A. Chang
Oregon State University,
United States
Keywords: microreactor, nanomaterials, synthesis, deposition, additive manufacturing
Summary:
Nanomaterials wield unique size-dependent properties that have revolutionized a variety of diverse fields such as medicine, electronics, sensing, energy storage and harvesting, catalysis, and more. As such, a key goal towards unlocking the optimization and application of nanomaterials in these fields starts with the ability to tune nanomaterial properties such as size, shape, morphology, and composition to selectively improve material performance for targeted applications. Although the growth and nucleation of nanomaterials is a complex mechanism, they can largely be controlled by integrated effects of reaction rate, temperature, concentration, mixing, residence time, solvent choice, and additives used. Although there has been tremendous progress in nanomaterial manufacturing and study using batch methods at the lab scale, experimental control over these parameters is difficult to control for large-scale systems. Alternatively, microreactor-assisted nanomaterial deposition (MAND) is a promising platform for nanomaterial synthesis that controls all the previously mentioned growth and nucleation parameters and fabricates reactive fluxes and nanomaterials to deposit nanostructured materials with distinct morphologies, structures, and properties at the point of use. Microreactor technologies offer large surface-area-to-volume ratios to accelerate heat and mass transport, allowing for rapid changes in reaction conditions and more uniform heating and mixing. It overcomes the scale-up barrier via process intensification at the microscale, and provides precise control over heat, mass, and momentum transport using well-defined microstructures of the reactor cell that can be numbered up at large scales for high throughput applications, opening the door towards a new avenue of scalable nanomanufacturing. Furthermore, the ability to synthesize nanomaterials in precise volumes at the point of interest eliminates the need to store and transport potentially hazardous materials and leads to low material waste and footprint. Currently, two main MAND techniques exist as microreactor-assisted solution deposition (MASD) and nanoparticle deposition (MANpD). Whereas MASD generates reactive fluxes of ions and molecules and is used primarily for heterogeneous growths of thin films, MANpD directly deposits nanoparticles onto a substrate surface. Using these techniques, MAND technologies have synthesized a variety of different materials for a diverse range of applications. For example, MAND can be used to deposit many of the layers in a photovoltaic device such as metal contacts, absorber layers, window layers, and coatings, while offering fine control over their nanostructure and morphology and leading to a variety of attractive properties such as improved light trapping, electron transport and collection, and antifouling. MAND has enabled the design of antireflective and antifouling coatings with distinctive nanostructures, leading to 13.4% power gains over an 8-month period on solar panels at a southern California location. MAND can also be combined with 3D printing technology to realize additive manufacturing of multifunctional materials. By employing a multi-chamber print head, in-situ chemical reactions during printing can occur in one or more chambers, allowing for solvent-free, drop-on-demand deposition and printing of functional nanomaterials. Patterned films may also be deposited on two-dimensional and three-dimensional surfaces. For example, the in-situ production of yttrium oxide and tungsten nanoparticles can be deposited using this technique.