Interdigitating Elastic Fibers with a Liquid Metal Core toward Ultrastretchable and Soft Capacitive Sensors: From 1D Fibers to 2D Electronics

Abstract

Ultrastretchable and elastic fibers with a liquid metal (EGaIn, eutectic alloy of gallium and indium) core were utilized to fabricate 2D capacitive sensors by arranging the fibers in an interdigitated structure. Once the fibers were prepared by simple roller coating, interdigitated structures were formed by plasma-activated chemical bonding of the fibers. EGaIn was injected into the core of the hollow elastic fibers, resulting in 2D capacitive sensors with dielectrics between the in-plane interdigitated electrodes. The liquid metal used in this work preserves the metallic conductivity upon strain because of the fluidic nature of the metal. Thus, the capacitance can be manipulated by the strain (upon mechanical deformation) of interdigitated fibers. The out-of-plane fringe electric field generated at the edges of the in-plane interdigitated liquid metal electrodes can be interfered with by adjacent objects or solvents surrounding the fibers due to various dielectric constants of the medium, resulting in a varying capacitance. This approach of fabricating 2D capacitive sensors from 1D fibers with a liquid metal core can be implemented in electronic textiles, wearable sensors, and soft robotics, owing to the fiber-form factor as well as the deformable electrical conductivity of the liquid metal wire.

Model-Free Control of a Soft Pneumatic Segment

“…Another possibility to manufacture capacitive sensors is to use, as done in [ 23 ], elastic fibres filled with liquid metal. By deforming the sensor, a change in the capacitance is achieved by the movement of the liquid metal inside the fibres.…”

Current Status and Outlook of Low‐Melting‐Point Metals in Biomedical Applications

“…These composite materials are used in sensors, which can effectively improve their performance. [140][141][142][143][144][145] For example, as shown in Figure 5a, Zhou et al designed and constructed a PVA-TA-EGaIn hydrogel system. [145] In their study, the conductivity of PVA-TA hydrogel was 0.44 S m −1 , but upon incorporating EGaIn into PVA-TA, the conductivity significantly increased to 3.63 S m −1 .…”

“…[141] Additionally, with numerous research surfaces, these EGaIn composite-based sensors can be applied in applications such as soft robotics, stretchable electronics, electronic skin, and wearable devices. [140][141][142][143]146,147] Won et al embedded EGaIn into soft polymers to form liquid metal-embedded elastomers that exhibited excellent electrical properties. [148] The composites that were printed with 80% EGaIn volume fraction demonstrated a volumetric electrical conductivity of 5 × 10 4 S cm −1 (Figure 5c).…”

“…Ultra-stretched elastic fibers with EGaIn alloy cores were fabricated into 2D capacitive sensors by arranging the fibers into an interdigitated structure, which maintains good conductivity under deformation (Figure 5b). [141] Additionally, with numerous research surfaces, these EGaIn composite-based sensors can be applied in applications such as soft robotics, stretchable electronics, electronic skin, and wearable devices. [140][141][142][143]146,147] Won et al embedded EGaIn into soft polymers to form liquid metal-embedded elastomers that exhibited excellent electrical properties.…”

“…These composite materials are used in sensors, which can effectively improve their performance. [ 140‐145 ] For example, as shown in Figure a, Zhou et al. designed and constructed a PVA‐TA‐EGaIn hydrogel system.…”