This review briefly summarizes the recent development in fabrication of conductive tracks with inkjet printing technology. Special emphasis will be placed on material selection and printing procedures. Troubleshooting guidelines for frequent problems in inkjet printing methods, such as material selection, ink formulation, ink-substrate interaction, and post-treatment of inks, are elucidated in this article to fabricate conductive tracks or electrodes with well-defined patterns. Related applications and unsolved challenges are also briefly reviewed in this article.

In this study, a highly responsive humidity sensor is developed by printing gold nanoparticles (GNPs) grafted with a hygroscopic polymer. These GNPs are inkjet-printed to form a uniform thin film over an interdigitated electrode with a controllable thickness by adjusting the printing parameters. The resistance of the printed GNP thin film decreases significantly upon exposure to water vapor and exhibits a semi-log relationship with relative humidity (RH). The sensor can detect RH variations from 1.8 to 95% with large resistance changes up to 4 orders of magnitude with no hysteresis and small temperature dependence. In addition, with a small thickness, the sensor can reach absorption equilibrium quickly with response and recovery times of ≤1.2 and ≤3 s, respectively. The fast response to humidity changes also allows the GNP thin-film sensor to distinguish signals from intermittent humidification/dehumidification cycles with a frequency up to 2.5 Hz. The printed sensors on flexible substrates show little sensitivity to bending deformation and can be embedded in a mask for human respiratory detection. In summary, this study demonstrates the feasibility of applying printing technology for the fabrication of thin-film humidity sensors, and the methodology developed can be further applied to fabricate many other types of nanoparticle-based sensor devices.

In this study, a thermally triggered self-reducible copper ink is developed to print conductive patterns on flexible substrates. Inks containing only copper formate (CuF) and monoisopropanol amine (MIPA) generated large bubbles in the CuF decomposing process, and thus the surface morphologies of prepared thin films were largely disturbed. With the addition of octylamine (OA), the bubbling disturbance was relieved due to the lower surface tension and the film uniformity was greatly improved. A low resistivity of 2 Â 10 À7 U m (8.5% of bulk copper) can be reached by heating the ink at 140 C for 5 minutes under a nitrogen environment. XRD results showed the synthesized copper films were comprised of pure metallic copper crystalline. The copper films were composed of closely packed spherical grains of 50 to 500 nm in diameter. After the addition of 1 wt% polyvinylpyrrolidone (PVP) in the ink, the synthesized copper thin films showed great adhesion on glass substrates, and sustained the same conductivity after repeated tape tests.The ink can also be printed on flexible substrates, such as polyethylene terephthalate (PET) or polyimide (PI) thin films, to create highly-conductive tracks with a strong mechanical stability. Finally, various conductive patterns were printed on flexible substrates to show the great potential of this ink for various printed electronic applications. IntroductionThe recent advancements in printing technology have provided a new fabrication method for exible and light-weight electronic devices at low costs. To fabricate these so-called printed electronic devices, inks containing conductive materials are printed on plastic sheets to produce exible microelectronic circuits. As the most essential part in every circuit, electrically conductive interconnects from metal inks have been widely used in these printed devices. To reduce the manufacturing cost, copper has recently attracted wide attention for printed conductive features because of its low price, and high electric conductivity. The most commonly used copper inks are nanoparticle suspensions. 1-7 The printed patterns can yield a low resistivity down to 2.2 times of that for bulk copper 2 aer sintering at 200 C for an hour. However, most plastic substrates might melt or deform at this high temperature. Alternatively, electroless plating approach offers a low-temperature synthetic route for copper thin lm fabrication on plastic surfaces. 8-11Solutions containing active agents are rst printed with microcontact 12-14 or inkjet printing 15-20 methods to produce patterns on plastic substrates. Copper metal are then deposited selectively on the printed patterns in a subsequent electroless plating bath. 12,13,15,16,19 Although electroless plating methods can produce highly conductive copper thin lms on exible substrates at low temperatures, the method needs two processing steps and the plating uid might contaminate or modify the plastic surfaces other than the patterned area. Thus, copper inks that can directly print on selected area with l...

In this work, a simple method was developed to fabricate micron scale three-dimensional (3D) conductive objects on a flexible PDMS substrate.

A new synthetic route was developed to modify cellulose nanofiber for water-repellent coatings with great sustainability after multiple washing cycles. Multiple functional groups were grafted on 2,2,6,6-tetramethylpiperidine 1-oxyl radical (TEMPO)-oxidized cellulose nanofibers (TOCN) to achieve superhydrophobic performance and strong adhesion on cotton cloth. First, hexadecylamine (HDA) was used to modify TOCN surface into hydrophobic derivatives via amidation. The amidation-modified TOCN (AMT) were then grafted with a polyisocyanate cross-linking agent (PCA). The final multimodified TOCN (MMT) had hydrophobic alkyls and isocyanate groups on the surface. These surface functional groups were confirmed by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). After spraying the MMT suspension on cotton fabrics, the isocyanate groups would react with hydroxyl groups on cotton fibers, leading to a uniform conformal layer of MMT on fabric surfaces. The MMT coating showed great water repellence and washing sustainability. A large contact angle of 150° and a small sliding angle of ∼10° were observed. The superhydrophobic performance retained even after 10 laundry washing cycles. Several examples were also demonstrated to show the capability and the possibility of applying this coating material for water-repellent applications.