Fabrication Of Liquid-metal-polymer Conductors On Different Substrates

The development of wearable devices promotes the progress of flexible electronics.Printed electronics is the key to industrial production of flexible electronics,which is determined by conductive ink,printing process parameters,and equipment.Traditional conductive ink is divided into carbon conductive ink,organic conductive ink,and metal conductive ink.After printing on substrates,metal conductive ink requires etching or sintering,which is with complicated fabrication.The preparation process of polymer conductive ink is relatively simple.However,the electrical performance of the device made by polymer conductors is poor.Combining advantages of metal and polymer,liquid metal has good electrical conductivity and processability,so it is increasingly used in the field of flexible electronics.Eutectic gallium-indium(EGa In)is the commonly used liquid metal,but with large surface tension and poor wettability to the substrates,often requiring pretreatment to improve its printability.Liquid metal and polymer materials are combined to prepare metal-polymer conductor(MPC)to achieve flexible wearable devices.The dissertation establishes two MPC systems for planar substrates and fiber-based substrates respectively.By examining the fabricating parameters of the two MPC systems,wearable devices for planar MPC and fiber MPC are designed respectively.In fabrication of MPC on different substrates,we selected two methods to prepare EGa In ink(preparation of liquid metal particle suspension and oxidation method)respectively,and two processing techniques(screen printing and dip coating method)respectively.The dissertation is aiming at determining effects on MPC fabrication,including processing parameters and substrate materials,by scanning electron microscope imaging,resistance measurement,contact angle measurement,stress-strain testing.For the preparation of planar MPC,we mix EGa In with polyvinyl pyrrolidone(PVP)and sonicate the mixture to get EGa In-PVP ink.The EGa In-PVP ink is screen-printed to pattern circuits.After drying printed circuits,MPC is obtained by mechanically sintering the ink without high temperature processing.The results show that when EGa In at 2.67 g/ml is sonicated in 5 wt% PVP solution for 90 s,the prepared ink has better uniformity and stability,and the printed MPCs have better electrical performance.Under these conditions,the average particle size of EGa InPVP ink particles is about 0.78 ?m.Also,the accuracy of the printed circuits reaches about 100 ?m.We use dip-coating method to coat a layer of EGa In on the surfaced-smoothmodified polyurethane fiber,and then to encapsulate it by a layer of silicone to fabricate fiber-based MPCs.The results show that using a dip-coating speed of 2.8 cm/min and three times of dip-coating can achieve good electrical properties for MPCs which achieve 200% tensile strain and 600 tensile cycles.In view of the above process parameters,we designed a lactate biofuel cell based on planar MPC and an electroluminescent fabric based on fiber MPC.The battery has good bending performance and certain tensile performance,as well as achieved a potential output of 60 mV in 20 mM lactic acid solution.The lightemitting fabric can be bent and stretched under working conditions.The essential goal of the dissertation is to explore the processing parameters of these two wearable devices.Further,it can be the guideline of their industrial production in the future.