Reactive Conductive Ink Capable of In Situ and Rapid Synthesis of Conductive Patterns Suitable for Inkjet Printing

Numerical Simulation of Solvent Evaporation in a Reactive Silver Ink Droplet Deposited on a Heated Substrate

Understanding the movement of silver ions (Ag+) in the solvent of a thermally evaporated particle-free reactive silver ink droplet is essential for optimizing the electronic inkjet printing process. In this work, a numerical study based on the Navier-Stokes equations is used to examine the microflows inside the evaporating solvent of a reactive silver ink droplet and to predict the morphology of the resultant Ag particle aggregations that form during the heat-activated processes. The droplet evaporation of the water-ethylene glycol ink solvent (H2O-(CH2OH)2) is simulated using COMSOL Multiphysics software. The model assumes that the evaporating fluid is heterogeneous due to the mass transfer of ethylene glycol molecules throughout the droplet by capillary flow. A layer of concentrated ethylene glycol forms at the fluid-substrate interface during solvent evaporation if the substrate is heated. The concentrated ethylene glycol molecules are then transported inward by the capillary action, and the resultant Ag particles, arising from the thermally driven reactions, accumulate at the bottom center of the drying droplet. The numerical simulations demonstrate that the droplet evaporation process depends on the water concentration in the solvent, substrate temperature, surface tension, and natural convection. Furthermore, the capillary flow dominates the fluid flow inside the evaporating droplet, causing some Ag particles to accumulate at the contact line, the commonly observed "coffee-ring effect". The results provide new insights into the chemical reactions that produce experimentally observed silver particle aggregations during the reactive silver ink droplet evaporation process and help establish realistic process parameters for improving the quality of inkjet-printed conductive silver films and electronic circuit microtraces.

Silver Nanoparticles for Conductive Inks: From Synthesis and Ink Formulation to Their Use in Printing Technologies

Currently, silver nanoparticles have attracted large interest in the photonics, electrics, analytical, and antimicrobial/biocidal fields due to their excellent optical, electrical, biological, and antibacterial properties. The versatility in generating different sizes, shapes, and surface morphologies results in a wide range of applications of silver nanoparticles in various industrial and health-related areas. In industrial applications, silver nanoparticles are used to produce conductive inks, which allows the construction of electronic devices on low-cost and flexible substrates by using various printing techniques. In order to achieve successful printed patterns, the necessary formulation and synthesis need to be engineered to fulfil the printing technique requirements. Additional sintering processes are typically further required to remove the added polymers, which are used to produce the desired adherence, viscosity, and reliable performance. This contribution presents a review of the synthesis of silver nanoparticles via different methods (chemical, physical and biological methods) and the application of silver nanoparticles under the electrical field. Formulation of silver inks and formation of conductive patterns by using different printing techniques (inkjet printing, screen printing and aerosol jet printing) are presented. Post-printing treatments are also discussed. A summary concerning outlooks and perspectives is presented at the end of this review.

Drop impact printing

Hydrodynamic collapse of a central air-cavity during the recoil phase of droplet impact on a superhydrophobic sieve leads to satellite-free generation of a single droplet through the sieve. Two modes of cavity formation and droplet ejection have been observed and explained. The volume of the generated droplet scales with the pore size. Based on this phenomenon, we propose a drop-on-demand printing technique. Despite significant advancements in inkjet technology, enhancement in mass-loading and particle-size have been limited due to clogging of the printhead nozzle. By replacing the nozzle with a sieve, we demonstrate printing of nanoparticle suspension with 71% mass-loading. Comparatively large particles of 20 μm diameter are dispensed in droplets of ~80 μm diameter. Printing is performed for surface tension as low as 32 mNm-1 and viscosity as high as 33 mPa∙s. In comparison to existing techniques, this way of printing is widely accessible as it is significantly simple and economical.