Thermal cure effects on electromechanical properties of conductive wires by direct ink write for 4D printing and soft machines

Abstract

Recent developments in soft materials and 3D printing are promoting the rapid development of novel technologies and concepts, such as 4D printing and soft machines, that in turn require new methods for fabricating conductive materials. Despite the ubiquity of silver nanoparticles (NPs) in the conducting electrodes of printed electronic devices, their potential use in stretchable conductors has not been fully explored in 4D printing and soft machines. This paper studies the effect of thermal cure conditions on conductivity and electro-mechanical behaviors of silver ink by the direct ink write (DIW) printing approach. We found that the electro-mechanical properties of silver wires can be tailored by controlling cure time and cure temperature to achieve conductivity as well as stretchability. For the silver NP ink we used in the experiments, silver wires cured at 80 °C for 10–30 min have conductivity >1% bulk silver, Young’s modulus <100 MPa, yield strain ∼9%, and can retain conductivity up to 300% strain. In addition, under stress controlled cyclic loading/unloading conditions, the resistance of these wires is only about 1.3 times the initial value after the 100th repeat cycle (7.6% maximum strain in the first cycle). Silver wires cured at 120 °C for 10–20 min are more sensitive to strain and have a yield strain of around 6%. These properties indicate that the silver ink can be used to fabricate stretchable electrodes and flex sensors. Using the DIW fabrication method, we printed silver ink patterns on the surface of 3D printed polymer parts, with the future goal of constructing fully 3D printed arbitrarily formed soft and stretchable devices and of applying them to 4D printing. We demonstrated a fully printed functional soft-matter sensor and a circuit element that can be stretched by as much as 45%.

High‐Speed 3D Printing of High‐Performance Thermosetting Polymers via Two‐Stage Curing

“…The hollow channels were then filled with silver nanoparticles paste by syringe (Figure b). After thermal curing, the silver particles were cured to form a conductive wire . Unlike the case in the open air, the curing of silver ink embedded in the channel took a longer time due to difficult evaporation of the solvent in the channels.…”

Metal particle-free inks for printed flexible electronics

“…6). 121,122 The ink filaments can maintain a similar size to the nozzle, which ranges from 0.5 mm to 1 mm. 123 The printed feature dimensions are determined by the ink rheology and printing parameters.…”

“…A pressure regulator is used to control the pressure applied to the syringe. Reproduced with permission from[122]. Copyright 2017, IOP Publishing Ltd.Journal of Materials Chemistry C ReviewOpen Access Article.…”

3D-Printing and Machine Learning Control of Soft Ionic Polymer-Metal Composite Actuators

“…Also, recent research has developed “4D printing” and origami-based robots, that are able to reconfigure into a functional shape after being fabricated (often as a flat sheet). These are very promising, but shape change is generally accomplished via heating or other nonelectric stimuli 65–68 . In general, the development of functional soft electroactive polymer based robotic platforms is limited.…”