Michael Layani

3D Printing of Shape Memory Polymers for Flexible Electronic Devices

The formation of 3D objects composed of shape memory polymers for flexible electronics is described. Layer-by-layer photopolymerization of methacrylated semicrystalline molten macromonomers by a 3D digital light processing printer enables rapid fabrication of complex objects and imparts shape memory functionality for electrical circuits.

Flexible transparent conductive coatings by combining self-assembly with sintering of silver nanoparticles performed at room temperature

Transparent conductive coatings are essential for fabrication of a variety of printed electronic devices such as flexible displays and solar cells. We report on a simple method to obtain such coatings by using aqueous dispersions of silver nanoparticles in an evaporative lithography process which is performed directly onto plastic substrates. In essence, a droplet containing silver nanoparticles is placed on top of a metallic mesh, instantaneously spreading over the mesh and the plastic substrate, and after the flow of the dispersion towards the wires of the mesh and drying, a transparent grid composed of the nanoparticles is formed. The silver nanoparticles are tailored to self-sinter upon short exposure to HCl vapors, due to the presence of polyacrylic acid salt on the surface of the particles. Therefore, immediate sintering of the silver nanoparticles in the thin lines of the grid occurs even at room temperature, enabling formation of transparent, flexible conductive grid on heat-sensitive substrates. The process yielded a conductive array having a very low sheet resistance, 9 ± 0.8 Ω/□, and a transparency above 75%. The application of the flexible conductive grid, which can replace conventional and expensive ITO, is demonstrated in an electroluminescent (EL) device.

Highly Stretchable and UV Curable Elastomers for Digital Light Processing Based 3D Printing

Stretchable UV-curable (SUV) elastomers can be stretched by up to 1100% and are suitable for digital-light-processing (DLP)-based 3D-printing technology. DLP printing of these SUV elastomers enables the direct creation of highly deformable complex 3D hollow structures such as balloons, soft actuators, grippers, and buckyball electronical switches.

Conductive patterns on plastic substrates by sequential inkjet printing of silver nanoparticles and electrolyte sintering solutions

A rapid and simple process for obtaining conductive patterns on plastic substrates by inkjet printing of silver nanoparticles is described. The process is based on causing sintering of the silver nanoparticles at low temperature by localized contact with solutions of electrolyte such as NaCl and MgCl2. The contact between the silver particles and the sintering agent is achieved by sequential printing of the two components. High conductivity, above 30% of bulk silver, is achieved by proper control of the type and concentration of the electrolyte and the number of layers of nanoparticles and sintering agent.

“Nano to nano” electrodeposition of WO3 crystalline nanoparticles for electrochromic coatings

A “nano to nano” electrodeposition approach for preparing nano-structured thin films from the dispersion of nano-objects is reported. A typical WO3 system is demonstrated, where nanocrystalline films are electrodeposited onto transparent conductive electrodes such as ITO and Ag grid printed PET (Ag grid/PET) from the water dispersion of WO3 nanoparticles without applying high potential, adding surfactants or polymers. The process is based on the reduction of WO3, which eliminates the electrostatic repulsion between the nanoparticles causing film deposition on the cathode. The reduced WO3 (HWO3) is conductive, thus it allows further film growth towards higher thickness and coverage. The electrodeposited films consist of stacked crystalline nanoparticles, which provide a highly active surface area, facilitate the penetration of electrolyte and the intercalation/deintercalation of Li+ in the nanocrystals and therefore result in outstanding electrochromic performance and stability (92% contrast, 9 s coloring and 15 s bleaching, retaining 76% contrast after 1000 coloring–bleaching cycles). The thickness, electrochromic performance and surface coverage of the films are well tuned by potential and time. This novel “nano to nano” electrodeposition approach based on the electrochemical redox of nano-objects can be extended to various transition metal oxide nano-objects with different sizes and shapes.

Bio-Inspired Mechanotactic Hybrids for Orchestrating Traction-Mediated Epithelial Migration.

A platform of mechanotactic hybrids is established by projecting lateral gradients of apparent interfacial stiffness onto the planar surface of a compliant hydrogel layer using an underlying rigid substrate with microstructures inherited from 3D printed molds. Using this platform, the mechanistic coupling of epithelial migration with the stiffness of the extracellular matrix (ECM) is found to be independent of the interfacial compositional and topographical cues.

3D printing of porous structures by UV-curable O/W emulsion for fabrication of conductive objects

The growing interest in the field of three-dimensional printing has led to great demand for new materials. In this paper we should like to present a new ink for printing porous structures that can be used for embedding various functional materials. The ink is composed of a UV polymerizable oil-in-water emulsion which converts into a solid object upon UV irradiation, and upon evaporation of the aqueous phase, forms a porous structure. The 3D objects with their various porosities, were printed by a Digital Light Processing (DLP) printer. The total surface area of the object can be controlled by changing the emulsions droplets size and the dispersed phase fraction. The printed 3D porous structures can be used in a variety of applications, and here we show a composite conductive object, made of silver and cross-linked polymer. After the porous object is formed, the pores are filled by vacuum, dipping in a dispersion of silver nanoparticles, followed by chemical sintering at room temperature, which results in conductive percolation paths within the 3D structure. Application of this structure is demonstrated for use as a 3D connector of an electrical circuit.

UV crosslinkable emulsions with silver nanoparticles for inkjet printing of conductive 3D structures

3D conductors are developed by inkjet printing a UV curable ink composed of oil-in-water emulsion combined with a dispersion of silver nanoparticles. Upon UV radiation by LED light the droplets immediately polymerize and form solid structures with embedded silver nanoparticles. The unique composition of the new ink enables sintering of the silver nanoparticles at room temperature by contact with NaCl solution, leading to a conductivity of 1.9 × 106 S m−1 while maintaining the 3D structure. The aspect ratio for photo-polymerized printed lines is more than 10 times larger than that of non-irradiated lines. The emulsion–dispersion new inks are potential materials for 3D fabrication of conductors and other functional materials in printed electronics.

4D printing shape memory polymers for dynamic jewellery and fashionwear

ABSTRACT 4D printing is a novel approach that enables dynamic functionality in ordinary static object. We used a methacrylated semicrystalline polymer to print objects exhibiting thermally triggered shape memory behaviour. By exploring various molecular weights, it was found that a methacrylated polycaprolactone polymer with a number average molecular weight of 10,000 g mol−1 exhibited the best thermal and mechanical behaviour. The effect of dyes’ addition to the ink formulation on the photopolymerisation and on the printing processes was evaluated. The ink was utilised for demonstrating fabrication of dynamic jewellery and a shoe accessory by Digital Light Processing printing.

Aqueous solution synthesis of (Sb, Bi)2(Te, Se)3 nanocrystals with controllable composition and morphology

The introduction of nanostructures has been considered as one of the promising strategies to enhance the thermoelectric performance of bulk materials. In this work, we report a low-cost and facile aqueous solution method to prepare (Sb, Bi)2(Te, Se)3 nanocrystals with controllable composition and morphology by using short ligands containing thiol, acid and amine groups. The control of the morphology of the nanostructures such as nanowires and nanosheets is studied, and both n-type and p-type nanoparticles have been prepared successfully. The results show that the thermal conductivities of these nanocrystals are effectively reduced due to phonon scattering and the thermoelectric performance is affected greatly by the morphology. TE measurements show that the electrical conductivity can be enhanced significantly by using Bi2Te3 nanosheets, and as a result, a maximum thermoelectric figure-of-merit (ZT) of 0.86 is obtained for Bi2Te3 nanosheets at 225 °C.