Periodic Reporting for period 2 - FloR3D (Flow-Reactor Coupled 3D Printing: Achieving Voxel-Level Control of Out-of-Equilibrium Materials)
Período documentado: 2025-02-01 hasta 2026-01-31
Nature is able to synthesize materials with spatially patterned optical, mechanical, and chemical properties by designing the local nano or microscale structure of the materials. For example, using a single chemical building block, such as cellulose in plants and keratin in bird feathers, natural materials tightly control and vary the arrangement of these building blocks to obtain tailor-made properties locally. This approach yields multifunctional materials that are highly optimized for their application: the helicoidal nanoscale arrangement of cellulose in the cell wall of the Pollia Condensata fruit provide enhanced mechanical strength while causing an iridescent blue coloration.
While such locally variable nanostructure is difficult and cumbersome to achieve through traditional manufacturing methods, additive manufacturing, or 3D printing, offers a method to bypass this limitation. By careful design of the print path, the property of the material can be controlled down to a ‘voxel’ (3D pixel) level. However, current 3D printing approaches that capable of generating nanostructured materials are primarily limited by the ‘thermodynamic’ assembly of the ink. This means that the resultant nanostructure is an inherent product of the ink’s chemical structure, and varying the nanostructure requires using a different feedstock. As such, on-the-fly variations of the microstructure are very difficult to achieve.
In FloR3D, we aim to develop an approach to design materials with locally controlled microstructures with a 3D printing system. In our custom-built FloR3D setup, the to-be-printed materials are synthesized in situ from a mixture of two starting materials. The product of this reaction can then be extruded using a ‘direct-ink writing’ system to create spatially patterned nanostructures with arbitrary geometry. Importantly, the material’s properties can be designed by varying the ratio of the starting materials during the printing process, leading to materials with spatially-varied optical properties.
While such locally variable nanostructure is difficult and cumbersome to achieve through traditional manufacturing methods, additive manufacturing, or 3D printing, offers a method to bypass this limitation. By careful design of the print path, the property of the material can be controlled down to a ‘voxel’ (3D pixel) level. However, current 3D printing approaches that capable of generating nanostructured materials are primarily limited by the ‘thermodynamic’ assembly of the ink. This means that the resultant nanostructure is an inherent product of the ink’s chemical structure, and varying the nanostructure requires using a different feedstock. As such, on-the-fly variations of the microstructure are very difficult to achieve.
In FloR3D, we aim to develop an approach to design materials with locally controlled microstructures with a 3D printing system. In our custom-built FloR3D setup, the to-be-printed materials are synthesized in situ from a mixture of two starting materials. The product of this reaction can then be extruded using a ‘direct-ink writing’ system to create spatially patterned nanostructures with arbitrary geometry. Importantly, the material’s properties can be designed by varying the ratio of the starting materials during the printing process, leading to materials with spatially-varied optical properties.
During the second part of this study, we discovered that the polymeric material we synthesised surprisingly exhibits fluorescence. As such, these materials emit light when illuminated in UV light, the colour of which can be tuned through changing the ratios of two reagents. However, from the chemical structures of the material, fluorescent is entirely unexpected. In this project, we not only demonstrated the origins of this optical behaviour, but also developed a new 3D printing method to locally control the fluorescent behaviour.
Origins of fluorescence:
We first demonstrated that the unusual fluorescent behaviour is a result of a newly-discovered mechanism called clustering-triggered emission. This mechanism means that during polymerisation, the monomers are forced together in such a way that results in a different electronic structure. This structure bypasses the normal requirements for fluorescent properties, leading to the unexpected luminescent behaviour. By controlling the local packing of the monomer, for example by changing the degree of crosslinking or the kinetics of polymerisation, we are able to control what colour of light is emitted under UV irradiation. These can range for blue/green for less crosslinked samples, to predominately red for more crosslinked materials.
Spatial control of fluorescence:
Since we are able to control the fluorescent properties of these materials through a wide range of parameters, we are able to design materials where the light emitted can be tuned locally. A simple method we employed is by changing the polymerisation conditions. By photopolymerising one region for longer amounts of time, we are able to control the colour, which allows us to create patterns by placing masks to control the local polymerisation kinetics. Moreover, by incorporating this material system into a multimaterial 3D printing setup, we can create a patterned material in which the local crosslinker content is varied. This result is exhibited in the attached image: under visible light, the material appears to be homogeneous, but under UV light, a clear difference in fluorescence can be observed between different regions. As 3D printing allows the 'stacking' of multiple layers, each layer does not have to have the same fluorescent pattern, which potentially allow us to create complex optical systems.
Origins of fluorescence:
We first demonstrated that the unusual fluorescent behaviour is a result of a newly-discovered mechanism called clustering-triggered emission. This mechanism means that during polymerisation, the monomers are forced together in such a way that results in a different electronic structure. This structure bypasses the normal requirements for fluorescent properties, leading to the unexpected luminescent behaviour. By controlling the local packing of the monomer, for example by changing the degree of crosslinking or the kinetics of polymerisation, we are able to control what colour of light is emitted under UV irradiation. These can range for blue/green for less crosslinked samples, to predominately red for more crosslinked materials.
Spatial control of fluorescence:
Since we are able to control the fluorescent properties of these materials through a wide range of parameters, we are able to design materials where the light emitted can be tuned locally. A simple method we employed is by changing the polymerisation conditions. By photopolymerising one region for longer amounts of time, we are able to control the colour, which allows us to create patterns by placing masks to control the local polymerisation kinetics. Moreover, by incorporating this material system into a multimaterial 3D printing setup, we can create a patterned material in which the local crosslinker content is varied. This result is exhibited in the attached image: under visible light, the material appears to be homogeneous, but under UV light, a clear difference in fluorescence can be observed between different regions. As 3D printing allows the 'stacking' of multiple layers, each layer does not have to have the same fluorescent pattern, which potentially allow us to create complex optical systems.
This method towards materials with cluster-triggered emission represents a large advance in designing fluorescent materials with non-traditional materials. While in the past few years, different custom-synthesised polymers have been shown to exhibit this behaviour, tuning the fluorescence previously still required redesigning and then resynthesising polymers. Here, instead of controlling factors such as backbone rigidity or end-group assembly properties, our method relies simply on crosslinking density, which can be tuned facilely using a range of different handles. This allowed for a facile one-step process towards materials with tuneable luminescence. Moreover, this method should be generalisable to a range of similar monomers, which can greatly broaden the applicability and ease-of-preparation of these materials as responsive optical devices. Due to the easy tuneability of our system, we were able to interface it with a 3D printing system, which has allowed us to design materials with arbitrary shapes and locally-controlled fluorescence. This has not been previously achieved for fluorescent systems, further enabling the design of highly complex optical components with properties that vary both across and through the depth of a material.