Ella Marushenko Studio
Artistic conceptual representation of the 3D printing of molecularly functionalised photochromic devices.
New research proves advanced materials containing molecules that switch states in response to environmental stimuli can be fabricated using 3D printing. Victor Sans from the Faculty of Engineering at University of Nottingham, explains ...
There is a profound and fundamental divide between the way engineers and physical scientists work in academia. Engineers are excellent in providing cost-effective and workable solutions to complex problems, such as providing food, chemicals, infrastructure, etc. at large scales. Nevertheless, there is a limitation in the toolbox of materials they can access in their designs and solutions, which somewhat limits the scope of innovation they can achieve.
Physical scientists, in concrete in the chemical sciences, excel in the understanding of molecular interactions, thus being able to create molecular and nanostructured materials with novel and emerging properties. Despite the level of sophistication achieved, the translation into practical materials and devices is cumbersome and typically requires lengthy timescales without any guarantee of success throughout the process. At the University of Nottingham, we believe that additive manufacturing (AM) has an untapped potential to bridge this gap. AM enables the rapid design and manufacture of unconventional geometries in a transformational fashion from an engineering point of view. The possibility to generate complex geometries in an increasing variety of materials, including polymers, ceramics and metals is having an increasing academic impact.
Photochromic device 3D printed with DLP based on a Schwartz P Surface Cube
Amongst the different materials that can be employed for AM, polymers are especially attractive due to the broad range of functionalities that can be added by material design. Polymerisable ionic liquids (PILs) are a class of polyelectrolytes with analogous functional units and properties to bulk ionic liquids (ILs), which are salts with highly tuneable properties depending on the choice of cations and anions. The large number of molecular functionalities that can be combined makes ILs and PILs highly versatile for a broad range of applications including catalysis, energy storage, antimicrobials and organic electronics. Furthermore, ILs and PILs are excellent media to stabilise advanced materials, like carbon materials, nanoparticles and biomolecules. It is highly surprising that despite the huge potential for applications from PILs, it has not been exploited for 3D printing. In 2014, the group of Professor Timothy Long in Virginia Tech demonstrated for the first time the possibility of 3D printing PILs employing microstereolithography.
Recently we have demonstrated for the first time the possibility to 3D print PILs with photoactive molecular materials employing digital light processing (DLP) (Figure 1). Devices with tuneable properties (e.g. hydrophilicity and hydrophobicity) were manufactured in a sequential fashion. In addition to the molecular functionalities added by the PILs, the introduction of molecularly engineered hybrid organic-inorganic molecular metal oxides known as polyoxometalates (POMs). The finely tuned combination of organic and inorganic functionalities allows us to control the bandgap to yield efficient photosensitisers. POMs absorb in the UV spectra in an oxidised state, while they exhibit a dark blue colour in the reduced state. A synergy between the polymers and the photoactive molecular materials allows us to manufacture devices with the POM in a dormant state. Upon controlled reduction with light, the POM reduction leads to a spatially resolved photochromic behaviour that was effectively reversed oxidising the material with oxygen (Figure 2).
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Exhibit at the UK's definitive and most influential 3D printing and additive manufacturing event, TCT 3Sixty.
Strategy to inkjet print viscous monomers by successive functionalisation of printed layers. Adapted from ACS Sustainable Chemistry & Engineering, 2018, 6 (3), pp 3984-3991
Developing reversible photochromic materials will lead to a broad range of interesting applications, the most obvious being the storage of information employing the controlled redox properties of the POMs, being the oxidised state a ‘0’ and the reduced state (blue colour) the ’1’. The success of this approach will require to simultaneously develop novel molecular materials, polymers and strategies for printing with high resolution techniques, like inkjet (Figure 3) and two-photon.
The possibility of effectively manufacturing molecularly designed materials with 3D printing via the employment of finely tuneable PILs is now an achievable method to bridge the gap between discovery and application. This approach will hopefully set a roadmap for engineers and scientists to work closer together to develop next generation devices with exciting emerging properties.
