors, and connectors are crucial for the fabrication of flexible devices. However, it remains a problem to get highly stretchable, conductive materials with low cost on a large scale. Another problem in production is the connection between soft and rigid components. Here, a new conductive nanocomposite is reported by mixing the 11-mercaptoundecanoic acid (MUA) modified liquid metal (LM) nanoparticles with polystyrene-block-polybutadiene-block-polystyrene (SBS), which is biocompatible (in vivo and in vitro), conductive (12 000 S cm −1 of conductivity), and stretchable (800% of elongation). Apart from its good performance, this material can be produced on a large scale by using a commercial polymer product and a straightforward physical production process. MUA is used to compromise the dense "gallium oxide shell" of liquid metal nanoparticles such that the whole composite can become conductive. By using resin to modify this composite, this new conductive material can be adhesive and highly conductive, and serve as a stable and efficient connector between soft conductor and rigid component. conductive and flexible materials, such as conductive polymers, [6] the other is to add conductive materials into the flexible elastomer. [7-10] The first method is often challenging to meet the need for conductivity and flexibility. Thus, many studies have adopted the second method to realize flexible conductors. [11] However, conventional conductive fillers such as carbon, [12] gold, [13] and silver [14] based nanodots, nanorods, and nanosheets are potentially toxic, difficult to synthesize, and relatively expensive. Maintaining high flexibility, high electrical conductivity, high biological safety, and low cost simultaneously is challenging due to a trade-off among these properties. Liquid metals (LM), especially gallium (Ga) and its alloy (EGaIn: 75% gallium and 25% indium), show sufficient conductivity and fluidity, which are highly suitable for stretchable conductors. [15-17] Injecting LM into the microfluidic channel can achieve stretchable conductors. [18] However, these methods are not suitable for more complicated circuits. Sonicating LM into micro/ nanoparticles yields LM ink. [19-21] LM particles are not conductive for the gallium oxide shell on the LM particles. Some conductive composites are achieved by adding LM particles into some elastomer matrix (such as polydimethylsiloxane (PDMS), ecoflex). [22-24] To make LM-elastomer composite conductive, apply pressure and str...

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Network topologies dictate electromechanical coupling in liquid metal–elastomer composites

Abstract: Conductive traces of elastomer embedded with liquid metal droplets exhibit little change in electrical resistance when stretched to large strains. Computational modeling is performed to better understand this remarkable piezoresistive property.

Cited by 48 publications

References 36 publications

Conductance-stable liquid metal sheath-core microfibers for stretchy smart fabrics and self-powered sensing

Conductance-stable liquid metal sheath-core microfibers for stretchy smart fabrics and self-powered sensing

Controlled Assembly of Liquid Metal Inclusions as a General Approach for Multifunctional Composites

Highly Stretchable and Biocompatible Liquid Metal‐Elastomer Conductors for Self‐Healing Electronics

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