Periodic Reporting for period 4 - CREAM4 (Chemical Reaction Engineering by Additive Manufacturing of Mesoscale MetaMaterials)
Berichtszeitraum: 2022-03-01 bis 2023-02-28
One of the current challenges in science and engineering is to understand and control the behaviour of matter and energy at distinct length and time scales. In many chemical processes, atomic, molecular, photonic, and electronic events occur in femtoseconds at a surface site. This nanoscale activity is connected to processes running in seconds at the mm scale in a bulk continuum, via a stepwise sequence of intermediate-scale architectures and phenomena. Mass transport in the fluid is generally well understood and can be modelled to the finest detail. For many systems also the chemistry at the nano-sized (catalyst, adsorption) site is known, from ideal model systems. The crucial link between the two regimes is formed by phenomena at the mesoscale, defined as being between the size of a molecule and several µm, the size of a representative amount of bulk material.
The management of mesoscale dynamics is the missing link in gaining complete control over chemical processes like heterogeneous catalysis. The ability to accurately position nanoscale active elements in cellular mesoscale (nm to µm-range) structures with high symmetrical order is instrumental in streamlining vital molecular or energetic paths. 3D periodicity in the structure that supports active or adsorption sites minimizes spatial variations in mass transport, whereas mesoscale control of the location of these sites gives a route to tuning activity and functionality. The introduction of mesoscale metamaterials expands the on-going trend in chemistry, of more and more dimensionally refined structured elements, a so to speak "Moore's law in Process Intensification". The roadmap to higher process efficiency dictates a next, disruptive step in mastering manufacturing control at smaller dimensions. om in shape, symmetry and composition.
To realize the required paradigm shift, active (catalytic or photoresponsive) nanoparticles will be positioned at nanometer-precise optimal distances on an optimized ordered and open 3D supporting architecture, which ensures that all molecules flow through the material at the same speed, whereas they also experience exactly the same interaction with the nanoparticles. The game-changing technology to achieve this is by additive manufacturing.
For the above innovation to become real, two major, crucial advances in fabrication technology have to be created, which are the main objectives of this project:
Objective 1. Electrospinning of complex nanowires with complete freedom in the choice of wire material or material combinations, dimensions, porosity, and surface properties, and complete freedom in the type, shape and relative position of the nanoparticles along the nanowires. In all electrospun nanowires reported until today, the nanoparticles are randomly and inhomogeneously positioned on the wires, because the particles form from dissolved ingredients during deposition and calcination or are applied by a post-deposition step. The electrospinning method itself does not offer a mechanism to control the position of particles in the wire, and a real breakthrough is needed to arrive at Objective 1.
Objective 2. Positioning and connecting uniform electrospun nanowires via localized and switched electrical fields, with nanoscale precision on a 3D grid to create ordered cellular materials of sufficient mechanical stability for chemical applications. Electrospinning is a cheap and unique technique, with excellent industrial perspective, to produce fibres with a diameter in the range from less than 3 nm to several µm, and is based on a jet created by an electric field (~1kV/cm) between a dispenser outlet and a collector, where solid wires form in a solidification process. Due to an electrically driven bending jet instability, electrospinning mostly produces randomly positioned nanowires, and as yet not a single demonstration of nanoscale precision in 3D has been given. Definitively also a major breakthrough is needed to arrive at Objective 2.
The management of mesoscale dynamics is the missing link in gaining complete control over chemical processes like heterogeneous catalysis. The ability to accurately position nanoscale active elements in cellular mesoscale (nm to µm-range) structures with high symmetrical order is instrumental in streamlining vital molecular or energetic paths. 3D periodicity in the structure that supports active or adsorption sites minimizes spatial variations in mass transport, whereas mesoscale control of the location of these sites gives a route to tuning activity and functionality. The introduction of mesoscale metamaterials expands the on-going trend in chemistry, of more and more dimensionally refined structured elements, a so to speak "Moore's law in Process Intensification". The roadmap to higher process efficiency dictates a next, disruptive step in mastering manufacturing control at smaller dimensions. om in shape, symmetry and composition.
To realize the required paradigm shift, active (catalytic or photoresponsive) nanoparticles will be positioned at nanometer-precise optimal distances on an optimized ordered and open 3D supporting architecture, which ensures that all molecules flow through the material at the same speed, whereas they also experience exactly the same interaction with the nanoparticles. The game-changing technology to achieve this is by additive manufacturing.
For the above innovation to become real, two major, crucial advances in fabrication technology have to be created, which are the main objectives of this project:
Objective 1. Electrospinning of complex nanowires with complete freedom in the choice of wire material or material combinations, dimensions, porosity, and surface properties, and complete freedom in the type, shape and relative position of the nanoparticles along the nanowires. In all electrospun nanowires reported until today, the nanoparticles are randomly and inhomogeneously positioned on the wires, because the particles form from dissolved ingredients during deposition and calcination or are applied by a post-deposition step. The electrospinning method itself does not offer a mechanism to control the position of particles in the wire, and a real breakthrough is needed to arrive at Objective 1.
Objective 2. Positioning and connecting uniform electrospun nanowires via localized and switched electrical fields, with nanoscale precision on a 3D grid to create ordered cellular materials of sufficient mechanical stability for chemical applications. Electrospinning is a cheap and unique technique, with excellent industrial perspective, to produce fibres with a diameter in the range from less than 3 nm to several µm, and is based on a jet created by an electric field (~1kV/cm) between a dispenser outlet and a collector, where solid wires form in a solidification process. Due to an electrically driven bending jet instability, electrospinning mostly produces randomly positioned nanowires, and as yet not a single demonstration of nanoscale precision in 3D has been given. Definitively also a major breakthrough is needed to arrive at Objective 2.
Two main types of additive manufacturing are investigated: two-photon stereolithography and electrospinning. Both methods have the perspective for nanometer precision. Both methods are well-known for the fabrication of polymer nanostructures. In this project, however, the focus is on metal oxides as (catalytic, photoharvesting, semiconducting or simply mechanical) supports for (mainly) metal nanoparticles, which has not that extensively been investigated. Preliminary results have been optained for two-photon stereolithography of zirconia nanostructures, for which a publication is in preparation.
A more intensive focus has been on electrospinning of nanoparticle-contained nanowires, lined out in ordered 3D networks. The key innovative aspect of this strategy is that first the nanoparticles of choice are queued with exactly defined spacing, which arrangement is then fixed by solidifying the material between the nanoparticles. At the front-end of the electrospinning equipmen, a microfluidic system with a micromachined nozzle will create a liquid thread and deposit it by near-field electrospinning, whereas at the back-end an electronic circuit acts as the collector that exactly positions the nanowire in a 3D framework. In particular the deposition of a well-ordered 3D nanowire network is a serious challenge because the behavior of the nanowire during electrospinning can become chaotic, for as yet not completely understood reasons. Two main directions have been investigated, one being the control of the liquid meniscus at the electrospinning nozzle, by shaping the nozzle outlet such that the contact line of the meniscus becomes pinned, and the second being the implementation of auxiliary electrodes at or near the collector electrode.
The main achievements so far have been:
1) a novel nozzle layout, fabricated with silicon micromachining; this nozzle pins the precursor solution at a precisely defined position, ensuring a stable Taylor cone during electrospinning
2) a novel tool changer, for switching between different nozzles during electrospinning (instead of switching solutions through one and the same nozzle, which can give rise to undesired side reactions and comtamination)
3) novel composite catalytic materials for photocatalysis, including a very promising nickel oxide with an unexpectedly active surface; this material is currently been modelled theoretically by a European collaborator,
4) a novel electrochromic device based on electrospun nanowires
5) novel luminescent 3D nanostructure with implications for integrated optics
A more intensive focus has been on electrospinning of nanoparticle-contained nanowires, lined out in ordered 3D networks. The key innovative aspect of this strategy is that first the nanoparticles of choice are queued with exactly defined spacing, which arrangement is then fixed by solidifying the material between the nanoparticles. At the front-end of the electrospinning equipmen, a microfluidic system with a micromachined nozzle will create a liquid thread and deposit it by near-field electrospinning, whereas at the back-end an electronic circuit acts as the collector that exactly positions the nanowire in a 3D framework. In particular the deposition of a well-ordered 3D nanowire network is a serious challenge because the behavior of the nanowire during electrospinning can become chaotic, for as yet not completely understood reasons. Two main directions have been investigated, one being the control of the liquid meniscus at the electrospinning nozzle, by shaping the nozzle outlet such that the contact line of the meniscus becomes pinned, and the second being the implementation of auxiliary electrodes at or near the collector electrode.
The main achievements so far have been:
1) a novel nozzle layout, fabricated with silicon micromachining; this nozzle pins the precursor solution at a precisely defined position, ensuring a stable Taylor cone during electrospinning
2) a novel tool changer, for switching between different nozzles during electrospinning (instead of switching solutions through one and the same nozzle, which can give rise to undesired side reactions and comtamination)
3) novel composite catalytic materials for photocatalysis, including a very promising nickel oxide with an unexpectedly active surface; this material is currently been modelled theoretically by a European collaborator,
4) a novel electrochromic device based on electrospun nanowires
5) novel luminescent 3D nanostructure with implications for integrated optics
We have developed several novel inorganic materials as well as devices (e.g. reactive membranes, luminescent nanostructures) with performance that goes beyond current state of the art.
Furthermore, by the implementation of microfluidics and micromachining, electrospinning equipment will be largely improved, in particular in the area of near field electrospinning
Furthermore, by the implementation of microfluidics and micromachining, electrospinning equipment will be largely improved, in particular in the area of near field electrospinning