Investigation Of The Preparation And Application Of Flexible Conductive Materials

Because of their light weight,flexibility,stretchability,and portability,flexible and wearable electronics have great potential in many fields,such as health monitoring devices,information and electronic skin.Flexible conductors and devices play important roles in the fabrication of flexible wearable electronic devices.In this dissertation,flexible conductive materials were prepared for flexible electronic devices.The main results are as follows:(1)Conductive fibers were prepared by depositing metals on the Kevlar fibers with the aid of polymer-assisted electroless deposition.First,the Kevlar fibers were treated with plasma and then silanized.Second,poly(methacryloxyethyltrimethylammonium chloride)(PMETAC)brushes were synthesized on the fibers by radical polymerization.Third,Cu,Ag,Au and Ni were deposited on the fibers by polymer-assisted electroless deposition respectively,and then Cu-,Ag-,Au-and Ni-Kevlar were obtained.Finally,the conductive fibers were coated with polydimethylsiloxane(PDMS).These conductive fibers have good mechanical stability and excellent electrical conductivity,and still maintain electrical conductivity after 10,000 cycles of bending.Without coating with PDMS,the fibers still have stable conductivity after storage for 600 days,demonstrating that the fibers are durable.In addition,Cu-and Ag-Kevlar conductive fibers can be used as interconnects in flexible LED circuits to successfully light up the LED lamp under various deformations.(2)Liquid metal conductive sponges were prepared by loading the liquid metal(GaIn Sn)into a silicone rubber(Ecoflex~?00-30)sponges which were fabricated by using a conventional sugar-templating method.The conductive sponges were used as interconnects in flexible LED circuits and can light up the LED lamps under tensile strain of 0,100%,200%,300%,and400%with applied voltage of 1.8 V.The LED lamps can still be lighted up when the conductive sponges are bent or twisted.Moreover,the conductive sponges still retain the conductivity after 10000 stretching and releasing cycles.More importantly,the conductive sponges were used to connect a small hand model with a LED lamp,and can light up the lamp upon bending,indicating that the conductive sponges have potential applications in fabricating joints for robots.(3)The capacitive pressure sensors were prepared by using a three-dimensional and porous PDMS-Ecoflex composite sponge as the dielectric layer,and two copper foils as the electrodes.The PDMS-Ecoflex composite sponges are consisted of two silicone elastomers(PDMS and Ecoflex).The sponges are hydrophobic with water contact angle higher than 110°,enabling the capacitive pressure sensors to work at high-humidity environment.By adjusting the mass ratio of PDMS and Ecoflex,the tensile and compressive modulus of the composite sponges are changed,and therefore the sensitivity and relative capacitance variation range of the capacitive pressure sensor can be modulated.When the mass fraction of Ecoflex is 70%,the capacitive pressure sensor has good performance with the minimum detectable pressure of0.06 Pa.After 10,000 compressing and releasing cycles,the performance of the sensor does not decay.The capacitive pressure sensor was successfully applied to monitor the motion of human body,such as the pulse of neck,blink,finger movement,and walking,indicating that the sensor have great potential applications in health monitoring Systems.