Project description:The inkjet printing process is a promising electronic printing technique for large-scale, printed, flexible and stretchable electronics because of features such as its high manufacturing speed, environmental friendliness, simple process, low cost, accurate positioning, and so on. As the base material of printed conductive patterns, conductive ink is the foundation of the development of printed electronics technology, and directly affects the performance and the quality of electronic products. In this paper, conductive ink with silver nanowires (AgNWs) was prepared, with AgNWs of lengths of 2-5 µm and diameters of 20 nm or so, isopropyl alcohol and ethylene glycol as the mixed solvents, and modified polysilane as the wetting agent. We discussed the relationship between the formula of the AgNWs ink and the surface tension, viscosity, contact angle between ink droplet and poly(ethylene) terephthalate (PET) surface, as well as the film-forming properties of the ink. Further, we analyzed the effects of the number of printed layers and the ink concentration of the AgNWs on the microstructures, photoelectric properties and accuracy of the printed patterns, as well as the change in the sheet resistance of the film during different bending cycles. The experimental results show that flexible transparent conductive patterns with a light transmittance of 550 nm of 83.1-88.4% and a sheet resistance of 34.0 Ω∙sq-1-78.3 nm∙sq-1 can be obtained by using AgNWs ink of 0.38 mg∙mL-1 to 0.57 mg∙mL-1, a poly (ethylene terephthalate) (PET) substrate temperature of 40 °C, a nozzle temperature of 35 °C, and heat treated at 60 °C for 10 min. These performances indicate the excellent potential of the inkjet printing of AgNWs networks for developing flexible transparent conductive film.
Project description:With the help of photonic sintering using intensive pulse light (IPL), copper has started to replace silver as a printable conductive material for printing electrodes in electronic circuits. However, to sinter copper ink, high energy IPL has to be used, which often causes electrode destruction, due to unreleased stress concentration and massive heat generated. In this study, a Cu/Sn hybrid ink has been developed by mixing Cu and Sn particles. The hybrid ink requires lower sintering energy than normal copper ink and has been successfully employed in a hybrid printing process to make metal-mesh transparent conductive films (TCFs). The sintering energy of Cu/Sn hybrid films with the mass ratio of 2:1 and 1:1 (Cu:Sn) were decreased by 21% compared to sintering pure Cu film, which is attributed to the lower melting point of Sn for hybrid ink. Detailed study showed that the Sn particles were effectively fused among Cu particles and formed conducting path between them. The hybrid printed Cu/Sn metal-mesh TCF with line width of 3.5 μm, high transmittance of 84% and low sheet resistance of 14 Ω/□ have been achieved with less defects and better quality than printed pure copper metal-mesh TCFs.
Project description:Copper-based nanoinks are emerging as promising low-cost alternatives to widely used silver nanoinks in electronic printing. However, the spontaneous oxidation of copper under ambient conditions poses significant challenges to its broader application. To address this issue, this paper presents an economical, large-scale, and environmentally friendly method for fabricating Cu@Ag nanoparticles (Cu@Ag NPs). The as-prepared nanoparticles exhibit a narrow size distribution of approximately 100 nm and can withstand ambient exposure for at least 60 days without significant oxidation. The Cu@Ag-based ink, with a 60 wt% loading, was screen-printed onto a flexible polyimide substrate and subsequently heat-treated at 290 °C for 15 minutes under a nitrogen atmosphere. The sintered pattern displayed a low electrical resistivity of 25.5 μΩ·cm (approximately 15 times the resistivity of bulk copper) along with excellent reliability and mechanical fatigue strength. The innovative Cu@Ag NPs fabrication method holds considerable potential for advancing large-scale applications of copper-based inks in flexible electronics.
Project description:Wood is an eco-friendly and abundant substrate and a candidate for functionalization by large-scale nanotechnologies. Infiltration of nanoparticles into wood, however, is hampered by the hierarchically structured and interconnected fibers in wood. In this work, delignified wood is impregnated with gold and silver salts, which are reduced in situ to plasmonic nanoparticles via microwave-assisted synthesis. Transparent biocomposites are produced from nanoparticle-containing wood in the form of load-bearing materials with structural color. The coloration stems from nanoparticle surface plasmons, which require low size dispersity and particle separation. Delignified wood functions as a green reducing agent and a reinforcing scaffold to which the nanoparticles attach, predesigning their distribution on the surface of fibrous "tubes". The nanoscale structure is investigated using scanning transmission electron microscopy (STEM), energy-dispersive spectroscopy (EDS), and Raman microscopy to determine particle size, particle distribution, and structure-property relationships. Optical properties, including response to polarized light, are of particular interest.
Project description:Optical metasurfaces enable novel ways to locally manipulate light's amplitude, phase, and polarization, underpinning a newly viable technology for applications, such as high-density optical storage, holography, and displays. Here, a high-security-level platform enabled by centimeter-scale plasmonic metasurfaces with full-color, high-purity, and enhanced-information-capacity properties is proposed. Multiple types of independent information can be embedded into a single metamark using full parameters of light, including amplitude, phase, and polarization. Under incoherent white light, the metamark appears as a polarization- and angle-encoded full-color image with flexibly controlled hue, saturation, and brightness, while switching to multiwavelength holograms under coherent laser illumination. More importantly, for actual applications, the extremely shallow functional layer makes such centimeter-scale plasmonic metamarks suitable for cost-effective mass production processes. Considering these superior performances of the presented multifunctional plasmonic metasurfaces, this work may find wide applications in anticounterfeiting, information security, high-density optical storage, and so forth.
Project description:Despite progress in the field of electrochromic devices, developing structural color-tunable photonic systems having both high transparency and flexibility remains challenging. Here, an ink-deposited transparent electrochromic structural colored foil displaying reflective colors, tuned by an integrated heater, is prepared in a single-substrate method. Efficient and homogeneous heating is induced by a gravure printed silver nanowire-based substrate, delivering an electrothermal response upon applying an electrical potential. On top of this flexible, transparent heater, a cholesteric liquid crystal ink is bar-coated and subsequently photopolymerized, yielding a structural colored film that exhibits temperature-responsive color changes. The transparent electrochromic foils appear colorless at room temperature but demonstrate structural color tuning with high optical quality when modifying the electrical potential. Both optical and electrothermal performances were preserved when deforming the foils. Applying the conductive and structural colored inks via the easy processable, continuous methods of gravure printing and bar-coating highlights the potential for scaling up to large-scale stimuli-responsive, transparent optical foils. These transparent structural colored foils can be potentially used for a wide range of photonic devices including smart windows, displays, and sensors and can be directly installed on top of curved, flexible surfaces.
Project description:Recent advances in three-dimensional (3D) printing technology has enabled to shape food in unique and complex 3D shapes. To showcase the capability of 3D food printing, chocolates have been commonly used as printing inks, and 3D printing based on hot-melt extrusion have been demonstrated to model 3D chocolate products. Although hot-melt extrusion of chocolates is simple, the printing requires precise control over the operating temperature in a narrow range. In this work, for the first time, we directly printed chocolate-based inks in its liquid phase using direct ink writing (DIW) 3D printer to model complex 3D shapes without temperature control. We termed this method as chocolate-based ink 3D printing (Ci3DP). The printing inks were prepared by mixing readily available chocolate syrup and paste with cocoa powders at 5 to 25 w/w% to achieve desired rheological properties. High concentrations of cocoa powders in the chocolate-based inks exhibited shear-thinning properties with viscosities ranging from 102 to 104?Pa.s; the inks also possessed finite yield stresses at rest. Rheology of the inks was analyzed by quantifying the degree of shear-thinning by fitting the experimental data of shear stress as a function of shear rate to Herschel-Bulkley model. We demonstrated fabrication of 3D models consisting of chocolate syrups and pastes mixed with the concentration of cocoa powders at 10 to 25 w/w%. The same method was extended to fabricate chocolate-based models consisting of multiple type of chocolate-based inks (e.g. semi-solid enclosure and liquid filling). The simplicity and flexibility of Ci3DP offer great potentials in fabricating complex chocolate-based products without temperature control.
Project description:In this work, polycaprolactone-polyethylene glycol (PCL-PEG) based waterborne polyurethane-urea (WBPUU) inks have been developed for an extrusion-based 3D printing technology. The WBPUU, synthesized from an optimized ratio of hydrophobic polycaprolactone diol and hydrophilic polyethylene glycol (0.2:0.8) in the soft segment, is able to form a physical gel at low solid contents. WBPUU inks with different solid contents have been synthesized. The rheology of the prepared systems was studied and the WBPUUs were subsequently used in the printing of different pieces to demonstrate the relationship between their rheological properties and their printing viability, establishing an optimal window of compositions for the developed WBPUU based inks. The results showed that the increase in solid content results in more structured inks, presenting a higher storage modulus as well as lower tan δ values, allowing for the improvement of the ink's shape fidelity. However, an increase in solid content also leads to an increase in the yield point and viscosity, leading to printability limitations. From among all printable systems, the WBPUU with a solid content of 32 wt% is proposed to be the more suitable ink for a successful printing performance, presenting both adequate printability and good shape fidelity, which leads to the realization of a recognizable and accurate 3D construct and an understanding of its relationship with rheological parameters.
Project description:Coaxial fiber-shaped supercapacitors with short charge carrier diffusion paths are highly desirable as high-performance energy storage devices for wearable electronics. However, the traditional approaches based on the multistep fabrication processes for constructing the fiber-shaped energy device still encounter persistent restrictions in fabrication procedure, scalability, and mechanical durability. To overcome this critical challenge, an all-in-one coaxial fiber-shaped asymmetric supercapacitor (FASC) device is realized by a direct coherent multi-ink writing three-dimensional printing technology via designing the internal structure of the coaxial needles and regulating the rheological property and the feed rates of the multi-ink. Benefitting from the compact coaxial structure, the FASC device delivers a superior areal energy/power density at a high mass loading, and outstanding mechanical stability. As a conceptual exhibition for system integration, the FASC device is integrated with mechanical units and pressure sensor to realize high-performance self-powered mechanical devices and monitoring systems, respectively.
Project description:Living tissues dynamically modulate their structure and functions through physical and biochemical interactions in the three-dimensional (3D)-microenvironment for their homeostasis or the developmental process of an embryo. However, the manipulation of cellular functions in vitro is still challenging due to the lack of a dynamic material system that can vary the 3D-cellular microenvironment in time and space. Here, we show an in situ 3D-printing technique based on multiphoton lithography using a biocompatible photoresist, bio-ink. The bio-ink composed of protein-photosensitizer conjugates has the ability to cause singlet oxygen and cross-linking reaction to fabricate protein gels with submicrometer-scale precision. Remarkably, the conjugates substantially improve the cytocompatibility and the efficiency of gelation due to the stealth effect of rose bengal (RB) and efficient transfer of singlet oxygen to bovine serum albumin (BSA). 3D-printing in the presence of cells allows for the microfabrication of a protein scaffold and controlled single-cell behavior. This dynamic material system to direct cell fate may offer emerging applications for drug discovery and regenerative medicine.