Preparation Of Gallium-based Liquid Metal Stretchable Conductor For Wearable And Flexible Sensors

With the advancement of flexible electronic technology,wearable sensors are continuously developing towards the direction of flexibility,integration,intelligence,and biocompatibility.Currently,it has become one of the forefront research hotspots in academia and industry.Gallium-based liquid metal(LM)has excellent room temperature flowability,metallic conductivity and non-toxicity properties.Based on Ga-based LM materials,wearable flexible sensors have been developed for motion monitoring,sports rehabilitation,flexible displays,and many other fields.The application of Ga-based LM materials in the field of flexible wearable sensors is of great significance for supporting and providing information on human health.However,Ga-based LM flexible sensors still face problems such as complex 3D conductor preparation,low sensing sensitivity,low device integration,and poor electromechanical property and biocompatibility of sensing interfaces.To address these issues,this project proposes an innovative approach to transform Ga-based LM into solid state and utilize plastic deformation to prepare 3D stretchable conductors and wearable flexible sensors.The method of using gold(Au)thin film conductors on the surface of Ga-based LM-elastomer composite is adopted to construct the sensing interface.This has pushed forward and broadened the development of Ga-based LM stretchable conductors in the field of flexible wearable sensors.To address the complex fabrication process of 3D structured conductors,this study investigates and demonstrates the mechanism by which the In alloying element content influences the volume fraction of the micron-sized A6 phase,and thus determines the strength,plasticity,and phase transformation behavior of Ga-In alloys.A Ga-10In alloy with excellent comprehensive properties,including a yield strength of 33.9 MPa,elongation of 14.2%,melting point of 22.7℃ and significant undercooling effect is selected as the material for the channel-free preparation of 3D conductors.The proposed method involves the solid-liquid transition and plastic deformation of Ga-10In wires to achieve the desired 3D structures,which are subsequently encapsulated with elastic silicone.After encapsulation,the Ga-10In wires are heated to restore their fluidity.This approach features "solid-state processing,liquid-state service," and enables the efficient fabrication of hand motion sensors,heart rate sensors,and flexible LED arrays.It simplifies the complex steps involved in constructing Ga-based LM flexible 3D conductors in elastic materials and overcomes the efficiency bottleneck of complex 3D structured conductor preparation.For optimizing and improving the sensitivity and comfortability of Ga-based LM wearable flexible sensors.Starting from the extrusion of Ga-based LM channels under stress concentration,combined with 3D structural conductor design and the stress/strain redistribution mechanism caused by the difference in elastic modulus of the elastomer at different parts of the sensor,the extrusion effect of the Ga-based LM channel under tensile stress is greatly enhanced,resulting in a sensor sensitivity of over 2000 at 100%strain,which is the highest reported sensitivity for Ga-based LM stretchable strain sensors.In addition,using the 3D conductor fabrication method of Ga-10In plastic deformation and solid-liquid transition,this study designed and fabricated a hollow structure wearable 3D finger motion sensor that can provide thermal therapy while sensing finger motion.The integration of the 3D finger motion sensor with a 3D flexible multilayer circuit board with wireless transmission capabilities achieved high comfort wireless finger motion monitoring.The 3D conductor structural design greatly improves the sensitivity,comfortability,and integration of wearable flexible devices,providing a new development idea for the industrial application of Ga-based LM wearable flexible sensors.To improve the electro-mechanical performance and biocompatibility of the sensing interface of Ga-based LM electrophysiological signal sensors,this study proposes a compensation mechanism based on Ga-based LM micro-particles(LMMPs)for cracks in Au thin films.By sputtering nano-thickness Au film conductors onto the surface of LMMPs-polydimethylsiloxane(PDMS)composite materials,a sensing interface with a resistance change of only 7.1 times and a resistance value below 70Ω under 269%tensile strain is achieved.In addition,the LMMPs-PDMS composite material as a flexible substrate reduces the risk of Ga-based LM leakage,and the Au film as the interface in contact with tissue exhibits better biocompatibility.This sensing interface has been applied in the fields of flexible electromyography electrodes and invasive electroencephalography electrodes,and the results show that flexible electrodes based on this sensing interface can collect high signal-to-noise ratio electromyography signals,and successfully identify the onset of epilepsy in rats based on collected electroencephalography signals.The sensing interface addresses the issues of biocompatibility and poor electrical-mechanical performance that are often overlooked in Ga-based LM electrophysiological signal sensors,and therefore has tremendous clinical application value.Starting from the perspective of the application of Ga-based LM wearable flexible sensors,this article addresses the issues of the preparation process of Ga-based LM stretchable conductors,the sensitivity and integration of sensors,and the surface electroconductivity.From the perspective of material and process innovation,targeted solutions are proposed for the solid-liquid phase transition and plastic deformation of Gabased LMs,as well as for the development of Ga-based LM composite conductor materials.This will further promote the development of Ga-based LM stretchable conductors in the field of wearable flexible sensors.