A Research On Nano-Silver Ordered Meshes Flexible Transparent Conductive Films Based On Coffee-Ring Effect

With the continuous advancement of technology,the new generation of optoelectronic devices is developing towards portability,lightness,and wearability.Flexible and transparent electrodes,as the basic building blocks of flexible optoelectronic devices,are the core and key of the flexible optoelectronics field,with very broad market prospects.However,currently the most widely used transparent electrode in the market is indium tin oxide(ITO),which cannot meet the long-term development needs of future optoelectronic devices,especially the needs of flexible optoelectronic devices,due to its brittleness and non-renewable indium material.Therefore,in recent years,researchers have been exploring various new materials for preparing flexible and transparent conductive thin films to replace ITO,in order to meet the needs of future development in the flexible optoelectronics field.Among them,nano-silver ordered meshes,with their high conductivity,high transparency,and excellent uniformity of light,electricity,and heat distribution,have become the most promising alternative materials.This thesis mainly studies how to use the coffee ring effect and the template-free spray self-assembly strategy to prepare nano-silver(silver nanowires,silver nanoparticles)ordered meshes transparent conductive films,and develop optoelectronic devices based on this.The specific research work of this thesis mainly includes the following aspects:(1)Based on the coffee-ring effect,a simple,low-cost,and scalable template-free spray self-assembly and transfer strategy on the PDMS substrate was utilized to prepare a hightemperature-resistant silver nanowire bundle ordered meshes conductive film embedded in a polyimide matrix(Ag BMs/ePI).By the synergistic protection of closely packed silver nanowire bundles and embedded structures,the two major technical problems of thermal instability and the tendency to produce local hot spots of traditional silver nanowire-based conductive films were solved.The prepared conductive film exhibits excellent thermal stability(maintain stable for at least 1 hour in a 370℃ air atmosphere and a 400℃ nitrogen atmosphere),good electrical uniformity(sheet resistance variation<4%,10 cm × 10 cm),and low surface roughness(RMS,4.57 ± 2.42 nm),chemical and mechanical robustness.As an application for heating,we have utilized the thermal stability of the Ag BMs/ePI conductive film to develop a heater that can rapidly heat from room temperature to～204℃ within 8 s at 8 V voltage,far exceeding the highest saturation temperature of traditional random silver nanowire heaters.Furthermore,this heater exhibits excellent thermal uniformity(temperature variation<3℃,6 cm × 6 cm),greatly reducing the impact of local hotspots on device performance.This work provides a platform for emerging flexible and transparent electronic devices to adapt to extreme environments.(2)Quantitative analysis revealed the range of instantaneous water contact angles required for the formation of coffee-ring ordered meshes structures with Ag NWs/ethanol ink(～55°～160.6°)and explained the mechanism behind this range formation.By manipulating the contact angle between the Ag nanowires(Ag NWs)/ethanol ink and the target substrate,this template-free spray self-assembly strategy demonstrated good universality within this contact angle range.Ag nanowire ordered meshes structures can be prepared on arbitrary substrates through this spray strategy,and this self-assembly strategy is also applicable to various alcoholbased silver nanowire inks(such as isopropanol and methanol),various sizes(diameter,-20100 nm;length,～20-200 μm)of silver nanowires,and various concentrations(0.05-1 mg/ml)of silver nanowire inks.A capacitive pressure sensor with a sandwich structure of Ag BMs/PET was constructed,which can be used to monitor real-time pressing and physiological activities such as finger and wrist bending,and has broad application prospects in the field of real-time human motion detection.In addition,the conductive film also demonstrated good electromagnetic shielding effect.The sheet resistance of Ag BMs/PET conductive film was 10Ω/sq,and the electromagnetic shielding efficiency in the X-band(8.2-12.4 GHz)reached 34.1 dB,far exceeding the industrial standard of 20 dB.(3)Compared with flammable Ag NWs/ethanol ink,Ag NWs/water ink is safer,more suitable for storage and transportation.Different from the boundary conditions and formation mechanism of the alcohol system,the instantaneous water contact angle boundary conditions(～56.7°-～147.2°)required for the formation of coffee ring ordered meshes structure by Ag NWs/water ink.By manipulating the contact angle between Ag NWs/water ink and the target substrate,silver nanowire ordered meshes structure can also be prepared on arbitrary substrates(such as polymer film,silicon wafer,paper,wood board,curved glass beaker,uneven petals and leaves,etc.).This strategy is applicable to various sizes(diameter,～20-100 nm;length,～20-200 μm)of silver nanowires and various concentrations(0.05-1 mg/ml)of Ag NWs/water ink.Based on this ordered meshes conductive film,a color-changing chameleon display screen and encrypted QR code were constructed using 3D printing,and the color-changing effect of the pattern was demonstrated by voltage/temperature control,showing its application prospects in anti-counterfeiting labels,information security,and information encryption.(4)The template-free spray self-assembly strategy based on the coffee-ring effect was extended from 1-dimensional silver nanowires to 0-dimensional silver nanoparticles(Ag NPs),and for the first time,a uniformly distributed silver nanoparticle ordered meshes(Ag OMs)conductive film was obtained.Benefitting from the enhanced conductivity of Ag OMs under high-temperature sintering,when combined with hot-press transfer and spin-coating encapsulation processes,a high-performance electric heater with high temperature resistance,low-voltage drive,and uniform heat distribution can be prepared.This overcomes the drawback of low saturation temperature caused by Rayleigh instability in silver nanowire-based electric heaters.The highest saturation temperature of Ag OMs electric heater under 3.8 V low voltage exceeds 415℃,with temperature fluctuation less than 3℃,and can work stably and repeatedly for more than 2 hours,exhibiting excellent environmental adaptability to daily environments,organic solvents,acid-base solutions,mechanical deformation,and other stimuli.